There are a wide range of influences on vehicle speed. They are described in the following. Each of these influences sets an upper bound on the vehicle speed. The actual speed in any given situation is the minimum speed of all influences.

maxSpeed

The <vType>-attribute maxSpeed models the maximum speed that a vehicle will travel. It can be thought of as the maximum speed of the engine or the maximum speed desired by the driver under any circumstances (possibly these two aspects will be modelled with separate attributes in the future).

edge/lane speed

The speed-attribute is usually defined for edges but may also differ among the lanes of the same edge. It models the legal speed limit. Each vehicle can be assigned an individual speed multiplier which then lets it exceed this limit.

Car Following Model

The car following model of a vehicle defines its speed in relation the vehicle ahead. The default model always selects the maximum speed which is safe in the sense of being able to stop in time to avoid a collision.

Dawdling

Most car-following models support the sigma-attribute which models driver imperfection. For values above 0, drivers with the default car-following model will drive slower than would be safe by a random amount (between [0, accel]).

Intersections

Vehicles approaching an intersection without the right-of-way have to slow down. If the intersection is used by other vehicles which have the right of way, stopping may be necessary until a safe time-window is found. Even if a vehicle has the right-of-way it may need to slow down due to impatient drivers which drive across the intersection. The right-of-way rules at an intersection are defined by the node type-attribute and by traffic lights.

Lane Changing

Vehicles may decide to slow down in order to execute a lane-change maneuver. They may also slow down in order to aid other vehicles with lane-changing. If the lane a vehicle is on does not have a connection to the next edge on a vehicles route, the vehicle will decelerate and stop.

Stops

Vehicles will decelerate when approaching the position of stop-definition.

Acceleration / Deceleration constraints

Vehicles can only change their speed by a certain amount each time step. This is defined by the <vType>-attributes accel and decel

departSpeed / arrivalSpeed

Vehicles enter the network using their defined departSpeed. When approaching the end of their route they will adapt their speed to match their defined arrivalSpeed

Variable Speed Signs

Variable speed signs are used to modify the speed limit of an edge for a defined time interval.

Calibrators

Calibrators are used to adapt the flow on an edge for a defined time interval but may also be used to modify the speed limit of an edge.

TraCI

Vehicles can forced to adapt their speed using TraCI commands. Using the speed mode command, The above influences can be selectively overridden.