Environmental Management

, 42:480 | Cite as

An Assessment of Road Impacts on Wildlife Populations in U.S. National Parks

  • Rob Ament
  • Anthony P. Clevenger
  • Olivia Yu
  • Amanda Hardy


Current United States National Park Service (NPS) management is challenged to balance visitor use with the environmental and social consequences of automobile use. Wildlife populations in national parks are increasingly vulnerable to road impacts. Other than isolated reports on the incidence of road-related mortality, there is little knowledge of how roads might affect wildlife populations throughout the national park system. Researchers at the Western Transportation Institute synthesized information obtained from a system-wide survey of resource managers to assess the magnitude of their concerns on the impacts of roads on park wildlife. The results characterize current conditions and help identify wildlife-transportation conflicts. A total of 196 national park management units (NPS units) were contacted and 106 responded to our questionnaire. Park resource managers responded that over half of the NPS units’ existing transportation systems were at or above capacity, with traffic volumes currently high or very high in one quarter of them and traffic expected to increase in the majority of units. Data is not generally collected systematically on road-related mortality to wildlife, yet nearly half of the respondents believed road-caused mortality significantly affected wildlife populations. Over one-half believed habitat fragmentation was affecting wildlife populations. Despite these expressed concerns, only 36% of the NPS units used some form of mitigation method to reduce road impacts on wildlife. Nearly half of the respondents expect that these impacts would only worsen in the next five years. Our results underscore the importance for a more systematic approach to address wildlife-roadway conflicts for a situation that is expected to increase in the next five to ten years.


Data collection Habitat fragmentation Mitigation Mortality National park Survey Road ecology Road network Transportation Questionnaire Wildlife management 


“ promote and regulate the use of the...national parks...which purpose is to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations.” (National Park Service Organic Act, 16 U.S.C.1.)

Overview of Wildlife-Transportation Issues

Currently, public roads have direct ecological effects on an estimated one-fifth of the area of the United States (U.S.) with the “road-effect zone” extending hundreds of meters from the road itself (Forman 2000). These effects include: habitat loss, degradation, and fragmentation; direct wildlife mortality; and road avoidance behaviors by wildlife (Andrews 1990; Bennett 1991; Forman and Alexander 1998). Further, wildlife-vehicle collisions affect the safety of drivers; nation-wide, deer (Odocoileus spp.)-vehicle collisions have been estimated at 720,000–1.5 million annually (Conover 1995; Huijser and others 2007a). More recent data by State Farm Insurance indicate that nationally there are approximately 1,000,000 wildlife-vehicle collisions per year based on the number of claims for collisions with deer, elk (Cervus elaphus), and moose (Alces alces) and the company’s proportion of the market share of each state’s auto insurance policies (Miles 2006).

During the next 25 years, significant growth and changes in the nation’s economy and population are expected to pose major new challenges for transportation and the environment (TRB 2002). In some areas of the U.S. today, roads are a serious obstacle to maintaining ecological connectivity and a threat to the long-term persistence of key wildlife populations (Noss and others 1996; Sweanor and others 2000; Gibbs and Shriver 2002; Epps and others 2005), and may significantly affect wildlife population demographics (Gibbs and Steen 2005).

Adverse road effects are amplified with increasing road size (Fahrig and others 1995; Lovallo and Anderson 1996), speed limits (Gunther and others 2000), and traffic volume (Seiler 2003; Waller and Servheen 2005). For every kilometer (0.62 mile) of highway construction, an estimated 644 hectares (1591 acres) of land is converted from its original vegetative cover or made available for further development, cumulatively resulting in a significant loss of habitat to wildlife (Wolf 1981). Wildlife populations using areas adjacent to roads face increased mortality risk due to collisions with vehicles (Mumme and others 2000).

Populations of threatened or endangered species and migrating species are especially vulnerable to road mortality (Kline and Swann 1998; Aresco 2003; Huijser and others 2007b). The habitat fragmentation effects of roads can isolate wildlife populations unwilling or unable to cross roads (Wayne and others 1992; Gerlach and Musolf 2000), while increased noise, pollution, and edge effects can make habitat less favorable for many species (Chomitz and Gray 1996). Population densities for large mammals tend to be lower within 100–200 m of roads (Lyon 1983; Yost and Wright 2001; Rowland and others 2000; Chruszcz and others 2003). Other road effects include habituation of wildlife to humans resulting in increased human-wildlife encounters (Mattson and Blanchard 1992; Olson and others 1997; Gibeau 1998).

An emerging area of interest is the effects of roads on fragmenting wildlife populations. A study of bobcat (Lynx rufus) and coyote (Canis latrans) populations affected by a busy southern California freeway indicated that although individuals successfully crossed the highway, they did not always contribute to gene flow through reproduction (Riley and others 2006). The home ranges of these two territorial species, abutted, but did not cross the highway, resulting in significant genetic differentiation between populations on either side (Strasburg 2006).

U.S. National Park System and Wildlife-Transportation Issues

There were more than 273 million recreational visits to U.S. National Parks in 2005 with projections of nearly 270 million and 268 million in 2006 and 2007, respectively (National Park Service 2005). Much of the public’s access within these parks is provided by an estimated 8855 kilometers (5500 miles) of paved roads and 7245 kilometers (4500 miles) of unpaved roads. There are many additional roads, paved and unpaved, that run adjacent to, access, or pass through national parks that are maintained by state and local agencies. The U.S. National Park Service (NPS) also has 115 alternative transportation systems in 99 parks, such as shuttles or buses, although 34 of these are water-based (National Park Service 2007a). This surface transportation system provides the American public with a variety of options for visiting national parks via motorized transport.

By providing protection and habitat for nearly one-quarter of the threatened and endangered species in the U.S., national parks are important conservators of biodiversity (National Parks Conservation Association 2004). In addition to preserving threatened and endangered species, the NPS is mandated to protect all resource values as well as provide for visitor enjoyment (National Park Service 2003). These dual roles are often difficult to balance as individual park visitation levels increase, transportation systems are strained, and increased recreational use adds pressure on natural systems (Truett and others 2002; Kelly 2003).

National park wildlife populations are increasingly vulnerable to road impacts. From 1989 through 2006 there were 116,000 vehicle collisions documented in the national parks. Approximately 10 percent of these crashes were wildlife-vehicle collisions; they accounted for 12,577 of the reported crashes from 1989 through 2006 (National Park Service 2007b). Traffic-related mortality of wildlife is a concern in several national parks (Bernardino and Dalrymple 1992; Rosen and Lowe 1994; Kline and Swann 1998; Hawes 2000; Burson and others 2000). Research suggests that increasing bus traffic on the Denali park road has affected caribou (Rangifer tarandus) and grizzly bear (Ursus arctos) movements (Singer and Beattie 1986; Yost and Wright 2001). Even at low speeds, heavy traffic has been known to block animal movements in parks such as Yellowstone and Great Smoky Mountains (Gunther and others 2000). Other road-related impacts include the habituation of wildlife to food from passing vehicles and invasion of nonnative plant species (Tyser and Worley 1992; Gibeau 2000; Strittholt and Dellasala 2001; National Park Service 2003; Hansen and Clevenger 2005).

Wildlife populations within national parks are not necessarily more protected than those residing outside their boundaries (Newmark 1995; Parks and Harcourt 2002). Some parks can have wildlife road mortality rates in the tens of thousands (Kline and Swann 1998) with significant impacts on certain populations, e.g., moose (Bangs and others 1989); snakes (Bernardino and Dalrymple 1992; Rosen and Lowe 1994); large mammals (Gunther and others 1998). Canadian parks lose hundreds to thousands of animals each year (Damas and Smith 1982). Other than isolated reports on incidences of traffic-related wildlife mortality, there is little knowledge of how roads might affect wildlife populations in U.S. National Parks and adjacent lands. Mortality, road-effect zones, and habitat fragmentation effects have been the focus of few studies in national park lands. However, Glacier National Park, Montana, has invested in mitigation measures to allow mountain goats (Oreamnos americanus) to safely cross under a busy park road to access a mineral lick (Singer and Doherty 1985). Park studies of road impacts have been primarily focused at the level of individuals, whereas population- and ecosystem/community-level impacts have not been contemplated to our best knowledge. A synthesis of information obtained from a system-wide survey of resource managers in U.S. National Parks could provide information capable of characterizing current conditions and help identify future wildlife-transportation conflicts and potential mitigation measures in these important landscapes.

The purpose of this study was to assess the degree to which park resource managers were concerned about road impacts on wildlife populations in NPS management units (NPS units). By surveying park managers we attempt to qualitatively assess the magnitude of their concern. Being able to identify and assess wildlife issues involving transportation will help the NPS gauge the ecological impact of roads systematically.

The specific objectives of this study were to survey NPS staff responsible for resource conservation to (1) obtain information characterizing their NPS unit’s road system, (2) describe data collection practices and estimates of the extent of road impacts affecting wildlife groups, (3) identify whether mitigation practices are being used to reduce impacts to wildlife, and (4) assess future park transportation trends and potential impacts to wildlife populations.

The findings of this survey will fill an important gap in knowledge about the broad impacts of public roads on wildlife throughout the National Park system. This synthesis will help provide qualitative information characterizing current and future wildlife-transportation issues so that appropriate mitigation measures can be planned and parks ultimately managed for the dual needs of visitor access and natural resource conservation. Lastly, it should be noted this study is based on qualitative information based on NPS employee perceptions; therefore, further analyses may be needed to better quantify and understand key findings.


We identified 388 NPS units to include in our survey; however, only 196 (51%) had public access roads. For these 196 NPS units we created a contact list from a NPS employee directory that consisted of one park service employee per NPS unit. Questionnaires were sent via electronic mail to the park service employee that we estimated could best answer questions about wildlife and resources for his or her NPS unit; this was generally the resource management specialist or the superintendent if a particular unit was small.

We requested information on the following four main areas:

Background information regarding the survey participant’s experience in the NPS unit and its road network (e.g., length of public roads, posted speed limits, traffic volumes, road construction history, road capacity, existence of a public transportation system, and location of the nearest U.S. Interstate highway).

Data collection and management: Assessment of data collection and management of traffic-related mortality of five wildlife groups (amphibians, reptiles, large herbivores, large carnivores, small/medium-sized mammals) and studies of habitat fragmentation caused by park roads. Respondents were asked for which wildlife group they had data regarding road-related wildlife mortality and habitat fragmentation. Additionally, the survey requested data on who reported road-kills and how the effects of habitat fragmentation caused by roads were assessed.

Wildlife-transportation conflicts: The survey asked respondents to characterize road impacts on wildlife populations by direct mortality, habitat fragmentation, habitat loss, human habituation, and risks to human safety. They were also requested to assess the respective magnitude of these same factors within and outside of the NPS unit. In addition, we wanted NPS experts to estimate the extent of road-related mortality and habitat fragmentation on the five wildlife groups.

Mitigation practices: Respondents were asked whether mitigation practices were being used in their respective NPS unit, what they consisted of, and if the measures were monitored and evaluated for their effectiveness.

Survey data from each responding NPS unit were entered in a Microsoft® Excel spreadsheet and summary statistics were generated. The entire questionnaire with methodological details can be found in Appendix 1, and the list of NPS units that responded to the survey in Appendix 2.


Background Information

Of the 196 disseminated surveys, we received 106 completed surveys for a 54% response rate. Nine respondents indicated the survey was not applicable to their situation. Of these nine who responded but did not complete a survey, three were National Historic Trails that cross over several state boundaries, five were National Heritage Areas or Corridors that have a combination of private and public properties, and one was a working farm. An additional four NPS units could not reply as the responsible personnel were not available. Two of the returned questionnaires covered multiple NPS units. The Flagstaff Area questionnaire included information corresponding to three units, Sunset Crater Volcano National Monument (NM), Walnut Canyon NM, and Wupatki NM. Also, questionnaires that were sent out to NPS units in the Washington, DC., area (Fort Washington Park, Greenbelt Park, and Suitland Parkway) were consolidated into National Capital Parks-East.

Survey Respondents

Of those officials responding, 64% were resource managers, 20% were wildlife/ecology specialists, 14% were park superintendents, and 22% held some other position in the park. Of those responding, 43% had been at their position for 1–5 years, 28% had been at their position for 6–10 years, 23% had been at their position for more than 10 years; and only 7% had held their position for less than 1 year.

National Park Service Road System

The NPS units represented by this survey range in size from 16 hectares (40 acres) to over 809,371 hectares (2 million acres) with 49% containing less than 34 km (21 miles) of roads, 17% with 34–64 km (21–40 miles) of roads, 11% with 66–129 km (41–80 miles) of roads, 11% with 130–257 km (81–160 miles) of roads, 9% with 259–644 km (161–400 miles) of roads and 3% with more than 644 km (400 miles) of roads.

Ten percent of the respondents indicated their NPS unit’s entire road system was posted with maximum speeds less than 33 km per hour (21 miles per hour [mph]) and more than half (52%) had all their roads posted with maximum speeds of less than 66 km per hour (41 mph) (Table 1A). However, 59% responded that they have at least some road sections in their NPS unit with speeds greater than 64 km per hour (40 mph).
Table 1

Characteristics of the U.S. National Park Service road system


NP units responding positively (n = 106)

Percent of responses

A. Speed lIimits on roads

(Posted speed limit in kilometers per hour (kph))

Road sections >64 kph (>40 miles per hour [mph])



Road sections 33–64 kph (21–40 mph)



Road sections 16–32 kph (10–20 mph)



Road sections <16 kph (<10 mph)



All road sections <16 kph (<10 mph)



All road sections <33 kph (<21 mph)



All road sections <66 kph (<41 mph)



B.1. Road system capacity

Existing system below capacity



Existing system at capacity



Existing system above capacity



Uncertain of existing system capacity



B.2. Public transportation

Public transportation available



Public transportation not available



C.1. Traffic volumes










Very high



C.2. Traffic volume forecast

Expected to increase



Expected to stay the same



Expected to decrease



Expected trend unknown



D.1. Road construction

New construction within last 10 years



No new construction within last 10 years



D.2. Road construction forecast

Planning to build new roads



Not planning to build new roads



Uncertain about plans to build new roads



Data collection practices in U.S. National Park units concerning traffic-related mortality and habitat fragmentation effects on five wildlife groups

Fifty-four percent of the responses indicated that the existing transportation systems in their NPS unit were being strained at, or above capacity (Table 1B.1). Slightly more than one-third reported their NPS unit’s transportation systems below capacity. Public transportation was not available in 79% of the NPS units (Table 1B.2). Traffic volumes were categorized as high or very high in 26% of the NPS units with expected increases in traffic expected in 76% of the NPS units (Table 1C). No new road construction occurred in nearly three-quarters (74%) of the NPS units, and 21% had plans for new road reconstruction, resurfacing, or rehabilitation projects (Table 1D).

The distance to the nearest U.S. Interstate highway was reported by 74 of the NPS unit respondents. Eleven of the 74 reporting had Interstate highways bisecting the NPS unit, while 12 had an Interstate highway traversing along a NPS unit border or one which was located less than 1.6 km (1 mile) from a border. Sixteen of the respondents had Interstate highways 3–16 km (2–10 miles) away from their NPS unit, nine had Interstate highways 18–32 km (11–20 miles) away, 19 had Interstates 34–80 km (21–50 miles) away, and eight had Interstate highways greater than 80 km (50 miles) away. Of the 74 NPS units that responded, the furthest reported Interstate highway was 128 km (80 miles) away.

Data Collection

Road Mortality

According to national park websites and national park biologists, not all of the five wildlife groups are present in all NPS units. Small- and medium-sized mammals are the only wildlife group in all 106 NPS units responding to the survey. Amphibians and reptiles are in 104 (98%) NPS units, large herbivores are in 100 (94%) NPS units, while large carnivores are in only 63 (59%) of the 106 NPS units. NPS units were most likely to collect road mortality data for large herbivores and large carnivores and least likely to collect data for amphibians (Table 2).
Table 2

Data collection practices in U.S. National Park units concerning traffic-related mortality and habitat fragmentation effects on five wildlife groups

Wildlife group

NP units with group present (n = 106)

NP units collecting dataa

Road mortality (n = 53)

Habitat fragmentation (n = 11)









Large herbivores




Large carnivores




Small/medium mammals




aSee Appendix 1

Half of the NPS units responding (n = 53) collect some kind of road mortality data for wildlife. This information was collected mostly via park rangers or other law enforcement personnel (59%), followed by resource management staff (56%), visitor reports (46%), volunteers or interns (42%), maintenance staff (9%) and researchers (6%).

Habitat Fragmentation

Only 11 NPS units responding (10%) collected data on the effects of roads on wildlife habitat fragmentation. The large herbivores wildlife group was the only category for which more than half of the 11 respondents collected habitat fragmentation data (Table 2).

Nine of the 11 (82%) NPS units reporting on habitat fragmentation effects of roads used radiotelemetry as their main method of data collection, 6 of the 11 (55%) used field surveys, six (55%) used observational methods, and two (18%) used noninvasive sampling methods. Five of the 11 NPS (45%) units that collected data on habitat fragmentation effects used one method, while only two (18%) used all four of the abovementioned methods.

Wildlife Transportation Conflicts

Of the 106 NPS units that returned the survey, 51 (48%) responded that road mortality greatly affected wildlife populations within their NPS unit. This was exceeded only by habitat fragmentation at 57 (54%). Forty-two (40%) reported that habitat loss strongly affected wildlife, 33 (31%) reported wildlife populations also were strongly affected by habituation to humans-wildlife feeding, and 12 (11%) responded that habitat intrusion by roads was affecting wildlife populations. A further 14 (13%) reported there were other critical issues affecting wildlife populations within their parks. These issues included high visitor numbers during peak breeding and migration seasons, illegal hunting, disease, increased stress levels from high visitor presence, human development, unleashed dogs, overpopulation, and invasion by exotic species.

Most respondents estimated that the impacts of road mortality (54%), human habituation-wildlife feeding (43%), and habitat intrusion (32%) were most significant at the local scale (Table 3). The estimates of the effects of habitat fragmentation and habitat loss were more consistent, but the greater number of respondents put them at the landscape level (30% and 29%, respectively).
Table 3

Estimated spatial scale at which road impacts are impacting wildlife populations in U.S. National Park units

Impact of roads on wildlife

Local scale (n = 106)

Regional scale (n = 106)

Landscape scale (n = 106)

Road mortality

57 (54%)

16 (15%)

15 (14%)

Habitat fragmentation

28 (26%)

21 (20%)

32 (30%)

Human habituation-wildlife feeding

45 (43%)

9 (9%)

7 (7%)

Habitat intrusion

34 (32%)

5 (5%)

7 (7%)

Habitat loss

25 (24%)

17 (16%)

31 (29%)

With the exception of habitat intrusion and human habituation-wildlife feeding, most respondents reported that all issues were more severe outside of their NPS unit on adjacent lands (Table 4). Road-related mortality was believed to be equally or more severe outside of the NPS units by 85% of the respondents. The effects of habitat fragmentation were considered by more than two-thirds of the respondents to be more problematic outside park boundaries. Fifty-five (54%) of the respondents reported that habitat intrusion was not a problem on adjacent lands, while 35 (35%) reported that human habituation-wildlife feeding was not a problem, with another 35 (35%) reporting that it was more severe outside of the park.
Table 4

Estimated degree of severity of road impacts on adjacent lands compared to within U.S. National Park unit lands

Severity of road impacts on wildlife on adjacent lands (n = 106)

No problem

Less severe

Same severity

More severe

Road mortality

13 (12%)

4 (4%)

37 (35%)

48 (45%)

Habitat fragmentation

18 (17%)

1 (1%)

16 (15%)

67 (63%)

Human habituation-wildlife feeding

35 (33%)

15 (14%)

15 (14%)

35 (33%)

Habitat intrusion

55 (52%)

8 (8%)

20 (19%)

19 (18%)

Habitat loss

22 (21%)

2 (2%)

13 (12%)

65 (61%)

When asked about factors that contributed to road mortality (respondents could check more than one response), speeding was the most commonly indicated factor (n = 65, 62%), although there were no known data on actual traffic speed. This was followed by unpredictable wildlife behavior (n = 64, 61%). Other factors included nighttime driving (n = 59, 56%), weather (n = 22, 21%), and feeding of wildlife (n = 12, 11%). Eighteen respondents added additional factors to the list including: drivers deliberately running over reptiles; wildlife on or crossing roads during migration or other movement events; poorly designed roads; driver inattention; and right-of-way fencing.

Sixty-seven NPS units (63%) that responded had wildlife species listed under the Endangered Species Act and of those, 21 (31%) reported that roads in these parks threatened those populations. Twenty-eight NPS units (42%) reported that roads had little effect on their endangered species populations, while a further 18 (27%) were uncertain if roads posed a threat to the populations. Thirty-eight respondents (37%) indicated that roads bisected what they considered critical wildlife habitats in their parks, while 19 (18%) were uncertain about road impacts on their parks critical habitats.

Most respondents (>50%) characterized road mortality and habitat fragmentation effects as a low concern for all five wildlife groups. However, 58% cited the effects of road mortality on small- and medium-sized mammals as medium or high (Table 5).
Table 5

Estimated road mortality and habitat fragmentation effects on populations of wildlife groupsa

Wildlife group

Effects of road mortality

Effects of habitat fragmentation







Amphibians (n = 94)

69 (69.0%)

20 (20.0%)

5 (5.0%)

62 (60.2%)

18 (17.5%)

16 (15.5%)

Reptiles (n = 96)

57 (55.9%)

29 (28.4%)

10 (9.8%)

60 (58.3%)

20 (19.4%)

16 (15.5%)

Large herbivores (n = 96)

52 (52.0%)

39 (39.0%)

5 (5.0%)

58 (56.9%)

25 (24.5%)

14 (13.7%)

Large carnivores (n = 62)

57 (90.5%)

4 (6.4%)

1 (1.6%)

41 (65.1%)

15 (23.8%)

4 (6.4%)

Small/Medium mammals (n = 98)

36 (34.0%)

44 (41.5%)

18 (17.0%)

52 (49.1%)

36 (34.0%)

11 (10.4%)

a n = number of National Park units responding which contain that wildlife group

Mitigation of Transportation-Wildlife Conflicts

Only 38 (36%) of the 106 NPS units that responded to the survey reported using some type of mitigation measure to reduce road impacts to wildlife within their NPS unit (Table 6A). The most common technique used was wildlife signs (53%), followed by speed reduction and public education (both 47%). Other techniques included wildlife crossings and fencing (34% combined). Of the 38 NPS units that used mitigation techniques, 17 (45%) used only one technique, 10 (26%) used two techniques, and 11 (29%) used three or more techniques (Table 6B).
Table 6

Types and number of different road mitigation techniques used by U.S. National Park units (if mitigation efforts were in place)

A. Type of mitigation technique

NP units using technique (%) (n = 38)

Wildlife warning signs

20 (53%)

Speed reduction

18 (47%)

Public education

18 (47%)

Wildlife crossings

7 (18%)


6 (16%)

Road design

4 (11%)

Road closures

2 (5%)

Public transportation

1 (3%)


4 (11%)

B. Number of mitigation techniques used

Number of NP units (%) (n = 38)


17 (45%)


10 (26%)


6 (16%)


2 (5%)


1 (3%)


2 (5%)

Twelve of the 38 NPS units (32%) with mitigation programs in place monitor the effectiveness of those measures, 19 of 38 (50%) did not monitor, while two NPS units were developing monitoring plans; and three did not know whether the measures were being monitored for performance. Of the 12 NPS units that monitored the measures, five found them to be effective, one did not, and six had not completed assessments yet.

Seventy-two respondents (68%) reported attending a national park meeting relating to road construction, maintenance, or mitigation within their NPS unit at least once. If the respondent did not attend a road meeting of this type, there was only a 6% chance that the NPS unit would have mitigation programs in place. If the respondent had attended a road meeting, there was a 50% chance that the NPS unit had a mitigation program in place.

When asked to predict how road impacts to wildlife will evolve in their NPS units over the next five years, 44 respondents (42%) believed that impacts will increase and 48 (45%) thought they will stay the same. Only 11 (10%) of the respondents thought that road impacts to wildlife in their NPS unit would improve over the next five years. Three of the 106 respondents did not answer this question.


Just over half (196 of 388) of the National Park Service’s management units have public access roads, making wildlife-transportation interactions a broad issue for the Service. This survey on the impacts of roads on terrestrial wildlife had a fairly robust response, with 106 units (of the 196 queried) providing information by replying to our survey. The responding NPS units were not significantly different in size than all the NPS units with public access roads, allowing us to obtain a representative sample of the NPS system through our questionnaires. Therefore the results of this survey, although based on perceptions, provide insights into transportation-wildlife management issues as the NPS balances the dual goals of providing for visitor use and enjoyment and the protection of wildlife and their habitats.

NPS Road System Characterization

Questions regarding the road transportation system for the NPS highlighted several emerging issues. First, over half (57%) of the NPS units’ existing transportation systems were perceived to be at or above capacity, with traffic volumes currently high or very high in one quarter of them (26%). This may prove to be problematic given traffic volumes are expected to increase in over three-quarters of the units (76%). Additionally, of those responding, 79% do not have access provided by public transit or alternative transportation systems. Roughly 75% of the units have not upgraded or built new roads in the last 10 years. Infrastructure development for automobile travel is one of the most intractable problems in the National Park system (Dilsaver and Wyckoff 1999).

To address the environmental and social consequences of growing automobile use in the National Park system, the NPS is increasingly considering and implementing alternative transportation systems. The U.S. Congress supported this effort in 1998 with the passage of the Transportation Equity Act for the 21st Century (TEA-21). To meet these infrastructure demands, the NPS established the Alternative Transportation Program in cooperation with the U.S. Department of Transportation to implement its responsibilities under TEA-21. Between 1999 and 2003, 131 planning projects and 54 alternative transportation construction projects in 75 different NPS units were approved costing $46.3 million (U.S. GAO 2002). However GAO estimated that as much as $1.5 billion may be needed to address NPS alternative transportation needs in the next 20 years (U.S. GAO 2002).

NPS Road Effects Data Collection

Nearly half of the respondents (48%) thought road-related mortality strongly affected wildlife populations in their NPS unit. Although one-half of the NPS units collected some road-related mortality data, only 16% collected data on all the wildlife groups present in their NPS unit. The tendency has been to collect data on large-bodied wildlife as it is likely that large animals pose greater threats to motorist safety.

Similarly, limited efforts to record road-related mortality of animals were discovered in a recent survey of the animal road-kill reporting practices of state transportation departments and natural resource agencies in North America (Huijser and others 2007). Their synthesis showed that only half of the responding natural resource agencies (50%, n = 36) and even fewer transportation agencies (37%, n = 38) collected road-killed animal carcass data. Their draft report suggests that a national standard for the recording of animal-vehicle collisions would likely stimulate transportation departments and other organizations to collect more spatially accurate data related to road mortality of wildlife. Further, these improved practices would lead to better integration and analyses of the data and ultimately provide useful information to managers. Some transportation agencies are beginning to use Personal Data Assistants (PDA’s) in combination with a Geographical Positioning System (GPS) for routine highway maintenance activities (e.g., Washington State; Huijser and others 2006). Standardized data collection in combination with new technological tools could help state agencies and the NPS with data collection that is more efficient, spatially accurate, and standardized. This will help develop more informed analyses for transportation-related decision-making.

Over half of the respondents deemed habitat fragmentation by roads to adversely affect wildlife populations within their NPS unit. Yet, the NPS does not systematically measure the effects of roads on wildlife habitat fragmentation. Habitat fragmentation data were collected by 10% of the NPS units responding to this survey, with none measuring impacts for all of the wildlife groups present in their NPS unit. Roads cause changes to wildlife habitat that are more extreme and permanent than other anthropogenic sources of fragmentation (Spellerberg 1998, 2002). When compared to other agents of habitat fragmentation the isolating effect of roads has received surprisingly little attention by conservation biologists and has gone relatively unnoticed (Forman and Alexander 1998). The general lack of published studies and methodologies by the scientific community measuring the effect of habitat fragmentation by roads may explain why few NPS units collect this information (Roedenbeck and others 2007), given most respondents deem habitat fragmentation by roads to be problematic.

Transportation-Wildlife Conflicts

Over one-half of the respondents perceived that habitat fragmentation affected wildlife populations and nearly one-half believed that road-related mortality impacted wildlife populations in their NPS unit. However, when asked in a more wildlife-specific manner, most NPS respondents (>50%) characterized road-related mortality and habitat fragmentation effects by roads as low for all wildlife groups in their NPS units, with the exception of the effects of road-related mortality on small- and medium-sized mammals. This may be explained by the fact that respondents acknowledged that roads play a role in direct mortality of wildlife and in habitat fragmentation on NPS lands, but they are not perceived as problematic by most. This may be due to their interpretations of individual-level mortality compared to population-level effects. Wildlife may die on roads but whether the mortality translates to population-level impacts will vary greatly among species and areas. It should be noted that this feedback is based on perception, as only 16% responded that they collect data for all the wildlife groups present in their NPS units. The disparity over habitat fragmentation may be explained by the fact that most respondents lacked quantitative data that measured the indirect effects of habitat fragmentation by roads in their NPS units on their groups of wildlife.

Protecting endangered species is a higher priority for NPS managers and nearly two-thirds of the NPS units responding had wildlife listed under the Endangered Species Act. Of the NPS units with endangered species, nearly a third reported that roads in the park threatened those populations, while a further 27% were uncertain as to whether park roads pose a threat to their imperiled populations. This implies that over half of the NPS units responding may have roads that adversely impact populations of endangered species. In addition, of the 67 NPS units with endangered species, 36% indicated that roads bisected critical habitats for these species. The extent to which roads impact endangered species on NPS lands should be further researched.

Wildlife Conflict Mitigation

Roughly a third of the survey respondents indicated that their NPS unit is using at least one type of mitigation technique intended to reduce road impacts to wildlife. Yet, nearly half of the respondents (48%) thought road-related mortality strongly affected wildlife populations in their NPS unit. This dissonance suggests additional mitigation may be needed in NPS units throughout the system; however, mitigation strategies will best be applied on a case-by-case basis and vary among species and areas.

Most visitors arrive and travel through national parks by car or bus, so mitigating road impacts to wildlife populations is good stewardship that will help maintain the biological integrity of park ecosystems (Forman and others 2003). Several National Parks in Canada and the U.S. have implemented projects that have successfully reduced road-wildlife conflicts. In Banff National Park, Alberta, Canada, seasonal closure of a section of the Lake Minnewanka Loop road was a successful effort to restore connectivity for predator and prey species in critical valley-bottom montane habitat (Duke and others 2001). Highway mitigation measures such as wildlife fencing and crossings have been installed along roads with high traffic densities in national parks such as Everglades, Glacier, and Banff (Singer and Doherty 1985; Foster and Humphrey 1995; Clevenger and Waltho 2000). A more recent example involves the NPS working with Caltrans to mitigate road impacts on wildlife along State Route 23 near the Santa Monica Mountains National Recreation Area. This ongoing project involves installing fencing, clearing culverts and monitoring the effects of these actions before and after construction (R. Sauvajot personal communication, March 16, 2007).

Other mitigation practices include animal-detection systems (Huijser and McGowen 2003), and novel or moveable signage on low volume roads (Hindelang and others 1999; Messmer and others 1999). Managers in Jasper National Park, Alberta, Canada, introduced 70 kph (43 mph) “slow down for wildlife” zones in three areas of the park and monitoring proved them to be effective for elk, deer, and moose, but not for bighorn sheep, Ovis canadensis (Bertwistle 2001).

More than two-thirds of the respondents reported attending a meeting related to road construction, maintenance, or mitigation within their NPS unit at least once. If the interviewee did attend a meeting of this type, there was a 50% chance of the NPS unit having a mitigation program in place. This suggests that additional training and exposure to successful roadway mitigation techniques and successes in other parks may aid parks in developing mitigation strategies and implementing measures.

When asked to predict how road impacts to wildlife will evolve over the next five years, nearly half of the respondents indicated the impacts would increase. An equal proportion of respondents felt that road-related impacts to wildlife would remain at their existing level. Thus, the perception by most Park Service managers suggests that nearly 90% of the respondents expected road impacts to wildlife populations to increase or remain at their existing level. This is consistent with the responses which predicted three-quarters of the management units in the survey will have increased traffic volumes and there will be few new road re-construction projects or other improvements to road infrastructure (21%).

Americans own 243 million motor vehicles and use those vehicles for 89% of all daily travel (Bureau of Transportation Statistics 2005). Travel by car continues to grow faster than the U.S. population or the economy, with more cars, more drivers, and more miles per person each year (National Research Council 1997, 2002). Automobiles allow easier access to national parks and other recreational areas, changing both the length and frequency of travel: for example, in Yosemite National Park, the availability of overnight accommodation is capped, yet the number of visitors continues to increase—the result of day-users commuting in cars and tour busses from nearby regions (Forman and others 2003). Over time, increasing vehicle traffic on park roads may alter behavior of individual animals and decrease habitat quality (Gibeau 2000).

Vehicle travel is growing despite the fact that the capacity of roads serving the Sierra region and Yosemite National Park is not expanding. The problem of transportation infrastructure development and carrying capacity is prevalent throughout the National Park system. Alternative transportation is being promoted in the NPS as a means of easing the tension between automobiles, roads, and park preservation. Although it is not the ideal solution for all the NPS problems, alternative transportation does hold the potential to mitigate many environmental impacts, including road-related mortality and habitat fragmentation effects, which are associated with transportation infrastructure and a reliance on personal automobiles as the primary means of public access (White 2007).


Our article indicates that road impacts on wildlife are perceived as major concerns by NPS managers. Increasing the agency’s attention to address the impacts of roads on wildlife and ecosystem values is a responsibility consistent with the NPS Organic Act and current NPS policies. Road-related mortality and habitat fragmentation effects by roads are measurable causes of loss to wildlife populations, yet a minority of NPS units measure, mitigate, and monitor these impacts on their wildlife populations, including species listed under the Endangered Species Act.

Our report highlights the importance for the NPS to recognize the need for a systematic approach to reducing wildlife-roadway conflicts, particularly because this situation is predicted to deteriorate over the next five to ten years. If road-related impacts to wildlife should deteriorate, it will be important that park managers have reliable information to make informed decisions regarding potential mitigation strategies and conservation actions. Monitoring of wildlife mortality on roads can be improved by using standardized data collection methods with high spatial accuracy (Clevenger and others 2003; Ramp and others 2005; Huijser and others 2007a). New tools are being used to facilitate data collection in studies researching the effects of roads on wildlife mortality and habitat fragmentation (Waddle and others 2003; Whittington and others 2005; Travaini and others 2007). Lee and others (2006) successfully engaged local citizens in reporting wildlife observations using a web-based GIS mapping tool. Interested citizens were thus able to contribute information that was useful for decision-makers mitigating the effects of a highway expansion. There are many low-cost means of reducing road impacts on wildlife (FHWA 2007) and park managers should be kept abreast of the current technologies available (Huijser and others 2007b). There are many opportunities to assist the NPS in the planning, design, and construction of wildlife-sensitive roadways.

It is noteworthy that this study represents the results of a survey based on the perceptions of NPS employees. Perceptions do not always equate with reality, thus further analyses may be needed to better quantify and understand the key findings from our report. Our article, however, does provide strong support from the perspective of NPS professionals, that road impacts to wildlife are a current and future challenge. We are hopeful and confident that this article and other similar efforts will help catalyze improvements by the NPS to provide safe public access while conserving park wildlife resources in perpetuity.



This work was conducted as part of the 2004 WTI Research for Undergraduates (REU) Program at Montana State University. The Western Transportation Institute’s Summer Research Experience for Undergraduates (REU) Program in Rural Transportation provided support each summer to eight undergraduate students from colleges and universities nationwide to pursue a ten-week research program at Montana State University in Bozeman. The program was funded by the National Science Foundation/Department of Defense and the U.S. Department of Transportation’s Research and Special Programs Administration. Olivia Yu was the REU student who helped conduct the survey. We would like to thank the many employees of the National Park Service who took the time to assist us in our survey as well as Jim Evans and Susan Grosser who checked our facts and reviewed a draft of the manuscript. We are particularly grateful to Natasha Kline and Ray Sauvajot for their review and constructive input, which greatly improved the final draft. The following people provided support and assistance on the project: Meredith Evans Wagner helped fill in gaps from the original article. Angela Kociolek reviewed and commented on a draft of the manuscript. Kate Heidkamp provided generous support to complete the manuscript. We thank Susan Gallagher for her help in planning and coordinating the Research Experience for Undergraduates program at Montana State University-Bozeman.


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Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • Rob Ament
    • 1
  • Anthony P. Clevenger
    • 1
  • Olivia Yu
    • 1
    • 2
  • Amanda Hardy
    • 1
  1. 1.Western Transportation InstituteMontana State UniversityBozemanUSA
  2. 2.USDA Environmental Microbial Safety LaboratoryMarylandUSA

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