13.4.5.1 Traffic Control Devices

Traffic control devices are an important part of network coding. There are numerous ways to code the different traffic control devices such as signalized intersections, AWSC intersections, two-way stop control (TWSC) intersections, roundabouts, etc. in Vissim. below provides a summary of the main network objects that are used to code the different types of traffic controls and their applications
Table 13-1: Traffic Control Devices
Traffic Control
Description
Application
Signal Heads
Signal heads are used to code signalized intersections and are assigned to the signal controller created for that intersection. Signal controllers are typically created using an *.RBC file that is imported from Synchro or created based on signal timing plans.
  • Used for coding signalized intersections
  • Can be imported from Synchro or developed natively in file
  • Is typically placed on top of links and confirm that connectors do not cross the signal head
  • Is assigned to the corresponding signal group, which includes the signal controller and the signal phase associated with the timing plans
Detectors
A detector is used to model traffic sensors in the field that help detect vehicles for actuated signal operations.
  • Is placed directly behind the signal heads and are typically coded to a length of 30 - 90 ft to match the detection area in field.
  • Is assigned a port number (signal phase) and a signal controller number associated with the signal head and signal timing plan.
Stop Signs
Stop signs are used to model unsignalized intersections.
  • Is placed at the location of the stop bar.
  • Used to model right-turn on red operations.
  • Used to model AWSC and TWSC intersections.
Conflict Rules
Conflict rules occur where two links or connectors overlap each other. They are initially set to a passive stage. If an actual conflict exists, the rules need to be adjusted to give one movement priority over the other based on the actual ROW for the conflict vehicles.
  • Used to model yield conditions.
  • Is used for all basic types of conflicts such as right-turns, stop control intersections, permissive left-turns at signalized intersections, etc.
  • Use them were necessary and restrain from exorbitant use of conflict rules as they could lead to gridlock, especially in congested networks.
Priority Rules
Priority rules are similar to conflict rules. They are used to model yield conditions, however, they allow for more customization and are recommended for use in complex situations.
  • Used to model yield conditions.
  • Minimum gaps and headways are typically modified by vehicle type.
  • Can be tied to specific phases of signal.
  • Are used for more complicated conflicts that are not easily coded with a conflict rule such as multi-lane roundabout entries, keep clear of intersection, etc.
Roundabout
Roundabouts are typically coded using a combination of links, connectors, and priority rules/conflict areas. There are example demos within Vissim that can be used to understand the principles of coding a roundabout.
  • Use priority rules to code multi-lane roundabouts.
  • Use the HCM critical gap values for starting off points for minimum gaps for roundabouts. Adjust as needed per visual audits and other factors.
  • Links typically have their attributes modified to not allow lane changes within the circulating lanes.
  • RSA are typically used to model approach speeds and circulating speeds of a roundabout based on the fastest path/design speed or speed measured in field.