Use signage to warn motorists about wildlife presence

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Five studies evaluated the effects of using signage to warn motorists of wildlife presence on reptile populations. Three studies were in the USA and one was in each of Dominica and Canada.




  • Survival (5 studies): One of two before-and-after studies (one replicated and controlled) in the USA found that installing road signs reduced road mortalities of massasaugas in autumn but not summer. The other study found that installing road signs did not reduce road mortalities of painted or Blanding’s turtles. Two before-and-after studies (one replicated) in Canada and the USA found that a combination of installing road signs with either fencing and tunnels or a hybrid nestbox-fencing barrier resulted in fewer road mortalities of massasaugas and diamondback terrapins. One before-and-after study in Dominica found that a combination of using road signs and running an awareness campaign resulted in fewer road mortalities of Antillean iguanas.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A before-and-after study in 1981–1982 on a road through a prairie in Missouri, USA (Seigel 1986) reported that when road signs were installed to warn motorists of snakes, a lower percentage of total massasaugas Sistrurus catenatus found were dead on the road in one of two seasons compared to when signs were not present. Results were not statistically tested. Of the total number of snakes found during the study (172 individuals), the percentage that were dead on the road was similar before (19% dead) and after signs were installed (24%) in summer, but lower after signs were installed in autumn (after 13%; before 32%). Road signs warning motorists of snakes were installed in 1981 (month not given). Surveys for snakes were conducted on a prairie and bordering roads and dykes, and trapping was carried out using drift fences with wire-mesh funnel traps (number and timing of surveys not provided). 

    Study and other actions tested
  2. A replicated, controlled, before-and-after study in 2008–2010 on 18 roads through swamps and wetlands in New York, USA (Johnson 2012) found that road signs did not decrease painted Chrysemys picta and Blanding’s Emydoidea blandingii turtle road mortality. The percentage of turtles encountered that were dead was similar on roads with signs (2009: 49 of 72, 68%; 2010: 20 of 31, 65%) and roads without signs (2008: 40 of 71, 56%; 2009: 28 of 53, 53%; 2010: 16 of 28, 57%). Road signs warning drivers of turtles were installed during the nesting season (1 June–1 July) on five roads in 2009 and nine roads in 2010. Driving (daily) and walking (100 m transect, 1–2 times/week) surveys were conducted to count the number of turtles encountered (dead and alive) before signs were installed in 2008 (9 roads) and after signs were installed in 2009 (Signs: 5 roads; no signs: 5 roads) and 2010 (Signs: 9 roads; no signs: 9 roads). Dead animals were removed to prevent double counting. Results from 2010 include only driving surveys.

    Study and other actions tested
  3. A before-and-after study in 2008–2010 on coastal roads on the Caribbean Sea side of Dominica (Knapp et al. 2016) found that using road signs and running an awareness campaign reduced lesser Antillean iguana Iguana delicatissima road mortality by half. After putting up road signs and running an awareness campaign, lesser Antillean iguana road mortality reduced by approximately 50% (0.3 fatal collisions/day) on coastal roads compared to beforehand (0.6 fatal collisions/day). An awareness campaign about protecting iguanas was carried out in May 2008–June 2010. On 1 July 2009, road signs asking people to slow for iguanas were put up on coastal roads near known nesting locations (see original paper for details). The campaign included lectures at schools, presentations to government employees, radio and television interviews and distributing bumper stickers across the island asking people to slow down for iguanas. Two coastal road segments (11–29 km long) were surveyed for iguanas during the nesting season from April 2008–June 2010, 122 days before signs were put up and 94 days afterwards.

    Study and other actions tested
  4. A replicated, before-and-after study in 2002–2014 on three roads in Ontario, Canada (Colley et al. 2017) found that eastern massasauga rattlesnake Sistrurus catenatus road mortality was reduced after signs for motorists, guide fencing and tunnels were installed. The number of rattlesnakes found, both dead or alive on roads decreased after sign, fence and tunnel installation (dead: 6, alive: 14) compared to before installation (dead: 41, alive: 68) and during installation (dead: 15, alive: 37). In 2007–2013, four signs to encourage motorists to slow down for snakes were installed near known snake road crossing locations (precise installation dates not provided), and three sets of mesh barrier fences were installed (600 m–1 km apart; 600–900 m of fencing on one or both sides of the road). In 2010–2011, within each of the two sets of fencing on both sides of the road, two grate-top tunnels (8.5 m long x 1.2 m wide x 0.5–0.6 m deep) were installed. Eastern massasauga rattlesnakes on the road were surveyed from May to October by car before (2005–2007) and during installation (2008–2012), and by bicycle after installation (2013–2014).

    Study and other actions tested
  5. A before-and-after study in 2009–2015 on saltmarsh in Georgia, USA (Crawford et al. 2018) found that adding a flashing terrapin-warning sign to alert motorists and partially fencing a causeway reduced the likelihood of mortality for diamondback terrapins Malaclemys terrapin crossing the road. When the flashing signs and hybrid nestbox-fence barrier were installed on a road, survival of crossing female diamondback terrapins increased from 24% to 53% (data reported as statistical model outputs). In 2011, a 22 m hybrid nestbox-fence barrier was built along a 9 km long causeway. In 2013, two terrapin crossing signs with flashing warning beacons were added to warn motorists entering a 6 km stretch of causeway. The signs were activated for 2 hours/day during peak terrapin crossing times. Terrapins were surveyed on the causeway and in adjacent creeks during the nesting season (May–July) in 2009–2015.

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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Reptile Conservation

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Reptile Conservation - Published 2021

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