Comparison to Case Study Logic

The gap acceptance logic presented here and used in the March 1998 Transims microsimulation is different from the logic used in the ``Dallas/Fort Worth Case Study'' (80,13). The logic during that case study was: ``Accept an unprotected movement if in all opposing lanes the gap is larger than $v_{max}=5$.'' This means that at low density on the major road, more turns were accepted, whereas at high density on the major road, less turns were accepted - with the extreme case that no turns were possible against oncoming traffic of speed zero.

Fig. 32.7 compares the results for the current gap-acceptance logic and the one used in the case study for the case where the major road is a 3-lane road. Note that the results for the turns into other traffic are not that much different whereas the result for the turns across other traffic yields much higher uncongested and much lower congested flows with the case study logic. This is due to the fact that for turns into other traffic, there is a capacity constraint of the form that the joint flows from the major and the incoming road cannot exceed capacity of the major road, see last section. Such a constraint obviously does not exist for turns across the major road.