Driving simulator analysis of the first time driving on a diverging diamond interchange

The Diverging Diamond Interchange (DDI) is an innovative design alternative that enhances safety and operations, but its unconventional crossover maneuvers might confuse first-time drivers. The first DDI in Puerto Rico opened in 2023 at the interchange of highways PR-30 and PR-189 to improve the level of service of a conventional diamond interchange. Due to the lack of experience with a DDI in Puerto Rico, a driving simulation experiment was conducted in three phases to analyze future user behavior and performance. The simulation was conducted with 96 subjects who completed eight driving scenarios representing different maneuvers at the DDI and provided feedback about the effectiveness of the traffic control devices (TCDs) in assisting the driving task. Over 2,600 individuals also participated in training sessions with the simulator to experience the DDI. Speed profiles and vehicle trajectories were analyzed to reveal first-time drivers' challenges at the DDI, such as confusion with the crossover maneuvers, speeding, wrong route selection, and incorrect maneuvers. The results from the simulation and the survey responses assisted in identifying recommendations for modifications to TCDs and the DDI characteristics. Subsequent simulation phases served to evaluate the impacts of the implemented changes, resulting in a 47% reduction in the number of critical driver errors and a 26% reduction in total driver errors at the DDI. This study demonstrates the significant role of a driving simulator during the design process of innovative facilities like a DDI, aiding in assessing proposed design features and identifying effective improvements to TCDs.