Can quiet roads be dangerous for wildlife too?

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Collisions with vehicles are a major negative effect of roads on wildlife, so reducing roadkill is an important part of conservation. Roadkill is influenced by traffic volume and road features. A unimodal relationship between traffic volume and roadkill probability has been theorized, but empirical evidence has been lacking.

Researchers used a large-scale roadkill database covering 18 wildlife species in Israel, 2,846 km of roads and 10 years. They used a multivariate generalized linear mixed model to explore how traffic volume and road attributes, including lighting and verge vegetation, related to roadkill probability.

The striped hyena (Hyaena hyaena) showed a unimodal relationship with traffic volume. Five species showed a different, quadratic U-shaped relationship, including the golden jackal (Canis aureus). Four species showed a negative linear relationship, including the wild boar (Sus scrofa).

Road attributes also had varying relationships with roadkill. Road lighting and roadside trees were associated with less roadkill for several species, while bus stops and concrete guardrails were associated with more roadkill.

The researchers suggested that the theorized unimodal relationship may apply only to large, agile species, and that the U-shaped relationship could be related to differences within a species in traffic avoidance behavior. Overall, both high-traffic and low-traffic roads could pose a high mortality risk for wildlife.

The researchers recommended monitoring roadkill on low-traffic roads and adapting road attributes to reduce it. Their suggested road design measures include reducing concrete guardrails and median barriers where possible and avoiding dense bushes in verge landscaping. They also recommended wildlife detection systems, driver warnings and seasonal speed reductions on low-traffic roads identified as roadkill hotspots.