Collisions

SUMO tracks gaps between vehicles that are on the same edge either fully or partially. By default, whenever these gaps are reduced to below a vehicles minGap a collision is registered. Currently, this threshold is fixed to the vehicles minGap value (default 2.5m). This (potentially) surprising behavior is used to detect issues with the car-following models that are supposed to never reduce the gap below the minGap. The threshold will likely be made configurable in the future (ticket1102.

When setting the option --collisions.check-junctions, collisions between vehicles on the same intersection are also checked by detecting overlap of the vehicles shapes.

The consequence of a collision is configured using the option --collision.action using one of the following keywords:

• teleport: (the default): the follower vehicle is moved (teleported) to the next edge on its route
• warn: a warning is issued
• none: no action is take
• remove: both vehicles are removed from the simulation

Deliberately causing collisions

To force collisions at a set time, TraCI must be used. Besides setting the speed, it is also necessary to disable safety checks using the commands speedMode and laneChangeMode.

To create rear-end collisions with some probability one can configure vehicles with a value of 'tau' that is lower than the simulation step size (default 1s) and use the default Krauss model.

Safety-related parameters

Simulation of unsafe behavior is a developing subject. Expect model additions and extensions. The following vehicle type parameters are safety related:

car-following model

• speedFactor: higher value causes speeding (driving above the speed limit)
• accel, decel: higher values lead to abrupt speed changes
• tau: lower values lead to reduced gaps to the leader vehicle. When setting tau lower than the simulation --step-length parameter (default 1s), collisions may occur

Lane-Changing Model

• lcCooperative: lower values cause less cooperation during lane changing
• lcSpeedGain: higher values cause more overtaking for speed
• lcKeepRight: lower values cause less driving on the right
• lcPushy: setting this to values between 0 and 1 causes aggressive lateral encroachment (only when using the Sublane Model)
• lcAssertive: setting this to values between 0 and 1 cause acceptance of smaller longitudinal gaps in proportion to driver impatience(only when using the Sublane Model)

Junction Model

• impatience: higher values lead to acceptance of smaller time gaps at intersections. These are still safe in the sense of collision avoidance.