Running the Simulation

Main Page > Technical Documentation > Running the Simulation

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/s.

Warm-up Time

This field dictates how long the traffic simulation will run before performance measurement data are collected. Enter a number between 1 and 1800 s. Anything entered above 1800 s will be defaulted back to 1800. For a small network such as the isolated intersection, a warmup time of 300 s (5 min) should be sufficient. Press the ‘Tab’ or ‘Enter’ key to save the duration value before pressing the ‘Run Simulation’ button.

Simulation Duration

This field dictates how long the traffic simulation will run after the warm-up time. Enter a number between 1 and 7200 s. Any entered value above 7200 s will be defaulted back to 7200. Press the ‘Tab’ or ‘Enter’ key to save the duration value before pressing the ‘Run Simulation’ button.

Random Number Seeds

The random number seeds affect the various items within the simulation program that rely on random numbers. More specifically:
 * 1st Random Number Seed – Applies to vehicle entry generation
 * 2nd Random Number Seed – Applies to vehicle type generation
 * 3rd Random Number Seed – Applies to driver type generation
 * 4th Random Number Seed – Applies to all other randomly generated inputs

For the same inputs, a simulation run results will be at least slightly different if any of the random number seeds are varied. The seed numbers can be entered manually (any integer value), or they can be automatically created by pressing the “Auto Generate” button. If you desire to recreate the results exactly of a previous simulation run, use the same random number seeds. Note: When a simulation is run, a “RandSeedNumbers” text file is outputted. This file allows for previous seed combinations to be accessed. These values are also saved in the project file (discussed later in this guide).

Single Run The Single-Run option can be used to run a single replication on a network geometry.





To set parameters for single-run simulation select “Simulation” to access the “Simulation Control Panel”.



From here warm-up time, simulation duration, number of replications, and random number seed can be set. Various output options can be selected as well.

Warm-up Time: During the warm-up time, performance measure statistics will not be collected. This time should be long to fill the network with traffic.

Sim Duration: This is the amount of time the simulation will run beyond the end of the warm-up time. Performance measure statistics are collected during this time.

Random # Seeds: selecting ‘Auto Generate” will yield random seed numbers to vary each replication

Number of Replications: the number of times single run simulation will run

If the number of replications is more than one, the random number seed will be set randomly for each one run. The seed values will be written to the file 'RandSeedNums.txt' in the project output folder.

Once all parameters have been set, select “Run Simulation”

Multi-Run

The Multi-Run option is used to facilitate automatically running the simulation any number of times. This could consist of multiple replications of one set of traffic data inputs and/or multiple traffic data inputs, for a given network geometric configuration. For any multi-run execution, the network geometry must remain consistent and should be created first.

To input traffic data for multi-run, select “Simulation” to access the “Simulation Control Panel”.





Then select the “Multi-Run” tab on the “Simulation Control Panel” to input data.



Begin by pressing the “Add Scenario” button to add a new scenario. Repeat this as necessary for the total number of scenarios desired.



Settings

Include in Simulation: If this box in unchecked, the corresponding scenario settings will be excluded from the multi-run.

# of Replications: The settings for this scenario will be run the number of times as specified by this value.

Warm-up Time: During the warm-up time, performance measure statistics will not be collected. This time should be long to fill the network with traffic.

Sim Duration: This is the amount of time the simulation will run beyond the end of the warm-up time. Performance measure statistics are collected during this time.

Random # Seeds: Pressing the ‘Set’ button will load the following input screen. The number of rows in this form will correspond to the number of replications specified. To run a scenario replication with random number seed values, use ‘0’ in the four cells to the right. Pressing the ‘Generate’ button in the second column (‘Use Random Values’) will place zeros in these cells. To use specific random number seed values, but have them generated randomly by the program, press the ‘Generate’ button in the third column (‘Generate Values’). You can also directly enter any specific values desired into these cells. The values need to be positive integers in the range of 0-65535.



Traffic Data: Pressing the ‘Set’ button will load the following input screen. This is where the flow rate, percentage of passenger cars, and percentage of heavy vehicles can be input for both directions of traffic.



“Entry Flow Rate” must be input first before “Entry Percentage” are input. After inputting flow rate and vehicle percentages make sure to select “Save Changes” in Direction 1 before inputting data for Direction 2. If the same percentages are to be input into both directions, values can be copied by selecting “Copy Values to Clipboard” and pasted by selecting “Paste Values from Clipboard”. The output data can be specified by checking the boxes within the “TSD Output”, “Detector Output”, “Link Performance Data”, and “Lane Change Data” columns. These output options are described in Simulation Output Data.

Once all simulation parameters are input, select run simulation.