Wyoming Demonstration Project: Diverging Diamond Interchange Project at College Drive

The Wyoming diverging diamond interchange (DDI) project, which was 90 percent Federally funded and 10 percent State funded, was located at the College Drive Interchange on Interstate 25, approximately 3 miles south of Cheyenne at reference marker 7.85. The project received a Highways for LIFE grant of $400,000 and was the first of its kind in the State. The total length of the project was 1,080 feet, and the total length of the bridge was 220 feet. The project sought to reduce the congestion caused by slow-moving trucks and to increase pedestrian and vehicular safety throughout the interchange. The project converted the conventional diamond interchange into a DDI by incorporating minor structure alterations, ramp realignments, signal installations, and lighting. The construction was carried out in four phases. During these phases, one lane was left open for traffic in each direction, and the traffic was controlled with flaggers and traffic control. Reduced speed limit signs, advanced warning signs, traffic drums, and arrows were also installed. Highways for LIFE safety goals for worker and motorist safety were met on this project. Per Wyoming Department of Transportation’s (WYDOT's) estimates, a typical interchange reconstruction or rehabilitation would have taken, on average, two construction seasons, with a shutdown for the winter season and temporary traffic control for 18 months or longer. In contrast, the DDI was completed within 9 months. Thus, the as-built scenario resulted in 50 percent reduction in the time highway users are impacted, compared to traditional methods, thereby meeting the Highways for LIFE goal for faster construction. During the construction period, WYDOT did not find any significant travel time delays or queuing along the College Drive interchange and ramps of I-25. The use of DDI, which cost $3,056,898.43, is expected to result in an estimated present worth savings of $8,782,000, which accounts for the reduction in user delays over 20 years and the cost of signalizing the interchange. Overall, the traveling public expressed satisfaction with the new facility and the construction approach.