Suppose we could move gloriously and quietly along in our own comfortable car compartment some 20 feet high between the trees, yet with no engine running, no fossil fuel use, no greenhouse gas emissions, and no need to watch the road (Figure 1). Or, we could zip along in channels dug just below ground level and topped with translucent covers. No unpredictable drivers to worry about or vehicles to crash into. No driver fatigue, indeed, no driving. Barely any traffic noise. We watch nature around us, remember the bad old days of polluting traffic, play family games, work on the computer, or read. When ready to return to ground level, we simply take manual control of our fully charged battery “pod” car and drive off on local roads to our destination.
Why is this vision of travel, perhaps a generation ahead, so appealing and so important? In it, not only is nature restored and reconnected on a massive scale, but both fossil fuel use and greenhouse gas emissions are eliminated, mobility for people and goods is safer and more efficient, and there are significant benefits for food production and recreation near towns and cities.
Two Giants: Transportation and Nature in Uneasy Embrace
Roads slice the land into pieces yet also tie it together for us. For centuries, spreading roads have progressively degraded nature. The direct ecological impacts of the road system have been estimated as affecting one-fifth of the U.S. land surface, with indirect effects spreading much further.1 A core objective of this article is to outline a transportation system that doesn’t just slow or stop the degradation process but reverses the trajectory. At first glance the solution appears visionary, but a second look reveals a close-to-feasible transportation system.
The 4 million miles (6.25 million km) of public roads across the United States were largely built before Earth Day 1970 and the rise of modern ecology.2,3 A quarter billion vehicles use this network, which penetrates almost everywhere. Beyond transporting people and goods, effects reverberate widely through society. But how does this massive system of roads and vehicles affect nature and its processes?2,4–8
Look at these impacts:
- Habitat loss. Roads and roadsides cover 1–1.5 percent of the entire United States, including Alaska, significantly affecting natural vegetation and animal populations and contributing to greenhouse gas emissions.
- Roadkilled animals. Millions of animals per year are hit, and some cars and people are also smashed.
- Barrier to wildlife movement. Animals must move across the land for food, water, escape, and reproduction but are widely blocked or inhibited by roads.
- Fragmented habitats. With animals largely stuck in small, separate habitats, their populations shrink and often disappear, leading to overall loss of biodiversity.
- Traffic noise. Within 0.25–0.75 miles on each side of a busy highway, many sensitive birds, reptiles, amphibians, carnivores, and ungulates are scarce or have disappeared.
- Degraded roadside. Common weeds and nonnative species often take over roadside strips that are constantly disturbed and bathed in chemicals.
- Erosion. Water and wind widely erode soil from construction sites, road cuts, and, especially, downslope surfaces of fill.
- Sedimentation. Eroded material commonly reaches streams and lakes, where it degrades water quality, bottom habitat, and fish.
- Ditch water and groundwater. Ancient Romans built arrow-straight roads surfaced with large rocks for wagons, even chariots.9 Since then, most roads have been somewhat fit to the topography, with slightly curved earthen or paved (sealed) surfaces that shed water to roadside ditches. Road/vehicle-polluted water, often sun warmed, degrades countless nearby streams and lakes, as well as wells and water supplies.
- Altered wetlands. Water blocked by roadbeds inundates land, even creates wetlands, while at the same time road-related drainage channels shrink or eliminate wetlands.
- Dispersed land use. Road-related sprawl, rather than compact growth, accentuates all of the above road/vehicle impacts, from greenhouse gas emissions to roadkill.
The result is a huge cumulative effect on nature. Although “road ecology” emerged barely a decade ago,2,4-6,8,10–12 few people have begun pondering solutions for such a broad set of issues.13,14 Our vision for transportation eliminates, or noticeably mitigates, this entire array of problems.
Even more familiar are transportation’s big problems for society.3,6,15 Safe and efficient mobility for people and goods remains a transportation goal, yet the system of roads and vehicles is fraught with dangers and inefficiencies, from deteriorating roadways and deficient bridges to traffic jams and vehicle crashes. Furthermore, the massive worldwide road network, with its extensive fleet of motorized vehicles, is powered by relatively cheap but increasingly depleted fossil fuels3,15 that are also used for road construction, maintenance, and repair. Finally, widespread atmospheric pollution—from greenhouse gases to vehicular nitrogen oxide (NOX), heavy metals, salt, and road dust—is a major, growing issue and societal cost. The proposed system outlined here is safer and more efficient, drastically reduces fossil fuel use, employs renewable energy as its foundation,15,16 and dramatically reduces transportation pollutants.
As a bonus, our solution addresses two key issues around cities and towns: food production and recreation opportunities. Road-related construction, erosion, and sedimentation too often reduce food production on good soil—such as on cropland outside cities or rice farming on floodplains—and the road system blocks the movement of farmers and livestock. Highways also act as barriers, traffic-noise makers, and danger zones for walkers and cyclists. In the system we describe, food is produced near communities, minimizing transportation and its associated costs; and convenient walking and cycling trail networks are built in.
In most areas, the bulk of the road network and its consequent environmental problems have been in place for decades. Yet newer issues—a billion vehicles, coalescing streams of noxious tailpipe emissions, greenhouse gases, permeating traffic noise, wide asphalt ribbons with polluted runoff, and smaller fragmented habitats—now also pose great challenges.
Big things have inertia and normally change slowly. What could significantly change our existing road network?2,6 Road closures and removals, disaster events, and highway widenings are effectively local, affecting but a bit of the overall infrastructure. Even war only causes a temporary change, though for a larger area. Planned expansion has happened, however, as with America’s interstate highway system, built in the 1960s and 1970s, or the multilane expressways now rolling across China, India, and eastern Europe. The netway system described here is also an ambitious planned change.
We focus on remote, rural, and outer suburban areas of the United States, where the benefits to nature would be enormous, though the basic approach also applies to cities and regions worldwide. Specifically, our solution targets large areas containing busy highways and society’s most valuable nature. On these highways, more than 3,000 vehicles per day pass any given point,17–21 and the posted safe speed limit is more than 50 miles per hour (Figure 2).22,23 Landscapes containing large natural areas, major green corridors, and/or many water bodies are of prime ecological importance. The vision is no panacea, but it does strongly enhance biodiversity, water quality, mobility, energy, atmosphere, food production, and recreation. Moving quickly to implement this system will enhance success, and the leaders who initiate this effort will have by far the greatest impact.
The Netway System
Imagine starting a commute to work or trip to the city by walking to a nearby netway service center. The place is attractive, safe, and welcoming, with a small convenience store. You step into a large public (or social) “pod,” like a streamlined, comfortable van or bus, which operates with a service attendant but no driver. The pod is carried along the netway until you decide to disembark at one of the frequent on/off stops, which may be another service center or simply a structure with stairs and a ramp to ground level plus protection against weather.
Alternatively, at the small service center an attendant provides you with a personal pod, which may be your own or may be rented for an hour or day or week or year. It has the feel of a ski gondola or a car compartment with comfortable seats. You enter and the pod moves smoothly ahead under automated control. No driving, no traffic jams, no accidents to worry about. Just time to relax, write, or even bird-watch. You depart the netway at another service center, usually located in a town, a village, or at an intersection. Here you can either leave the personal pod or drive it away on local ground-level roads.
These comfort and safety benefits come from converting busy highways to netways elevated at various heights (“elevated ways”) or partially or fully sunken belowground (“earthways”), and replacing today’s cars with simple, lightweight, aerodynamic vehicle-like pods. These pods provide space for personal comfort and have a strong protective shell with doors and windows. The pod electronically “attaches” to the netway infrastructure using power embedded in the paved surface. Using automated controls, pods can be moved as a platoon close together, even inches apart, to minimize air drag, or can be far apart in sparse traffic.24,25
Transportation that concentrates the flow of objects linearly has two theoretical values: transport efficiency and protecting the surrounding land. Netways and pods are not merely for city or airport transportation, nor for creating carless communities, though they could be quite desirable in such situations. Rather, the netway system especially focuses on the extensive land between cities, where half the world population lives and natural patterns and processes are prominent. Naturally, this system must and does meet the basic goals of transportation2—providing safe and efficient movement of people and goods without significantly degrading nature’s patterns and processes.
The broad solution outlined results from, and requires, “road ecology,” which has emerged10,11 and coalesced2,5,6,8,13 in the past 15 years. The field of road ecology studies and catalyzes solutions for the interactions among vehicles, roads, plants, animals, earth, water, and air across the land. Netways permit unimpeded movement of streams, animals, walkers, cyclists, and vehicles (on small roads) across the land. Today’s transportation-related problems, outlined at the outset of this article, will disappear or plummet without busy ground-level highways.
Many of the insights outlined here have been separately proposed in engineering, energy, or social contexts, and some related local projects are operational. However, major new thinking and solutions for restoring or reconnecting nature’s water and biodiversity in the face of transportation have yet to appear.2,6,13,14 Where nature benefits, so does society, and thus the netway approach applies to all busy highways. However, we give priority to converting nonurban highways to netways because this is where the greatest gain to nature will be achieved.
The last transformation of transportation from horsepower to motorpower was accomplished in a mere 25 years.9 Today the inertia of our road-and-vehicle system faces the looming and coalescing issues of fuel cost/shortage, pollutants/greenhouse gases, excessive traffic, and degradation of water and biodiversity. Assuming that society increasingly demands solutions for these issues, a 25-year time frame from the onset of netway evaluation and planning to widespread operation in key large areas of the USA seems achievable. Most of the technologies needed to convert highways to netways exist, and targeted research and development should spur solutions for remaining problems. This article outlines the netway system framework and provides some details for illustration. The process can begin for our next-generation transportation.
Worldwide, and especially in China, road construction and vehicle numbers are rapidly growing, while in the United States both characteristics are now relatively constant and at high levels.2,3,8 Mitigation or retrofitting is especially needed in the United States, whereas wise ecological design from the start is essential in most other nations. The goal in all cases is a transportation system lightly imprinted in nature’s patterns and processes of water, wildlife, and biodiversity.
Pods, Vehicles, and Energy
As illustrated, netways will be lined with solar panels, wind turbines, and other local energy sources designed to minimize effects on natural processes and bird populations. These predominantly renewable energies will run netway machinery, spaced at intervals. Using inductive coupling, electricity from wires embedded in the netway surface will cross a small air gap to an electric motor in the pod.24,26,27 Thus, pods holding people and goods will be electronically guided smoothly and safely across the land by a netway control center. With a small battery, many pods can also store electricity for driving off the netway on ground-level local roads. At the frequent on/off small service centers, the netway energy supply can charge batteries for a fleet of stored pod cars.
Energy from the sun, wind, and earth’s heat is plentiful, widespread, and permanent—unlike oil, which fuels current vehicles plus most road construction, maintenance, and repair and is increasingly limited.3,15,16 Renewable energy sources represent a flexible and dependable foundation for transportation, and they do not emit CO2. In the system outlined, although these energies will feed locally into the netway system, energy transmission and storage will also be required when the wind is not blowing and the sun is not shining. Excess energy produced could be sold to support local communities or could be fed into the larger electrical grid.
We expect that solar collectors will become ubiquitous on and alongside netways. Wind energy is expected to be of particular importance in netway development. Power generated from wind is a function of the cube of wind speed (which increases with height aboveground) and, for turbines, the square of blade length.28,29 Thus, tall and large turbines produce the most power, but even small turbines high above elevated ways could produce useful power, with little noise or visual intrusion. Considerable “high-temperature” geothermal energy is available with expensive deep drilling in certain areas, while inexpensive shallow drilling in many areas can produce small amounts of “low-temperature” geothermal energy. Also, hydro, wave, and tidal energy are local non-CO2-emitting energy sources.
Three types of pods will be carried along netways: (1) personal pods for up to, say, six people; (2) long public pods for hyperefficient public transport; and (3) freight pods for transporting goods. All will be strong and lightweight to minimize electrical energy use as well as wear on the netway system. In the system outlined here, we focus on personal pods—the next phase after walking, horse power, and cars—where individuals largely choose their timing and routes. Public pods will be an important supplement to group transport in buses, electric streetcars, subways, light rail, fast trains, and airliners.30 Freight pods when full can be separated in the flow of pods to evenly distribute weight on elevated ways and to accommodate different destinations for the goods carried. Also, freight pods will carry lighter-weight goods, not dense material such as coal or grain shipped by rail.
While some lightweight pods, outfitted with a tiny battery or ultracapacitor, will operate exclusively on the netway system, other pods with somewhat larger batteries (though much smaller than in today’s electric cars) will be able to move off the netway onto urban streets and low-traffic local roads. Compared with today’s typical 2,000- to 4,000-pound car, personal pods moving only on netways might weigh about 1,000 pounds. Pod cars that also can move on roads would be somewhat heavier (for the battery and for stronger structural integrity). Small netway-pod systems exist at London’s Heathrow Airport; in Morgantown, West Virginia; and in Korea. In Masdar City in the United Arab Emirates, a passenger enters a driverless pod, pushes a button for a destination, and is automatically carried there.
Although creative designs allow a rich array of forms, we envision all pods as aerodynamic and somewhat oval or elongate in form,25 analogous to certain tropical coral-reef fish.31 All will have windows, doors, and comfortable seats. All will be securely and easily linked electronically to the netway transport system. No driving. No oil consumption, greenhouse gas emissions, brake wear, or traffic accidents. When off the netway, drivers will operate autonomously under their own control and with onboard energy storage.
Batteries in personal pods charged en route on the netway will provide flexibility by permitting local ground-level driving. These pod cars with a small battery could drive about 20 miles on the ground or longer distances when designed with a bigger, heavier, and more expensive battery. But, as the netway system expands over time, off-network vehicle use should noticeably decrease.
Compare the three pod types to present road-system conditions:
Personal pods and pod cars. Today, private cars burn fuel, encounter traffic jams, require parking lots, occasionally hit animals, rapidly lose value, and emit particulates, aerosols, greenhouse gases, and other pollutants. With almost a billion cars worldwide, and growing, private cars dominate transportation in many nations and soon will in many more.
Personal pods traveling along netways will have virtually none of these characteristics of private cars—an enormous gain for nature and for society. Personal pods will also be flexible: pod designs can proliferate because they won’t be constrained by petroleum-powered engines, uneven road surfaces, the need for extensive driving, and collision hazards with different-sized vehicles and unpredictable drivers. Frequent on/off locations with small service centers will provide access and rest-stop choices. And, because there will be no driving or traffic to constantly watch, travel time can be used in many pleasant and productive ways, which will be particularly welcome.
Public pods and pod buses. Beyond inefficient cars, the movement of people in many large cities emphasizes some combination of ground-level buses and underground subways. Urban subway systems are commonly constructed through water-saturated earth and many rock types at great expense. Commuter rails and bus lines, radiating from a city center, serve surrounding areas.
Though the netway system is not specifically designed for use in cities, public pods carrying five to 50-plus people will move efficiently and quietly in areas outside of cities and between urban areas. Frequent on/off stops for passengers will include the small service centers but also numerous intervening spots with weather-protected space for waiting and with access to ground level. Many, especially lightweight, public pods will only move along the netways, while others will be able to depart at the less-frequent large service centers and travel local roads under battery power. The public pods will be stored and serviced at these large service centers and made available either for use on the netways or as pod buses for ground-level travel on small roads.
Planning and technology, as well as different cultural preferences, will determine the specifics of public pod systems. But flexibility is central, with passenger access to pod cars at service centers, different public-pod sizes, and so forth. Reducing today’s transportation-related negatives, as well as providing flexibility and energy dependability, are the same key benefits as for personal pods.
Freight pods and pod trucks. At present, trains carry heavy loads and are limited to narrow strips of railway across the land, whereas trucks normally carry light to medium loads and can access any place with a road. Road surfaces and bridges are wider, thicker, and wear out faster because of truck use. Trucks consume fuel and produce pollutants at a high rate per mile (km) traveled, require drivers, and congest many intercity highways. A considerable portion of traffic noise on busy highways is due to trucks.
Freight pods transported along netways will effectively eliminate or sharply reduce these problems. These pods will enter and exit at the large, less-frequent service centers. When full, freight pods will be spaced at appropriate intervals by the netway automated control system to maintain an even, light weight on the netway. On the ground, they may move individually or be hooked together to transport goods locally on small roads. Thus, freight pods will have low operating costs and many of the efficiencies and benefits characteristic of pod cars.
Technology and planning can produce lightweight pods, aerodynamic forms for different-size vehicles, efficient electric/hybrid propulsion, modular designs, and so forth.25,27 In essence, the environmental benefits of pods are large and the economic benefits to commerce considerable.
Structural Characteristics of All Netways
In the netway system, pods of different types will be relatively constant in width and move quietly both ways along a netway. Each lane will be about 7 feet (2.1 m) wide for pods being transported along a fixed line, and a strip 9 feet wide down the center will allow access for service and emergency use (Figure 3). The total width of a netway will be approximately 27 feet (8.5 m), which is slightly more than the width of a soccer goal or the goal posts in American football, or about 325 inchworms end-to-end across the netway. Small service centers, where pods attach and detach from the main electronic netway line, will have a surface about twice the normal netway width.
The transport mechanism proposed mainly uses renewable energy to produce electricity, which will flow through wires embedded just below the netway surface (or other connector) to power electric motors in lightweight pods. The electric current in the wires will be transferred to vehicles across air gaps of up to about 12 inches by inductive coupling,26 a well-understood technique currently used experimentally. (Alternatively, vehicles might receive electricity conductively from a thin rail alongside the lanes, as is done in electric subways.) No exposed shock or electrocution hazard exists with inductive coupling.
Automated controls, with pods linked electronically to the netway-system control center, will provide for smooth, efficient travel. Pods, large and small, could travel in platoons just a few inches apart or could be more separated.24,25 Such controls are already in use for automated trains and “unmanned” aircraft and are quite advanced. For instance, the U.S. military is ambitiously planning for one-third of its future combat vehicles to be autocontrolled; some new cars sold today use automated controls to park themselves; and cars operating under automated control have been successfully tested on California freeways.
Netways in our system mostly will have gradual turns reminiscent of railways. For sharp turns, a pod will be gently slowed down and then gradually sped up in the changed direction. The system’s regenerative braking will capture energy from the slowing of a pod for a sharp curve or upon arrival at a service center.25 At intersections where netways cross at different levels, a pod will be moved to the outer lane at a bifurcation of the embedded electric wire, slowed down, gradually curved upward or downward to the new level, and gently accelerated into the mainline flow in the new direction.
The constant safe running speeds of pods might be in the range of 40 to 55 miles per hour (65–90 kph) in suburban areas, where on/off netway locations are frequent or many freight pods are present. However, we expect relatively few netways to be initially deployed in suburbia where priority natural areas are scarce and trips are diffuse. In more rural or remote country, pod speeds on netways would normally be higher.
Netways are a traffic engineer’s dream. With no traffic jams, no speed-up-and-wait driving, no cross-traffic, no crashes, and no speeding “crazy drivers” (indeed no drivers at all), pods moving safely at a good, constant speed will reach destinations very quickly. Travel time will be noticeably reduced, less stressful, and productively used, so passengers will arrive relaxed—a huge benefit.
A safe, secure netway system for people is a priority, easily achieved and sustained. Sleek, narrow, fast emergency “vehicles” (perhaps with autonomous hydrogen-powered fuel-cell electric engines) can streak down the emergency lane of a netway. Wires and sensors embedded in the netway structure will automatically pinpoint the presence of a tree branch, person, or debris. Trips will be made safer with locked pods with good visibility, individual control over where to enter/exit, personal communications to the frequent small service centers, real-time system communications to pods, lights, video cameras where appropriate, service-center attendants, and patrol officers.
Today’s busy road surfaces are designed to be repaved every three to ten years, depending on levels and types of traffic. Cars are designed to last some ten to 15 years before major costly repair or replacement is needed. We anticipate that the design and construction of netways will be for some 50-plus years, depending on the structural material used and the amount of freight-pod usage. This is the time frame for most houses and small bridges built today, before expected major repairs or replacement (large bridges and buildings are typically designed to last a century).
Biomimicry (biomimetics)—that is, constructing objects in ways that mimic how nature works or makes things—might eventually be used as an alternative approach for transportation.32,33 Instead of relying on high-temperature processes to make heavy steel, concrete, and asphalt or synthesizing plastic, metal alloys, and rubber, the goal would be to build our structures with more natural materials and in more natural ways. Of course, the materials would have to meet rigorous engineering standards of strength, resistance, resilience, and safety. Consider, for example, the lightweight “struts” (bones) in a heavy pelican and its remarkable flying, diving, and fish-carrying ability. Or consider a surface composed of several thin sheets of natural material, separated by tiny spheres and space, that is stronger than steel yet also highly flexible. Or picture moving objects that expand and contract according to load size; or objects that readily biodegrade after a known period of use; or self-cleaning surfaces mimicking a lotus leaf process; or trees with fibers arranged to minimize stress and that are thicker where strength is needed, producing a strong, resilient, bendable structure; or air flow systems, using spirals like seashells or our inner ears, with sharply lower energy use. The list of nature’s materials and ways of making things goes on and on.
Looking ahead, many components of the netway system can be designed with backups or in pairs so that repairs/replacement can be accomplished with minimal or no effect on system functioning. Furthermore, modular design can be widely used, with lightweight pods, pillars, service-center facilities, stairways/ramps/lifts, and so forth standardized and prefabricated off-site. Components can be made regionally and conveniently stockpiled for quick repairs or replacement. Visual nuances can be incorporated into the system to highlight local/regional nature and culture.
The tires of the pods and the narrow strips of netway surface on which the tires will run should both be designed for long life, low wear, low pollution, and low noise, an easier task without the wide range of road conditions facing today’s drivers. Although moving pods will produce very little pollution, the usage and maintenance of diverse netway components inevitably will produce some chemical and particulate pollutants. Small retention ponds or basins along many netways can contain these pollutants for treatment or removal.
Netways will also be designed to withstand or rapidly recover from floods, small/medium earthquakes, hurricanes/cyclones, and so forth, preventing such disturbances from becoming disasters. Other gradual degradation processes will be eternally at work: bacterial decomposition, rusting/corrosion, mold/rot, termites/ants/beetles, weathering, ice freezing/thawing, seawater rise/intrusion, sinking/subsiding, extreme heat/cold, UV radiation, and vibrations due to trains, traffic, and machinery. Design and construction for these realities is a universal challenge and an adaptive learning process.
In case of a system breakdown, such as loss of power, a pod’s driving apparatus (steering, brakes, etc.) would be automatically enabled and sufficient to drive slowly to the next service center. In case of a pod breakdown, the pod would be automatically moved out of the mainline and slowed to a stop in the emergency strip. A backup option of widening the central maintenance and emergency strip to 17 feet would add costs but provide additional flexibility.
Points along the main transport line where people can get on and off, and where system personnel work, will also be keys to success. Four infrastructure nodes are important:
Numerous on/off pedestrian-access locations. These will be stops (somewhat like bus stops) available for passengers on public pods or for emergency use. They will have simple lighted, weather-protected spaces, with stair and ramp access to ground level, where there will be walkways and sometimes a parking lot.
Frequent small service centers. Usually located at intersections and at the edges of cities, towns, and villages, where netways typically rise or drop to ground level, service centers will be attractive structures staffed by attendants. Service centers might be about an acre (0.4 hectare) in size and perhaps heated, when needed, with relatively inexpensive geothermal heat. They will be safe and appealing, with a small convenience store with take-out food and common necessities and maintained toilets. Two lifts that carry pods to and from ground level will be present where necessary. Storage and maintenance for personal pods will be available, along with battery-charging stations.
Attendants will put pods in place, assist people in and out of them, and oversee the gradual controlled acceleration of pods on an outer electric line, which then joins the main transport line. Analogously, to exit from the main electric line, at a bifurcation of the buried electric line a pod will be moved to an outer line where it will be slowed down in a service center. Rest areas along netways will not be be needed, because there will be no driving or driver fatigue, and toilets will be available at the frequent small service centers.
Transit-oriented development will be particularly appropriate around netway service centers.6,34 Residential and commercial development, plus ample protected parkland and safe, appealing walkways can be concentrated within a half mile (or 1 km) of a service center.
Less-frequent large service centers. Like the smaller service centers, these larger versions will provide basic services for people and personal pods in an attractive and safe setting, but they also will serve public pods (like bus terminals) and freight pods (like truck stops). The eateries will be larger, as will be the shopping areas, the security control center, and the lifts, which will be for large pods. Attendants will assist people in public pods and freight pods as the pods enter and leave the netway. The large pods will be stored, maintained, and battery-charged if needed. Considerable amounts of freight and goods will be channeled through these large centers, functioning somewhat like a truck distribution center, where pods with goods can be efficiently transferred and directed to different local and long-distance destinations.
Netway machinery and maintenance centers. Not open to the public, these will contain the large electric engines mainly powered by solar, wind, and other renewable energy sources that run the transport system. Perhaps like large versions of the engines that lift big trams bulging with skiers up high mountain slopes, netway engines might be spaced many miles or tens of miles (km) apart. Netway maintenance and repair experts, with both service pods for netway work and trucks for ground-level work, will be based at these locations. Replacement components for the system can be conveniently stockpiled at these centers as well.
Although no netway as described exists, a lot of related transport systems currently carry people, vehicles, or trains above ground level.12,13,25,27,35 Think of monorails, as in Sydney or Seattle, or high-mountain gondolas and tramways on cables. Small gondolas moving in opposite directions, one above the other, reduce the width of damage to a rainforest canopy, as in Costa Rica. Other elevated examples include causeways with raised roadbeds and viaducts on rows of pillars, like long horizontal bridges over land (occasionally used to protect farmland in China). Consider suspension and many other types of bridges, including bridges with traffic in opposite directions on one level over another, as in Rio de Janeiro. Walkways and bikeways cross over highways. Wildlife overpasses, from massive2,10,12 to lightweight,36,37 facilitate movement of many species across highways.
Unlike today’s large cars, buses, and trucks, the pods anticipated will be relatively lightweight. Pods, separated at intervals, will move in two opposite-direction lanes. Consequently, the elevated way itself, using strong durable pillars beneath a netway surface structure, will be relatively lightweight, perhaps like a hybrid between a walkway and a small road bridge over a highway (Figure 4). Netway sections might be supported by single (or paired) pillars, perhaps 4.5–5 feet in diameter to provide extra solidity. Pillars might be 80 to 110 or more feet apart (25–35 m or more), with some variability to fit topography.
We expect clearance under the netway to be only about 13 feet (4 m), suitable for all North American wildlife to easily pass, though awkward for giraffes. In places, clearance could rise to 16–20 feet or more, for small roads to cross and for streams/rivers and their floods to flow. Thus the supported surface sections of netways, some 13–17 feet aboveground, will be roughly at the height of second-story windows or the tops of apple trees. In moist climates, trees existing or planted along elevated ways could visually screen the structures and may provide some shade and wind protection for moving pods.
Pillars and surface sections of elevated ways might be made of familiar inexpensive, long-lasting concrete. Or they could be made of thoroughly tested, lightweight composite material (e.g., fiberglass-like carbon fiber), potentially with structural and chemical integrity for 50-plus years. Bridges made of recycled plastic (fiber-reinforced polymer composites) may be very strong and long lasting, requiring little maintenance and repair.36
A netway surface section may be a “spanner” (girder or box beam spanning the distance between pillars), with L-shaped “wings” attached on each side (Figure 3). Spanners could be efficiently lowered into place by small or medium-sized cranes on the service road alongside. In this way, components, such as a damaged pillar, spanner, or wing can be readily removed and replaced with relatively little disruption to pod flows.
In short, in the system outlined, the compact elevated ways carrying lightweight pods will be somewhat narrower than two-lane highways and lower than highway bridges. Elevated structures will be simple, modular, and flexible, composed only of pillars, spanners, and wings. Construction time and cost, as well as environmental damage, will be reduced. Spanners will contain embedded electric wires to power the system as well as slots for channeling stormwater and snow to ground-level depressions below. The simple design will also facilitate automated control of many maintenance activities.
Transport on elevated ways will produce negligible air pollutant emissions, and any pollutants produced would be dispersed by the wind. Very little traffic noise will be generated by the netway system. Lighting on the netway will be easily shielded from migrating birds and from people below. Fallen branches or trees along netways (e.g., in high winds) will rarely occur because of the height of elevated ways and can be detected by sensors in the netway. Grounding everything against lightning will be standard. Snow and ice (which will not affect the electric induction drive system)24 will be mainly eliminated through designed openings in the netway, possible electric heating in spots, and service personnel. Finally, although farmland under four-lane highway viaducts doubtless has lower crop production due to limited light and rain, plant growth under netways that are 27 feet wide would be only slightly affected.
Large portions of today’s road infrastructure are in need of repair or replacement, including 30 percent of America’s bridges, plus numerous culverts functioning as major bottlenecks for surface-water flow and fish movement.2 Netways will require no culverts for water flow, and will largely avoid the need for massive highway bridges, which are continually pounded by traffic and require frequent maintenance and repair. Pods zipping across streams and rivers on lightweight netways will have less impact on river flows, stream habitats, and fish.
Another attraction of elevated ways is that they will practically eliminate animal-vehicle and traffic crashes. Consequently, human fatalities, injuries, medical treatments, and time lost will be reduced to nearly nil. Auto insurance costs should plummet. Elevated aerodynamic pods moving at efficient constant speeds will also virtually eliminate roadkilled wildlife.
In addition to elevated netways, we recognize the need for covered U-shaped troughs called earthways below, at, or somewhat above ground level (Figure 4). Nearly invisible at a distance, these partially or entirely sunken netways may be particularly useful in dry areas such as desert and grassland/pastureland where groundwater is low and trees grow poorly. In moist landscapes trees can partially hide elevated ways.35
In densely populated suburban and urban areas that already have subways, partially or fully sunken structures would be unobtrusive. However, in cities, building underground infrastructure is relatively costly. So if the netway system were extended to urban areas, a mixture of elevated ways, partially sunken earthways, and underground earthways would probably be desirable. Replacing highways with earthways and elevated ways would reduce impervious surface area and increase soil and vegetation cover, an important benefit in urban areas.
Cut-and-cover construction (digging a trough and adding a cover) is especially convenient for excavating sand or other unconsolidated material, or for drilling out soft rock such as limestone or shale. Underground construction may involve large boring machines, drill hammers, and/or using dynamite to create tunnels through hard rock such as granite or metamorphic types,13 but tunneling may be expensive and leave water-porous unstable rock above. Bored tunnels are desirable for protecting valuable habitat on the surface, while cut-and-cover construction is valuable where connecting separated habitats is the primary goal.12 Either method produces plenty of porous fill, which in many areas is a valuable resource for construction uses. Earthways would be designed so that small and medium earthquakes produce minimal disruption to the flow of pods.
Sunken netways need to effectively handle water, light, and air. Preventing water intrusion into earthways is essential to their design and uninterrupted functioning. The sides and bottom of an earthway will be waterproofed and the top well covered. Where groundwater is near the soil surface, earthways, like subway systems and highway tunnels, will be sealed against seepage using impervious concrete with polymeric (plastic) and/or bituminous membrane layers. And dependable hydrologic drainage or pump systems with backups will be designed to handle any groundwater or rainwater/snowmelt that does seep into the earthways.
Earthways should have no significant effect on groundwater flow in a dry climate with a low water table, or in porous sand and gravel soil, or where groundwater flows are parallel to the earthway. Groundwater flow perpendicular to an earthway in clay and silt soil could result in a locally higher water table on the upward side (perhaps useful for irrigating agricultural production on the earthway cover) and lower on the downward side. Maintaining relatively natural groundwater levels is valuable for nearby wetlands and streams.
Because they will be covered, earthway surfaces would normally not experience roadbed sinking, cracking from frost, snow accumulation, or surface ice, and they would have few erosion/sedimentation problems. Earthways would essentially escape the weather variations outside, including extreme heat, cold, winds, rainstorms, snowstorms, and ice storms, all of which may increase with global climate change. This means that earthways would have low maintenance and repair costs.
The earthways will be able to accommodate the aerodynamically designed low and long freight pods, with a 10- to 12-foot (3–3.5 m) vertical clearance, such as in some parking garages. However, a 16-foot clearance would be needed for a rare oversized load.
Where the earthway is shallower—for example, only 6–8 feet (2–2.5 m) below ground level—windows could line the upper sides under a shallow-pitch cover (Figure 5). The earthway covers themselves could also be translucent in places, providing sunlight. Passengers in the moving pods would enjoy views of surrounding vegetation, buildings, mountains, and sky. Even vegetation under fluorescent lighting in spots within the earthways would be welcome, like the much-appreciated tiny tropical rainforests near some of the Metro stations in Paris. Eternal artificial light where needed would be generated by renewable energy sources, which have fewer uncertainties associated with long-distance transmission and extreme weather events.
Pods will have no running motors and will produce no exhaust, which should make it easier to vent the earthways. And temperature and moisture conditions within earthways will remain relatively constant, at least daily and within a particular season. In the case of partially sunken earthways, the strips of open air on both sides of the earthway would eliminate the need for fresh-air venting. In windy areas, shipboard funnel-like structures or Middle Eastern wind-tower cooling structures along the earthway covers could funnel in fresh air. Electric air-venting systems would operate as needed.
Earthways would dip maybe 3–5 feet (1–1.5 m) under most streams (Figure 4), 1–2 feet under major intermittent channels, and could simply be elevated across most rivers and major valleys. Frequent low, vegetated wildlife overpasses, facilitating the free flow of animals, would readily cross over even the raised earthways2,12,23,36 (Figures 1 and 5). In hilly and mountainous terrain, wildlife overpasses would conveniently fit with the topography.
There are many options for covering the 27-foot-wide (8.5 m) earthways. The covers could be somewhat mounded or slanted upward above ground level (Figure 5) or could be flat. Large trees could grow alongside the earthway covers, with shrubs on the outer portion of the covers and grasses and herbs over the central portion (Figure 4). One foot of light sandy soil would be the minimum thickness to sustain drought-resistant shrub growth on the covers. One and a half feet of such soil, perhaps with small drainage pipes at the bottom, could permit growth of some small trees without adding excess weight from water-saturated soil.
Features at Ground Level along Netways
Ecological and other features at ground level, whether under elevated ways or above earthways, are key elements for the netway system. Plenty of design options and flexibility exist.38–41 In place of a multilane highway, the netway would normally use less than a quarter of the current right of way. Therefore, considerable area would be restored to nature and other uses, a large gain for society.
Most important in this system is reasonably continuous vegetation or natural habitat so that wildlife can readily cross from one side of a netway to the other. In moist climates, both tree and shrub vegetation will be optimal. In drier areas, shrubs will be important, with certain trees being a local option. In this manner, habitats on opposite sides of a netway will be effectively connected for virtually all wildlife species. In addition, streams and rivers crossing a netway will flow in relatively unaltered natural condition, with negligible netway-caused pollution, scouring, or blockage of fish movement. Frequent convenient crossings will also be available for local residents and farmers and their livestock. In essence, replacing highways with netways will reconnect our land.
Yet the linear characteristic of netways offers another huge benefit to nature and wildlife, especially in much-altered and habitat-fragmented landscapes. At present hardly any species moves efficiently along highways and roadsides.2 Vegetation strips of shrubs with or without trees along a netway would form wildlife corridors, helping to reconnect fragmented habitat patches to sustain wildlife populations.39,42 These netway habitat corridors could also function as valuable recreational trail routes for local residents, walkers, hikers, and cyclists.
A narrow, unpaved, slow-traffic road, sometimes with limited access, along one side of the netway would provide maintenance and repair access. Various infrastructure pipelines and conduits serving society would parallel these dirt roads (such infrastructure would probably not be incorporated in the netway structure, where easy repair/replacement of modular components is important). Buried pipes could include water supply, sewer and electrical conduits, and potentially even supercooled long-distance energy transmission from huge wind- or solar-energy farms.
We anticipate that many specific land uses will also be associated with netways. Arrays of solar panels and wind-energy-capturing devices will power the netway system. Small neighborhood parks bordering the netways would generate public support, plus stewardship. Various types of food production should prosper along netways, including community gardens, market gardening/truck farming, greenhouse production, poultry production, narrow livestock pastures, and long, thin crop fields worked with tractors. Food production along netways near cities and towns would be especially valuable for minimizing transportation costs and providing fresh produce. All of these land uses would have to be compatible with two goals for the netway system: to eliminate traffic disturbance effects and to robustly reconnect natural flows and movements between opposite sides of the netways.
Netway Benefits for Society
By reversing the centuries-long trajectory of ecological degradation by road systems, the netway system would primarily restore nature’s resources. However, major benefits would reverberate widely through society in four categories: (1) safe and efficient mobility; (2) renewable energy, fossil fuel use, air quality, and greenhouse gas emissions; (3) food and recreation near cities and towns; and (4) biodiversity, wildlife, water quantity and quality, and aquatic ecosystems.
Safe and Efficient Mobility
The basic goal of transportation is safe and efficient mobility of people and goods, while minimizing environmental degradation.2 When the human population was small, almost everyone could choose his or her own routes and timing, whether walking, horseback riding, driving a wagon or buggy, bicycling, and so forth. Even with today’s high population, the individual approach to transportation remains, in part through the use of cars. Personal pods and pod cars represent the next generation. Personal pods, also known as personal rapid transit, exist in various small-scale and prototype systems.27,43
Moving groups of people in buses, trains, ships, airliners, and even trams increases the efficiency of mobility, especially around cities where people are concentrated. For example, some 550 cities worldwide have electric streetcar or light-rail systems, and about 350 have electric trolleybus systems.30 In these examples, electricity is generated in a centralized power facility and directly conducted by wire or rail to the motor of the moving train or bus. The netway-and-pod system is similar except that the electric induction wire is safely, and aesthetically, buried in the netway. Electricity also drives heavy freight and passenger trains on tracks between major cities in Japan, China, and Western Europe. High-speed intercity passenger trains for mass travel reach some 200–300 miles per hour (325–500 kph) in these regions.27
Freight pods and pod trucks would be a welcome alternative to today’s heavy trucks, which degrade road surfaces, emit pollutants, create considerable noise, and clog traffic. As the transport of light- and medium-weight cargo grows, the netway system will provide impressive efficiencies and cost benefits. Goods will be transported by renewable energy–based electricity rather than fossil fuel. Goods will move in separate, compact aerodynamic pods according to type or destination. Large service centers along the netway will also function as truck distribution centers, where goods and pods will be directed to different local and long-distance destinations. Finally, the compact pods can be hooked together for ground-level transport. These efficiencies will be a boon for commerce and society alike.
Enhanced safety is a watchword for netways. Today’s road system is beset with hazards: widespread worn and bumpy road surfaces; wet or icy driving conditions; hills, sharp turns, and dangerous intersections to navigate; tired or “crazy” drivers; fender benders and lethal crashes; insurance, repair, and medical costs; and more. Netways will minimize or eliminate all such hazards. Relaxing in a pod as it smoothly moves along beats the stress and hazards of manual driving. Travelers will arrive at their destinations relaxed rather than tired or aggravated—a highlight of the netway system.
Travel time is a key measure of efficient movement in transportation. In the netway system outlined, accelerating and decelerating, creeping along in bumper-to-bumper traffic, and the continual dangers and frustrations of “speed-up-and-wait” driving will be replaced by smoother and quicker trips in netway pods. Near cities, where there is higher transport capacity, more public pods and freight pods will be provided. Yet there will never be gridlock because access would be limited if the netway system became too full. Over time, as the netway system matures, accessibility to cities, towns, villages, intersections, and elsewhere will increase, as is the case for any successful transportation system.
Renewable Energy, Fossil Fuel Use, Air Quality, and Greenhouse Gas Emissions
Renewable energy and fossil fuel use. Energy to power netways from the sun, the wind, and potentially from the earth’s heat is plentiful, widespread, and permanent,15,16,44 unlike oil supplies. Using these and other mainly renewable sources provides energy diversity and dependability. Recharging batteries en route while transporting people and goods also provides flexibility and dependability for users.
Currently, vehicles are major consumers of petroleum, a fossil fuel in limited supply especially outside the Persian Gulf.3,30,45 With nearly a quarter billion vehicles in the United States and an average of 500 gallons of gasoline per vehicle used annually, motorized surface transportation is a giant consumer of oil. Vehicle numbers and associated fuel use are growing rapidly in most other nations. Road construction, maintenance, and repair also depend on oil. In the startup transition phase to netways, fossil fuel may be an important energy source, but it can be phased out as renewable energies come online.
Netway pods will consume no fuel but rather will be powered by electricity provided by the netway system. Renewable energy—primarily wind, solar, and potentially geothermal—will be converted to electricity and fed to the system at local sources and generated at major netway machinery and maintenance centers.15,16,30,44 Other local sources can include hydro, wave, and tidal energy. Municipal organic solid waste and wood-and-crop residues (biofuel) could also be used as energy sources, but, like fossil fuel, they emit CO2. In addition to local energy sources, electricity can also be transmitted long distances in powerlines. Not only will renewable energy dominate energy supply for netways, but it could feasibly be the dominant source of energy everywhere by the end of the century.15,16 Indeed, the Danish government recently concluded that Denmark can remove fossil fuels entirely from its energy system, including transport, by 2050, and achieve this with a cost that is barely more than a business-as-usual scenario. Any excess power generated along netways, beyond the needs of transportation and construction/maintenance/repair, can be used to support local communities or can be fed into a continental electric grid.
Solar energy will be collected from large and small arrays of solar panels on the land. In addition, solar collectors will be widespread at ground level along many netways, as well as on the elevated-way structures themselves. Photovoltaic semiconductor- and silicon-based solar cells will probably predominate, though other types might include solar mirror thermal-steam generators or solar thermoelectric-material devices.
Wind energy will be captured and converted to electricity by turbines on large and small wind farms.44 Also wind turbines both on and alongside netways will help power the netway system. Tall structures can produce useful power with small-diameter turbines, but much more power can be generated with large turbines. Miniaturized devices capturing energy from even small gusts of wind from any direction might be developed.
Geothermal energy will be captured where available. Deep drilling (cautiously, and currently expensive) in certain areas for a high-temperature source, or shallow drilling for lower temperatures (perhaps usable with metal-organic heat carriers), may generate useful energy for the netway system. Easily accessed geothermal energy from shallow drilling may provide heat for the netway service centers, melt snow on elevated ways, and so forth.
Pod cars for ground-level driving will be stored or rented at the frequent small service centers along a netway, where batteries for the pods’ electric motors will also be charged. These same pods will have their batteries charged by the system while en route and thus can seamlessly leave the netway and be driven to local destinations.
Finally, the netway system will likely catalyze renewable-energy production from countless landowners and energy companies on lands near netway routes. The cumulative effect of the netway system, thus, will be an overall decrease in energy use, a huge drop in fossil fuel use, and a significant increase in the use of solar, wind, and other renewable energies.
Air quality and greenhouse gas emissions. Today, roads and moving vehicles release and widely disperse particulates into the air, including chemicals from the wear of road surfaces, tires, brake linings, and engines; from rust; and from fuel combustion.2,46 Many gases and aerosols are also emitted or formed secondarily in the air from emissions, including nitrogen oxides, volatile organic compounds, ozone smog, sulfur oxides, and carbon monoxide. Heavy metals (zinc, lead, copper, chromium, nickel), nitrogen, phosphorus, and organic chemicals from roads and vehicles are spread both locally and regionally, with detrimental ecological and human-health effects.
Pods moving along netways—with no running engines, fuel use, brake use, and so forth—will drastically reduce or eliminate particulates and gaseous/aerosol pollutants. Even ground-level driving of pod cars on small roads will produce noticeably less pollution, because pods will be lightweight electric vehicles (perhaps in some cases powered by zero-emission hydrogen fuel cells). Certain pollutants would emanate from the netway structures, machinery, surfaces, and service centers, but stormwater runoff could carry these into containment and treatment basins along the netways.
Today’s vehicles emit large amounts of greenhouse gases, especially CO2.30,44 With some 10,000 pounds of CO2 emitted by an average vehicle annually in the United States, road systems are a prime cause of atmospheric greenhouse gas buildup and its effects. In contrast, pods moving on netways would carry and use no fuel for combustion and produce no greenhouse gases. The large electricity-generating engines that will power the netway system should run on renewable energy and produce virtually no greenhouse gases.
Food and Recreation near Cities and Towns
Agriculture and market gardening. Today’s extensive surface area of roads and roadsides disproportionately covers good agricultural soil and productive farmland, especially surrounding cities and towns.34 Highways are also barriers to the efficient movement of livestock, farm machinery, and water in irrigation systems. Globally, good soil and food production are limited, hunger is a major problem, long-distance food-transportation costs are high, and the estimated two to three billion new people who will be born in the next 25 years will need to eat too. Protecting and restoring good agricultural soil has an ethical dimension.
Replacing highways with elevated ways can open up valuable farmland and begin to reverse some of these food-production problems by mitigating transportation’s disruption to existing farming activities. Indeed, food production will be particularly well suited to netways that are adjacent to existing farmland. As mentioned earlier, China has constructed some elevated highways, in part, to protect shrinking agricultural land.
Market gardening (truck farming) along netways will have special value.34 Intensive small-plot food production can take place in proximity to cities and towns. Thus, with minimal transportation cost, fresh vegetables, fruits, and other products will become readily available in nearby markets and restaurants. Supporting local families and farmers in this way is an economic and social value.
Recreational trail systems. Today’s highways are rarely used as routes for walking, and in some cases bicycling, because a busy highway is dangerous and noisy.6 Local residents, walkers, and cyclists also often avoid crossing such highways because doing so is hazardous or prohibited. Indeed, safe and attractive trail systems for recreation are in short supply in areas surrounding cities and towns where people are concentrated.
Both elevated and sunken netways will remove the highway barrier and permit free movement from one side of a netway to the other (Figures 3 and 4). Communities split in two by highways will be reconnected. Local residents and farmers will no longer have to drive circuitous routes to cross highways. Indeed, road bridges over highways (and highway bridges over roads), seemingly always needing repair, will no longer be needed.
In addition, both elevated ways and earthways will be suitable for trails along their length, either below or above the quietly moving pods carrying travelers. Bikeways will be best located at ground level rather than on netways to keep the system simple and cost-effective, to prevent accidents between objects moving at different speeds, and to provide recreation close to nature. Trail networks, especially near population centers, will fit nicely with the netway system’s interconnected form. The combined result will facilitate much-needed walking for exercise, cycling for recreation, and nonmotorized commuting to work.
Biodiversity, Wildlife, Water Quantity and Quality, and Aquatic Ecosystems
Road networks and vehicle usage. Looking at road density (the average total road length per unit area) and the current road network form (e.g., grid, irregular, or hierarchical) provides valuable insight into the ecological effects of road systems at a landscape, or regional, scale.2,47,48 Roadkills, animal population size, fire frequency, remoteness, human access, and various hydrological attributes have been correlated with road density. The fine-scale road grid of today’s road network (a form that overall is considered ecologically damaging) can be greatly improved by concentrating roads in one corner; making fewer larger roads for the same amount of traffic; and adding wildlife- and water-corridor structures under or over roads to connect large green natural patches on opposite sides. But the netway transportation vision presented here is ecologically far superior to even those improvements.
The average speed of motor vehicles on roads is a useful indicator for determining priority locations for building netways. Consider the results of a detailed study of moose-vehicle collisions on Swedish roads.22,23 Few crashes occurred where the posted speed limit was up to 45 miles per hour (70 kph) (Figure 2). At 55 miles per hour (90 kph) and above, the moose-vehicle collision rate was high. Indeed, this high collision frequency occurred over a wide range of traffic levels (from 1,000 to 7,000 vehicles per day). Other studies show that two-lane highways generally have the highest rates of roadkilled mammals and birds as well as car crashes.2,6
The risk of collisions involving human fatalities increases exponentially with vehicle speed, so even slowing a small amount can provide a significant benefit.36 When the perceived width of a two-lane road ahead is narrower, drivers slow down49 and presumably hit fewer animals. Nevertheless, a posted speed limit of about 50 miles per hour (80 kph) can be a useful threshold for estimating which two-lane roads have both many roadkilled animals and many smashed vehicles and people—and thus which locations might be the most important for building the first netways. Other ecological effects of roads are only slightly increased by higher vehicle speeds. On busy multilane highways, for example, few animals attempt to cross or are killed.6,22
Traffic level has considerably more effect on wildlife than does road width or traffic speed.20 Traffic noise, primarily due to road and tire surfaces (plus truck traffic), is strongly correlated with traffic level.2 Therefore traffic level, defined as vehicles per day (the annual average number of vehicles passing a certain point), is important for understanding ecological road effects as well as for determining priority locations for netways.
A few dozen studies, the majority focused on roadkills, have related traffic level to transportation’s effects on wildlife.17–21,36,50-52 Overall, studies indicate that increasing traffic level up to about 3,000 vehicles per day raises the roadkill rate, sometimes with significant effects on vertebrate populations (amphibians, reptiles, mammalian carnivores, ungulates, and birds). With increased traffic from about 3,000 to 10,000 vehicles per day, the roadkill rate initially remains moderately high and then may drop, in part because this traffic range can deter wildlife crossings, especially for carnivores and ungulates. Above about 10,000 vehicles per day, deterrence remains high and wildlife’s avoidance of adjacent degraded habitat is typically significant, though roadkills of some species continue to occur. The result is that rather few animals successfully cross busy roads with greater than 10,000 vehicles per day. A recent literature review suggests that 3,000 vehicles per day is the approximate level above which “substantial” ecological impacts are present for these wildlife groups and that a traffic level at or above 10,000 vehicles per day is a “severe” barrier to wildlife crossings.21 Thus, highways with greater than 3,000 vehicles per day will be priorities for replacement by the netway transportation system.
Habitat effects. A good way to approach complex transportation and nature interactions is to consider the three major road and vehicle effects on habitats: (1) habitat loss; (2) habitat degradation near roads; and (3) habitat fragmentation by the road network.47
Direct habitat loss due to roads and roadsides is estimated at nearly 1.5 percent of U.S. land.2,48 In Germany the figure is about 2.5 percent. More than a third of the American habitat loss is from roads themselves and a third is from the mostly open roadsides. The remainder is from private roads, driveways, parking lots, newly built public roads, and extensive, largely unmeasured off-road-vehicle tracks. Still, ecological effects reach almost everywhere, perhaps less because of total road surface area and more because of the network form. About 10 percent of America’s public roads consist of U.S. Forest Service roads, just over 1 percent are multilane interstate highways, and about 30 percent are unpaved earthen roads. In the 3.1 million square miles (5.0 million sq km) of the contiguous United States, the most remote spot (farthest from a road used by vehicles) is 21 miles (34 km) from a road near the Continental Divide, whereas the most remote spot in Iowa is but a half mile (0.8 km) from a road.
Habitat degradation near roads results from several transportation-related processes,2,5 including significant effects from erosion, sedimentation, heavy metals, and road salt, even though these effects extend only feet (meters) outward from any given road. Microclimatic changes in wind, sunlight, temperature, and moisture often extend tens of feet (meters) from a road. Most significant are the long-distance effects, such as traffic disturbance (especially noise) inhibiting sensitive birds and other vertebrates or chemical and sediment inputs at bridges that affect downstream/downriver species over long distances. The resulting “road-effect zone” of habitat degradation, produced by long- and medium-distance effects on both sides of a road,2,5,13,53 is the land significantly affected by transportation.
Habitat fragmentation by the current road network results from roads acting as barriers or filters against wildlife that need to move across the land.12,48 Animals forage for food, travel to water sources to drink, move away from or escape predators, join in social behaviors, search for mates, disperse to a new home range, and may migrate seasonally. When encountering a road in such movements, an animal typically slows down to cautiously cross the road or turns back from the barrier. Perhaps because the area around busy roads is noisy and dangerous (and probably smelly), few species effectively move along them. In essence, the current road system has fragmented formerly continuous habitat into smaller habitats, thus confining the many species that seldom cross roads. Combining roads with commercial or residential development, as in strip or ribbon development, disrupts the movement of most wildlife species.
Biodiversity and roads. The insidious dimension of habitat fragmentation by a road network is that formerly large species populations are sliced up into small populations, all at greater risk of locally disappearing.36,40,42 Demographically, small populations fluctuate in size over time more than large populations, so the chance of dropping to zero (disappearing) in a fragmented habitat patch is greater. Genetically, inbreeding by mating individuals of a small population over time leads to loss of genetic variation and thus more weak or sterile offspring. These demographic and genetic problems mean more local extinctions in small, fragmented habitat patches.
Three specific road effects on wildlife warrant special mention: (1) roadkills; (2) damage to remote natural areas; and (3) traffic disturbance.
The public sees dead rabbits, squirrels, house cats, house sparrows, raccoons, deer, and so forth along roads.4,6,23 These flattened fauna are of little consequence ecologically, because such common animals can reproduce much faster than cars can hit them. However, roadkills of slowly reproducing small-population predators, such as bears, big cats, and large turtles, are serious because each animal counts in a small shrinking population.
Roads to remote natural areas are particularly detrimental because they provide human access, which results in many types of damage to sensitive habitats and species.2,36 Removing spur roads has exceptional ecological benefit. In addition, new road construction is making remote areas themselves progressively scarce,54 impoverishing our planet.
Traffic disturbance, particularly noise, produces a wide swath of degraded habitat on both sides of a busy road, where sensitive animals are scarce or absent.18,19 The width of this degraded habitat and the species affected seem to especially depend on the amount of traffic, typically extending outward several hundred feet (meters) in each direction with traffic levels from about 1,000 to 15,000 vehicles per day.
It now seems clear that three interacting effects of roads on wildlife are central:17,19,55,56 degraded adjoining habitat (the zone of animal avoidance or population decrease); roadkill by vehicle; and animal deterrence or repulsion from crossing a road. The barrier effect, indicated by a low (or zero) success rate of crossing by animals approaching a road, effectively fragments habitat.12,22,50 Wildlife-vehicle collisions are a special case, whereby animal roadkill, as well as damage to vehicle and/or people, occurs. Road width and surface type (paved vs. earthen) appear to be of minor importance to wildlife, except for some invertebrates and small mammals.20,38
When a new highway, Carretera de los Túneles, was proposed recently near Barcelona, Spain, the Ministry of Transport designed it and by law provided the design plans to the Ministry of the Environment for review and approval. The Environment Ministry pointed out that a highway that served as a barrier to movement across the landscape was inappropriate. So, the Transport Ministry built the highway with a few vegetation overpasses for easy crossing by local people and wildlife.12,23,57 The highway slices through an extremely important large natural area, and though the overpasses provide some valuable connectivity, the highway still creates a swath of degraded habitat and remains a barrier to some natural flows. The netway system is a superior alternative that can transport people and goods in a way that reconnects valuable natural areas.
Water quantity and quality. Presently roads widely alter or disrupt water flows in wetlands, streams, lakes, and groundwater.2,5,10,11,13 Vehicles, roads, and roadsides pollute these water bodies with sediment, heavy metals, nitrogen, hydrocarbons, road salt, and other pollutants. These materials degrade water quality, aquatic ecosystems, and fish. Also, the transportation system’s chemicals and sediment often degrade clean freshwater supplies in wells and reservoirs.
One of the main criteria in initially locating the most critical sites for netways will be to protect the most ecologically significant water bodies. Thus, rare types and outstanding representatives will be avoided and protected, as will be those with large undeveloped shorelines or a concentration of rare species.
With elevated ways, hydrological flows of water across the land will be relatively unimpeded and natural. In contrast, earthways would alter groundwater flows in some locations, though designing such netways to fit groundwater patterns could eliminate or limit effects to a narrow adjacent zone or local area. Thus, overall, replacing the road network with the netway system will result in significant benefits for water levels and flows, as well as better water quality and aquatic ecosystems in diverse water bodies across the land. Fish populations and fishermen will greatly benefit from this transformation.
With no running motors, fuel consumption, or emissions, pods moving on netways will cause very little water pollution. By channeling stormwater to small retention ponds or basins at intervals beneath elevated ways, pollutants can be contained, thus minimizing dispersion to natural water bodies. In these constructed ponds and depressions, pollutants can be treated, diluted, or removed, thus reducing almost all pollution to nearby streams, lakes, and aquatic ecosystems.
The netway system therefore can produce clean water bodies, including groundwater, rivers, and lakes used for drinking-water supplies. As urbanization spreads, water supplies will become progressively scarce, distant, and costly. The netway system, by helping to ensure the preservation of clean water supplies, will have substantial social and economic benefits.
Aquatic ecosystems. By its design, the netway system will sustain high biodiversity, natural ecosystems, and fish populations in surface water bodies. Natural hydrologic flows of water will be maintained, and pollution of clean water supplies will be prevented. And because the netway system will cause minimal disturbance to water bodies, natural habitat heterogeneity will be maintained within a water body. Clean-water and biodiverse aquatic ecosystems with natural food webs and fish populations will result from replacing busy highways with elevated ways and earthways.
Fitting Netways to the Land
The broadest objective of the netway system is to restore and sustain nature on our planet, especially biodiversity, wildlife habitat, and aquatic ecosystems. This requires converting our widely permeating heavy-imprint road system to a light-imprint transportation system that dovetails with nature’s major patterns and processes. Simply removing a road from an important natural area is the ecologically best and most cost-effective strategy. However, where road removal seems to be impossible, the netway system is an effective alternative that also provides for transportation. Netways will replace busy highways and will carry the same amount or more of people and goods.
In the current road system, virtually all conflicts with wildlife are at ground level. Highways, typically wide and with considerable fast-moving traffic, have the greatest impact on nature, though small roads may also have significant effects. As described in the preceding section, the priority locations for initial netways will be highways with a traffic level of more than 3,000 vehicles per day on average and with posted speed limits at or more than 50 miles per hour (80 kph) (Figure 2).2,19,21,56,58
But within these priority locations, which are the most important? To consider which highways are most damaging to nature, think about where the most important nature exists today and might exist tomorrow. Three major habitat patterns encompass our most valuable nature: (1) large natural areas, or “emeralds”; (2) wildlife and water corridors; and (3) vegetation that protects water bodies.23,34,38–42,59
Large natural areas, or “emeralds,” sustain unpolluted aquifers, lakes, and major clean-water supplies; animals with large home ranges; viable populations of many habitat-interior species; connected natural stream networks; and sources of rich biodiversity that can disperse across our human-imprinted land. Major natural areas exist at many scales, from extensive, remote forests/woodlands and deserts/grasslands to local, large woodland and wetland patches.
Wildlife and water corridors connecting these large green areas sustain key species as they move about the landscape and also enhance biodiverse natural conditions in the big green areas. Protect these large natural areas first, and then connect them, to restore our highway-disrupted emerald network.38,47
Vegetation that protects streams and rivers, ponds and lakes, vernal pools and reservoirs, and diverse wetlands provides numerous benefits to nature, and to us. These values include a clean water supply; natural flood control; unpolluted water bodies; diverse aquatic habitats; healthy fish populations; commercial fish harvest; wildlife habitat; aesthetic qualities; and a wide array of recreational opportunities. Especially valuable water bodies are the rare types and outstanding representatives, including those with a concentration of rare species or a largely undeveloped margin. Diverse coastal wetlands, often changing with sea-level rise, are exceptionally valuable for both nature and society.
The priority areas for building netways have both busy highways (greater than 3,000 vehicles/day and with a posted speed limit greater than 50 mph (Figure 2)) and one or more of these three most valuable types of nature. Converting roads to netways is expected to have the greatest benefit in the following large areas, where road systems currently disrupt and degrade the preceding key resources (Figure 6).2,5,10,12,23,34,53,59
Extensive forest, woodland, grassland, or desert areas. Busy highways bisecting or dissecting these extensive natural areas degrade nearby habitat and also form a barrier or filter against the movement of certain key species, thus partially fragmenting the natural landscape. Netways replacing these highways restore our last best nature. Where an extensive natural landscape has many patches of large cropland or built areas, the natural habitat between these patches is especially valuable and hence a priority area for replacing highways with netways.
Large cropland areas. In a cultivated landscape, the few remaining natural-vegetation patches are of central ecological importance, so highways cutting through or alongside them are priorities for conversion to netways. Where large natural patches are close together in cropland, highways between them disrupt the flows of wildlife and water between natural patches and thus are priorities for replacement by netways.
Suburban/sprawl landscapes and cities. In suburban and sprawl areas, continued urbanization, now and in the decades just ahead, will render sustained protection of biodiversity, rare species, clean water, and aquatic ecosystems unlikely. Thus the only priority netway site in such areas is a highway bisecting a scarce large natural patch or passing between two nearby ones. In cities, where but shreds of nature persist, netways for nature protection are normally unnecessary.
Of course, plenty of nature and wildlife are extremely valuable at a local scale. But these three priorities areas are the most important at regional, national, and global scales.
Consider an example of transportation and nature in Florida. Twenty-three 98-foot-wide underpasses were constructed in 1986–1993 under a 76-mile (122 km) multilane highway (Alligator Alley, Interstate 75) to increase surface-water flow for the adjoining Everglades, reduce roadkills of the threatened Florida panther (Puma concolor coryi), and provide limited public recreational access.2,36 Each goal was achieved, and in addition seemingly all appropriate vertebrate species moved through the underpasses. In the next phase, 1 mile of the road is currently being elevated, with 9 more miles of elevated highway planned. This new phase should achieve even more success, specifically the reversal of habitat loss, habitat degradation, and habitat fragmentation due to the highway, thus effectively restoring the land. Still, the large, new, relatively expensive elevated highway will have little of the mobility, energy, and atmosphere benefits provided by the netway system.
For effective road planning, maps of busy highways are now laid over maps of priority nature patterns. In almost exactly this fashion, the Dutch Ministry of Transport and the Florida Department of Transportation have identified key conflict or bottleneck locations, where cost-effective mitigation/compensation efforts and resources have been concentrated to eliminate the conflicts.2,6,13
Similarly, using this map-overlay process in planning the netway system will pinpoint the priority conflict locations in every state or regional planning area. Large areas with clusters of conflict locations will be the highest priorities for the replacement of highways with netways. The netway system of elevated ways and earthways in these areas will provide the greatest benefit, indeed will restore nature, for society’s future.
What alternatives exist? Eliminating vehicles carrying individuals in favor of group transport by rail and air seems unlikely in the foreseeable future. Extensively reducing and rearranging the road system on the ground is improbable. If nature is to be protected, the only alternative to a netway-type transformation currently on the table is to massively and incrementally mitigate the existing roads and vehicles system.2,5,6,10–12,36 In this alternative path, one would start with the two major goals of applying road ecology for society: improve the natural environment alongside every road segment; and integrate roads and traffic with a sustainable emerald network of biodiversity and near-natural water conditions across the landscape. Then let specific mitigations, such as the following, add up: perforate roads with underpasses and overpasses for reestablishing natural wildlife movement patterns; cut traffic noise effects with quieter road and tire surfaces, plus roadside soil berms; convert most open roadsides to woody roadsides to increase wildlife habitat and decrease barrier/fragmentation effects (and always drive at a safe speed according to changing conditions along a road); improve and add countless culverts to reestablish natural groundwater patterns, stream flows, and fish movements; and remove remote roads and spur roads in every jurisdiction to repair the integrity of large natural areas.
Multiplied at the scale of our road system, these and numerous other mitigations would produce a mammoth cumulative benefit for nature. But alas, the current rate of such changes is woefully inadequate. Worldwide urbanization, road construction, and vehicle usage are all vastly outstripping mitigation efforts. The best strategy may be to accelerate the mitigation of our existing road system while at the same time launching the ambitious netway system for our future.
Timing, Costs, and Opportunity
The last transformation of U.S. transportation happened in a mere 25 years. In about 1900, almost all passenger transport was by rail or was horse powered on roads, with people traveling by horseback and in buggies, carriages, and wagons.9,60 Roads beyond cities were muddy and dusty. By 1925, motorcars and trucks powered by fossil fuel were widespread, and roads were rapidly transformed to black strips of asphalt.
Today’s transformation to a netway system can begin promptly. For example, in years one to five, we can create a plan to (1) review the ecological goals and proposed solutions; (2) review the diverse engineering dimensions; (3) map the major ecological network of large natural patches, major wildlife-and-water corridors, and highest-priority water bodies, and map traffic levels on busy roads (and with right-of-way width estimates) in remote, rural, and outer-suburban areas; (4) identify existing and potential renewable (and other) energy sources; (5) identify potential materials, manufacturers, and contractors in each region; (6) consider frontier technologies;32,33 (7) identify large pilot-project areas in all regions; (8) build local public interest and support in the pilot-project areas; (9) generate policymaker support at federal, state, and local levels; and (10) conduct cost/benefit analyses.
During years five to ten, we can build, monitor, and test the pilot projects. From approximately year ten onward, we can then expand the pilot projects and construct the netway system in all nature priority areas (Figure 6), beginning with those regions and corridors where interest and funding are strongest. Early in this final phase, large numbers of people will likely be using pods on netways and many may have, or may want to have, their own pod car. This is likely to quickly generate interest in extending the netway system into other areas, such as lower-traffic areas (e.g., with a threshold of greater than 1,000 vehicles/day), suburban areas, and as fingers into the city so that everyone has ready access to the netway system. Over time, perhaps like the horsepower-to-fossil-fuel conversion, our land transportation system will be transformed.
Understanding costs is central to success—private as well as social and environmental costs. Costs of planning, construction, energy generation, pods, and conversions of highways to green corridors are obvious and should be made explicit. Benefits to nature’s biodiversity, to wildlife and their movement, and to diverse water bodies and aquatic ecosystems should be made equally clear, though they will be more difficult to specify. There will be benefits from recycling today’s vehicles, highway asphalt (gravel and fossil fuel), guardrails, signs, sandy roadbed fill, and so forth. Reducing oil and energy consumption will be a major gain. Explicit significant benefits will likely include flood reduction, meeting increasingly urgent clean-water needs, reduced air pollution and climate change, fewer polluted aquatic ecosystems and less loss of fish, enhanced food production and transport near population centers, and valuable trail-recreation opportunities. Pursuit of these nonmarket and market benefits will stimulate further benefits.
Financing for the netway system could come mostly from netway users, similar to how the massive U.S. interstate highway program begun in 1956 was financed. A share of today’s national transportation trust fund could be invested in the netway system. Gasoline and diesel fuel taxes mainly feed the trust fund today, but future fees might be based on vehicle miles traveled (a more appropriate fee for financing infrastructure, especially as gasoline consumption plummets). Concern over reallocation of public funding would be mitigated by the huge cost savings of a netway system, which eliminates extensive and expensive maintenance and rebuilding of roads and bridges. Sale of considerable unneeded land, e.g., from multilane highways, provides revenue. Also, ongoing revenue streams from the sale of renewable energy and from food products and recreation fees on netway land near cities and towns would offset many costs.
The netway system promises a boon for industry and jobs. Vast new fields of research and development would be energized; automotive manufacturers would build new types of vehicles; a new industry for manufacture of netway components would be launched, including for pillars, spanner sections with wings, large engines, and earthway covers. Construction of elevated ways, earthways, and netway service centers would boom. Energy investments in solar- and wind-energy devices, geothermal (including low-temperature) production, and batteries would rapidly expand.
Here we have focused on creating an entirely new netway system. But many incremental approaches can facilitate the transition phase. Constructing an elevated way with pillars on an existing road shoulder, and providing 16 feet clearance beneath, would permit concurrent use of the existing highway during a transition phase, and thus minimize traffic disruption. Fossil fuel can be a significant energy component at the outset of the netway system and then be rapidly phased out as renewable energy sources are linked to the system. Sections of an existing road can be removed at different rates, for example, beginning where streams/rivers cross and between major wildlife areas. Perhaps elevated ways could also be used as demonstration projects in high-visibility corridors—such as Boston to Washington, Milwaukee to Chicago to Detroit, and San Francisco to San Diego—to accelerate public usage and support for netways and pods.
The netway system would also be effective in cities to address key societal issues of mobility, fuel, and air quality. Thus most urban streets would be converted into grass-and-tree spaces to sharply reduce urban heat buildup and unhealthful air pollutants. Ground level resources could emphasize neighborhood spaces, shopping centers/markets, playgrounds/recreation spaces, and gardens. All would be connected for walkers, bicycles, rickshaw-like vehicles, and slow electric bikes/scooters. Narrow portions of some existing streets would support small, electrically powered vehicles probably under manual control. Closely packed automated pods would run on elevated ways at second-story window level. Public transport on netways and perhaps at ground level would be greatly expanded.
A Future for Transportation and Our Land
Netways are a promising solution to the pervasive conflict between transportation and nature. Today’s highway system can be changed to tomorrow’s netway system, benefiting both transportation and nature. The litany of problems associated with our current highway infrastructure will evaporate.
The primary outcome of a netway system will be to reconnect the land for nature, providing a massive improvement in biodiversity, wildlife, water flows, and aquatic ecosystems across America. Other significant benefits include safe and efficient mobility of people and goods, a treasure chest of major energy and atmosphere benefits (eliminating fossil fuel use and greenhouse gas emissions), and food production and recreation resources (market-gardened, fresh vegetables and fruits, plus trail systems) near cities and towns.
The netway system promises to reverse centuries of environmental degradation by road systems and humans. A key to transforming transportation in this way is flexibility—thinking beyond our cities; building on engineers’ creative design of new cost-effective technologies; using marketplace competition; and meshing solutions with ecological patterns and processes. Such solutions—building from vision to imminent feasibility and reversing rather than slowing or stopping downward spirals—are far too rare. Certainly a far brighter future for both nature and us can lie ahead.
No single solution or recipe will solve our long accumulation of issues related to transportation and the environment. But we can now outline the theater, and even parts of the stage. Leaders with bold ideas, new alliances, and novel solutions will play primary roles in the rapidly unfolding play ahead. Success will be a land and road system where both nature and people thrive long-term.
We warmly thank Heim van Bohemen, Lawrence Buell, Anthony P. Clevenger, Barbara L. Forman, Jochen Jaeger, Michael B. McElroy, Joe Roman, Daniel Schodek, Daniel P. Schrag, and Andreas Seiler for valuable insights and Taco Iwashima Matthews for wonderful color graphics.