Wildlife crossing signs have limited effectiveness in reducing vehicle speeds

Despite the societal benefits that roads provide, they have significant negative impacts on biodiversity, particularly through wildlife-vehicle collisions, which can also pose serious risks to the people involved in these accidents. To reduce wildlife-vehicle collisions, various mitigation measures have been implemented. Wildlife crossing signs (WCSs) are the most widely adopted due to their low cost and ease of maintenance, though their effectiveness remains a topic of debate. In this study, we assessed the effectiveness of different WCSs in preventing wildlife-vehicle collisions by analyzing their impact on vehicle speed reduction. We examined four types of signs: educational, risk-oriented, standard, and control signs, along the BR-262 highway in Mato Grosso do Sul (Brazil), known for its high wildlife-vehicle collision rates. Vehicle speed was collected from different vehicle categories, and at different distances before and after the signs, across different times of the day. We found that only the risk-oriented signs were associated with a decrease in speed, although this effect was minimal. Furthermore, vehicles tended to regain their speed shortly after passing the signs, sometimes even exceeding previous speeds. These findings highlight the limited effectiveness of WCSs in reducing vehicle speeds. It underscores the importance of implementing additional mitigation strategies beyond signage to effectively prevent wildlife collisions.