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Learn the factors available to adjust the 'car following' and 'lane changing' behavior in Paramics

UPDATED: June 13, 2017


To adjust the car following behavior, specify following factors:
1. Mean Target Headway
  • Vehicle type, Motorway merges movements at traffic signal intersections, aggressiveness, and awareness
2. Vehicle Kinematics
  • Acceleration,Cruising,Braking


To adjust the lane changing behavior, specify following factors:
1. Link behavior factors
  • Reaction factor – the Mean Driver Reaction Time for all vehicles on the link can be modified using this factor. For example in high flow high speed sections of freeway vehicles may react to vehicles ahead of the vehicle they are following, this will have the result of reducing shock wave effect where drivers are aware of the surrounding conditions. To simulate this phenomenon, a factor of less than 1 should be entered into the Reaction Factor box.
  • Headway factor – the Mean Target Headway for all vehicles on the link can be modulated using this factor. For example in a tunnel, the user might know that drivers commonly extended their headway by 50%. To model this phenomenon, a figure of 1.5 should be entered into the Headway Factor box.
2. Vehicle Behavioural Factors
  • HGV following factor - In the real world drivers in smaller cars tend to keep a larger min. gap behind HGV’s. The HGV following factor is used to factor up/down the use of the minimum gap. This factor only applies to non-HGV types following HGV types. HGV is determined by the Heavy Vehicles Weight value in the Advanced Configuration tab. The core min gap is a configuration parameter with a default of 2m. A factor for vehicle type A of 1.5 would mean type A stopping behind a HGV would want to use a min gap of 3.0. Note – PT vehicles are included if they are deemed HGV.
  • Mean driver reaction factor - The mean reaction time of each driver, in seconds.  The value is associated with the lag in time between a change in speed of the preceding vehicle and the following vehicles reaction to the change. The reaction factor is set at the global level, at the individual link level and here, for the vehicle types.
Note: These factors are multiplicative so "overall reaction time will" = global * link * vehicle type. A factor of 1.0 will have no effect.
  • Mean target headway factor - Specifies the mean target headway, in seconds, between a vehicle and a following vehicle. The headway factor is set at the global, at the category level, at the individual link level and here, for the vehicle types.
Note: These factors are multiplicative so "overall headway will" = global * category or link * vehicle type. A factor of 1.0 will have no effect.

3. Gaps file
  • User definable gap rules can be used to localize and fine tune gap acceptance and merging criteria at specific points in the network. The gaps file can contain following two types of entries:
  1. Crossing gap: It is a gap where two vehicles are heading for different exit links out of the junction, but their paths cross or conflict as either would move through the junction from their respective entry links into the junction.
  2. Merge gap: It is a gap where both vehicles are heading for the same target exit link and lane out of the junction but each has a different starting or entry link into the junction.

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