Wildlife fencing, crossings and animal detection systems: what works and what fails
Which road fixes cut animal collisions, why upkeep matters and what to ask for
Safety Behind the Wheel Foundation built this guide from Insurance Institute for Highway Safety (IIHS) fatality data, the federal law behind the Wildlife Crossings Pilot Program, and published road ecology and traffic safety research from North America and Europe. Every source is listed at the end.
Why animal collisions call for road level fixes
A wildlife vehicle collision is a crash between a vehicle and a wild animal. For most drivers, that means a deer. In nine states from 2000 to 2002, a review of 147 deadly crashes with animals found that deer made up 77% of the animals struck [1].
Deaths are rare, but they have not gone away. They rose from 89 in 1975 to 210 in 2024, though the rise has flattened in the last ten years [1].
Injuries and costs add up too. Police in Texas logged 51,522 animal related crashes from 2010 through 2016, which cost Texas drivers more than $1.3 billion a year [2]. About 64% of those reports involved wild animals [2]. The authors warn that crash reports undercount these events, so the true toll is higher [2].
Timing matters. Texas reports jumped twice a day, from 5 to 8 a.m. and from 5 to 10 p.m. [2]. Wild animal collisions were most likely in October, November and December [2]. Most happened after dark in unlit spots, typically on lightly traveled rural roads [2]. National deaths in 2024 peaked from July through September, so crash counts and deaths follow different calendars [1, 2].
A single driver cannot change where deer cross. A road agency can. That is why it helps to treat animal collisions as a problem of place: the same road segments, seasons and animal routes. A fix on one corridor protects every driver who uses it.
The toolbox in plain words
Road agencies use four main kinds of measures. Each works differently.
- Exclusion fencing: tall fence along the road that keeps animals off the pavement.
- Crossing structures: underpasses (passages beneath the road) and overpasses (bridges over it) that give animals a safe way across.
- Animal detection systems: roadside sensors that spot large animals and trigger flashing signs for drivers.
- Signs and reflectors: low cost tools meant to change driver or animal behavior.
The figures below come from a pooled analysis, which combines the results of 50 studies [3].
Comparison compiled by Safety Behind the Wheel Foundation
Pooled results for four wildlife road measures
| Measure | Pooled result (large mammals unless noted) | Main limit |
|---|---|---|
| Fencing with crossing structures | 83% less road kill [3] | Gaps and fence ends [3, 6] |
| Animal detection system | 57% less road kill [3] | Needs working sensors and slower drivers [4, 9] |
| Wildlife reflectors | 1% less road kill [3] | Animals may stop reacting [3] |
| Crossing structures alone | No detectable effect (all animals) [3] | Animals can still reach the road [3] |
Fencing: the backbone of most successful projects
Across the pooled studies, fences cut road kill by 54% on average, with or without crossing structures [3]. For large mammals, fencing combined with crossing structures cut it by 83% [3]. Across all animal types, fencing alone showed an 86% drop and fencing with crossings 51% [3]. The authors tie that gap to fence length and study design, not a flaw in the crossings [3].
Design details matter. A fence can have an overhanging lip to stop climbing and a buried base or skirt to stop digging [3]. Some fences include jump outs, also called escape ramps. These let an animal that ends up inside the fence leave the road corridor [3].
The weak spot is the end of the fence. Collisions can concentrate where a fence stops [3]. Only six of the 25 fencing studies in the pooled analysis counted road kill beyond the fence ends. Studies that did not look there reported larger average reductions (59%) than studies that did (46%) [3]. In plain terms, a project can look better on paper than it performs on the road. Longer, unbroken fencing helps shrink the problem [3].
A Texas project shows the same pattern. Five crossings and exclusion fencing went in along State Highway 100, mainly to protect ocelots (a small wild cat) and similar midsized animals. Animal road deaths per survey day fell after construction. Most remaining hot spots sat near fence gaps. The authors noted that gates and guards at side roads may have let animals reach the highway [6].
Crossing structures: underpasses and overpasses
Crossing structures can link habitat on both sides of a road [10]. They only keep animals off the road when fences guide animals to them. In the pooled analysis, crossing structures without fencing showed no detectable effect on road kill. That finding rests on a small sample of six results from three studies [3]. Without fences, animals can still walk onto the road.
Animals also need time to trust a new route. A South Texas road got eight crossing structures and fencing. After construction, tracked bobcats and ocelots still crossed on the pavement more often than through the structures [10]. The authors say animals may take years to get used to new structures. They add that more fencing could help protect ocelots [10].
Size and setting matter too. In Sweden, roe deer and moose used ordinary underpasses built for people and domestic animals. They favored those at least 11.5 meters wide and 5 meters tall. Roe deer also chose spots with little human use [11].
Ordinary drainage culverts, which are pipes or tunnels that carry water under a road, are a poor substitute. Along a Quebec highway, only about half of the 20 species seen near culverts were detected making a full crossing. High water and plastic culvert material both discouraged entry. The authors concluded that plain drainage culverts cannot stand in for purpose built wildlife passages [12].
Animal detection systems and warning signs
An animal detection system does not keep animals off the road. It senses them near the road and warns drivers with flashing signs [4]. Sensors may use infrared, video or radar. Some use a beam that an animal breaks [9].
The pooled analysis found a 57% drop in large mammal road kill [3]. A Texas cost study estimated benefit to cost ratios, meaning dollars saved for each dollar spent. It put them at up to 30 for fencing and detection systems and near 3 for large crossing structures [2]. Those are model estimates, not guarantees.
Drivers are the other half of the system. In a Florida national park, a flashing animal warning cut vehicle speeds during the busy tourist season. It did not do so in the off season [4]. A warning only helps if drivers slow down for it.
Reliability is the second challenge. A 2022 review reported that earlier systems gave false alarms in thick vegetation, struggled in bad weather and missed more animals in high wind [9]. A system that cries wolf can lose drivers’ trust. One that misses animals gives false comfort. That is why agencies should test these systems before and after installation.
What about standard warning signs? A 2025 review of driver behavior studies found that the effectiveness of warning signs varies considerably. It also found that few studies directly tested how drivers notice animals [5]. Reflectors cut large mammal road kill by about 1% in the pooled analysis [3]. Animals may react at first, but that response generally fades as they get used to the reflectors [3].
How agencies choose where and what to build
Start with two questions: where do collisions cluster, and where do animals actually move? Collision records alone lack information on where animals cross safely [13], and crash reports undercount events [2]. A Massachusetts study combined GPS collar crossing locations for moose with collision records. That method found road segments with both heavy animal use and high collision risk [13].
Here is the order a careful project follows.
- Map where collisions cluster, by month and time of day [2].
- Check where animals really cross, using tracking collars or cameras [10, 13].
- Match the tool to the species, the road and the traffic.
- Budget for inspection and repair before anything is built.
- Count collisions before and after, including the road just past the fence ends [3].
Step 5 deserves emphasis. The pooled analysis found that studies with “before” data were much better at detecting results. It recommends at least four years of study for a before and after design [3]. Safety Behind the Wheel Foundation encourages road agencies to plan for the same kind of measurement. Most pooled studies came from North America (82%) and focused on mammals (90%) [3]. Evidence for reptiles, amphibians and birds is thinner.
Upkeep: where good projects quietly fail
A fence is only as good as its weakest section. A Spanish study of motorway fences built to protect chameleons found that animals could cross where metal sheeting was missing and where plants had grown around the fence. The authors said upkeep of such structures is often inadequate [7].
In Ontario, a highway project added reptile fencing and passages. Turtle numbers on the road did not differ between the treated and untreated highway. The share of dead snakes and turtles rose after the work, which suggested the fencing was not effective [14]. When fences fail, animals take the open route, and that weakens the crossing structures too [14]. Those were reptile projects, but the lesson carries over. Any gap becomes the crossing.
The Texas hot spots tell the same story. They lined up with fence gaps [6].
Who decides, who pays and where you fit in
Wildlife fencing, crossings and warning systems on public roads are chosen, designed and installed by the road owner. That may be a state transportation department, a county or tribal government, or a federal land agency. Residents should never install signs, fences or sensors in a public right of way, which is the strip of land that belongs to the road.
Federal grants can help with the cost. A federal law added the Wildlife Crossings Pilot Program to the U.S. Code, effective October 1, 2021. Its goals are fewer wildlife vehicle collisions and better habitat connectivity, meaning links between the places animals live [8]. State highway agencies, regional planning bodies, local governments, tribes and federal land agencies can apply, among others [8]. At least 60% of each year’s grant money must go to rural projects [8]. Federal reviewers also weigh whether a project includes monitoring to measure results [8]. This is a grant program, not a requirement for any road.
Agencies buy fencing, structures and sensor systems through engineering firms, construction contractors and roadside equipment suppliers. Drivers, RV owners and fleets cannot buy a corridor fix. Auto and outdoor stores sell reflector style add ons, but the evidence for them is weak [3]. Fleets can plan routes and schedules around the dawn, dusk and fall peaks [2]. Rural property owners should talk with the road owner before doing anything near the road edge.
If animal collisions keep happening on your road, send a written request. Name the road owner, the exact location, the dates and what happened. Our guide to safer road design explains how to find the right agency. Then use these questions.
Driving through a managed corridor
Fences, crossings and warning signs lower risk. They do not remove it. Treat them as information.
- Slow down when a flashing animal warning is on. Lower speeds are what make these systems work [4].
- Scan both road edges far ahead, especially near dawn and dusk [2].
- Expect more than one animal. If one crosses, others may follow.
- Stay alert where a fence ends or has a gap, because collisions can concentrate there [3, 6].
- Report animal strikes to the road owner or local police, even when no one is hurt. Reports are how agencies spot hot spots, and records undercount these accidents [2].
For what to do when an animal is already in your lane, see our guide to rural road safety.
Frequently asked questions
Do wildlife reflectors work?
In the pooled analysis, reflectors cut large mammal road kill by about 1% [3]. Animals may react at first, but that response generally fades over time [3]. The researchers advised road agencies not to assume they have solved the problem with low cost measures like reflectors. Fences and crossing structures had far stronger results [3].
Are deer crossing signs enough?
Signs warn drivers, but they do not change how animals move. A 2025 review found that the effectiveness of warning signs varies considerably [5]. In one Florida study, flashing animal triggered signs slowed drivers during the busy tourist season but not in the off season [4]. Signs work best as one layer among several.
Why do collisions still happen on a fenced road?
Fences leak. Gaps, open gates, damaged sections and fence ends all let animals reach the road [3, 6, 7]. Collisions can bunch up near fence ends, and short fences make that worse [3]. Regular inspection and repair keep a fence doing its job.
Can an ordinary culvert or farm underpass serve as a wildlife crossing?
Sometimes, but not reliably. In Sweden, roe deer and moose used ordinary underpasses, and they favored those at least 11.5 meters wide and 5 meters tall [11]. In Quebec, ordinary drainage culverts were poor substitutes, and high water kept animals out [12].
Can a landowner or fleet put up its own fence or sensor beside a public road?
Not in the public right of way. Work near a public road usually needs the road owner’s approval, and signs and sensors on a public road should come from the agency responsible for it. A landowner or fleet can document the problem, share records and ask for a review.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation encourages communities to push for corridor fixes that are maintained and measured, and urges drivers to slow down for every animal warning. Animal collisions are a place problem, and the best fixes work on whole corridors. Long fences paired with crossing structures have the strongest record. Detection systems can help when sensors work and drivers slow down. Reflectors did little, and signs alone gave mixed results.
None of it lasts without upkeep and careful measurement. Ask your road agency where the collisions are, what measure fits, who will maintain it and how results will be counted. As a driver, treat every warning as real information, especially near dawn and dusk.
Related articles
- Rural road safety: why country roads are deadlier and how to drive them
- Safer road design: a field guide to the safety fixes on your street
- How to use local crash data to choose community safety priorities
- Night driving safety: how to see hazards and stop in time after dark
- Motorcycle riding in rain, wind, cold and darkness: stay in control
Sources and further reading
- 1Insurance Institute for Highway Safety. Fatality Facts 2024: Collisions with fixed objects and animals. Posted June 2026. Data year: 2024 (national trend since 1975; state totals for 2015-2024). iihs.org/…/collisions-with-fixed-objects-and-anim…
- 2Accident Analysis & Prevention (Wilkins, Kockelman and Jiang; PubMed record). Animal-vehicle collisions in Texas: How to protect travelers and animals on roadways. Published 2019. Data year: 2010 to 2016. pubmed.ncbi.nlm.nih.gov/31277019
- 3PLOS ONE (Rytwinski and colleagues; PubMed record). How Effective Is Road Mitigation at Reducing Road-Kill? A Meta-Analysis. Published 2016. pubmed.ncbi.nlm.nih.gov/27870889
- 4Accident Analysis & Prevention (Grace, Smith and Noss; PubMed record). Reducing the threat of wildlife-vehicle collisions during peak tourism periods using a Roadside Animal Detection System. Published 2017. pubmed.ncbi.nlm.nih.gov/29031047
- 5Accident Analysis & Prevention (Pakula, Rhodes and DeVault; PubMed record). Evaluating causes of animal-vehicle collisions through the lens of driver behavior. Published November 2025. pubmed.ncbi.nlm.nih.gov/41273822
- 6Ecology and Evolution (Yamashita and colleagues; PubMed record). Assessing changes in clusters of wildlife road mortalities after the construction of wildlife mitigation structures. Published 2021. Data year: 2015 to 2019. pubmed.ncbi.nlm.nih.gov/34646471
- 7Scientific Reports (Farfan and colleagues; PubMed record). Lack of maintenance of motorway fences works against their intended purpose with potential negative impacts on protected species. Published 2020. pubmed.ncbi.nlm.nih.gov/31964998
- 8Legal Information Institute, Cornell Law School. 23 U.S. Code 171 – Wildlife crossings pilot program. Statute text read October 2026 (added by Pub. L. 117-58, effective October 1, 2021). law.cornell.edu/uscode/text/23/171
- 9Sensors (Nandutu, Atemkeng and Okouma; PubMed record). Intelligent Systems Using Sensors and/or Machine Learning to Mitigate Wildlife-Vehicle Collisions: A Review, Challenges, and New Perspectives. Published 2022. pubmed.ncbi.nlm.nih.gov/35408093
- 10Ecology and Evolution (Lehnen and colleagues; PubMed record). Highway Crossing Rates of Wild Felids Before, During, and After Wildlife Crossing Structure Installation. Published December 2024. Data year: 2013 to 2021. pubmed.ncbi.nlm.nih.gov/39720638
- 11Journal of Environmental Management (Bhardwaj, Olsson and Seiler; PubMed record). Ungulate use of non-wildlife underpasses. Published 2020. pubmed.ncbi.nlm.nih.gov/32734891
- 12Journal of Environmental Management (Brunen, Daguet and Jaeger; PubMed record). What attributes are relevant for drainage culverts to serve as efficient road crossing structures for mammals? Published 2020. pubmed.ncbi.nlm.nih.gov/32510423
- 13Environmental Management (Zeller, Wattles and DeStefano; PubMed record). Incorporating Road Crossing Data into Vehicle Collision Risk Models for Moose (Alces americanus) in Massachusetts, USA. Published 2018. pubmed.ncbi.nlm.nih.gov/29744581
- 14PLOS ONE (Baxter-Gilbert and colleagues; PubMed record). Mitigating reptile road mortality: fence failures compromise ecopassage effectiveness. Published 2015. Data year: 2012 to 2013. pubmed.ncbi.nlm.nih.gov/25806531
This article reflects the safety priorities of animal collision prevention and safer rural road design. It is general education, not legal, insurance, medical or financial advice. Rules and grant programs change, so verify details with official sources. For a specific road, contact the agency that owns it, such as your state transportation department or county road office, and your state wildlife agency. For your own claim or injury, contact your insurer or a licensed professional. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Wildlife fencing, crossings and animal detection systems: what works and what fails.” drivewithcare.org, https://drivewithcare.org/wildlife-fencing-crossings-animal-detection-systems/. Reviewed October 2026.
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