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Providing evidence to improve practice

Action: Use road lighting to reduce vehicle collisions with mammals Terrestrial Mammal Conservation

Key messages

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  • Two studies evaluated the effects on mammals of using road lighting to reduce vehicle collisions with mammals. Both studies were in the USA.



  • Survival (2 studies): One of two studies (one controlled and one before-and-after), in the USA, found that road lighting reduced vehicle collisions with moose. The other study found that road lighting did not reduce vehicle collisions with mule deer.


Supporting evidence from individual studies


A controlled study in 1974–1979 along a highway in Colorado, USA (Reed & Woodard 1981) found that highway lighting did not reduce vehicle collisions with mule deer Odocoileus hemionus. There was no significant difference between deer-vehicle collision rates with lights on (39 collisions from 2,611 crossings) or off (45 collisions from 2,480 crossings). Lighting did not alter the location of crossings, with accidents not occurring closer to the lights when they were off. Lighting did not alter vehicle speeds (lights on: 79 km/h; lights off: 80 km/h). Thirteen 37,000-lumen, 700-W, clear, mercury-vapour lamps (12 m high) were installed along 1.2 km of a four-lane highway (speed limit 88.5 km/h). Nine were spaced at 59–69-m intervals along 0.5 km of highway (full lighting) and two at each end were spaced at 119 and 302 m (transition lighting). Lights were alternately turned on and off for one-week periods in January–April of 1974–1979. Deer-vehicle collisions were recorded each morning and evening. Deer crossings were recorded during nightly spotlight surveys and using snow track counts. Deer behaviour was observed for two hours/night. Vehicle speeds were recorded during 35 nights in 1974.


A before-and-after study in 1977–1990 along a highway in Alaska, USA (McDonald 1991) found that road lighting reduced vehicle collisions with moose Alces alces. There were 65% fewer moose-vehicle collisions when lighting was installed compared to before its installation (actual numbers not stated). There were 95% fewer moose-vehicle collisions along the section with lighting, fencing with one-way gates and an underpass after they were installed (0.7/year) than before (17/year). Overall mortality along the entire stretch of road was lower after installation of lighting, barrier fencing and an underpass, with fewer collisions (12/year) than previously (38/year). In October 1987, road lighting was installed along 11.5 km of the highway. Fencing and 30 one-way gates were installed along 5.5 km of this section and an underpass was created. Moose-vehicle collisions were monitored before (1977–1987) and after (1987–1990) installation.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.