13.5.4 CORSIM Calibrating Capacity at Bottlenecks

Calibrating a CORSIM model begins with a calibration of the capacity at key bottlenecks. Replicate the location and severity of bottlenecks, if present. This can be accomplished by evaluating a few key locations in the model and adjusting model parameters in a repeatable process that adjusts throughput volume downstream of the bottleneck until throughputs and queues are similar to local conditions.
When calibrating capacity on a freeway, there are several model parameters that can be adjusted. The parameters and their definitions are listed here:
  • Car-following sensitivity factor
    – A global parameter that represents the primary factor used to calculate headway between a lead-follow pair. The higher the value the more space between vehicles and therefore a lower freeway capacity.
  • Car-following sensitivity multiplier
    – This parameter is adjusted for individual segments. A higher value represents more space between vehicles and therefore a lower freeway capacity.
  • Lag acceleration and deceleration time
     – A global parameter that represents the reaction time necessary for drivers to accelerate or decelerate. A higher value represents a slower reaction time and therefore a lower freeway capacity.
  • Pitt car-following constant
     – A global parameter that represents the minimum amount of space between the rear of the lead vehicle and the front of the follow vehicle. A higher value represents more space between the vehicles and therefore a lower freeway capacity.
When calibrating capacity on surface streets there are several model parameters that can be adjusted. The parameters and their definitions are listed here:
  • Mean discharge headway
     – This parameter is adjusted for individual segments and represents the mean headway between the rear of the lead vehicle and the front of the follow vehicle in a standing queue. A higher value represents a longer headway and therefore a lower capacity.
  • Mean startup delay
     – This parameter is adjusted for individual segments and represents the mean startup lost time for the first vehicle in a standing queue. A higher value represents a greater startup delay and therefore a lower capacity.
  • Acceptable gap in oncoming traffic (left turns and right turns)
    – These are global parameters that represents the minimum acceptable gap in seconds for left turns and right turns. A higher value represents a higher minimum acceptable gap and therefore lower capacity.
  • Cross-street acceptable gap distribution (near-side and far-side)
    – These are global parameters that represent the minimum acceptable gap in seconds at stop signs. A higher value represents a higher minimum acceptable gap and therefore lower capacity.