Replication of Work Zone Capacity Values in a Simulation Model

Evaluating the traffic impacts of work zones is vital for any transportation agency for planning and scheduling work activity. Traffic impacts can be estimated using microscopic simulation models. One challenge in using these software models is obtaining the desired work zone capacity values which tend to vary from one state to another. Thus, the default parameter values in the model which are suitable for normal traffic conditions are unsuitable for work zone conditions let alone for conditions specific to particular states. A few past studies have been conducted on parameter selection to obtain desired capacity values. However, none of these studies have provided a convenient look-up table (or a chart) for the parameter values that will replicate the field observed capacities. Without such provision it has not been possible for state agencies to utilize any of the research recommendations. This study provides the practitioner a simple method for choosing appropriate values of driving behavior parameters in the VISSIM micro-simulation model to match the desired field capacity for work zones operating in a typical early merge system. The two most significant car-following parameters and one lane changing parameter were selected and varied to obtain different work zone capacity values. CC1 is the desired time headway, CC2 is the longitudinal following threshold during a following process, and the safety distance reduction factor is representative of lane changing aggressiveness. Additionally, for each recommended set of driving behavior parameters, lane distribution of the closed lane at different points upstream of the taper is collected. It was verified that the recommended parameter values not only produce the desired capacities but also create traffic conditions consistent with traffic flow theory.