The National Academies

NCHRP 25-25/Task 113 [Final]

Road Passages and Barriers for Small Terrestrial Wildlife: Summary and Repository of Design Examples
[ NCHRP 25-25 (Research for the AASHTO Committee on Environment and Sustainability) ]

  Project Data
Funds: $125,000
Research Agency: Louis Berger U.S. Inc./Western Transporation Institute/Eco-Kare International
Principal Investigator: Dr. Marcel Huijser and Kari Gunson
Effective Date: 3/20/2018
Completion Date: 9/19/2019

STATUS: Research is complete. A brief summary report is available HERE (.pdf; 495 KB). Presentation slides summarizing the project are available HERE (pptx; 43 MB).  

The repository of design examples is available for download HERE (.zip, 528 MB; includes repository materials, a spreadsheet index to the repository, and information on how to access repository material; please note this is a large file and will take some time to download).

A series of illustrated case studies is available HERE (.zip, 6.2 MB). 

Design considerations for 6 categories of crossings and barriers are available HERE (.zip, 9.1 MB).

A literature review and summary of a expert survey are available HERE (.zip, 4.8 MB)


Since the Nutty Narrows squirrel bridge was constructed in Longview, Washington in 1963, a wide range of projects have been implemented by state DOTs, local governments, and non-governmental organizations to remedy situations with high levels of road-related mortality for smaller wildlife,  reptiles and amphibians. These projects include incorporation of measures into new roads, retrofits of existing infrastructure, and addition of infrastructure specifically for wildlife use. Many of these projects have also implemented post-construction monitoring to evaluate effectiveness. However, many of these projects are not known beyond the local area or state where they were constructed. As a result, the designs and lessons learned from their implementation are not available to inform current projects. 


The purpose of this study is to gather and summarize existing information on crossing structures, passages, and exclusion barriers for small terrestrial mammals, reptiles, and amphibians.  The information will be organized in a repository of design examples, plan sheets, and case studies of successes and lessons learned for a representative selection of projects.

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