The current expansion of the road network is reaching unprecedented levels aimed to accelerate economic development and territorial expansion of human settlements, facilitating the transportation of people and goods. However, roads have several pervasive impacts on wildlife, such as pollution, habitat loss, roadkills or being barrier to animal movement. The most common mitigation action to minimize the last two impacts (roadkill and barrier effect) is the placement of wildlife barrier fencing and crossing structures.

GPS collars have become commonplace as a tool to monitor wildlife movement at fine and broad scales. These datasets comprise some of the most compelling evidence for the impacts of infrastructure on wildlife connectivity and can guide efforts to improve animal flow across human-modified landscapes. Movement data can be analyzed via diverse methods to select appropriate sites for wildlife fencing and crossing structures, but certain considerations emerge as common to many workflows.

Wildlife crossing structures (WCS) are often proposed as the way to improve wildlife connectivity across transportation and other infrastructure. Barrier fencing is used independently or tied to WCS to reduce wildlife-vehicle collisions (WVC). Effectiveness of WCS and fencing depends on understanding the influences of wildlife needs, topographic constraints, human development and activity, land ownership and management, and other variables. There are no published, science-based, and objective methods for decision-support for WCS and fencing at US state extents.

Since the winter of 2018, thousands of Pacific newts, including California newts (Taricha torosa) and rough-skinned newts (Taricha granulosa) have been recorded dead on Alma Bridge Road in Santa Clara County, California. Alma Bridge Road is a part-time recreation access and commuting road that bisects the largest known population of Pacific newts’ upland forest habitat and breeding grounds in the Lexington Reservoir. This bisection results in one of the world’s highest-reported rates of amphibian roadkill each rainy season.

Highways put wildlife at risk of negative effects from habitat fragmentation, altered survival and reproduction, disrupted gene flow and more. Interstate 5 (I-5) is a high-traffic highway that runs an unbroken 1,381 miles, from Canada to Mexico, potentially acting as a continental barrier to wildlife.

Anthropogenic noise and light impact wildlife behavior, distribution, movement, and population fitness and survival. Traffic noise and light can inhibit wildlife use of areas adjacent to roads, impair wildlife perception of traffic risks, and cause a barrier effect to wildlife occurrence and movement well beyond road edges. Planning the location and design of new wildlife crossings and enhancements of existing structures currently does not take into account traffic impacts on wildlife approaching the structures.

Wildlife monitoring is crucial for informing conservation efforts, providing valuable insights into animal infrastructure use, movement patterns, and population dynamics. Traditional monitoring methods that include motion activated cameras and manual analysis are not only time-consuming but also expensive and prone to human error (e.g., data transcription). 

There are approximately 290 million registered vehicles in the US, traveling over 3 trillion miles per year on over 4 million miles of rural and urban roads. Vehicles traveling through wildlife habitat can strike wildlife, resulting in a wildlife-vehicle collision (WVC). WVC acts as both an artificial predator, causing direct mortality, and a barrier to population connectivity, eventually limiting gene flow (because dead animals don’t contribute to connectivity).

Transportation infrastructure impacts wildlife by restricting movement and increasing mortality through wildlife-vehicle collisions (WVCs). WVCs cost Californians $250 million each year in property damage, personal injuries, and wildlife and driver fatalities. Roadways typically feature medians that separate opposing lanes of traffic and include: concrete barrier, metal guardrail, cable, vegetated strip, gravel strip, and pavement marking. Transportation planners select a median type based on safety concerns (i.e., crashes) and other conditions.

Roads are used by humans for travel and by wildlife to cross to the other side, leading to wildlife vehicle conflict (WVC), a problem that results in high costs to wildlife and society. The California Roadkill Observation System (CROS) was launched in August 2009 as a proof of concept for a US-state scale WVC-reporting system.