Calculation of additional lost green time for upstream approaches at diamond interchanges considering downstream queue effects

Most diamond interchanges are composed of two closely-spaced signalized intersections where the downstream queue has strong influences on the system performance. The analysis methodology of isolated intersections may not reflect properly the downstream queue effect in the internal link at diamond interchanges. This paper proposed a new analytical model to estimate the additional lost green time for the upstream intersection at signalized diamond interchanges considering the queue effects in the internal link. The model calculates the additional lost green time at TTI three-phase and four-phase diamond interchanges using field traffic and geometric data. As in the HCM 2010 procedure, the model estimates the initial internal queue length, based on which the additional lost green time is calculated. The initial internal queue length is estimated taking a diamond interchange as a simple input-output system that processes the OD demand. The additional lost green time is calculated applying a method of kinematic waves. The performance of the model is evaluated using simulated data under various traffic and geometric conditions. The model evaluation results show that the proposed model provides close values to those by the simulation. The model can be applied to the design or operation analysis of diamond interchanges.