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Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268 (2002)

Chapter: 3 Research Area 2: Ecology and Natural Systems

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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3
RESEARCH AREA 2
ECOLOGY AND NATURAL SYSTEMS

A 4-million-mile public road network carrying 200 million vehicles covers about 1 percent of the United States—equal to the size of South Carolina. A recent article published in Conservation Biology presenting the first calculation of the ecological effects of this road system suggests that roughly one-fifth of the total U.S. land surface is directly affected (Forman 2000).

The extent of what is unknown about the ecological effects of transportation is even more surprising. For example, no one has calculated how many streams, lakes, and wells are polluted by chemicals from roads, airport runways, and railroads, or how many species are potentially endangered because of roadkills and habitat changes. While traffic noise by highways may prove bothersome, little is known about whether it has serious negative effects on numerous native animals. Nor is it known how often the many nonnative plants along roadsides and railroads invade nearby ranchlands, farmlands, and nature reserves. In addition, research remains scarce on how well road-crossing structures for wildlife are working, as well as on the influence of road systems on habitat fragmentation and the ecology of landscapes. And compared with roads, still less is known about the ecological effects of railroads.

The current road network was essentially built prior to the first Earth Day in 1970, long before the explosion in environmental knowledge represented by modern ecology. The numbers of vehicles, vehicle-miles traveled (VMT), and traffic jams have continued to increase, along with resultant air pollutants, traffic noise, water-transported chemicals, barriers to wildlife crossing, and pressure for additions to the road network. Therefore, it is no

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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surprise that the cumulative damage to nature due to surface transportation continues to expand and permeate the land. Today, then, the environmental effects of the road system are extensive and growing (as illustrated in Box 3-1), yet they are barely recognized by most people and poorly understood by the scientific community.

The ecosystem services provided to humankind include drinking water, fishing, hunting, nature appreciation, swimming, aesthetics, inspiration, flood control, and more. Indeed, society demands, votes for, funds, and treasures these services. Fortunately, nature is resilient. Although the degradation is substantial, much can be done to mitigate the damage to groundwater, biodiversity, soil surfaces, native vegetation, streams, lakes, fish, and wildlife populations caused by surface transportation.

Major issues loom on the horizon, however. As noted earlier, the American population is expected to grow by another 60 million people in the next 25 years. Where the expanded population will decide to live and the resulting changes in land use are linked directly to changes in the transportation system. Similarly, it is important to estimate how many more vehicles and how much traffic will appear on the road network, as well as which roads will likely be widened and where new roads will emerge. These considerations lead to the further critical questions of how much land will be consumed for development and how many natural systems will be significantly altered or damaged by roads.

A window of opportunity now exists. The key step in exploiting this opportunity is to catalyze and integrate research on transportation and natural systems. New research methods, including displays and models for analyzing geographic information, tracking emissions of pollutants, performing DNA analyses of wildlife, and assessing road/rail-crossing mitigation designs, are beginning to offer major new insights. Research should lead to valuable results. For example, research on alternative road/rail-side designs and road/rail-crossing structures should lead to less habitat fragmentation and more-natural wildlife movement. Studies on chemicals and sediments associated with roads, culverts, airport runways, railroads, and bridges can be expected to result in more native fish populations in streams. And research on the transport of fine particles and dust from vehicle use should help produce clearer lake water and more naturally functioning ecosystems. In view of today’s massive road network and vehicle fleet, such restorations of nature will not return the land to a pretransportation state. However, implementation of research results should lead to improvements in natural systems across the road network, as well as

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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Box 3-1

WHAT NATURE IS LIKE NEAR A BUSY HIGHWAY

Consider taking a leisurely stroll or nature walk along the edge of a woods by a busy two-lane highway. The noise level quickly eliminates leisurely from your mind, especially if, say, every 20th vehicle or so is a truck. Underfoot an abundance of objects appears that could have been recycled. If you briefly emerge at the roadside, speeding vehicles evoke a new sense: danger. Drivers stare and occasionally reach for their cell phones. Busy roads and people outdoors seem incompatible.

So you move back into the woods’ edge to look more closely. Many of the native forest birds seem to be missing; apparently it is too noisy for them, even quite a distance into the forest. Indeed, few other forest vertebrates— mammals, frogs, turtles, snakes—tend to be around; this must be a road-avoidance zone for them, too. If you had ventured to walk along the roadside, you might have seen roadkilled animals, though carcasses do not last long in areas populated by roadkill scavengers. The combination of a road-avoidance zone and a roadkill strip makes you suddenly realize what a barrier the busy highway is, dividing large natural populations into small ones that could be prone to extinction. Moreover, wildlife movement corridors that connect distant patches across the landscape may be severed. You wonder if this is an inadvertent collective assault on biodiversity.

Unlike the adjoining forest interior, the forest edge is commonly full of generalist “weedy” plants, some being nonnative exotics and all persisting because of the open environment of the frequently mowed roadside. The roadside vegetation growing on earth that was homogenized and smoothed during road construction appears monotonous, largely devoid of its natural heterogeneity and richness. Grasses and exotic plants tend to be abundant at the expense of native wildflowers. Straight open roadside ditches carry warmed-up water, alternating with pulses of rainwater, into a narrow wooded stream that lost its valuable curves during road construction. An array of invisible chemicals has blanketed the roadside and penetrates the forest; heavy metals such as zinc and cadmium, nitrogen oxides, hydrocarbons, herbicides,

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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and road salt are typical. Entering the streams, wetlands, and groundwater around you, they inhibit all kinds of natural processes and are toxic to countless species.

What is it like next to a busy road? There is no place for a neighborhood walk, or a path in a park, or even a nature reserve. Here nature is both severed and impoverished. With a well-used 4-million-mile infrastructure, U.S. transportation faces a unique challenge: to reconnect nature. Targeted research undertaken now could bring us notably closer to meeting this challenge.

reestablishment and protection of near-natural conditions in areas especially important to society.

It must be recognized that the application of research results poses a formidable challenge because of dispersed data, unclear relationships between transportation and natural-resource bodies, and inertia. Nonetheless, high-quality targeted research precedes effective applications, and therefore is an immediate priority. As in the examples just given, applications based on research should produce visible results quickly, whereas if the research is not done, problems will persist, and effective applications will be delayed.

SURFACE TRANSPORTATION AND NATURAL SYSTEMS

As discussed earlier, although surface transportation includes rail corridors and managed waterways with barge transport, the focus here is on road systems. Four major groups of issues highlight the close linkage between road transportation and natural systems. These issues, together with a summary of the state of knowledge on each, are described below.

Biodiversity and Wildlife

Headlines such as “Roadkill Causes Crash,” “Wildlife Corridor Severed,” “Amphibian Tunnels Work,” and “Rare Plant and Butterfly Discovered in Roadside” increasingly reflect the importance of this subject to society.

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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Roads and traffic are often mentioned in discussions of endangered species, impacts on stream fish, and the spread of exotic species. In essence, transportation’s effects on biodiversity and wildlife are a primary reason why, in state after state, the public raises questions about the environmental impacts of roads and vehicles (Conover et al. 1995; Natuur Over Wegen 1995; Evink et al. 1999; Harper-Lowe 1999). Calls for new solutions also are increasingly heard from environmental scientists, the transportation community, and decision makers.

Only two aspects of biodiversity and wildlife associated with surface transportation are well documented: common roadside plants and animal roadkill (Bennett 1999; Fahrig et al. 1995; Romin and Bissonette 1996; Harper-Lore 1999). Many aspects remain as little-explored frontiers: rare plants; habitat heterogeneity related to construction, mowing, maintenance, and management regimes; exotic species invading from roadsides to surrounding lands; the barrier effect on wildlife movement (Fahrig et al. 1995); optimal designs of road-crossing structures for animals (Clevenger and Waltho 2000); roadside microclimate altering adjacent woods; effects of traffic noise on populations (Reijnen et al. 1996); road-avoidance zones of different animals (Rost and Bailey 1979); and designs that can reduce disturbance effects. Because the road system is so extensive, biodiversity and wildlife movement near roads are an enormously important research challenge for the nation. [Similarly, the ecological effects of rail and barge transportation are little known (Nelson et al. 2001)].

Water and Aquatic Ecosystems

Transportation facilities are a defining feature of the hydrologic system of numerous landscapes. Roads crisscross streams, rivers, and wetlands on the land surface, as well as underground lakes in the form of groundwater and aquifers. Drainage patterns are commonly blocked and altered. Thus, because of the need to control water on and around a road, road systems normally have a distinctive defined set of hydrologic conditions. Furthermore, roads typically are the places along streams and rivers where human use and the environment interact most intensively. These interactions may be benign or damaging. Highway runoff can deliver a wide range of contaminants from road surfaces to receiving streams and other bodies of water (GKY and Associates 2001). In fact, to control water on and around the roadway, highway designs usually reflect an attempt to accelerate water flows away from the

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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road. The result is that natural hydrologic regimes in the surroundings are altered by highway construction, and aquatic ecosystems are regularly shocked by large flushes of water and contaminant loading (Nelson et al. 2001). As a consequence, the overall environmental quality of aquatic systems suffers.

An extensive literature exists on the overall characteristics and composition of water running off of highways. These studies confirm that the wide range of human-produced materials that reach the road surface and roadside, together with spills of diverse materials, contribute heavily to contamination of highway runoff. In contrast, the effects of highway runoff on receiving streams and lakes are less well understood. Contaminants are funneled through road drainage systems to aquatic ecosystems. Some of the direct effects of this runoff on certain plant and animal species have been identified, but most contaminant–species interactions remain unknown. Perhaps more important, the direct effects of highway runoff on patterns and processes of aquatic ecosystems are poorly understood. One major constraint has been that ecosystems typically encompass both the highway and the surrounding landscape. The effects of highway runoff have been difficult to separate from those due to changing land use, permitted pollutant discharges, and natural change that may occur in the absence of a road. Furthermore, placing limits on the assessment of effects transportation systems on the environment is difficult. Separating the direct effects of the road/highway and its design from the numerous broader effects of a road, such as providing access to a new or remote area, remains a research challenge.

Ecological Effects of Air Pollutants

Transportation systems are the path for moving sources of air pollutants (see Chapter 2). Engines combusting fuel produce pollutant emissions, and the passage of vehicles generates dust and suspensions that carry pollutants away from the transportation corridor. Thus an array of pollutants consistent with the traffic volume, type, and, to a lesser extent, road surface emanate from road corridors. These pollutants have numerous effects on the environment— some short term, such as a smog alert, and others long term, such as climate change. At a local scale, wind carries an assortment of materials from roads and vehicles onto roadsides, as well as adjoining lands and communities. Dead foliage from herbicides and road salt catch the eye. Most dust and heavy metals tend to be carried short distances from the road surface. However, materials

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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such as sulfur dioxide, carbon dioxide, hydrocarbons, nitrogen oxide, and perhaps fine particulates may spread over a larger surrounding area and produce significant ecological effects (TRB 1997; Angold 1997; IPCC 2001). At a regional scale, ozone and nitrogen oxide sometimes accumulate in the lower atmosphere at levels sufficient to alter plants and natural communities. Globally, the greenhouse gas carbon dioxide (plus aerosol-particulate matter) is associated with climate change, which is expected to lead to a range of major ecological alterations at all scales from local to global. Some of these alterations will not only affect natural systems, but also have significant effects on the ecology of infectious disease.

Much is known about the production of pollutants from the internal combustion engine, as well as their aerial transport, destinations, and breakdown. For example, we understand the mechanisms of smog formation and can trace certain pollutants enormous distances around the globe. In contrast, the ecological effects of these airborne pollutants are much less well understood. For instance, dust and fine particles reaching Lake Tahoe and the Great Lakes are believed to be a significant cause of eutrophication, yet little is directly known about the role of road systems—adjacent, nearby, or distant— in this phenomenon. The effects of air pollutants both on terrestrial and aquatic ecosystems and on key plant and animal species need to be studied.

The ecological effects of certain locally airborne pollutants, such as salt, herbicides, and some heavy metals, are well understood relative to those of many other pollutants (TRB 1997; IPCC 2001). As a key greenhouse gas, for example, carbon dioxide is actively studied, but its ecological impacts, though assumed to be large, are uncertain. At the regional scale, ozone, sulfur dioxide, and nitrogen oxide damage certain crop plants and forest trees, but the effects on biodiversity in natural communities remain relatively obscure (Winner 1994). Similarly at the local level, studies have often focused on the relative tolerance of species to road and vehicle pollutants, instead of on the pollutants’ effects on food chains or natural communities. Research appears to be scarce as well on the effects of particulates on wildlife populations, and on the ecological effects of hydrocarbons and certain heavy metals.

Landscape Ecology of Transportation Systems

Landscape ecology is a rapidly developing body of knowledge and research that represents a relatively new, highly useful, and far-reaching dimension for consideration in transportation planning and activity. Landscape ecology

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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(including the related areas of conservation biology and watershed science) provides principles and models that directly address habitat fragmentation, arrangements of green patches, wildlife corridors for foraging–dispersal– migration, groundwater and surface-water flow paths, effects of small populations in enclosed polygons, remote-area impacts due to human access, sources and sinks in the landscape, changing spatial patterns over time, and ecologically optimum spatial models (Forman 1995; Reed et al. 1996; Turner et al. 2001), all of which can be related to transportation networks. Focusing precisely at the scale of road systems, this approach integrates the science of ecology with spatial pattern, process, and change at the whole-landscape, or human, scale. Integrating road systems with these principles, patterns, processes, and models represents a key collaborative opportunity for engineers, ecologists, and planners (Findlay and Houlahan 1996; Canters 1997; Evink et al. 1999). The results of such collaboration should have notable application in transportation planning, evaluation of transportation projects, and overall environmental stewardship. Most important, the results should become visible on the road system and on the land.

Although transportation systems and ecological flows across landscapes operate at the same spatial scale, the two subjects have just begun to be linked (Canters 1997; TRB 1997; Evink et al. 1999). Scattered studies and research done for other purposes point to a promising frontier. Ecologists’ rigorous spatial models and analyses of landscapes now need to incorporate road systems (Forman 1995; Reed et al. 1996; Turner et al. 2001). The workings of the major ecological flows and movements across the landscape should be integrated with traffic flows on road networks. Effectively incorporating principles and models of landscape ecology into transportation planning and project evaluation and meshing ecological solutions with other societal goals, such as recreation and reintegration of bisected communities, represent important research opportunities. The development of models for landscape effects near roads is a promising area for collaboration among engineers, ecologists, and planners, but will require research and testing (Forman and Alexander 1998; Forman 2000).

RECOMMENDATIONS

The recommendations presented below fall into the four areas discussed in the previous section. These four research foci differ markedly from the existing

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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research priorities and programs in transportation. While they represent largely new initiatives, the proposed work would build on strong foundations in transportation research in such areas as hydrology, sediment flow, roadside vegetation management, roadkills, traffic flows, and pollutant emissions. Funding agencies and sources both inside and outside the transportation field have shown little interest in supporting the proposed research; thus very little research is being done in most of these areas. Successful research on the topics outlined below will require expertise from both within and outside the transportation community. Thus research funding mechanisms will be required that can attract researchers from other key disciplines to collaboration with the transportation community. The results produced will then provide a sound basis for effective planning, policy, and implementation.

Biodiversity and Wildlife

Recommendation 2-1.
Expand research and thinking on the uses for and vegetation of transportation corridors in the United States.

Roadsides in the United States cover an area equal to 100,000 football fields for every state,1 and on intensively used land, railroad rights-of-way are often refuges for rare native plants. With few ecological benefits provided, these areas represent an enormous societal resource warranting creative thinking and careful research. Roadsides today are designed primarily for the safety of vehicles that run off the road, with little attention to other values important to society, such as visibility for wildlife, absorption of some toxic chemicals, harboring of rare plants, and aesthetics. Currently, much is known about the types of roadside plants and vegetation and the relative abundance of native and exotic (nonnative) plants present in these areas (Harper-Lore 1999). On the other hand, only a partial picture emerges for rare plants at roadsides, the ecological effects of mowing, and the effects of vehicle- and road-generated chemicals.

Many important roadside-related questions remain unanswered. For example, which spatial and temporal controls are ecologically best for native plants, butterflies, birds, and whole communities (Natuur Over Wegen 1995,

1

This assumes that about 1 percent of the U.S. land area is road right-of-way (TRB 1997), perhaps half of that is roadside, and a football field averages approximately 1 hectare.

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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Forman and Alexander 1998)? What wildlife species should and should not be encouraged by increasing food and/or cover in roadside areas? How can bridges, signs, and other road structures be designed to increase the populations of desirable species? What are the main sources for colonization of roadside exotic species, and how often do exotics spread along roadsides (Harper-Lore 1999)? Which chemical substances from vehicles and roads affect roadside vegetation and animals (FHWA 1996)? How much absorption and breakdown of chemicals occurs at roadsides, and would this increase if there were more woody vegetation and wetland? Finally, how can roadsides be designed to educate neighbors and travelers ecologically?

Recommendation 2-2.
Expand research efforts aimed at understanding wildlife movement near corridors, roadkill rates, and road-barrier effects and at developing efficient mitigation designs for road crossing by animals.

Although crashing into a large animal with a motorized vehicle may involve damage, human injury, or death (Conover et al. 1995; Romin and Bissonette 1996), roadkills overall appear to be a minor problem ecologically. Most animals simply reproduce at a rate that outpaces the losses. The exceptions include flagship species, such as the Florida panther and key deer, and some other state-level endangered species that probably suffer significant roadkill rates. Perhaps equally important are the many wildlife species whose foraging, dispersal, or migration movements are blocked by roads. These disruptions in natural movement patterns doubtless reverberate widely, affecting the nature of both natural ecosystems and production lands.

Certainly wildlife road-crossing structures capture the public’s imagination (Evink et al. 1999; Clevenger and Waltho 2000). Humble salamander tunnels, “tunnels for toads,” and “tunnels of love” for tiny mountain mammals serve to catalyze aficionados and draw ongoing media attention. Examples include some 30 Florida underpasses that have successfully provided groundwater to Everglades National Park, reduced the roadkill mortality of the threatened Florida panther, restored corridor connectivity for black bear populations, and been used by a wide range of other terrestrial fauna. The impressive wildlife over-passes in Canada’s Banff National Park and in several European nations (with antecedents in New Jersey and Utah) are treasured by the respective national publics. A significant information base exists on the numbers of roadkill, and possible ways of reducing roadkill rates have been the subject of considerable

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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study (Romin and Bissonette 1996). A limited amount of research is also available on the road as a barrier to movement, including the frequencies of attempted and successful crossing by various animals.

Striking research gaps in knowledge also exist, however. For example, how does the arrangement of the surrounding landscape, including wildlife movement corridors, affect where different species tend to cross roads (Evink et al. 1999)? How does road and roadside design affect crossing location? Which species have the highest and lowest road kill rates? And what tunnel, underpass, and overpass designs are most effective and affordable for road crossing by which species (Clevenger and Waltho 2000)?

Recommendation 2-3.
Catalyze research on the effects of corridors and traffic on adjoining land, including traffic disturbance and the spread of invasive species.

People dislike the noise from busy highways, as evidenced by the noise barriers frequently used to separate busy roadways from residential communities. Not surprisingly, other vertebrates, such as birds, also appear to be sensitive to traffic noise (Reijnen et al. 1996). Recent research suggests that traditional avian habitat near roadsides is diminishing as a result of excessive noise levels produced by busy highways, which must have a large cumulative effect across America. Indeed, a similar avoidance zone has been noted for certain mammals, amphibians, and reptiles (Rost and Bailey 1979, Fahrig et al. 1995). Thus the evidence indicates that nature reserves and busy highways are incompatible. Indeed, the effect of roads on endangered species may often be tied to this avoidance zone.

More familiar is the concern with exotic species (Harper-Lore 1999). Ranchers fight range-weed invasions. Farmers spray herbicides and other pesticides against competitors and pest invaders. Park and wildlife refuge managers battle exotics threatening their prime lands. And nature conservationists decry the invaders that threaten the natural functioning of native ecosystems. Roadsides tend to be laden with exotic species, suggesting transportation as the source.

None of the above topics has been well researched. Some information is available on the avoidance zones near highways, where native mammals, amphibians, and reptiles tend to be at low density (Rost and Bailey 1979). Few, though more detailed, analogous studies are available on avian communities (Reijnen et al. 1996). The published literature on microclimate around roads

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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appears to be limited, though the basic principles are generally clear. These research gaps are surprising because of the potential importance of the issues involved. Research is needed to determine whether the population size and species diversity of birds within hundreds of feet, even miles, of busy roads have been sharply decreased by traffic disturbance, especially noise (Reijnen et al. 1996, Forman 2000). The effect of traffic volume on species’ habitats near lightly traveled roads should also be examined. More research should be conducted as well on which endangered or threatened species are affected by roads and what solutions are best for long-term protection of such species (Evink et al. 1999, Forman and Alexander 1998).

Water and Aquatic Ecosystems

Recommendation 2-4.
Conduct further research on means of restoring natural hydrologic and sediment flows and distributions in the vicinity of roads.

Because roads interact with hydrology in many ways, developing a better understanding of the interactions between roads and hydrologic systems, along with faunal connectivity, is important. These linkages are both critical and conspicuous to society in affecting streams and their channelization/restoration, natural water tables and aquifers, wetland drainage and mitigation, peak flows and floods, stream and river migration, and other natural floodplain processes. In each case, water quantity and quality are linked. For example, road drainage that changes stream flows alters both the physical form and the habitat of the stream channel, as well as the water quality conditions within the channel, and may have a direct impact on faunal movement.

Because hydrologic conditions around corridors are the result of transportation-system design processes, the major patterns of road hydrology are well documented. It is generally clear, for example, how highway hydrology interacts with the hydrologic system of the landscape, as well as how basic geomorphic processes relate changing hydrology to changing channel form. In addition, the principles of erosion and sediment transport appear to be clear. How highway runoff might be modified to mitigate road–hydrology impacts remains a challenge, however, because that goal can be attained only through a better understanding of the specific effects of changing hydrology on aquatic ecosystems. Thus the effects of varying highway runoff levels on the stability of channels or the functioning of wetlands cannot be predicted. Likewise, the

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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deposition patterns of roadway-generated sediment in streams, rivers, and lakes warrants further study because of the array of ecological effects produced. Although awareness of watershed processes and management has increased in recent years, transportation systems, for the most part, still are evaluated separately from those processes. To build a foundation for mitigating the impacts of transportation systems on watersheds, a better understanding is needed of how road hydrology can be designed to meet the objectives of watershed management programs, which are increasingly focused on maintenance and restoration of environmental quality. Research on water and sediment distributions and flows that link the road corridor to the surrounding land will be key in this regard. Research should also be conducted on the various methodologies for handling and treating highway stormwater quantity and quality to prevent downstream effects.

Recommendation 2-5.
Expand research on transportation’s effects on water quality, aquatic ecosystems, and fish in various bodies of water and on ecologically effective solutions.

Major and visible effects—such as shoreline alteration, reduced connection to adjacent upland, sediment filling-in, eutrophication, reduced oxygen levels, and altered fish populations—are attributable to roads altering coastal, lake, reservoir, pond, and vernal-pool ecosystems. Similarly, stream and river water quality is significantly altered by roads, as illustrated by bridge effects, eroded sediments, turbidity, reduced diversity of stream habitats, warm water from roadside ditches, movement of chemical substances, truncated food webs, and altered fish populations (FHWA 1996; Findlay and Houlahan 1996; Evink et al. 1999). However, a broader view of the cumulative impacts is critical.

Transportation systems provide a major mechanism for dispersing human influences across the landscape. This dispersion begins with single pathways, expands to networks, and culminates in increasing release of contaminants and corresponding environmental damage around the networks. The cumulative effects of transportation systems on water quality, considering all points of corridor–waterway interaction, must be recognized. Such a cumulative-effects analysis would go beyond simple toxicity determinations or parameter-specific regulation to examine the effects, both small and large, of water quality change over expansive spatial and temporal scales, focusing in particular on the functioning of aquatic ecosystems.

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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An extensive literature on the hydrology of transportation systems includes the effects of roads on water and of water on roads. The contaminants in highway runoff have also been widely characterized, though much remains poorly known. For example, the specific ecosystem effects of highway runoff and their relative contribution to overall environmental quality in receiving waters remain elusory. The situation is complicated by the fact that some effects of highway runoff are site-specific, while others are general; moreover, runoff may exacerbate problems created by other activities in watersheds. Although general consequences may sometimes be predicted, the information available on the aquatic effects of roads often is inadequate to support effective planning. For example, although contaminant loading can be estimated, regulatory authorities often require site-specific studies, which seldom follow a uniform protocol that would permit extrapolation to other sites. Research on certain aquatic–ecosystem processes operating over decades and centuries, as is the case with road systems, also would enhance extrapolation for planning. Thus both the state of knowledge and transportation planning would be advanced by conducting broader analyses of cumulative effects instead of the narrower analysis of transportation-related effects.

Ecological Effects of Air Pollutants

Recommendation 2-6.
Support, expand, and initiate research on the ecological effects of air pollutants from roads and vehicles at the roadside, neighborhood, regional, and global levels.

Climate change is predicted to vastly alter major areas of the United States. New rainfall and temperature conditions not taken into account in initial road designs will have to be considered by transportation engineers and planners if unplanned-for failures of road components are to be avoided. At the same time, transportation is a major source of carbon dioxide, a leading greenhouse gas linked to global climate change (TRB 1997; IPCC 2001). The ecological ramifications of climate change include inundation and movement of coastlines far inland; greater climate variability; and rearrangement of soil erosion– deposition patterns, flood zones, water bodies, agricultural crops, livestock lands, and vegetation types. Regional ozone pollution in the lower atmosphere may also inhibit plants and vegetation (TRB 1997). In addition, nitrogen oxides may alter the soil, plants, and vegetation. Usually on a more local scale,

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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many road- and vehicle-related materials are carried and deposited by wind, producing ecological effects; these pollutants include herbicides, road salt, dust, nitrogen oxides, and heavy metals (Angold 1997). Developing solutions that can both support viable future transportation and reduce the ecological effects of air pollutants is extremely important.

There is an extensive literature on vehicle emissions and atmospheric pollutant levels, as well as a growing literature on contaminants associated with roadways. A limited amount of information has accumulated on ecological damage associated with pollutants close to roadways. Perhaps most is known about the ecological effects of salt, herbicides, sulfur dioxide, and some heavy metals. At least some useful ecological information is probably available on the remaining air pollutants. The fate of pollutants and the underlying processes involved are incompletely understood, however. Global climate models agree that major environmental changes are probable, but the amount, timing, and spatial distribution of those changes remain the subject of much disagreement. For effective transportation planning, research is needed on the ecological effects of pollution at both regional and local scales, as well as on measures that can be used to control the sources of pollutants.

In contrast with the high-profile subjects of greenhouse gases and aerosol particulates, climate change and ecological effects remain poorly understood (TRB 1997; IPCC 2001). Much of the research on ozone has centered on plants of economic value and on forest growth (Winner 1994; TRB 1997), whereas little is known about the effects of ozone on natural-community patterns. Despite large amounts of nitrogen being deposited on land and ecosystems from nitrogen oxide, the resulting effects, especially near highways, require study. Much of the research on airborne dust, salt, and herbicides focuses on the relative tolerance of different species, rather than on understanding effects on nat grasslands, deserts, and arctic areas also warrant study. Moreover, some heavy metals are not well understood in ecological terms, while others warrant further study with regard to toxic and food-chain effects. After all, if the size and density of fine particles is important to human health, wildlife populations are undoubtedly affected as well, and these impacts require study. Furthermore, little appears to be known about the ecological impact of hydrocarbons. Finally, while the effects of sulfur dioxide on vegetation located near point sources, as opposed to those located near highways, are relatively well known, significant questions remain about carbon monoxide, PCBs, and other pollutants. In short, for all of the transportation-generated pollutants, major knowledge gaps exist in

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Suggested Citation:"3 Research Area 2: Ecology and Natural Systems." Transportation Research Board. 2002. Surface Transportation Environmental Research: A Long-Term Strategy -- Special Report 268. Washington, DC: The National Academies Press. doi: 10.17226/10354.
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the timing, distance, amount, and interaction of effects on plants, animals, and ecosystems.

Landscape Ecology of Road Systems

Recommendation 2-7.
Develop road-network models and approaches for reducing habitat fragmentation, population extinction, wildlife-corridor, and remote-area impacts.

Road systems link human communities together and provide access to landscape and regional resources. However, the same networks slice the land and nature into pieces. Large mammal populations, fire, floods, and other important ecological characteristics are sensitive to road density (e.g., number of road-miles per square mile) (Findlay and Houlahan 1996, Forman and Alexander 1998). Yet the form of road systems, less well explored, is doubtless a better ecological predictor and basis for planning. Habitat fragmentation is widely cited as a major cause of declining biodiversity (Reed et al. 1996; Canters 1997). Road systems may play a role when a population is reduced and genetic inbreeding thus increases, with both processes heightening the risk of local extinction (Reh and Seiz 1990; Fahrig et al. 1995). Road networks also disrupt nature’s networks of green patches and corridors across the landscape, while remote roads built to provide human access result in disturbance to natural populations and communities.

A fair amount of information on the effects of road density on large mammals exists, although not on many other ecological aspects (Forman and Alexander 1998; Evink et al. 1999). Moreover, a limited but useful literature is available on the human impacts in remote areas and on the disruption of wildlife corridors. Some information developed in other fields may be useful for developing models of alternative road-network forms. Some information is available on reducing habitat fragmentation. However, little is known about small populations or genetic inbreeding leading to extinction relative to road networks (Reh and Seiz 1990), though the theory has been reasonably well developed in other domains.

Existing knowledge gaps in this area are significant. Issues that need to be examined include which road and roadside designs are crossed most successfully by animals and therefore serve to reduce habitat fragmentation (Romin and Bissonette 1996); which temporarily closed or permanently removed roads in a network best reduce human-access impacts in remote areas or produce the

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greatest ecological gain; which network designs best concentrate or distribute traffic disturbance impacts (e.g., how different road networks alter natural ecosystems and biological diversity by affecting fire frequency, size, and control); and what ecological form is best for a road network in a forestry landscape or, alternatively, in a rapidly developing exurban fringe area where roads are to be built (Reed et al. 1996; Findlay and Houlahan 1996).

Recommendation 2-8.
Foster collaborative landscape-wide environmental analyses by engineers, ecologists, and planners, with an emphasis on combining ecological solutions with other societal objectives.

Landscape ecology integrates traditional ecology with spatial patterns at the landscape or regional scale, precisely the scale of road systems (Forman 1995, TRB 1997). If transportation planners incorporated landscape ecology in the planning process for both improvements and additions, many useful insights might be anticipated (Natuur Over Wegen 1995; Canters 1997; Evink 1999). For instance, promising solutions should emerge to address ecological flows and movements across the landscape, including wildlife routes for foraging, dispersal, and migration; groundwater and surface-water flows; sediment and chemical sources, routes, and sinks; and sources and sinks for air-transported materials. In effect, how natural systems in the landscape work and how they interact with the road system would be elucidated. Further benefits would include an understanding of landscape spatial patterns, their linkage to the road system, and their changes over time, as well as ecological spatial models with and without the road system. The principles and models thus derived would aid in targeting restoration actions for a road system built largely in another era. Engineers and ecologists also would find much common ground in the environmental stewardship of transportation.

While transportation primarily provides safe and efficient transport, its secondary goals include maintaining ecological systems, public health, viable communities, and more (see Chapter 1). The basic infrastructure is in place. Thus, opportune times to accomplish goals related to natural systems are during maintenance, redesign, and upgrading of projects (Natuur Over Wegen 1995, FHWA 1996). Combining ecological and other public goals in the same project is an additional gain and—based on good research—should become the norm.

A scattering of useful studies appears to exist on using landscape-wide analysis to repair ecological damage, evaluate transportation projects, and

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mesh ecological and other societal objectives. A road-effect-zone model has been proposed and tested (Forman and Alexander 1998; Forman 2000). When a road or bridge is enlarged, an opportunity exists to enhance wildlife crossings, create recreational paths, and reconnect a community bisected by the road. Systematic interdisciplinary research is needed to fully capitalize on this highly promising area.

Recommendation 2-9.
Stimulate research on understanding public preferences for improvements in natural systems of both short- and long-term significance to society.

Both transportation and natural systems serve and generate support in society. Natural-resource economists seek monetary valuations of natural systems or components thereof. For instance, what are people willing to pay for a clean aquifer, an endangered species, or a distant wildlife refuge? Broadly speaking, values underlying public support can be divided into “use values” (e.g., a clean aquifer for drinking water) and “existence values” (e.g., the simple existence of an unseen wildlife refuge). Native foods and medicinal plants and vegetation along streams provide direct services to society. Their value is often less difficult to estimate, and tends to be lower, than existence values such as those of natural ecosystems for aesthetics or inspiration.

Research linking these issues to transportation is scarce. Yet to set planning and policy priorities for addressing the diverse dimensions of natural systems, it is important to consider people’s preferences and consequent public support when allocating scarce resource dollars. The research challenge includes not only understanding the attitudes of different groups of people, but also determining what is included in the valuation and developing the best methodologies for conducting the valuation. For example, the closing of a forestry road that borders a fragile pond and favorite fishing spot could be valuated on the basis of accessibility, or accessibility plus the fishing equipment used and the store where it would be bought. Furthermore, some implementation actions, such as restoring a trout population or planting shrub cover for deer, provide a short-term ecological gain. Others provide a long-term sustainable value for society, such as altering land uses to prevent eroded sediment from filling a key reservoir or planting trees far from a road for future harvest. Such long-term values, so important for planning and policy, may deserve but not receive strong public support.

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REFERENCES

Abbreviations

FHWA Federal Highway Administration

IPCC Intergovernmental Panel on Climate Change

TRB Transportation Research Board

Angold, P. G. 1997. The Impact of Road upon Adjacent Heathland Vegetation: Effects on Plant Species Composition. Journal of Applied Ecology, Vol. 34, pp. 409–417.

Bennett, A. 1999. Landscape Connectivity and Habitat Corridors. IUCN, Gland, Switzerland.

Canters, K. (ed.). 1997. Habitat Fragmentation & Infrastructure. Ministry of Transport, Public Works & Water Management, Delft, Netherlands, 474 pp.

Clevenger, A. P., and N. Waltho. 2000. Factors Influencing the Effectiveness of Wildlife Underpasses in Banff National Park, Alberta, Canada. Conservation Biology, Vol. 14, pp. 47–56.

Conover, M. R., W. C. Pitt, K. K. Kessler, T. J. DuBow, and W. A. Sanborn. 1995. Review of Human Injuries, Illnesses, and Economic Losses Caused by Wildlife in the United States. Wildlife Society Bulletin, Vol. 23, pp. 407–414.

Evink, G. L., P. Garrett, and D. Zeigler (eds.). 1999. Proceedings of the Third International Conference on Wildlife Ecology and Transportation. FL-ER-73-99. Florida Department of Transportation, Tallahassee, 330 pp. [1996 proceedings of the first conference, FL-ER-58-96, 395 pp. 1998 proceedings of the second conference, FL-ER-69-98, 263 pp.]

Fahrig, L., J. H. Pedlar, S. E. Pope, P. D. Taylor, and J. F. Wegner. 1995. Effect of Road Traffic on Amphibian Density. Biological Conservation, Vol. 74, pp. 177–182.

FHWA. 1996. Evaluation and Management of Highway Runoff Water Quality. Publication FHWA-PD-96-032. Washington, D.C.

Findlay, C. S., and J. Houlahan. 1996. Anthropogenic Correlates of Species Richness in Southeastern Ontario Wetlands. Conservation Biology, Vol. 11, pp. 1,000–1,009.

Forman, R. T. T. 1995. Land Mosaics: The Ecology of Landscapes and Regions. Cambridge University Press, Cambridge, United Kingdom.

Forman, R. T. T. 2000. Estimate of the Area Affected Ecologically by the Road System in the United States. Conservation Biology, Vol. 14, pp. 31–35.

Forman, R. T. T., and L. E. Alexander. 1998. Roads and Their Major Ecological Effects. Annual Review of Ecology and Systematics, Vol. 29, pp. 207–231.

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GKY and Associates and Louis Berger and Associates. 2001. Management of Runoff from Surface Transportation Facilities, Synthesis and Research Plan. Final Report Project 25-20. National Cooperative Highway Research Program.

Harper-Lore, B. L. 1999. Roadside Use of Native Plants. Federal Highway Administration, Washington, D.C.

IPCC. 2001. Climate Change 2001: The Scientific Basis. IPCC Secretariat, World Meteorological Organization, Geneva, Switzerland.

Natuur Over Wegen (Nature Across Motorways). 1995. Ministry of Transport, Public Works and Nature Management, Delft, Netherlands. 103 pp.

Nelson, P. O., W. C. Huber, N. N. Eldin, K. J. Williamson, M. F. Azizian, P. Thayumanavan, M. M. Quigley, E. T. Hesse, J. R. Lundy, K. M. Frey, and R. B. Leahy. 2001. NCHRP Report 448: Environmental Impact of Construction and Repair Materials on Surface and Ground Waters. TRB, National Research Council, Washington, D.C.

Reed, R. A., J. Johnson-Barnard, and W. L. Baker. 1996. Contribution of Roads to Forest Fragmentation in the Rocky Mountains. Conservation Biology, Vol. 10, pp. 1,098–1,106.

Reh, W., and A. Seiz. 1990. The Influence of Land Use on the Genetic Structure of Populations of the Common Frog Rana temporaria. Biological Conservation, Vol. 54, pp. 239–249.

Reijnen, R., R. Foppen, and H. Meeuwsen. 1996. The Effects of Car Traffic on the Density of Breeding Birds in Dutch Agricultural Grasslands. Biological Conservation, Vol. 75, pp. 255–260.

Romin, L. A., and J. A. Bissonette. 1996. Deer-Vehicle Collisions: Status of State Monitoring Activities and Mitigation Efforts. Wildlife Society Bulletin, Vol. 24, pp. 276–283.

Rost, G. R., and J. A. Bailey. 1979. Distribution of Mule, Deer, and Elk in Relation to Roads. Journal of Wildlife Management, Vol. 43, pp. 634–641.

TRB. 1997. Special Report 251: Toward a Sustainable Future: Addressing the Long-Term Effects of Motor Vehicle Transportation on Climate and Ecology. National Research Council, Washington, D.C.

Turner, M. G., R. H. Gardner, and R. V. O’Neill. 2001. Landscape Ecology in Theory and Practice. Springer-Verlag, N.Y.

Winner, W. E. 1994. Mechanistic Analysis of Plant Responses to Air Pollution. Ecological Applications, pp. 651–661.

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TRB Special Report 268 - Surface Transportation Environmental Research: A Long-Term Strategy defines a broad and ambitious research program to address and inform major public policy debates about the effects of surface transportation facilities and operations on the human and natural environments. The committee that conducted the study identified major gaps in knowledge that could be filled through a cooperative program of research involving federal agencies, states, and environmental organizations. The committee recommended creation of a new cooperative research program to carry out its recommended research agenda. Special Report 268 Summary

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