Tutorial: Vehicle Entry Headway Distribution

Main Page > Tutorials > Vehicle Entry Headway Distribution Vehicle Entry Headway Distribution 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 1800 veh/h 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/ln &#8594; Negative Exponential distribution
 * Entry flow rate ≥ 900 veh/h/ln &#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

Average Entry Headway  Average entry headway is calculated from headway results from the Link_Lane_Detector output file to match the Average Headway given in Detector Aggregate output file. Average entry headway is calculated through the equation, the number of vehicles, $$ N $$, traversing link during simulation time is, $$ N=N'-1$$, $$ N'$$ is the total number of vehicles which has Actuation Time On (from Link_Lane_Detector output file) greater than warm-up time. Entry Headway Distribution Entry headway distribution (random) is validated by counting frequencies of headways from the Link_Lane_Detector output file. Headway frequency distribution is plotted through Excel. Simulation Setup
 * Load network file under SwashSim &#8594; File &#8594; Project Properties, the network file MediumFreeway.nwf is downloaded from github.
 * Detectors can be added through Table View &#8594; Set Detector(s) for each segment. One detector (48.8 Position%, 48.8 Position (ft), 6 Length (ft)) is added to OnRamp segment (3, 602) to monitor entry vehicles. The performance measurement is carried out based on the outputs of this detector.
 * Change desired Entry flow rate and type of vehicle arrival distribution under Table View &#8594; Traffic Data. Average entry headway is validated for both uniform (2000 veh/h) and random (850 veh/h for negative exponential dist. and 2000 veh/h for normal dist.) arrival distribution. Entry headway distribution validation is conducted for the random arrival scenario.
 * Run simulation with 3 replications, 300s warm-up time and 1800s simulation time. Check Link Performance Measure Data, Detector Aggregate Measures Data, Detector Vehicle Actuation Data, Vehicle Headway Data under Output Options. Check Vehicle Time Step Data customized for LinkID 3602.