Overview of Simulation Logic

This section provides a general overview of the logic/models employed to control the movement of vehicles within SwashSim.

Simulation Time Step SwashSim employs a 0.1-s simulation time step. That is, it updates the properties of all simulation objects (vehicles, signal control, etc.) 10 times per second.

Vehicle Entry Two types of vehicle entry distributions can be specified: Uniform or Random. For a uniform distribution, each vehicle will enter at the same headway, i.e., 3600 s/h divided by the entry volume (in veh/h). For example, an entry volume will result in a vehicle entering the network every 2 seconds. If the ‘Random’ distribution type is selected, two different distributions will be used, as follows:
 * Entry flow rate < 900 veh/h &#8594; Negative Exponential distribution
 * Entry flow rate ≥ 900 veh/h &#8594; Normal distribution
 * The standard deviation for the Normal distribution is calculated as: (Average Headway × Number of Lanes - MinArrivalHeadway) / 2.5
 * The minimum arrival headway is calculated as: DesiredHeadwayMultiplier × 1.1 + (StopGap + MinVehLength) / DesiredSpeed

Two-Lane Passing Detail about the logic used for two-lane highway passing maneuvers is given in Appendix A. Below are screenshots of the associated parameter value input screens.

Desire to Pass (Oncoming Lane)

Acceleration Values (Oncoming Lane)

Acceleration Values (Passing Lane)

Emissions