Lane Changing

Main Page > Technical Documentation > Vehicle Movement Logic > Lane Changing

The lane-changing logic is composed of mandatory and discretionary.

First check for mandatory lane change. If mandatory lane change is not necessary, then check for discretionary lane change.



Mandatory Lane Changing A mandatory lane change is typically needed for one of the following conditions:
 * The vehicle is traveling on an acceleration auxiliary lane and must change lanes in order to merge with the mainline freeway traffic.
 * The vehicle is not on the proper lane for the desired movement on the downstream link.
 * The vehicle is on a lane which will be dropped downstream.
 * The vehicle needs to move to a special purpose lane (e.g., HOV)
 * The vehicle is on a lane which is blocked downstream.

An overview of the mandatory lane changing logic employed in SwashSim is as follows. Identify desired lane Identify leader and follower vehicle on desired lane Determine if gap is sufficient between two vehicles for subject vehicle to merge into If needed deceleration is less than acceptable risk, then allow vehicle to change lanes.
 * Based on movement direction (left, through, right)
 * Closest vehicle in front, closest vehicle behind
 * Two gaps to consider, one between subject vehicle and leader vehicles, and one between subject vehicle and follower vehicle
 * Make sure vehicles will not collide
 * Determine subject vehicle acceptable risk; Function of:
 * Urgency Factor
 * Driver aggressiveness factor
 * Ranges from 0.82 (driver type 1) to 1.18 (driver type 10)
 * Number of lane changes to reach desired lane
 * Link free-flow speed
 * Distance to last point where vehicle must exit lane (e.g., end of lane drop)
 * Minimum acceptable risk (-8 ft/s2), for driver type 1
 * Maximum acceptable risk (-15 ft/s2), for driver type 10
 * Urgency Threshold
 * If urgency factor < 0.2 (default), use minimum acceptable risk
 * If urgency factor > 1.0 (default), use maximum acceptable risk



Discretionary Lane Changing Discretionary lane changing refers to vehicles that change lanes in order to obtain a more favorable position (i.e., to attain a higher speed in order to reach the desired speed). For example, when a vehicle changes lanes to pass a slower-moving vehicle.

Check if subject vehicle is candidate to consider discretionary lane change
 * Does vehicle have a leader?
 * Is it traveling faster than 10 mi/h? Vehicles moving slowly (e.g., in a queue) do not consider discretionary lane changes.
 * Get subject vehicle desired speed (minimum of desired speed and maximum velocity). Maximum velocity might control for large truck on steep grade.

Calculate motivation to change lanes If subject vehicle actual speed ≥ desired speed, motivation = 0

Otherwise,

IntolerableSpeed = DesiedSpeed*IntolerableSpeedMultiplie * DriverAggressivenessFactor <\math>