Road Ecology's Promise: What's Around the Bend?

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Road Ecology's Promise: What's Around the Bend?Richard T. T. FormanPublished online: 30 Mar 2010.

To cite this article: Richard T. T. Forman (2004) Road Ecology's Promise: What's Around the Bend?, Environment: Scienceand Policy for Sustainable Development, 46:4, 8-21, DOI: 10.1080/00139150409604381

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effects-nature degrading roads and roads degrading nature-are costly to society. Increasingly, they catch the public’s eye.

The newly emergcd field of study known as “road ecology” explores and addresses the relationship between the natural environment and the road system.] In essence, road ecology is a coher- ent framework with a body of principles and a range of applications useful to transportation planning, practice, and policy. A compelling application of the principles could loosen the stranglehold of the road system giant. Could it even tame this giant system?

Road ecology coa- lesced with the first comprehensive book on the subject, a 2003 publication, Road Ecology: Science and Solutions, authored by a group of ecologists and transportation specialists.? The transportation community was intrigued by thc potential for further scientific development and application in order to address the diversc issues linking transport, ecology, and human communities. In the decade leading up to this volume. the pace of actions related to transportation and the environment had quickened. In 1991, the U.S. Con-

tees that published two books containing chapters highlighting the importance of road ecology.’

Meanwhile, European nations, which began road-ecology work perhaps a decade earlier, display a wide array of ecological solutions for transportation. A Dutch ecology team working within the Ministry of Transport has been in the forefront, but Germany, France, Switzer- land, Canada, India, Australia, and other countries have also achieved impressive results. Newer road ecology projects have blossomed in Estonia. Hungary, and

Natural Environment, takes an active interest in the growing field through specific projects. sponsorship of a “scanning” tour to study European cxperience. and publication of small handbooks for the transportation community and informed public. Certain statc departmcnts of transportation (with Florida often in the forefront) have taken leadership by accomplishing specific road-ecology planning and projects. ICOET meetings have pro- vided a catalytic forum for the diverse players to meet, present papers. and inter- act. The U.S. Department of Agriculture

Tl?is,four-lune lrighway in soutiieustern Mnssacliusetts bisects a large pcitclt of natural ,forests. Its potential efects include habitat loss. altered vegetation at the forest edge. and loss of species iniportunt to conserrdon efforts.

gress passed its big highway act (ISTEA, thc Intennodal Surface Transportation Efficiency Act), which permitted the use of some highway funds for environmental enhancements. In 1997 Congress passed a successor transportation act (TEA-21) to fund highways, including their environmental dimensions. A serics of road- ecology conferences (ICOET, the Interna- tional Conference on Ecology and Trans- portation) began, and the Transportation Research Board of the National Rescarch Council ( N R C m ) appointed commit-

Slovenia. An Infra Eco Network Europe group linked with European ministries of transport has just complcted a seven-year integrated program (the European Coop- eration in the Field of Scientific and Tech- nical Research Action, COST-341), bring- ing science and solutions together.4

In the United States, NRC/TRB appointed a Task Force on Ecology and Transportation in November 2003 to link the transportation community with ecological scientists. The Federal Highway Administration, including its Office of

(USDA) Forest Scrvicc incrcasingly cxanlincs its road system for impacts on thc environment. often with public scrutiny. Other federal agencies, including the National Park Service, Fish and Wildlife Service. Depart- ment of Defense, and Environmental Protection Agency. show intercst in road ecology. Consulting firms are increasingly attracted to the solutions pinpointed. Non-profit organizations including Defenders of Wildlife. Smart Growth America, and The Naturc Conser- vancy have initiatcd activities in this area. All players seem to bc motivatcd by the sensc that the science and the solutions of road ecology are signiti- cant for society.

What brings these major players together? Certainly the past two years of political discussions rclated to the pend- ing reauthorization of TEA-21. the U S . transportation-funding act, have servcd as a catalyst. Also, the transport community remains unhappy with the long delays and high costs of getting things donc. so while some leaders would prefer to simply facilitate proccsses, others increasingly recog- nize the value of seriously addressing environmental concerns along with transport issues. The primary goal of trans-

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portation is sate and efficient mobility, with a secondary goal to maintain undegraded natural systems. In practice. the former has tlourished while nature has sutfered. Yet a speck of hope appears. Safe and efficient mobility can indeed be effcctively meshed with undegraded natural processes and biodiversity.

Form of the Giant Road System Four million miles of public roads

crisscross the United States. and nearly a quarter of a billion vehicles use that network.5 Ameiicans annually drive 23 tril- lion miles on it and use their vehicles for 90 percent of daily travel.” How does such a system of roads and vehicles compare with that in other countries?

The number of vehicles, annual miles driven, and time one spends driving in the United States are all the highest any- where. The total U S . road length is five times that of Japan, which has the next- largest network. The road length per person, exceedcd only by Canada. is about three times that of Japan and thc major European countries. In essence, the U.S. road system is an outlier in the world.7

About 10 percent of the public road network is in Forest Service land, and the Interstate Highway System accounts for another 1 percent. Informal or unofficial roads make up a significant but poorly known additional road length. which incrcascs with thc growing use of four- wheel-drive and of-road vehicles. One- fifth of the public-road nctwork is urban and four-fifths rural. Nearly half of the rural road length is unpaved. Public road surfaces and roadsides cover about 1.1 percent of the U.S. land area (0.6 and 0.5 percent, respectively), equal to the area of South Carolina or Maine. The road infrastructure also includes bridges. culverts. pipes. barriers. signs, curbs, sidewalks. and much more. Almost 600,000 bridges exceed 20 feet in length, and an additional 12.5 million smaller structures. mostly culverts and pipes, mean that on average there is a structure every quarter mile.‘

Traffic changes seasonally, weekly, even hourly. In contrast. total road length barely grows (less than 1 percent) annual-

I Y . ~ Most new road building-other than forestry roads-now occurs in exurban fringe (sprawl) areas. These trends are expected to continue in the future.

Vehicle numbers in the United States continue a long, steep increase; today, vehicles exceed drivers. Travel has also increased annually since the 1970s, generally exceeding 3 percent. AU major cat- egories of highway travel-including commuting. recreation, and freight-are on the rise. Neverthcless. most other nations are experiencing a more rapid growth in vehicle numbers and miles traveled, with the highest growth rates in countries with considerable industry, such as China. India, and Mexico. In contrast to the minimal change in U.S. road length, China. India, and Eastern Europe have embarked on major highway- building programs. ’”

Driving cars characterizes early our twenty-first-century American culture. We drive more, bigger, and faster vehicles. Traffic jams grow, gas mileage drops. and neighbors chat on the street less often. Perhaps the social dimension of our road-system trends is best suggest- ed by the decrease of U.S. children who walk to school from more than 50 percent to just 10 percent over 30 years.’’

The vast road-system giant aKects not just our social lives, but also our rich treasure chest of plant and animal species; water, soil, and air quality; and the landscapes in which we live. Traffic “calming”-such as speed bumps and pedestrian-only streets-to “take back our neighborhoods from cars” grows in scattered locations as an alternative to always trying to “meet demand” for more vehicles, but as yet it has had little overall effect. Still, road ecology could become a springboard to address the conspicuous linkage of transport, ecology. and human communities.

different-colored, different-sized, and different-shaped bubbles. The screen is the land and a bubble is the habitat of an animal. Now add an irregular road grid of strips creating a thousand enclosures. The grid clearly imperils wildlife.” Habitat is lost to the grid, and animals crossing the strips are sometimes hit by vehicles. Con- siderable habitat near roads is degraded, and this degradation can extend outward for long distances. The strips are barriers that reduce connectivity for animal movement and fragment wildlife habitats (the bubbles), leaving species more at risk of local extinction.

Habitat loss is an obvious result of road construction. One percent of wildlife habitat in the United States-compared with 2 to 3 percent in densely populated Euro- pean nations-has disappeared under roads and roadsides.’ ’ Only agriculture, logging, and built areas have caused more habitat loss. However, because of its extensive interlocking shape, the road system may have caused the greatest impact on wildlife and biological diversity.

Roadkill of animals is a second also fairly obvious effect. Dead squirrels. sparrows, rabbits, raccoons, and housc cats are familiar sights along U.S. roads. Indeed, vehicles are almost surely now the largest direct means by which humans kill wildlife.’-‘ Roadkills of large animals including deer and moose are increasing, and they are upping the ante because of their effects on vehicle damage, insurance, and repair costs, as well as human injury, medical insurance, and human fatalities. Highest roadkill rates would be expected on unfenced. two-lane highways with high speed limits and at least moder- ate traffic, especially where a road crosses unmarked wildlife corridors.

Roadkills of large predators and of certain reptiles and amphibians can be high-

Wildlife lmaginc a computer

screen displaying thousands of

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ly significant. Such predators as wolves in Minnesota, bears in Alberta, panthers in Florida, and lynx in Spain are generally in low numbers and reproduce slowly. Vehicle-caused mortality of a few, or even one, of these animals may significantly increase risk for the population. For instance, in the early 1980s, 4 of the approximately 50 Florida panthers were hit and killed by vehicles each year.IF (Wildlife underpasses with fencing along the section of 1-75 known as “Alligator Alley” then reduced roadkills to an average 1.5 per year. a significant improvement.) Some reptile species live to a grand old age and reproduce slowly and thus are also at risk tiom roadkill. Amphib- ians and reptiles can be roadkilled in prodigious numbers where a fairly busy highway passes a wetland, vernal pool, or pond.

Fortunately, however. except for large predator and reptile and amphibian cases, roadkill is arguably of little overall ecological signifi- cance. In essence, most animals reproduce faster than vehicles hit them. An extensive 1960s study of roadkill in England found that house sparrows (English sparrows) were overwhelmingly the most often-roadkilled verte- brates.Ih But house sparrows multiply rapidly and can quickly repopulate a suit- able site.

Degraded habitat surrounding roads is a bigger problem, ironically nearly

dominated by common edge plants and animals, and interior species do poorly there. Many interior animal species are of conservation interest and are sensitive to the size of a forest interior.” Thus, the road that bisects a forest may leave forest patches too small for some important species. Such a road also may permit exotic (nonnative) plant or pest species to penetrate a forest. On the other hand, some alterations in surrounding habitat

Rocky Mountains often stay at least 100-200 meters back from highways with traffic. Moving visible vehicles and traffic noise may both play a role in creating this pattern. More striking, however, are the patterns for birds. Dutch studies found that 60 percent of the woodland breeding- bud species had lower densities near busy highways (with 10,OOO to 60,000 vehicles per day).IY The distance effects extended outward at least 2,500 feet in each direc-

tion. A companion study of highways in grasslands found bird-species densitics reduced outward for about 4.000 feet. Thc total population reduction ovcr this distance was approximately 60 perccnt. A morc rcccnt study in an outer suburban landscapc in Masrachu- setts found similar but additional patterns (see Figure 1 on pagc 13).19 In short, the avoid- ancc zone is a wide swath of degraded habitat surrounding roads with traffic, essentially invisible to travclers but casily mapped by an avian ecologist.

The banicr effect that re- duces landscapc conncctivity is the othcr big impact of road systems on wildlife. Animals “need’ to movc to forage foI food. escape a predator. find a matc. dispcrse to a new home. or even migrate scasonally.

8 Enclosing them in a ”mepa- $ 100’’ created by a highway 2 &rid on land degrades many

animal populations. 2 Consider a road slicing ;t ’ habitat with a larrc DoDula-

U

- L .

tion into two smaller habitats. each with a smaller population. Small populations fluc-

Roadkill rates me most likely the highest on uifenced. two-lane muds such NS tliis one, where speed limits are high and the road crosses an unmarked ~6rridor:

invisible to the driver speeding along a highway. A surprisingly wide zone is altered around a well-traveled road. Con- sider a forest next to a busy road. The outer portion. the forest edge, is quite different from the remaining forest interior. Wind, sun, desiccation, and various roadvehicle effects tend to be greater at the forest edge. Typically, this area is

could be considered beneficial. These include certain plants favored by elevated nitrogen in roadsides, birds that feed on plants by the roadside, and bats that roost in bridges.

Another dimension of degraded surrounding habitat is an avoidance zone, apparently generated mainly by traffic noise. For instance, deer and elk in the

tuate in size over time more than do large populations. Thus, from time to time, small populations naturally become even smaller. At this point, they are at risk of disappearing (local extinction). Furthermore, small populations tend to inbreed genetically, which may lead to less vigor in offspring and additional risk of local extinction.

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- Figure 1. Road traffic and grassland birds

Local collector

vehicles per day) (3,000-8,000

I I I 0' R'

Multilane highway (2 30,000 vehicles per day)

0 = Occasional presence of birds R = Regular breeding of birds ' = No significant effect

* O , R

I L I

(8,000-1 5,000 vehicles per day)

0 R

Two-lane highway

vehicles per day) (1 5,000-30,000

0 114 mile (400 meters)

112 mile 314 mile (800 meters) (1,200 meters)

NOTE: A Massachusetts study of grassland birds of conservation importance explored how much impact occurs near different-sized roads in an outer suburban landscape. The good news is that no effect was found near local collector streets in town (which had an average of 5,500 vehicles passing per commuter day). However, the bad news is that no regular breeding of the birds was found for about a quarter-mile on each side of a through street (averaging 11,500 vehicles per day), which connects suburban towns. The avoidance zone was about three-quarters of a mile wide on each side of multilane highways (equal to or more than 30,000 vehicles per day).

SOURCE: R. T. T. Forman, B. Reineking, and A. M. Hersperger, "Road Traffic and Nearby Grassland Bird Patterns in a Suburbanizing Landscape," Environmental Management 29 (2002): 782-800; and R. T. T. Forrnan et al., Road Eco\ogy: Science and Solutions (Washington, DC: Island Press, 2003).

A road with roadsides is a significant barrier or filter to certain wildlife attempting to cross, especially if the road is wide or has fencing. Add busy traffic and many animals do not even attempt to cross the road. Some of those that try are roadkilled and then quickly removed by roadkill scavengers. Clearly the barrier effect also depends on the species: Few if any salamanders may cross a multilane highway with a Jersey banier, whereas a bear or moose may cross almost anything.

To help alleviate these myriad road- system effects on wildlife, an array of mitigation or enhancement approaches to minimize impacts has evolved (see Figure 2 on page 15)." All the niitiga- tion solutions await policy initiatives to be widely applied. Traffic noise effects can be reduced with low. shrub-covered soil ridges (berms) and/or partially or fully sunken roads. Solutions also include making quieter road surfaces, tires, engines, exhaust systems, and vehicle aerodynamics, and reducing the

proportion of trucks on a road. For most other problems highlighted in this section, the primary goal is to recover landscape connectivity by reducing the barrier effect to wildlife movement. Often, a second goal is to reduce roadkills. Building small and large wildlife passages under and over highways is an increasingly important approach.

Experience and measurements from such passages in Europe, Alberta, and Florida highlight several important results. Fencing along the roadside near a passage is important. A view of vegetation at the far end is desirable. A wider passage is better, at least up to about 150 feet for large mammals. The longer the passage, the larger the opening should generally be. Lnterlinking engineering design with animal behavior for key target species is important. Pas-

with woody vegetation close by, and without human shuctures and activity in the vicinity, are desirable for many species. Passages are best located where they can enhance or establish effective wildlife movement between long-term protected habitats. And finally, two or three passages are much better than one.

Roadsides and Their Vegetation Roadside vcgetation provides home,

I'ood, and cover for wildlife, and roadsides cover an enormous area-equal to 100,000 football fields in every U.S. state." To understand the effects of the road system on plants and vegetation

sage openings

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requires insight from road construction, another phase invisible to travelers. Earth material from different nearby sites, or trucked in from afar, is intermixed, nearly homogenized. then contoured to a relatively smooth surface. Thus. the roadside begins without its natural heterogeneity in soil, water, chemistry. and microhabitats. Wet spots, sandy spots, rocks, and soil rich in organic matter are largely missing, and frequent mowing accentuates the impoverishment.

Reducing the growth of’ roadside shivbs and trees to incrcase traveler safety is the usual reason given for wide grassy roadsides. This is counterintuitive, however, and is ripe for new thinking. Studies indicate that drivers operate more slowly and cautious- ly with a narrower field of vision.” resulting in a safer road. U.S. highways, often with 30 feet or more of grassy roadside, seem to be designed for speed- ers. Providing “visual friction,” such as native shrubs and trees on both sides close to a road, slows down hivers. Visual friction has an ancil- lary benefit as well: Shrubs are much better than grass at absorbing the crash energy of a vehicle

and roadkill rates decrease sharply at vehicle speeds between 55 and 45 i d e s per hour (mph).” The narrowed field of vision, combined with strategically located guardrails for traffic and fencing for wildlife, means a safer road for drivers moving along at about 45 mph and for wildlife. Roadside trees, a wonderful fea- ture of many Australian roadsides, can be protected from errant vehicles by guardrails or shrubs. Tree saplings can be harvested for firewood and trees for paper products. The huge area of today’s largely wasted roadsides can be put to valuable ecological and other uses for society.

Where are woody roadsides appropri-

flies. The combined expertise of travel behaviorists, engineers, and wildlife ecologists should help to identify those locations that are inappropriate, as well as the guardrail/fencing designs for roadsides of native shrubs andor trees. It is especially difficult to design stretches that run through habitat of large, rare animals, such as grizzlies and Florida panthers. where a wildlife-vehicle crash is serious for the driver as well as for the whole wildlife population. Woody roadside vcgetation can also combine ecological values with cultural or aesthetic values, as, for example, in the recently improved Paris-to-Lexington Road in Kentucky

Road,yides cover an area equal to 100,000 jootballJelds in even U S . state. Planting vegetation along rocidsides adds exteiisive.food and cover,for wildlife.

that ims off the road. and over time, design changes could minimize vehicle damage. Speed kills: safe roads with fewer crashes per mile are preferable.

Shrub-covered roadsides add extensive, connected wildlife habitat. More impor- tantly, they provide wildlife favorable conditions for road crossing-an inexpensive partial solution to the problem of roads fragmenting habitats. However, more wildlife crossing the road could lead to more wildlife-vehicle crashes and roadkills. Fortunately, though, such crashes

ate? Good places normally are along guardrails: the approach to a town; straight, fairly flat road stretches; the approach to a distinctly marked crossing location of a major wildlife comdor; and many other places where safety is important. Bad places, in general, are around intersections; by inside curves to the right (in right side-driving nations); in places with dense moose populations, in native grassland and desert landscapes; and in sites, for example, of conservation importance for herbaceous plants and butter-

(and an in-progress Route 93 improvement in Montana).”

Along today’s roadsides. scattered evidence clearly in- dicates the presence of state-listed rare plants. Curiously. no state or nation has yet done a careful survey of roadsides for rare species, so no effective management plan exists. In contrast. interest in roadside exotic and invasive plants has mush- roomed in a decade.’5 In perhaps most roadsides, exotic plants are a significant proportion of the species pre-

sent, yet of special concern are the relatively few invasive species. Invasive species can raise havoc on farms. ranch- land, parks. and nature reserves. With strips of roadside exotics usually near these places, transportation officials are increasingly cdled on to do something. In some states, roadside management is beginning to address invasive species issues. Ironically, despite the frequency of exotics-lined roads near agricultural and natural areas, precious little evidence yet exists that exotics from roadsides

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- Figure 2. Wildlife passages

NOTE: The designs selected here from today’s array of wildlife underpasses and overpasses all work in the sense that target animals successfully cross the road. Future designs from collaborating engineers and ecologists or animal behaviorists will doubtlessly reduce costs and provide additional benefits for society.

SOURCE: R. T. T. Forman et al., Road Ecology: Science and Solutions (Washington, DC: Island Press, 2003); M. Trocme, ed., Habitat Fragmentation due to Transportation Infrastructure: The European Review, COST Action 347 (Brussels: European Comission, 2003); and B. hell et al., Habitat Fragmentation due to Transportation Infrastructure: Wildlie and Traffic: A European Handbook for Identifying Conflicts and Designing Solutions, COST 347 (Brussels: KNNV Publishers, 2003).

have invaded these valuable resource areas. (The sparse data available suggest that roadside plants only spread outward short distances.)

A new roadside design and management paradigm awaits discovery; broad intcrest-plus some controversy-should lead to big benefits. Variegated roadsides perhaps best capture the vision. Roadsides could accomplish a range of societal objectives, from species-richness recovery to traveler safety and carbon absorption/ storage. Several steps would quickly produce results. These include mowing roadsides patchily, infrequently. and at low intensity; minimizing fertilizer. pesticide, and roadsalt application; favoring rare plants by protecting rare microhabitats such as rocks and wet spots; increasing surface microtopography during upgrad- ing and maintenance projects; and adding brush piles, rock piles, and stump lines in kcy places. These improvements would transform vegetation and habitats from impoverished monotony to intriguing diversity. Hand-in-hand with this enhancement, plant ecologists, engineers,

wildlife ecologists. roadside managers, and other experts can address numerous additional human goals and services. High visual quality, stormwater-pollutant

tions for water’s effects dating back at least to the roads of ancient Rome. Every proposed modification must have a solution for water.

control, wood production, tloodwater detention, trafic-noise reduction. and cul- turehature education are opportunities for this vast, valuable roadside area surrounding us.

Water and Soil The arms of the giant road system

penetrate widely throughout the physical environment, commonly altering hydrology, increasing soil erosion and sedi- mentation. and degrading aquatic ecosystems. Water is the major enemy of roads. As such, the road and roadside are engineered to combat the effects of excess water as well as ice. This provides safe travel and minimal

Just as water is the great enemy 01 roads, roads, as well as development and certain other land uses, are a great enemy of water and aquatic ecosystems (see Fig- ure 3 on page 17). For instance. sediment and chemicals from around road bridges often degrade downstream water quality and smooth out stream bottoms, ehninat- ing holes for fish. especially big fish. Fishermen know this and typically go upstream from a bridge. In forestry areas. typically more eroded sediment comes from logging roads than from the areas logged. More generally, stormwater run-

maintcnancc and repair. We drive on timc-

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OR from roads has typically been chan- neled in ditches and pipes to streambanks, wetlands, and lakeshores. This arrangement has several big impacts. Water from storms and snowmelt rushes to the water bodies. causing high peak levels and floods. Second, the rushing water scours the banks and bottoms. It also commonly carries sediment-everything from sand to trash-into the water bodies, typically creating turbidity and reducing valuable habitat for fish and other aquatic species. Finally. road runoff carries the array of chemicals that also degrade water quality.

Disconnecting roads from water bodies is the core answer. In this scenario, instead of carrying stormwater directly from source to sink in pipes, canals, and ditches, the route is broken up with depressions and other structures that tem- porarily hold and disperse the water and chemicals to soil or air. Streams, lakes, and other water bodies greatly benefit. Moreover. these dispersed depressions. tiny to large, can provide other rich societal benefits, from aesthetics and neigh- borhood park recreation to wetland habitats and wildlife movement.

The United States has lost half its wetlands, and roads are among the thieves. Road construction has routinely drained or shrunk wetlands, though in places, blocked drainage has created or expanded wetlands. Rarely does a wetland escape the cffect of a nearby road on

atively natural stream bottom are best. and circular pipes worst for water flows and fish passage. Where one culvert (or stream area immediately above or below it) is impassable, migratory fish such as endangered salmon are excluded from the entire upstream drainage basin. Overall, culverts are inexpensive items in a transportation budget and offer good solutions for the effective passage of water. fish, and many terrestrial animals.

shortcoming is that a constructed wetland is commonly considered to be successful if it has live wetland vegetation and animals. Instead, getting the hydrology right-water levels plus water flows-is the most important measure of success. Wetland vegetation and animals will quickly follow on their own. The second-most important measure is the provision for disturbance events, such as infrequent floods. Beaver place

dams in appropriate locations and will maintain and quickly repair their dams. Constructed wetlands too often fail all three “beaver tests”: effective location, maintenance, and repair. Yet mitigation wetlands should pass these tests.

Water and soil issues trace back to the beginning of roads. Habitat degradation linked to roads, water, and soil should now be rare. not common.

To improve this degraded ivetland ecosystem, sedinient that had blocked tidal ebb and poll. n’as removed, alder trees were planted, and upland slopes were seeded with nutive plants to reduce erosion.

Chemicals and Air Some two dozen chemi-

cal pollutants-from heavy metals to nitrogen. PCBs (polychlorinated biphenyls), particulates, and petroleum products-predominate and accumulate along roads.’6 Road surface wear. herbicide use. de-icing agents, brake-lining wear, hydraulic fluids, t i e wear, fuel combustion, and en- gine wear (to name a few) are the sources. Accidental chcrnical spills (2.400 are reported annually in the United States), illegal dumping and washing of

groundwater and surface water flows. Wetland mitigation or compensation chemicals from trucks. and sevcn mil- Yet often the effect would be minimal if has grown recently yet remains con- lion vehiclc accidents annually add to the roadbed were perforated with a tentious. with few satisfied players. Esti- this chemical cocktail. The diversity of sequence of many pipes or culverts. mates suggest that only 40 pcrcent of sources means that no simple magic Good connectivity for the movement of mitigation projects are successful, answer will be found to produce clean- wetland animals would be a big bonus. though views range from hardly any to er roadsides and less-contaiminated Culverts with an arched form over a rel- almost all. Perhaps the most obvious stormwater runoff. “Source-control”


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- Figure 3. Hard-surface cover and suburban nature

Precipitation

10% & 20& 30% 55% F. 0 20 40 60 80 100

4 4 4 4 4 Natural 1 0.5 0.33 0.25 0.13 Industrial I Shopping

ecosystems acre acre acre acre acre centers I I Commercial

Residential house lots

Hard-surface cover (percent)

NOTE: The percent of hard-surface cover (due to roads, sidewalks, parking areas, driveways, and roofs) is a useful indicator of many environmental conditions in a built area. Planners consider overall stream quality and fish populations to be “good with 0-10 percent hard cover, “impacted with 10-30 percent, and “degraded with more than 30 percent. More hard-surface cover also means that flooding and stormwater pollutants increase, but water for plant growth and recharging groundwater decreases.

SOURCE: R. T. T. Forman et al., Road Ecology: Science and Solutions (Washington, DC: Island Press, 2003).

measures and “life-cycle” vehicle man- ufacturing that recycles almost all com- ponents offer promise for reducing many chemical inputs, as do more ecologically dominated road-and-roadside management practices.

Vehicle turbulence helps spread pollutants along roads. Wind sweeps the chemicals into surrounding or distant ecosystems. Water washes the chemicals into nearby groundwater and aquatic ecosystems. Fortunately. wind and water both dilute the concentrations of chemicals. What do the road system chemicals do? Some (such as lead, asbestos. and certain organics) produce direct toxic effects on plants. wildlife, or humans. Nitrogen and phosphorus enrich or eutrophicate ecosystems. causing a loss of species richness. Pesticides accumulate or magnify through the food chain, thus targeting top predators. Some relatively inert chemicals (such

as cadmium and 7hc) simply accumulate to toxic levels in the soil. And other chemicals such as methyl tertiary-butyl ether (MTBE) move rapidly in groundwater to pollute distant water bodies. While the known processes permit predictions, surprisingly few direct studies of the ecological effects (in contrast to public health effects) are available.

One exception is roadsalt. the same sodium chloride found in the saltshaker. Roadsalt is washed off roads by water, lift- ed and dispersed off roads by snowplows, and pulverizcd by vehicles to tine particles that blow near and far off the road. Sand mixed with roadsalt accumulates

pollutes wells and even penetrates tens of meters down into granitic bedrock. It also accumulates in the bottom layer of ponds, inhibiting vertical water circulation and devastating the community of bottom- dwelling animals. Roadsalt corrodes structures, thus adding heavy metals to water. Accumulating salt in roadsides causcs the loss of native vegetation and favors the spread of salt marsh species. In some places, road and roadside salt is a barrier to amphibian movement but, conversely, an attractant for moose or deer.

in and srnoothcs stream bottoms. reducing tich habitat. Salt accumulatcs in

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What can be done about the array of chemjcals along roads'? At present, transportation agencies use about two dozen best management practices, which are much like good housekeeping or road- keeping actions. Some are source-control techniques to reduce chemical inputs, such as limiting herbicide spraying and using protective covers when painting bridges. Other such practices are contain- ment approaches, such as concrete basins and vegetated depressions that hold stormwater, to limit the dispersion of chemicals and impacts. Many of these latter approaches permit water to slowly drain through the ground to groundwater andor evapo- rate into the air. At the same time, cheinicals are either broken down by microorganisms or are filtered and accumulate in the ground. More such ecological solutions are needed to thin the chemical blanket along roads.

Dust and roads are also linked. Dri- ving a car daily over a one-mile dirt road for a ycar gcnerates about one ton of dust. Not surprisingly then, in the United States, 43 percent of

speeds by on a dry afternoons often stay airborne for hours. At night. cool air draining down hillsides may carry the dust far out onto a lake-where particles sink slowly, perhaps for years if the lake is deep. The sinking "cloud' of particles slowly liberates toxic chemicals, as well as phosphorus, which eutrophicates the lake water.

Air pollutants have long filled our headlines, policy debates. and actions but still pose headaches.2x Local pollutants, including carbon monoxide, herbicides. light. traffic noise, and heat from road surfaces pr imdly affect adjacent ecosys-

centurics in the stratosphere. alteiing temperature. light pcnetration. and the ozonc shield. which j n turn affect animals, plants. and entire ecosystems. Green- house gases, including carbon dioxide and methane. also accumulate in the upper atmosphere, affecting global cli- mate. Diverse temperature and precipitation changes are predicted as likely or highly likely by the 2020s and 2050s, a manifestation of global climatc change. Consequently, widespread ecological effects on the land are considered likely or highly likely. Ecological conditions related to chemicals and air are changing

before our vcry eyes. Few people yet sce this direct linkage between roads and vchicles and altered nature across the land.

A timnel built dong the north shore of Lake Superior to protect scenic, geologic. and ecological values increrised hahitot sind reconnected the lake nnd,forest j b r wiltilife.

fugitive dust originating from the ground comes from roads, with the remainder mainly originating from construction and agriculture. Unpaved roads contribute 28 percent and paved roads 1.5 percent of the dust. Dust carries both benign and harmful elements (such as silica, which is bcnign. and lead, which is harmful). In addition, tine particles are of considerable public-health concern." Road dust can significantly change soil and vegetation near roads, but its effects can also extend to lakes at quite a distance.

The dust particles in the little whirl of dust from a road's shoulder as a vehicle

tems and surrounding neighborhoods. This local focus has the most direct effects yet seems to be the least studied ecologically. Regional pollutants-such as acid precipitation, lower-atmosphere ozone, and photochemical smog-persist for hours to years and produce regional effects. Nitrogen oxides. sulfur oxides. and hydrocarbons are considered to be of particular concern. Regional ecological effects are widespread, important. and poorly understood.

Global pollutants, including halocar- bons (containing fluorine) and nitrous oxide, generally persist for decades to

The Land and the Network

Turning to the big picturc. many cities. housing de- velopments, and logging arcas havc extremely dcnse road networks. in some cases with dcnsc traffic. A recent road-ecology article pointed out that 'Traffic is aud- ible from virtually

every location in England."'" Before exploring the eftects of the network on the land and possible solutions for major landscape-wide issues. it is useful to look at the network and its characteristics.

Topography and land-use patterns are major determinants of network form. which in tuin strongly afects society's delivery of goods and scrvices. Howevcr. network form is also a major determinant of unintended detrimental effects on nature and the land. Typically. roads inter- connect to fonn an irregular grid (or rectilinear network) with three especially important attributes. First, road density. a


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- Figure 4. Road network form

Bad Good Better

NOTE: Road networks with the smallest ecological impact are those that maintain large roadless natural areas and also concentrate traffic onto a small number of large roads. Large natural areas sustain clean water-supply aquifers, interior species of conservation interest, and much more. One large highway creates less area impacted by noise, emissions, and habitat loss than do two small highways.

SOURCE: R. T. T. Forman et al., Road Ecology: Science and Solutions (Washington, DC: Island Press, 2003).

simple useful measure of a network, is simply the average number of miles of road length per square mile of area. Road density for the United States is 1. I mile per square mile ( d m i ’ ) , while urban centers may have 65 dmi’ . Road density affects many ecological factors, including wildlife populations, interior species, hydrology, fire, and human access. A second useful network measure is the percent of hard-surface (impermeable-surface) cover in an area (see Figure 3). This is particularly useful in understanding suburban areas, where roads, sidewalks, driveways, and parking areas may be extensive. Stream quality and fish populations generally correlate with the percent of hard-surface cover. A third characteristic-network form-may be the best overall indicator of ecological conditions (see Figure 4 on this page). For example, road-related stream flooding and road- avoiding wildlife would both be highly sensitive to the form or arrangement of a network. Human access via dead-end or spur roads from a network into remote m a s often lead to impacts, so closing a spur road can be a particularly effective

way to protect or restore natural systems. Building a new road in a sprawl area or a logging area can causc either serious or minimal damage, depending on its location in the network. Thus, adding and removing roads and determining their optimum locations are important scientific and policy issues.

Four landscape types contain the bulk of North America’s roads, vehicles, and people: The built land of city, suburb, and sprawl has road networks, especially variable in suburban areas, which basi- cally link concentrated homes and jobs and facilitate social interactions. Forestry land has a road network with fairly regular interroad distances built to serve logging activities, though recrc- ation can be a conspicuous corollary usage. Agricultural land has mostly regular rectilinear road networks that serve dispersed farms of mainly rectangu- lar cultivated fields. Grazing and arid land has highly irregular road net-

distribution of water sourccs where human activities aggregate.

A fifth “natural landscape” type, illus- trated by remote areas, parkland, little- logged tropical rainforest, and the Arctic, has few roads, vehicles, and people. Here natural processes and ecosystems predominate. and changing even a single road (such as by road building and tem- porary or permanent road closure) can have big beneficial-r detrimental- effects. Arctic roads, for example, illus- trate unique and important patterns. A limited summer-road network alternates with an extensive winter-road network. Summer roads produce conspicuous long-lasting strips across the land, often marked by a band of dust deposition, degraded vegetation, melted permafrost

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soil, and soggy or inundated adjacent areas. Caribou tend to avoid roads with vehicles, even up to a distance of three miles. In winter, snow roads and ice roads built with varied technologies provide welcome intcractions for isolated residents. Although widespread, winter roads apparently cause less overall ecological impact. A hnal lesson learned from the Arctic road system is that the first road built into a natural landscape area has the greatest relative ecological effect, under- lining the importance of rigorously maintaining large roadless areas.

Taming the Giant for Nature and Us

A century ago, President Teddy Roosevelt emerged as a visionary: big thinker, trust-buster of big business, great expander of national forests, and a Nobel Peace Prize winner for mediating the Russia-Japan War. But even he could not have foreseen the transformation of transportation issues from mud and dust to today’s gridlock and greenhouse gases. Predicting years ahead normally only works if generic statements are made. Predicting decades ahead is rarely successful, though 30-50 years is a good time period to envision. Thus, while highlighting the implications of the preceding sections is important, it warrants caution. U.S. transportation offers some advantages because in 30 years the massive infrastructure can change rather little and, according to predictions, tens of millions more Amer- ican residents are expected.

The frontiers of science and engineering research most likely to expand are perhaps the easiest to decipher: The near term, relative to roads and vehicles, will most likely bring increased research on wildlife populations, roadside vegetation and its management, species richness, chemicals along roads, aquatic ecosystems and fish, local and regional pollutant effects, global atmosphere effects, road network patterns, network effects in different landscape types, and ecological planning. The rate of research discoveries and progress

depends mightily on the availability of new funding, new collaborations, and policy actions.

Recent transportation initiatives in planning and projects based at least in part on road ecology have produced initial tra- jectories, many with enormous potential:

wildlife passages, from amphibian tunnels to elk-and-grizzly overpasses;

exotic-species control and native vegetation enhancement in roadsides;

forestry roads that reduce stream sed- imentation and protect fish populations;

road closures on public lands to protect ecological resources characteristic of large natural areas;

quieter road surfaces laid down to reduce habitat degradation due to kaffic noise;

use of landscape ecology principles and GIS techniques for transportation planning;

ecological planning of regional road networks; and

incrcased hiring and decisionmaking roles of ecologists in state departmcnts of transportation.

Another category highlights those road-ecology concepts initially well received by the transportation community and expected to be implemented and expanded in the near future:

the roadeffect zone (a band with con- voluted margins along a road in which significant ecological effects of roads and vehicles are present) as a common planning ground between the highway engineer’s careful work in a narrow zone and the landscape ecologist’s work on important ecological flows and patterns across the land;

bridgdculvert repairs and upgrades as ongoing opportunities to provide other societal solutions, such as walking paths and wildlife routes; and

wildlife underpasses and overpasses that also help reknit a community split by a highway.

A final set of road-ecology actions offer promise for policy in a longer time frame:

maintaining rapidly growing trees on roadsides for carbon absorptiodstorage;

increasing the number of culverts and pipes 5-, lo-, or even 20-fold to reduce

hydrological disruption and reconnect the land for small animals;

reducing particulate matter and lower-atmosphere pollutants to enhance wildlife populations;

reducing greenhouse gases for ecological benefits;

closing one or more road in every local area to better protect large natural- vegetation patches and slightly reduce vehicular travel; and

planning scenarios with few vehicles-and even few roads.

How could implementation of such an array of transportation solutions be accel- erated? Clearly some person, group, or agency needs to step forward with leadership, in this case to achieve six goals:

require ecologists to be a key compo- nent of all transporation planning and major projects;

establish pilot projects for all road- ecology issues-together with monitor- ing, research, and public education-in every state;

fund quality road-ecology research and require collaboration between researchers inside and outside the transportation community;

convert competition to collaboration between departments of transportation and the natural resource agencies;

focus initial planninglproject implementation efforts on the metropolitan fringe or sprawl area where population growth, development, change, abundance of nature, and the probability of success are all high; and

initiate a regional approach to address biodiversity, wildlife, and water issues relative to transportation. Accomplishing these actions would rapidly produce enormous visible benefits.

Stepping back to consider the big pic- ture from different angles, do roads and vehicles have to be intrusive, or could they fit around nature and us’? Could we create a “gentle roadprint” on the land?

Two key perspectives address how to combine road-system values and uses with environmental dimensions: Sustain- able development highlights growth of the human enterprise as the central goal, adding that the current level of environ-

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mental degradation should not worsen. An alternative perspective, respecting the land that nurtures us, highlights the fact that nature and natural systems have their own important characteristics and that society fundamentally depends on, and must care for, the land and water. Road ecology can underpin either objec- tive, but only the latter one leads to the gentle roadprint.

Like the genie in Aladdin’s lamp, road ecology has emerged, looks pow- erful, and is expanding rapidly. This early stage of rapid expansion is exact- ly the moment when one can have the greatest impact. Leading to major policy areas are nine doors: road corridors perforated with wildlife passages; vegetated soil berms and depressed roads; improved designs of road surfaces, tires, motors and vehicles; concentrated and reduced traffic; cleaner fuels and life-cycled materials; remote-road closures and removals; roadside design and management; restored hydrologic flows; and enhanced streams and aquatic ecosystems. As trickles become streams of people-engineers, environmental scientists, planners, social scientists, decisionmakers, the public--entering each door, the cumu- lative impact of policy initiatives should indeed tame the giant for nature and for us.

Perhaps the real achievement will be safe and efficient transport elegantly embedded in nature’s species richness and processes. While driving, we will notice a conspicuous environmental improvement in natural systems along the entire road network, coupled with an emerald network of large natural areas linked across the land. The future is not just what is ahead. It is what we create with nature.

Richard T. T. Forman is the PAES Professor of Land- scape Ecology at Harvard University’s Graduate School of Design in Cambridge, MA. His research interests include landscape ecology. road ecology, urban region planning, and spatially meshing nmre and people on the land. He is the author or coauthor of several books, including Laird Mosaics: The Ecohgv of hd.scfipes mid Regions (Camhridge University Press, 19%). h n d - ,scope EcologY Principks in Londscupe Atrliirecrure und hiid-Usp Planning (Island Press. 1996), R u d €CO/U~.V:

Science and Sulirriom (Island Press, 2002). and Lmd

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MCJ.VI;C jiw Ihe Grealer B a n e h a Region: Planning u Funm (Gustavo Gili. May 2004). Forman may k con- tacted at Harvard University, Harvard Design School. Cambridge. M A 02 138. The idea5 expressed in this art- cle have emerged from sustained interactions about road ecology with Daniel Sperling, Jnhn A. Bissonetre, Anthony P. Clevenger, Carol D. CuLshall. Virginia H. Dale. Lenore Fahrig, Rohcrt France, Charles R. Goldman, Kevin Heanue. Julia A. Jones, Frederick J. Swanson, Thomas Turnentine. and Thoma5 C . Winter. The author also warmly thanks Marlin Lec-Cosselin. Alan Berger, Marcel P. Huijwr, and Grant Jones for ref- erences on vehicle driving relative to perceived road width, and John A. Bissonene. Lawrence Buell, A m n M. Ellison, Thomas E. Linkous. and Daniel Sperling Tor insightful reviews of this article.

NOTES

I . Most of the topics in this article are tliscusscd more fully in the synthesis volume by R. T. T. Forman et al., Rood Ec-olngy; Science und Solurions (Washington. DC: Island Press. 2002). which includes more than 1.ooO ref- erences for funher exploration. The only review anicle covering most of the topics is R. T. T. Forman and L. E. Alexander. “Roads and Their Major Ecological Ell’ecis:’ Annirul Review qf Ecohgv und S,?.~rernurir.s 29 ( 1998): 207-3 1.

2. Forman el al., ibid. 3. National Research Council, 7 i ~ i ~ i d a Susraiirubk

Furitre: Addre.s.sbrg rEie /J,,ig-Tcnn 6fecr.r qf Mofor Vehi- cle Trairsponariori ( ~ 1 C h a f e und E d o g y (Washing- ton, DC: National Academy Press, 1997); and National Research Council. Surface Transpunafiun Orvinminen- i d Rercanli: A Long-Enn Srraregy, Special Repon 268 (Washington DC: Transportation Research Board. 2002).

4. M. Trocme. ed., Habituf Fragrneimlion Due IO

Trunsporrarion /nfrasfnavure: The Eurrpean Revioc: COST Acrion 341 (Brussels: European Commission. 2003): and B. hell el al., Hobimr FraginenrufirJn Due 10

Trunsporrariuii Infrasfnicfiire: wildlife cind Trufic: A European Handbook .for Idenrifiirig Cocit1icr.s and Designing So/u~iUns. COST 341 (Brussels: K ” V Puh- lishers, 2003).

5. Forman ct al.. note I above. 6. Forman et al.. note 1 above. 7. Forman et al., note I above. 8. Forman et al., note 1 above. 9. Forman el al., note I above. 10. Forman et al., note I above. I 1. Noreen McDonald, personal communication with

author, January 2004. 12. There are several useful review anicles focusing

on wildlife and roads: A. F. Bennett, “Roads, Roadsides and Wildlife Conservation: A Review,” in D. A. Saunders and R. J. Hobbs, eds.. Nurure Cunsen~aiim 2: The Role of Corrkfors (Chipping Norton. Auslralia: Surrey Batty. 1991),9Y-117;1.F. SpellerbergandM. J.Gaywd.Liti- eur Femures: Linear Habifals ond wildlife Corridors. Rerean-h Repon 63 (Peterborough, UK: English Nature. 1993): H. Bekker, 8. van den Hengel, H. van Bohenien, and H. van der Sluijs, Narrurr over Wegeit (Nature acruss Momways) @lfl, Netherlands: Ministty of Timspolt, Public Works and Water Man-

(2000): 21-39 and S. C. Tronihulak and C. A. Frissell, “Review of Ecological Elfects of Roads on Terrestrial and Aquatic Communities;’ Consemirion Biu/o#y I4 (2003): 18-30,

13. Formnn et al.. note I above. 14. Forman and Alexander, notc I above. 15. Forman and Alexandcr, note I ahove. 16. N. L. Hodson and D. W. Snow,‘The RoadDeaths

Inquiry, 196M1,”BirdSr~dy 12 (1965): 90-99. 17. R. T. T. F o m i , k n d Mo.cuir.s: The Ecolugy of

knd.vcupe.$ orid Regkghn.~ (New York: Camhridge Univer- sity Press. 1995).

18. Forman and Alexander. note I above. 19. R. T. T. Forman. B. Reineking. and A. M.

Hersperg, “Rood Tr&k and Nearby Grassland Bird Patterns in a Suburbanizing Landscape,” ~ n ~ ~ i m J n t l i e n l ~ /

Munugetnemr 29 (2002): 782-800. 20. Fornian et al.. note I above: Trocme. note 1

above; and hell. note 4 above. 21. Fornian et 31.. note 1 ahove. 22. D. Appleyard, K. Lynch, and 1. Myer. The View

froiir fhe Romd (Cambridge, MA: MIT Press. 1964): B. N. Fildes and S. J. Lee, The Speed Revinv: Road Envi- miitnetit. Behaviol: Speed Liniifs, Ei!fi,rceinenr uird Crm/ie.q. Repon CR 127 (Canhem: Federal Otice of Road Sat‘ety, 1993): County Surveyors Society (R-U), Tkific Culmirrg in Prucrice (London: h d o r Publishing Co., 1994); European Transport Safety Council. Rcduc- ing Trufic Injuries Rurultirtg from Ercess arid Inuppro- prime Speed (Brussels. 1995); U.S. Depmmcnt of Transportation, FleSil,ilir>~ iii Highwuy Design. Reprrt FHWA-PD-97-062 (Washington, DC: Federal Highway Administration. 1997): S . H. Burringion and V. Thiehach. E r k Buck Hnfr Srreer.c Hon lo Proferf Cotit-

~nutririesfruni Asphulr und Trufic (Boston: Conservation Law Foundation. 1998): K. L. Schneidcr. The Prrris- kxingroii Road: Crsnrnriniry-Bused P/unnin$ and ~i~r?fe,~f-Serisirive Highway Design (Washington, Dc: Island Press, 2(X)3); J . S. Givens, “Rural Rustic Roads in Virgini+lrnplemenlation of Program Guidelines and Pilor Projects,.’ Trunsponution Research Reed I8 19 (2003): 15545; and S. T. Gtdley, T. J . Trigg~. and B. N. Fildw, “Perceptual Lane Widlh. Wide Percepnllll Road Centre Markings and Driving Speeds:‘ E~otumic.s 47 (201M): 237-57.

23. Fomian el al., note I above; R. M. Case. “Inter- date Highway Road-killed Animals: A Daca Source for Biologists,” Wildlife Socirfy Bulletin 6 (1978): 8-1 3; and A. Seiler, The 7id/ of rhe Auhmobile: Wldlife uiid Road.$ in Sweden. Dtrtoral thesis (Uppsakla: Swedish Universi- ty of Agricultural Sciences, 2003).

24. Schncider. note 22 above. 25. Forman et al., now 1 above. 26. Forman et A., note I above. 27. National Rescarch Council, 2002. note 3 above. 28. National Research Council, 1997 and 2002. note

29. Underbill and Angold, note 12 above. 30. Forman el al., note I above.

3 above.

agemsnt. 1995): J E. Underhill and P. C . AII~OI~. -l-:ffecrc Roadc on Wildlife in an Intensivel) ,Mndiliud Landsca~.” €1, I i rotrin e n ru I

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Documents

Road Ecology's Promise: What's Around the Bend?