In 2004, The Vermont Agency of Transportation, in cooperation with the Vermont Fish & Wildlife Department began a study of road-stream crossings to assess to aquatic habitat connectivity. Funding for the effort came as a research grant by the Federal Highway Administration and the Vermont Fish & Wildlife Department’s procedure was used as baseline criteria.

The Upper White River Watershed served as the study area. Results indicated that ~1/2 of all large culverts in the watershed never pass fish at any time of year, while the remainder only pass them during a portion of the year. No structure was found to pass fish at all flow rates.

The results indicate that there is a direct correlation between culvert size and the bankfull width of the stream channel, with regard to the ability to pass fish and stream sediments. From the study, the two agencies have begun to make recommendations as to how to retrofit the large culvert program to be more compatible with aquatic habitat connectivity and stream stability. Although many benefits of retrofitting the structures can be recognized, Vermont is now trying to address the inflated construction costs that come with the solution.