Decision-support for evaluating and improving wildlife crossing of transportation corridors

ICOET 2021
Brock Ortega, Dudek
Fraser Shilling, UC Davis
Norris Dodd, AZTEC Engineering
Travis Longcore, UCLA
Anna Cassady, Dudek

Existing transportation and linear conveyance (e.g., aqueducts, pipelines) already bisect blocks of otherwise intact habitat for species at all levels, inhibiting movement and genetic flow in some cases. Often for decades. There is an evolving toolbox equipped with many measures to minimize and mitigated the effects, but little consistent evaluation of the “who, what, why, and where” of implementation and management of the tools.

There are many models and resources that generally hypothesize where wildlife movement occurs, and thus where structures should be installed. Ideally, structure placement is based on identification of specific goals, actual wildlife occurrence and movement data and local site review prior to structure placement. We discuss a repeatable, systematic process for evaluating where to place structures based on actual site conditions and need. At a high level, we look at efforts to identify wildlife crossing need in Arizona, Wyoming, and California. We then look at an example of a transportation corridor-specific analysis to identify need and to identify specific recommendations at a more refined level, the recently completed State Route 62 (SR62) Wildlife Connectivity and Recommendations project. The scale of transportation corridor planning is both suitable for programming transportation projects (e.g., building crossing structures) and using and contributing to local conservation planning. Getting into the weeds. The first requirement is to identify the goal or focus of the analysis, whether is it to reduce Wildlife- Vehicle Collisions (WVC), to maintain or restore ecological processes, maintain individual connectivity, or to simply maintain long-term genetic connectivity. The next step is to perform site-specific studies to support mitigation decisions. The general area of SR62 had been modeled as being important for wildlife movement and our task was to evaluate the transportation corridor for actual constraints and opportunities for movement and possible solutions. As it turns out, while there is a 1.5-mile to 2-mile wide, apparently suitable movement area for desert bighorn sheep, they are constrained to a single bridge underpass in an area of high human activity. In order to evaluate the possible hot spots and constraints, and then inform our recommendations, we selected species important to wildlife and transportation agencies, reviewed existing species data and WVC data, performed road mortality, track, and camera studies, and modeled noise and light effects near specific crossing locations along the roadway. Following the analysis, we identify key critical areas for wildlife movement enhancement and developed several recommendations including overpasses and enhanced culvert maintenance. The overall process is one that could be easily duplicated for other transportation corridors to inform site-specific recommendations for infrastructure improvements to facilitate wildlife connectivity.