How Effective Is Road Mitigation at Reducing Road-Kill? A Meta-Analysis

Abstract

Road traffic kills hundreds of millions of animals every year, posing a critical threat to the populations of many species. To address this problem there are more than forty types of road mitigation measures available that aim to reduce wildlife mortality on roads (road-kill). For road planners, deciding on what mitigation method to use has been problematic because there is little good information about the relative effectiveness of these measures in reducing road-kill, and the costs of these measures vary greatly. We conducted a meta-analysis using data from 50 studies that quantified the relationship between road-kill and a mitigation measure designed to reduce road-kill. Overall, mitigation measures reduce road-kill by 40% compared to controls. Fences, with or without crossing structures, reduce road-kill by 54%. We found no detectable effect on road-kill of crossing structures without fencing. We found that comparatively expensive mitigation measures reduce large mammal road-kill much more than inexpensive measures. For example, the combination of fencing and crossing structures led to an 83% reduction in road-kill of large mammals, compared to a 57% reduction for animal detection systems, and only a 1% for wildlife reflectors. We suggest that inexpensive measures such as reflectors should not be used until and unless their effectiveness is tested using a high-quality experimental approach. Our meta-analysis also highlights the fact that there are insufficient data to answer many of the most pressing questions that road planners ask about the effectiveness of road mitigation measures, such as whether other less common mitigation measures (e.g., measures to reduce traffic volume and/or speed) reduce road mortality, or to what extent the attributes of crossing structures and fences influence their effectiveness. To improve evaluations of mitigation effectiveness, studies should incorporate data collection before the mitigation is applied, and we recommend a minimum study duration of four years for Before-After, and a minimum of either four years or four sites for Before-After-Control-Impact designs.

Informing snake roadkill mitigation strategies in Taiwan using citizen science

“…An important next step is to perform applied studies in Asia, testing the effectiveness of different mitigation methods such as drift fences, culverts, bridges, or other wildlife passages (Patrick et al , Ascensão et al , D'Amico et al ). There are currently no such studies in Asia, but a meta‐analysis of the success of mitigation measures in other regions reported that fences are more effective than passages, and the combination of both is the most effective (Rytwinski et al ). Finally, citizen‐reported roadkill databases have been reported to be accurate for information on location and identification (Ha and Shilling , Waetjen and Shilling , Périquet et al ), and we recommend their further use in wildlife conservation and management.…”

Identification of local factors causing clustering of animal‐vehicle collisions

“…Many projects involve implementing structures to keep wildlife away from roads (i.e., culverts, bridges; Rytwinski et al ). Roads are also fenced at places of frequent AVCs (Forman and Alexander ), audio and optical signal systems are installed to discourage animals from crossing roads (Rowden et al ), and speed limits, warning signals (Al‐Ghamdi and AlGadhi ), and thermal sensors draw the attention of drivers to the presence of large animals (Hirota et al ).…”

Road kills of non‐human primates: a global view using a different type of data

“…). These are cheap and perhaps effective methods to reduce risks to wildlife, and may also make roads safer for (human) pedestrians (Drews , WHO , McLennan & Asiimwe , Rytwinski et al , Staton et al ).…”