Which Parameters Can You Adjust in the traffic-simulation.de Onramp Model?

Updated

The onramp microsimulation on traffic-simulation.de exposes four groups of adjustable parameters: traffic flow and inflow, vehicle mix, car-following behavior, and lane-changing behavior. You can change any of them before or during a run to see how the merging traffic responds. The controls are grouped in the page's parameter panel, and the model is a browser-based HTML5 canvas simulation by Martin Treiber.

Traffic Flow and General Inflow

These settings define how much traffic enters the system and how the onramp is fed.

  • Traffic Flow — the mainline demand, i.e. how many vehicles per unit time enter the highway upstream of the merge.
  • General Inflow — the background inflow that feeds the network.
  • Onramp Flow — the demand arriving via the onramp itself. This is the key variable for studying merging and congestion at the ramp.

Raising onramp flow while holding mainline flow fixed is the standard way to push the merge toward breakdown; lowering it lets you observe free-flow merging.

Vehicle Mix and Timelapse

  • Truck Perc — the percentage of trucks in the traffic stream. Trucks typically have different acceleration and speed characteristics from cars, so this changes both capacity and the dynamics of the merge.
  • Timelapse — controls the playback speed of the simulation, letting you fast-forward through a long run or slow it down to watch a specific interaction.

Car-Following Behavior

These parameters govern how each driver follows the vehicle ahead.

  • Max Speed v0 — the desired speed a driver aims for in free traffic.
  • Time Gap T — the desired time headway to the leading vehicle. Smaller values mean tighter following and shorter gaps.
  • Max Accel a — the maximum acceleration available to the vehicle.

Changing these shifts the fundamental diagram of the flow and therefore how early or late congestion appears near the onramp.

Lane-Changing Behavior

These settings control how and when vehicles change lanes.

  • Politeness — how much a driver accounts for the disadvantage imposed on other vehicles when changing lanes. Higher politeness makes drivers more reluctant to cut in.
  • LC Threshold — the lane-change threshold, i.e. the incentive level required before a driver decides to change lanes.
  • Right Bias Cars and Right Bias Trucks — the tendency of cars and trucks respectively to keep to the right lane. Separate values let you model the common pattern where trucks stay right more consistently than cars.

How to Use These Together

A practical workflow is to set a baseline (for example, moderate mainline flow, low onramp flow, default car-following values), run the simulation, then vary one group at a time:

  1. Increase Onramp Flow until merging congestion appears.
  2. Raise Truck Perc to see how slower vehicles change the breakdown point.
  3. Reduce Time Gap T or raise Max Accel a to test whether more aggressive car-following delays congestion.
  4. Adjust Politeness and LC Threshold to see how cooperative or assertive lane-changing affects throughput at the merge.

The page also includes a Ramp-Metering Game and links to the offline sources on GitHub, the MovSim project, and the books Traffic Flow Dynamics and Verkehrsdynamik by the same author, which document the underlying models.