Wildlife crossing structures (WCS) are proposed as the primary way to improve wildlife connectivity across transportation. Barrier fencing is used independently to reduce wildlife-vehicle collisions (WVC). WCS effectiveness WCS depends on understanding the interacting influences of: wildlife and human activity. There are no published, science-based, and objective methods for decision-support for WCS siting at US state extents.

Interstate 5 (I-5) is a high-traffic highway that potentially acts as a continental barrier to wildlife. We propose the definition that “a continental barrier is any divide across a continent that restricts wildlife movement and creates habitat connectivity issues and/or behavioral changes across ecoregions along its length”. We conducted a meta-analysis of literature using an observed (in literature) to expected (from habitat suitability models) ratio.

Transportation infrastructure can restrict wildlife movement and increase wildlife-vehicle collisions (WVCs) that kill over 48,000 deer in California annually. Medians, which separate opposing traffic lanes, vary in type (e.g., concrete barriers, metal guardrails, vegetated strips) and may influence WVC rates. At Caltrans' request, we assessed the impact of median types on WVC rates along California highways.

Volunteers recorded 7+ years of mass roadkill mortality of one of California’s largest known populations of Pacific newts (Taricha spp.) on Alma Bridge Road (ABR) in Santa Clara County. ABR bisects newt habitat and Lexington Reservoir breeding grounds, resulting in one of the highest-reported rates of amphibian roadkill (34,231 dead newts, 2018-2024). The number of road-killed newts per hour of volunteer effort has been significantly declining ~10%/year (P=0.045).

Wildlife-vehicle collision (WVC) causes direct mortality and reduces population connectivity. Although the idea of WVC is well-characterized, its total impact on wildlife populations remains poorly understood. Here, we describe a method for estimating the impact of WVC at the US state scale, with a case study on California mule deer (Odocoileus hemionus). We used GenEst (USGS) (Dalthrop et al., 2018) to fit models, which incorporates rates of carcass observation, persistence, and effort, taken from our data collections systems, and search efficiency, from the literature.

The California Roadkill Observation System (CROS) was launched in August 2009 as a novel US-state scale wildlife-vehicle conflict (WVC) reporting system.  Since its inception, CROS has collected over 212,800 observations making it the largest WVC reporting system in the US. WVC observations have come from several sources, including amateur observers; state, federal, and local agencies; private entities; and highway patrol officers.

Wildlife-vehicle collisions (WVC) can result in property damage, injury and death to drivers. WVC can similarly cause wildlife injury and mortality, genetic fragmentation and other population impacts. State departments of transportation evaluating the need to reduce WVC use evidence of WVC and other data to inform mitigation decisions. Mitigation infrastructure, such as wildlife crossings with exclusion fencing, are effective measures for reducing WVC. Yet, states generally lack consistent  econometrics for evaluating the benefits of reducing WVC relative to the costs of mitigation.

Landscape linkages are hypothetical objects developed in geographic information systems (GIS) proposed to connect areas of habitat in fragmented landscapes. Although there are specific places and species (primarily ungulates) where hypothetical linkages represent where wildlife move, for the majority of places and species there is very little evidence that these GIS objects represent an ecological reality. Assuming they were used by organisms in nature, linkages could be an important tool for the maintenance of viable wildlife populations and biodiversity conservation.

Wildlife-vehicle collisions (WVC) can result in property damage, injury and death to drivers. WVC can similarly cause wildlife injury and mortality, as well as genetic fragmentation and other population impacts. State departments of transportation seeking to evaluate the need to reduce wildlife-vehicle collisions use evidence of WVC and other data to inform decisions about WVC mitigation. Mitigation infrastructure, such as wildlife crossings with exclusion fencing, are effective measures for reducing WVC.

Transportation and other agencies and organizations are increasingly planning and building under- and over-crossing structures for wildlife to traverse busy highways. However, if wildlife do not use these structures due to noise, light, and other factors, then the structures may have a low benefit to cost ratio. Several criteria are key for their success—sufficient safety and/or conservation need, cost, location, and anticipated use by wildlife.