Road Safety Audit: Twin Ports Interchange Work Zone

The Minnesota Department of Transportation (MnDOT) District 1 (Duluth region) is rebuilding the I-35, I-535, and US Highway 53 interchange in the city of Duluth, Minnesota. This interchange is known as the Twin Ports Interchange (TPI). The existing roadway and bridges are aging and structurally obsolete. This project will enhance safety by eliminating blind merges, left exits, and improve freight mobility.

The first year (2021) of this 4-year project had a severe impact on motorists due to mainline I-35 being reduced to a single lane in each direction. The Duluth area is a popular vacation destination and typically hosts many visitors during the summer months. With the reduction of COVID restrictions in 2021 the District expected an increase in traffic volume due to recovering commerce, tourism, and a resumption of special events. Thus, this project was flagged for extra temporary traffic mitigation measures.

Many of these work zone enhancements have been used on other projects but the concentration on this job warranted some additional study to determine the combined effectiveness. After consultation with the Traffic Engineering Organization (TEO) Temporary Traffic Control (TTC) subcommittee, it was determined that a process similar to a Road Safety Audit (RSA) would be an appropriate method to conduct this study to evaluate the enhancements and mitigation measures. Crash and delay data have been collected to summarize the general operation of the work zone. Each work zone enhancement is detailed, studied, evaluated by the team, and could be endorsed for use on other MnDOT projects or recommended for further improvements or refinements.