"A Passage Assessment System (PAS) was developed to help the Washington Department of

Transportation (WSDOT) evaluate existing transportation infrastructure for its ability to facilitate

terrestrial wildlife movement from one side of a roadway to the other. The outcomes of this

research provide mechanisms to allow transportation agencies to identify both opportunities and

barriers to wildlife passage along roads. The PAS presented in this report provides an assessment

process that differentiates – for different types of wildlife – between structures that are currently

functional, those that could be enhanced to become more functional, and those that are not based on how the wildlife respond to roads and crossing structures. Structural Functional Classes

were also defined to classify road infrastructure, such as bridges, culverts and pipes, to create a

common understanding of terminology related to wildlife crossings. The field research was

conducted for six months in six locations in central and western Washington with the objective of

ascertaining which species of wildlife approached and used different types of structures. The PAS

was then developed on the basis of these field data, research on wildlife use of crossings across

North America, and the organization provided by the Species Movement Guilds and Structural

Functional Classes. The PAS guides practitioners through a series of targeted questions designed

to characterize a bridge or culvert relative to its potential to function as a wildlife passage for the

full range of wildlife known to occur at a given site. The PAS is intended as an evaluation tool to

ensure that biologists ask the right questions in the field and fully document the conditions that

may affect passage functionality for the diversity of target species. By answering questions about

the structure characteristics, vegetation, land use, roadway, barriers and fencing, the biologist will

have a complete passage assessment including preliminary ideas for improving the structure,

which can be further refined during the project planning and design processes. The PAS provides

an effective mechanism for determining which structures are suitable for enhancements to

improve their functionality as wildlife passages or, if no such enhancements are appropriate,

identify structure replacement needs for improved highway permeability for wildlife. A Passage

Enhancement toolbox is provided to complement the PAS and presents a number of infrastructure

adjustments and maintenance actions that may be implemented to help wildlife better move

through structures. This toolbox may be used to help guide users in developing site-specific

recommendations.

The Passage Assessment System supports timely inclusion of wildlife passage needs from the

onset of highway corridor planning, project planning and design. It offers potential cost-savings

and minimized project delays by identifying passage modifications that may be significantly less

costly than new infrastructure. Where existing culverts and bridges can be shown to pass wildlife,

it would help to reduce future construction costs for wildlife crossings in those areas and