VISSIM 5.30-05 User Manual

5 Base Data for Simulation
5.1 Acceleration and Deceleration Functions
VISSIM does not use a single acceleration and deceleration value but uses
functions to represent the differences in a driver’s behavior. Acceleration and
deceleration are functions of the current speed. Combustion engines reach
their maximum acceleration at low speeds, whereas three-phase motors of
e.g. trams or trains show a constant acceleration within a wide range of
speeds.
For each vehicle type two acceleration functions and two deceleration
functions (graphs) need to be assigned:
► Maximum acceleration: Max. technically feasible acceleration. Regarded
only if an acceleration exceeding the desired acceleration is required to
keep the speed on slopes.
► Desired acceleration: Used for any other situation.
► Maximum deceleration: Max. technically feasible deceleration. Adjusted
on slopes by 0.1 m/s² for each percent of positive gradient and -0.1 m/s²
for each percent of negative gradient.
► Desired deceleration: If it is lower than the max. deceleration, then the
desired deceleration is used as the maximum for the deceleration
- caused by a desired speed decision,
- in case of Stop & Go traffic, when closing up to a preceding vehicle,
- in case of insufficient lateral distance for overtaking within the lane,
- towards an emergency stop position (route),
- for co-operative braking: In this case, 50% of the vehicle´s own
desired deceleration is used as the max. reasonable deceleration for
the decision, whether an indicating vehicle may change from the
neighbouring lane to the vehicle´s lane.
In any other case, the parameters of the car following model are relevant.
Predefined functions are provided with each of the default vehicle types in
VISSIM. They can be edited or new graphs can be created through BASE
DATA – FUNCTIONS... When one of the four types is selected, an edit window
opens to allow for editing the existing acceleration graphs.
106 VISSIM 5.30-05 © PTV AG 2011