This report presents the results of a functionality evaluation, by the I-15 Utah County Corridor Expansion (CORE) traffic team, of the first Diverging Diamond Interchange (DDI) in Utah, located at the intersection of American Fork Main Street (Pioneer Crossing) and I-15. The Pioneer Crossing DDI was opened to traffic in August 2010. This evaluation incorporates a review of population trends, traffic patterns, detoured traffic, and design features to understand how this new interchange operates for the travelling public. In general, this evaluation determined that the application of a new-construction DDI at this location resulted in better than expected traffic operation. Since the completion of the Pioneer Crossing DDI analysis, three other DDIs have been opened to traffic within Utah with differing site conditions and geometric provisions. Two of the DDIs were retrofits of previous conventional Diamond Interchanges. One was a new construction completed for the I-15 CORE project. The other three installations have added valuable insight to the traffic characteristics that influence the DDI design so that future DDIs can be even more successful. An observational study was completed at each of the new DDIs in Utah, and key characteristics were recognized for working well or not working well with the DDI design. These characteristics and conclusions from the study of the four DDIs currently in Utah are provided as lessons learned for use on future projects. Overall, the four DDIs have proven effective as viable interchange options at these locations. (Author/publisher)
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