Analyzing the Diverging Diamond Interchange Using Discrete Event Simulation

The diverging diamond interchange (DDI) can improve traffic flow by limiting the number of phases in the traffic signals and improve safety by eliminating left turns. A few instillations of these interchanges have been constructed and there is great potential to construct more. In an effort to develop a methodology to evaluate these interchanges, this paper presents the development of a discrete event simulation model of the diverging diamond interchange (DDI). Specific emphasis is on using simulation to model the DDI, a description of the operation of the simulation model, and using simulation to understand the operation of the DDI. The paper concludes that the use of the simulation package allows for rapid evaluation of the DDI and demonstrates that this interchange design will not work in all locations. 1. Introduction One of the major causes of accidents at interchanges is turning left into oncoming traffic. This is especially true on the overpasses where vehicles turn left to enter the interstate. One solution to this problem is the diverging diamond interchange (DDI). The DDI eliminates the left hand turns into free flowing oncoming traffic. The DDI uses traffic lights to allow vehicles to briefly shift to the left side of the road. The vehicles can then directly turn left on the access ramp without facing oncoming traffic. The first diverging diamond interchange in the United States opened in 2009 in Springfield, Missouri. Figure 1 is a photograph of the Springfield DDI. No new bridges or elevated lanes were required. Initial results indicate that the new interchange reduced total crashes by 46%, left turn crashes were eliminated, and rear-end crashes down slightly [1]. The study also indicated that over eighty percent of the public expressed that the traffic flow had improved and traffic delays had decreased. Figure 1: Diverging diamond interchange in Springfield, Missouri. This paper presents the development of a discrete event simulation model of the diverging diamond interchange. Specific emphasis is on the description of the operation of the simulation model and the use of simulation to understand the operation of the DDI. The hypothesis of the paper is to determine if a non-transportation simulation program can effectively model the DDI and simulate delays for a variety of test cases to demonstrate that the DDI is not the appropriate solution for all locations. The experimental design is to establish a DDI in the simulation program and develop cases to adjust traffic and monitor the response of the simulation. The simulation model is