Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Christopher M. Day
Peter T. Savolainen
Approximately 18% of fatal run-off-road crashes in the US are associated with either a culvert or a ditch. To reduce the risk of such crashes, safety treatments that can be implemented include installation of safety grates or guardrails or extending the culvert outside the clear zone, as mentioned in AASHTO’s Roadside Design Guide. The existing design practices do not indicate when a particular safety treatment should be chosen over others based on the given roadway and traffic conditions. The existing literature has also been quite limited with respect to this problem. To that end, this study aims to determine the potential impacts of installing various culvert safety treatments and the cost-effectiveness of these treatments.
Crash data were analyzed for culvert related crashes from January 2007 to August 2017 using two different methodologies. The crash data, culvert data, and roadway data were then linked to each other. After removing the culverts with missing lengths and culvert sizes from the data, the final dataset included 500 crashes on 481 culverts. The crash rates were calculated for different roadway classification and highway types. Roadway scenarios were modeled in an encroachment-based simulation software called Roadside Safety Analysis Program (RSAP). Based on the estimated annual crashes from RSAP, the estimated number of crashes and crash rates for the analysis period were calculated and compared with the actual number of crashes and crash rates for each scenario. The crash rates estimated using RSAP were generally 2 to 13 times higher than the actual crash rates.
The results indicate that in most cases, installing safety grates on culvert openings is a more cost-effective solution than other safety treatments. Guardrail installation proved to be the least effective alternative, as it appeared to increase the number of crashes as well as crash costs. Extending the culvert outside the clear zone appeared to be cost-effective to some extent, but was not found to be a better choice than installing safety grates.
Chawla, Hitesh, "In-service evaluation of culvert extensions" (2019). Graduate Theses and Dissertations. 16985.