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Publication Number: FHWA-HRT-08-034
Date: August 2008

Wildlife-Vehicle Collision Reduction Study: Report To Congress

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Chapter 6. Mitigation Methods that Seek to Influence Animal Behavior

These WVC reduction strategies are designed to change where, how, and when wildlife cross roads by modifying the animals' behavior without the use of major structures on or along the roadway. The specific mitigation measures reported on in this chapter are as follows:

  • Deer reflectors and mirrors.

  • Audio signals in right of way or attached to vehicles.

  • Olfactory repellents.

  • Deer flagging models.

  • Hazing.

  • Deicing alternatives.

  • Intercept feeding.

  • Influence species composition or minimize nutritional value of vegetation in the right of way.

  • Remove carcasses along transportation corridors.

  • Increase median width.

Deer Reflectors and Mirrors

Deer mirrors and reflectors are roadside installments intended to act as visual wildlife repellents. Mirrors directly reflect vehicle headlights off the roadway and into the surrounding right of way.(61) Reflectors beam colored reflected light from headlights into roadside habitat (Swareflex, D. Swarovski & Co., Wattens, Austria, http://www.swareflex.com/ (accessed January 26, 2007)) or onto the roadway itself (Strieter-Lite, Strieter Corp., Rock Island, IL, http://www.strieter-lite.com/). (246)

Most studies testing the effectiveness of mirrors and/or reflectors on reducing WVCs found that they had (1) no effect, (2) mixed results, or (3) inconclusive results. (See references 38, 59, 247, 248, 249, 250, 251, and 252.) Differences in experimental design and in the variety of models tested confound the comparison of results.(231) However, Schafer and Penland did find a significant reduction (88 percent) in WVCs using Swareflex reflectors in Washington State.(211) Pafko and Kovach found in Minnesota that reflectors reduced rural incidences by 50–97 percent, but suburban metropolitan WVC incidences increased.(250)

The Strieter-Lite company suggests there is scientific proof that their reflectors do work (78–90 percent reduction in DVCs) and that reflective luminance (brightness) is not a major factor, because wild animals have acute night vision.(253,254) Sivic and Sielecki conducted a spectrometric evaluation of Swareflex and Strieter-Lite wildlife warning reflectors and noted operational implications of low light reflection intensities.(255) Reflectors require suitable placement, alignment maintenance, and regular cleaning; however, in a roadside application it is impossible to keep reflectors clean at all times.(72,254,256) Possible reasons why reflectors and mirrors do not result in fewer roadkill include improper installation, lack of maintenance (no replacement of missing reflectors or realigning them after they became out of alignment), and dirty mirrors/reflectors (especially in winter).

Utah DOT discontinued use of reflectors due to an increase in deer kills and difficulty in keeping reflectors clean; high installation and maintenance/cleaning costs were also factors.(256) Thirty-nine percent of Swareflex reflectors used in Wyoming showed deterioration after 3 years.(248) In British Columbia, reflectors were prone to theft and vandalism.(72) Where mirrors and reflectors work in reducing WVCs, it may be a result of driver behavior, particular site characteristics, or rural versus suburban landscapes.(250,251,257)

Mirrors and reflectors are addressed in several literature reviews and annotated bibliographies. (See references 58, 61, 176, 231, 248, 258, and 259.) Knapp and others summarized 10 studies, five of which concluded that roadside reflectors did not appear to impact DVCs, two of which concluded that they did, and three reached inconclusive or mixed results.(53)

Studies testing the influence of reflectors on animal behavior found little or no evidence of avoidance.(59,246,257) A study of Strieter-Lite wildlife warning reflectors in four colors (red, white, blue-green, and amber) found them to be ineffective at altering white-tailed deer behavior so that DVCs might be prevented.(246) Interestingly, data indicated that deer increased negative behavioral responses toward vehicles in the presence of reflectors.(246) Ramp and Croft, however, found Swareflex reflectors produced a weak fleeing response in kangaroos.(260) Ujvari and others found that deer initially responded to reflectors with alarm and flight but then became habituated to the light reflection.(261) D'Angelo and others recommend that future development of deer-deterrent devices for WVC mitigation be based on empirical knowledge of deer senses and behavior.(246)

Case Studies and Contacts

For information on a couple of the reflectors that are available, contact Swareflex Reflectors, D. Swarovski & Co., Wattens, Austria, www.swareflex.com, and Strieter-Lite, Strieter Corp., Rock Island, IL, http://www.strieter-lite.com/(accessed January 26, 2007).

For information on effectiveness of reflectors on animal behavior, contact Gino D'Angelo, Daniel B. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, (706) 227-6867,gid4895@owl.forestry.uga.edu.

Direct Benefits

Roadside reflectors and mirrors are categorized as "tried" (as defined by AASHTO Safety Strategy Groups) and "used with conflicting safety analysis results" in a critical evaluation of DVC crash countermeasures.(176)

Indirect Benefits

This mitigation approach allows for animal movements at grade and allows animals to change where they cross over time.

Undesirable Effects

Deer have been documented to move toward vehicles in the presence of reflectors.(246)

Costs

A manufacturer advertises total cost of installation with reflectors, posts, equipment, and labor to be $4,000–6,000 per km ($7,000–10,000 per mi). The average life of reflectors is 12.5 years, so costs amount to $169–199 per km ($272–320 per mi) per year. Maintenance cost per mile per year is $500 ($300 per km per year) (Strieter-Lite, Strieter Corp., Rock Island, IL, http://www.strieter-lite.com/). (262) In British Columbia, reflectors cost approximately $10,000 per km ($16,000 per mi) to install along both sides of a highway, and maintenance costs range in the order of $500–1,000 per km ($800–1,600 per mi) annually.(72)

Guidelines

The manufacturers have installation guidelines. Regular maintenance, e.g., cleaning of the reflectors, may be needed.

Audio Signals in Right of Way or Attached to Vehicle (Deer Whistles)

Audio animal warning devices are intended to alert wildlife of oncoming traffic. Sav-A-Life Deer Alert (Sav-A-Life Industries, New York, New York, http://www.sav-a-life.com/(accessed January 26, 2007)) and Game Tracker's Game Saver, marketed as vehicle-mounted ultrasonic animal warning devices, elicited no response in 150 groups of free-roaming mule deer in with/without trials.(263) Behavioral observations of captive kangaroos in response to the Shu Roo, a vehicle-mounted ultrasonic kangaroo deterrent, did not differ in the on or off position.(264)

Many literature reviews and annotated bibliographies deem audio repellants ineffective in terms of modifying animal behavior for the goal of WVC reduction.(See references 58, 61, 74, 176, 216, 231, 265, and 266.)

A roadside wildlife warning system utilizing high-frequency sounds has been developed (International Road Dynamics, Inc., (IRD) Saskatoon, Saskatchewan, Canada, http://www.irdinc.com/(accessed January 26, 2007)). (267) Results from a study were not conclusive, and the system is no longer in service (Rob Bushman, IRD Inc., personal communication). While it is recognized that the results may not apply to highways, a wildlife warning system was installed along a railroad in Poland.(268) The system is activated when trains approach.(268) The effectiveness of this system has not been evaluated.

Another roadside wildlife warning system was developed by Firma Günter Josef Folda in Austria.(269) Headlights from approaching cars activate equipment that is integrated with the poles and reflectors that delineate the roadway (Edward Mulka, JAFA Technologies, Inc., personal communication). Once activated, the equipment emits a high-pitched alarm sound along with a supplemental blue light strobe light (Edward Mulka, JAFA Technologies, Inc., personal communication).(269,270) Unconfirmed data from Austria (between the cities of Nassereith and Imst in the Gurgltal on the Miemingerstraße road) indicate that the equipment may reduce WVCs by 85–93 percent.(270) The equipment is encased in a weather-resistant box and is powered by solar cells, batteries, or both (Edward Mulka, JAFA Technologies, Inc., personal communication).(270) The equipment weighs less than a pound and can be mounted on trees or small poles. The equipment can be directed such that the sound and strobe emitter face away from the road in the direction of wildlife that may be in the process of approaching the road (Edward Mulka, JAFA Technologies, Inc., personal communication).(270)

A study of fallow deer (Dama dama) behavioral responses to acoustic road markings showed that while behavioral responses differed initially, deer became completely indifferent to the acoustic stimuli within 10 days.(271)

In a comparison of whistle acoustic frequencies and intensities and deer hearing abilities, Scheifele and others determined closed-end whistles produced frequencies of ~3.3 kHz with little variation with changes in air pressure, while open-end whistles emitted frequencies of ~12 kHz with significant variation depending on air pressure.(272) Deer hearing sensitivity is estimated to be between 2 kHz and 6 kHz.(272,273) Taking into consideration the masking effect of road and car noise, however, deer are not likely to be able to hear the whistles.(263,272) Recordings made during dynamic drives found that the Shu Roo signal was not detectable above the noise of four vehicles traveling at different speeds, yielding no difference whether the device was turned on or off.(264) Further, if whistles were audible in combination with vehicle and road noise, there is no evidence that they affect animal behavior and habituation to these sounds is possible. (See references 263, 264, 271, 272, and 274.)

Case Studies and Contacts

Contacts for some audio signal manufacturers are:

Direct Benefits

Deer whistles are categorized as "tried" (as defined by AASHTO Safety Strategy Groups) and "used with conflicting safety analysis results" in a critical evaluation of DVC crash countermeasures .(176)

The effectiveness of the IRD system is inconclusive. Maintenance staff anecdotally felt the system was effective, but the data were inconclusive, possibly since not enough data were collected. Currently the IRD system is not in use.(Rob Bushman, IRD Inc., personal communication).

The effectiveness of the WIWASOL-II system may be 85–93 percent, but these results are currently unconfirmed.(270)

Indirect Benefits

This approach accommodates unrestricted animal movements at grade.

Undesirable Effects

Audio signals may frighten animals away in areas where there may be interest in establishing or improving habitat connectivity across a highway.

Costs

The Sav-A-Life Deer Alert individual vehicle-mounted devices cost $23.50 each.

For a test installation of a roadside-based audio signal system along a 6-km (3.7-mi)-long road section, the costs were about €19.000.(270)

Guidelines

If auditory warnings are used, their frequency must be within the auditory range of the species, and they must not be drowned out by the surrounding road and vehicle noise.

Olfactory Repellents

Olfactory repellents involve odorous chemical or organic compound applications along roadways to act as deterrents for wildlife.

A literature review of capsaicinoids, synthesized animal odors, other animal products, garlic, particulates, soaps, thiram, bittering agents, natural predator excretions, and putrescent egg determined the latter two hold the most potential for keeping ungulates away from roadways but have not been field tested.(176,275) An experimental study and literature review found olfactory repellents did not prove effective as area repellents for large-scale application on travel corridors, making them unsuitable for use in reducing WVCs.(276) Other literature reviews that addressed effectiveness in terms of reducing WVCs have determined that olfactory repellents have not been adequately tested, show only limited effectiveness, or are impractical because of the need to repeat applications, especially after precipitation events. (See references 22, 58, 61, 176, 216, 277, and 278.) Future development of olfactory repellent measures requires further study of wildlife behavioral responses on a range of species and of the potential for animal habituation.(176,260,279)

Experimental scent marking using Duftzaun (HAGOPUR GmbH, Landsberg am Lech, Germany), a mixture of bear, gray wolf, Eurasian lynx (Lynx lynx), and human components, showed an 85 percent reduction in moose-train collisions in Norway, but results were questionable given that short treatment distances (500 m (1,640 ft)) yielded small and variable samples sizes for the number of collisions.(227)

Captive trials of Wolfin® (Pro Cell Biotenik, Hornefors, Sweden), a synthetic scent repellent, showed no repellency of caribou or black-tailed deer.(280,281) The repellent Plant Plus (Roe Koh and Associates Pty. Ltd., Mornington, Victoria, New Zealand), a synthetic canine predator odor, had aversive effects on one species of marsupial but attracted another, indicating a need for more research.(260) Captive trials of Deer Away® Big Game Repellent (Intagra, Inc. Lakeville, Minnesota), a putrescent whole egg repellent, initially altered caribou feeding behavior, but feeding times and amount eaten returned to pretreatment levels.(280)

Manufacturers of a proprietary "chemical fence" (repellent chemicals encapsulated in slow release organic foam and applied to roadside posts or trees) reported some repellency and a reduction in frequency of roe deer-vehicle collisions in one treated section.(9,282) However, a more detailed assessment found DVCs rose in untreated sections.(58,283) A roadside wildlife warning system utilizing scent repellents has been developed (International Road Dynamics, (IRD) Inc., Saskatoon, Saskatchewan, Canada, http://www.irdinc.com/), but results from a study were not conclusive and the system is no longer in service (Rob Bushman, IRD Inc., personal communication).(267)

Case Studies and Contacts

For information about effectiveness of repellents on animal behavior, contact Lisa Shipley, Department of Natural Resource Sciences, Washington State University, (509) 543-8955 or Marion Carey, Project Monitor, Environmental Affairs Office, Washington Department of Transportation, (360) 705-7404.

Direct Benefits

In terms of reducing WVCs, evidence for effectiveness remains sparse and temporary at best.(22) Repellents are categorized as "experimental" (as defined by AASHTO Safety Strategy Groups) and "not generally used and rarely studied for safety impacts" in a critical evaluation of DVC crash countermeasures.(176)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

Kinley and Newhouse caution that unintended negative effects may arise from olfactory repellent application and recommend a cost-benefit analysis of associated safety, economic, and ecological factors.(275) Potential negative effects may include attracting predators to the roadside and causing a panic reaction (instead of avoidance) in ungulates resulting in erratic movements toward the roadway.

Costs

Costs should take into consideration maintenance requirements, time intervals for reapplications, the area to be treated, and ecological impacts.(22,176)

According to the literature, one liter of Plant Plus concentrate costs $30 (currency was not specified, but presumably Australian dollars).(284)

Guidelines

If olfactory repellents are used, it is important to ensure that the repellant works to deter animal movement and that animals do not become habituated to them.

Deer Flagging Models

Deer flagging models are based on the behavioral characteristic of white-tailed deer that raise their tails to expose the white underside when fleeing. Tail flagging, however, has not been shown to act as a warning signal to other members of the species.(285)

A single deer flagging model study was found.(286) The researchers used painted wooden silhouette models of deer with painted or actual deer tails in a control/treatment experiment and found the models to be ineffective for deterring deer from the roadway.(286) A number of confounding factors make it difficult to determine whether or not this mitigation alternative is viable.(176) Future studies that consider pertinent variables (e.g., fluctuations in deer movements) could validate or refute this study and address potential safety or DVC impacts of deer flagging models.(176)

Case Studies and Contacts

For review information about deer flagging models, contact Keith Knapp, Texas Transportation Institute, Work Zone and DMS Program, Room 410D, 3135 TAMU, College Station, TX 77843‑3135, (979) 845-5686,k-knapp@tamu.edu.

For further information about deer tail flagging, contact Tim Caro, University of California-Davis, Wildlife, Fish, and Conservation Biology Department, 1395 Academic Surge Building, 95616, (530) 752-0596,tmcaro@ucdavis.edu.

Direct Benefits

Deer flagging models are categorized as "experimental" (as defined by AASHTO Safety Strategy Groups) and "not generally used and rarely studied for safety impacts" in a critical evaluation of DVC crash countermeasures.(176)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

No undesirable effects were identified in the literature review.

Costs

No costswere identified in the literature review.

Guidelines

No guidelines were identified in the literature review.

Hazing

Hazing or aversive conditioning is the practice of dispersing wildlife by frightening them, which has been done using such things as lights, lasers, water sprays, pyrotechnics, cannons, guns, helicopters and predatory-resembling chases. (See references 287, 288, 289, and 290.)

Romin and Bissonette found 3 of 43 natural resource agency respondents used hazing as a method to reduce deer road mortality, one of which reported success.(3) Hazing was not effective in moose-vehicle collision mitigation efforts in Alaska.(78) In British Columbia, Roosevelt elk (Cervus canadensis roosevelti) were relocated when hazing failed as a WVC mitigation measure.(72)

Green and blue lasers were found to be ineffective as frightening devices to disperse deer at night.(290) During treatment and control (observation with no laser) behavioral experiments, deer saw and followed the laser light and appeared to be more curious than frightened.(290) Red lasers were not tested because deer cannot see in the red portion of the spectrum.(290) Lasers have been proven to be effective on birds but not on deer, probably a result of species-specific threat perception (i.e., animals may not associate the disturbance with danger).(287,290) Lights and water sprays have only limited effectiveness.(287)

Hazing with sounds (e.g., pyrotechnics, cannons, guns, and helicopters) may offer a temporary solution for dispersing animals, but noise is a consideration in areas of human populations.(287,288) In a study of Key deer capture techniques, hazing with helicopters or shooting out of vehicles in residential areas was not attempted.(288)

Aversive conditioning treatments resembling predatory chases by humans and dogs were effective in increasing flight responses in 24 moderately habituated radio-collared elk; habituated animals have been associated with WVCs in Banff National Park.(289) Natural wolf activity, however, appeared to reduce the efficacy of the aversive conditioning techniques (i.e., elk remained closer to town sites).(289) Aversive conditioning has shown some success in keeping grizzly bears off roadsides.(291)

No scientific studies have been done to test the effectiveness of hazing on reducing WVCs, and hazing is not covered in other pertinent reviews on WVC mitigation measures.(61,176,231) DeNicola and others address hazing in managing deer in suburban environments but not within the context of WVC reduction.(287) Hazing can be difficult to implement in established conflict situations, because animal behavioral habits are difficult to change and habituation is possible.(287)

Case Studies and Contacts

For information about aversive conditioning in Banff National Park, contact Elsabe Louise Kloppers, University of Alberta, Canada,elsabekloppers@yahoo.ca.

Direct Benefits

Direct benefits are unknown. No scientific studies have been done to test the effectiveness of hazing on reducing WVCs.(61)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

No undesirable effects were identified in the literature review.

Costs

Aversive conditioning using humans was 15 percent less expensive than conditioning with dogs (Can$4,300).(289)

Guidelines

No guidelines were identified in the literature review.

Deicing Alternatives

The principal deicers used by highway agencies are chloride-based salts such as sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2), and acetate-based deicers such as potassium acetate, sodium acetate, and calcium magnesium acetate (Xianming Shi and Laura Fay, Western Transportation Institute, Montana State University, personal communication).

The use of chloride salts in winter maintenance can attract wildlife to the right of way and may increase WVCs, especially in areas without natural salt licks.(See references 61, 74, 176, and 292.) A study of 11 radio-collared moose in New Hampshire determined that all of their home ranges converged on the area containing roadside salt (NaCl) licks formed by runoff of road salt.(293) Implications associated with these roadside salt licks include increased moose-vehicle collisions and increased brain worm infections in moose and white-tailed deer.(293) Reducing the amount of salt or using alternative deicers (without salt), especially in areas of high WVCs, may reduce the attractiveness of the right of way.(294)

Lithium chloride, a gastrointestinal toxicant, was found to effectively discourage captive caribou from eating treated food and may prove useful in reducing WVCs by discouraging ungulates from licking road salt.(280) CaMg-acetate has been recommended as an alternative to deice roads in Finland instead of NaCl.(74) Attempts at discouraging animals from road salt using the deicer calcium chloride were unsuccessful in Jasper National Park, Canada.(295)

A study of the pattern of moose-vehicle collisions in relation to the presence of roadside saltwater pools showed that 43 percent of moose-vehicle collisions occurred within 100 m (328 ft) of a saltwater pool, higher than what would randomly be expected.(296) About the same number of collisions happened more than 300 m (984 ft) from a roadside saltwater pool.(176) Knapp questions the assumption of the study (i.e., all locations have an equal chance for a collision).(176)

Road salt and deicing alternatives are addressed in literature reviews; however, whether the reduction or replacement of the road salt would reduce WVCs involving ungulates remains unknown.(61,176,292)

Case Studies and Contacts

For further information on efforts using deicing alternatives, contact Jim Bertwistle, Warden, Jasper National Park, Alberta, Canada, (403) 852-6155.

Direct Benefits

Whether the reduction or elimination of the road salt would reduce WVCs remains unknown.(176) Deicing salt alternatives are categorized as "experimental" (as defined by AASHTO Safety Strategy Groups) and "used but not studied for safety impacts" in a critical evaluation of DVC crash countermeasures.(176)

Indirect Benefits

The intake of road salt has been found to be toxic to several bird species, porcupines, rabbits, deer, and moose that ingest it.(292,297) Reduction or elimination of road salt may reduce or eliminate this toxicity.

Brain worm in moose and white-tailed deer is associated with road salt; elimination of road salt may reduce this occurrence.(293)

Undesirable Effects

While the reduction or elimination of road salt may benefit certain species, alternatives to chloride salts may also be toxic to wildlife (Xianming Shi, Western Transportation Institute, Montana State University, personal communication), but this has not yet been specifically studied.

Costs

No costs were identified in the literature review.

Guidelines

No guidelines were identified in the literature review.

Intercept Feeding

Intercept feeding provides strategically placed supplemental food sources in an attempt to divert animals away from roadways.(176)

A two-year control/treatment experiment tested the effectiveness of intercept feeding as a means to reduce DVCs by diverting mule deer from roadsides in Utah.(298) The researchers concluded that intercept feeding may have reduced DVCs by as much as 50 percent.(298) However, no information was provided on the number of DVCs before intercept feeding stations were operational.(176)

After testing the effectiveness of scent marking, forest clearing, and supplemental feeding, researchers in Norway determined such mitigations might help reduce (but not eliminate) moose-train collisions if applied over long distances.(227) Attempts at discouraging animals from road salt using intercept mineral baiting were unsuccessful in Jasper National Park, Canada.(295)

Intercept feeding may work in some cases, such as for short-term reductions in areas of high deer concentrations or in combination with other mitigation measures. (See references 61, 176, 216, and 298.) Intercept feeding is labor intensive and may create a dependency on supplemental food and actually increase population size.(216,298) Intercept feeding is addressed in several pertinent literature reviews. (See references 61, 176, 216, and 231.)

Case Studies and Contacts

For further information on intercept feeding efforts, contact Jim Bertwistle, Warden, Jasper National Park, Alberta, Canada, (403) 852-6155.

Direct Benefits

Intercept feeding is categorized as "experimental" (as defined by AASHTO Safety Strategy Groups) and "not generally used and rarely studied for safety impacts" in a critical evaluation of DVC crash countermeasures.(176) Additional study that can refute or validate the effectiveness of intercept feeding in reducing DVCs would be appropriate.(176)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

Intercept feeding may create a dependency on supplemental food or increase population size.(298)

Costs

Intercept feeding is labor intensive.(216,298)

Guidelines

No guidelines were identified in the literature review.

Influence Species Composition or Minimize Nutritional Value of Vegetation in Right of Way

Roadside vegetation can attract wildlife to roads and increase their vulnerability to WVCs.(299,300) The practice of planting trees near roadways for landscaping reasons can attract ungulates to the right of way and increase the risk of WVCs.(9) Several sources recommend managing vegetation in the right of way so that it does not serve as an attractant to wildlife (i.e., by planting unpalatable species, reducing forage quality, or applying noxious chemicals), while others focus on improving roadside habitat for wildlife. (See references 9, 74, 301, 302, 303, 304, 305, and 306.) Techniques employing forage repellents, unpalatable species, and roadside brush removal have been used with limited effectiveness or are not cost efficient when broadly applied.(304)

An experimental study of vegetation removal along a railway line (20–30 m (66–98 ft) on each side) in Norway caused a 56 percent (+/- 16 percent) reduction in moose-train collisions.(228) The researchers concluded that there would be an economic benefit to perform vegetation removal treatments in areas with more than 0.3 collisions per km (0.48 per mi) but that local evaluations are necessary to confirm that vegetation cover is the main contributor to collisions in specific sections.(228) It is possible, however, that the experimental design may have overstated the collision reduction potential of vegetation removal.(176,228)

A detailed literature review on roadside vegetation management, plant response to tissue removal, and ungulate foraging behavior yielded recommendations for more carefully designed cutting regimes as a countermeasure for reducing moose-vehicle collisions.(304) Willows cut in mid-July were found to be high in digestible energy and protein compared to plants cut at other times of the year and uncut controls, suggesting that summer brush cutting regimes may inadvertently be attracting moose with nutritious regrowth.(304,307) Cutting in early June results in browse with significantly less nutritional value for the first two years after cutting compared to plants cut later in the growing season and uncut controls.(304,307) Rea recommends cutting roadside brush in early spring soon after leaves develop to keep nutritional value and palatability to a minimum but recognizes operational challenges and limitations (i.e., ground too wet for tractor use, different ungulate species-specific responses to same management regime, etc.) and cautions that this countermeasure may not be suitable for all management areas.(304)

No studies were found that specifically analyze the WVC safety impacts of roadside management policies or plantings; however, a 1999 report by the Arizona Department of Transportation (ADOT) describes a future five-year monitoring plan to address the effectiveness of a number of mitigation measures (including those related to vegetation/habitat changes) on reducing WVCs.(176,308) The need to properly study the safety impact of vegetation management along roadways remains.(176)

Note: see also the section titled "Increase Visibility of Animals to Drivers: Vegetation Removal" in chapter 5.

Case Studies and Contacts

For information about roadside vegetation management, contact Roy Rea, Natural Resources and Environmental Studies, University of Northern British Columbia, Canada,reav@unbc.ca.

Direct Benefits

Roadside vegetation management is categorized as "tried" (as defined by AASHTO Safety Strategy Groups) and "used but rarely studied for safety impacts" in a critical evaluation of DVC crash countermeasures.(176)

Indirect Benefits

No indirect benefits were identified in the literature review.

Undesirable Effects

Minimizing the nutritional vegetation may restrict the use of native vegetation along the roadside. In addition, reducing habitat quality may increase the road effect zone.(83)

Costs

No costswere identified in the literature review.

Guidelines

Some guidance for implementing this mitigation measure is presented by Rea.(304)

Remove Carcasses Along Transportation Corridor

Highway safety is an impetus for timely removal of road-killed animals, and carcass composting may yield economic, ecological, and aesthetic benefits.(176,309) The carcasses of road-killed animals that are not removed may serve as food sources for other wildlife, attracting them to roads and increasing their vulnerability to WVCs.(176) Evaluation of the impact of roadside carcass removal on reducing WVCs has not been studied and has rarely been considered.(176) While carcasses may be an attraction for scavengers, ungulates are not likely to be attracted or deterred by the presence of carcasses in the right of way. Therefore, carcass removal may not have a substantial effect on the number of DVCs and the total number of WVCs. Nonetheless, omnivores and carnivores, including some rare, threatened, or endangered species, may experience less road mortality as a result of the removal of food sources along the roadway.

Case Studies and Contacts

For information about carcass removal efforts in New York State, contact Elisabeth Kolb, Maintenance Environmental Coordinator, New York State Department of Transportation, (845) 575-6158.

Direct Benefits

Carcass removal, as an element in "roadway maintenance, design and planning policies," is categorized as "tried" (as defined by AASHTO Safety Strategy Groups) and "used but rarely studied for safety impacts" in a critical evaluation of DVC crash countermeasures.(176)

Indirect Benefits

Carcass removal may reduce the frequency of secondary roadkill of scavengers that feed on carcasses.

Undesirable Effects

No undesirable effects were identified in the literature review.

Costs

In Canada, the clean-up and carcass removal and disposal costs for animal carcasses were estimated at Can$100 (deer), Can$350 (elk) and Can$350 (moose).(72) In Pennsylvania, the average cost for deer carcass removal and disposal in a certified facility was $30.50 per deer for contractors and $52.46 per deer for the Pennsylvania Department of Transportation in 2003–2004 (Jon Fleming, Pennsylvania Department of Transportation, personal communication).

Guidelines

Carcass removal allows for easy data collection of roadkill, which helps with planning and monitoring mitigations for WVCs. A composting plant would mitigate the waste management issue.

Increase Median Width

Crossing several lanes of traffic moving in opposite directions is a difficult task for an animal to perform. Wider medians can provide a "refuge" for the animals, giving them a break in their roadway crossing. Medians allow animals to deal with only one direction of traffic at a time, enabling them to stop partway across the roadway and identify and wait for an adequate gap in traffic before crossing the second half of the roadway. A literature review by Clevenger and Kociolek found that it was unclear whether or not a vegetated median increased the ability of wildlife to cross the road safely.(310)

Case Studies and Contacts

No case studies were identified in this literature review.

Direct Benefits

No direct benefits were identified in the literature review.

Indirect Benefits

A wider median may provide a more aesthetically pleasing view to the driver. It may also allow for high beams to be kept on for longer periods at night to aid visibility.

Undesirable Effects

No undesirable effects were identified in the literature review.

Costs

No costs were identified in the literature review.

Guidelines

No guidelines were identified in the literature review.

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