Evaluation of Alternative Intersections and Interchanges

Diverging diamond interchanges (DDIs) have been growing in usage over the past few years and have gained considerable attention and interest. The advantage of the DDI over a conventional diamond interchange is that DDIs eliminate the need for left turn phases at the two intersections of the diamond, while occupying roughly the same geometric footprint as the conventional diamond. At the beginning of this project, no DDIs had yet been constructed in Indiana, and there was a need to evaluate methods of signal timing for them. Also, at the beginning of this project there had not yet been any studies nationally on coordinating DDIs with neighboring intersections along an arterial. There is still relatively little guidance on phase configuration for DDIs, especially with pedestrians. This project report includes results from a field study of an existing DDI in Utah, a second field study of Indiana’s first DDI in Fort Wayne (which is the first field study of optimizing signal offsets in a corridor including a DDI), a simulation comparison of DDI signal timing strategies, and guidelines for DDI phasing with pedestrians (including both interior and exterior pedestrian paths).