Traffic flow in SimTraffic is based on a series lane changing and car following algorithms. There are ten different driver types to provide various driver behaviors, including both aggressive and passive drivers. As vehicles are added to the network, they have a pre-determined path and already know several of their upcoming movements. This pre-determined path and the driver type will influence each driver’s lane change behaviors.
The decision on when a vehicle change lanes is based on two key parameters. The first is the Mandatory Distance and is defined as the distance from an intersection that a vehicle must have changed lanes to complete a required movement. If the vehicle has not changed lanes by this point, the vehicle will stop and wait for a gap. The second parameter is the Positioning Distance and is defined as the distance from the location of the Mandatory Distances that a vehicle will attempt to make a lane change to avoid being forced to complete a mandatory lane change. The figure below highlights the relationship of these parameters.
Notice the Mandatory Distance for EB vehicles is 100 ft., while the Positing Distance for EB vehicles is 1,980 ft. Using the default values in SimTraffic’s Drivers Parameters for Driver Type 1, we can calculate the positioning distance to be 1,980 x 150% = 2,970 ft. This means that vehicles will begin making lane changes over 0.5 miles from the lane drop. With this in mind, the queuing shown below seems reasonable. However, this queuing may not match what might be observed in the field.