org.opentrafficsim.road.gtu.lane.tactical.util

Class CarFollowingUtil

java.lang.Object

org.opentrafficsim.road.gtu.lane.tactical.util.CarFollowingUtil

public final class CarFollowingUtil
extends Object

Static methods regarding car-following for composition in tactical planners.

Copyright (c) 2013-2018 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved.
BSD-style license. See OpenTrafficSim License.

Version:

$Revision$, $LastChangedDate$, by $Author$, initial version May 23, 2016

Author:

Alexander Verbraeck, Wouter Schakel

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	CarFollowingUtil.CarFollowingHeadway Simple headway implementation for minimum car-following information.

Method Summary

Modifier and Type	Method and Description
static Acceleration	approachTargetSpeed(CarFollowingModel carFollowingModel, Parameters parameters, Speed speed, SpeedLimitInfo speedLimitInfo, Length distance, Speed targetSpeed) Returns an acceleration based on the car-following model in order to adjust the speed to a given value at some location ahead.
static Acceleration	constantAccelerationStop(CarFollowingModel carFollowingModel, Parameters parameters, Speed speed, Length distance) Return constant acceleration in order to stop in specified distance.
static Acceleration	followSingleLeader(CarFollowingModel carFollowingModel, Parameters parameters, Speed speed, SpeedLimitInfo speedLimitInfo, HeadwayGTU leader) Follow a set of headway GTUs.
static Acceleration	followSingleLeader(CarFollowingModel carFollowingModel, Parameters parameters, Speed speed, SpeedLimitInfo speedLimitInfo, Length distance, Speed leaderSpeed) Follow a set of headway GTUs.
static Acceleration	freeAcceleration(CarFollowingModel carFollowingModel, Parameters parameters, Speed speed, SpeedLimitInfo speedLimitInfo) Calculate free acceleration.
static Acceleration	stop(CarFollowingModel carFollowingModel, Parameters parameters, Speed speed, SpeedLimitInfo speedLimitInfo, Length distance) Stop within given distance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

followSingleLeader

public static Acceleration followSingleLeader(CarFollowingModel carFollowingModel,
                                              Parameters parameters,
                                              Speed speed,
                                              SpeedLimitInfo speedLimitInfo,
                                              Length distance,
                                              Speed leaderSpeed)
                                       throws ParameterException

Follow a set of headway GTUs.

Parameters:

carFollowingModel - car-following model

parameters - parameters

speed - current speed

speedLimitInfo - speed limit info

distance - distance

leaderSpeed - speed of the leader

Returns:

acceleration for following the leader

Throws:

ParameterException - if a parameter is not given or out of bounds

followSingleLeader

public static Acceleration followSingleLeader(CarFollowingModel carFollowingModel,
                                              Parameters parameters,
                                              Speed speed,
                                              SpeedLimitInfo speedLimitInfo,
                                              HeadwayGTU leader)
                                       throws ParameterException

Follow a set of headway GTUs.

Parameters:

carFollowingModel - car-following model

parameters - parameters

speed - current speed

speedLimitInfo - speed limit info

leader - leader

Returns:

acceleration for following the leader

Throws:

ParameterException - if a parameter is not given or out of bounds

stop

public static Acceleration stop(CarFollowingModel carFollowingModel,
                                Parameters parameters,
                                Speed speed,
                                SpeedLimitInfo speedLimitInfo,
                                Length distance)
                         throws ParameterException

Stop within given distance.

Parameters:

carFollowingModel - car-following model

parameters - parameters

speed - current speed

speedLimitInfo - speed limit info

distance - distance to stop over

Returns:

acceleration to stop over distance

Throws:

ParameterException - if a parameter is not given or out of bounds

constantAccelerationStop

public static Acceleration constantAccelerationStop(CarFollowingModel carFollowingModel,
                                                    Parameters parameters,
                                                    Speed speed,
                                                    Length distance)
                                             throws ParameterException

Return constant acceleration in order to stop in specified distance. The car-following model is used to determine the stopping distance (i.e. distance remaining at stand still, e.g. 1-3m).

Parameters:

carFollowingModel - car-following model

parameters - parameters

speed - current speed

distance - distance to stop over

Returns:

constant acceleration in order to stop in specified distance

Throws:

ParameterException - on missing parameter

freeAcceleration

public static Acceleration freeAcceleration(CarFollowingModel carFollowingModel,
                                            Parameters parameters,
                                            Speed speed,
                                            SpeedLimitInfo speedLimitInfo)
                                     throws ParameterException

Calculate free acceleration.

Parameters:

carFollowingModel - car-following model

parameters - parameters

speed - current speed

speedLimitInfo - speed limit info

Returns:

acceleration free acceleration

Throws:

ParameterException - if a parameter is not given or out of bounds

approachTargetSpeed

public static Acceleration approachTargetSpeed(CarFollowingModel carFollowingModel,
                                               Parameters parameters,
                                               Speed speed,
                                               SpeedLimitInfo speedLimitInfo,
                                               Length distance,
                                               Speed targetSpeed)
                                        throws ParameterException

Returns an acceleration based on the car-following model in order to adjust the speed to a given value at some location ahead. This is done by placing a virtual vehicle somewhere near the location. Both the location and speed of this virtual vehicle are dynamically adjusted to resemble a car-following situation. To explain, first consider the situation where a virtual vehicle is placed at the target speed and such that the equilibrium headway is in line with the location:

 
  ___    location of target speed --)|        ___
 |___|(--------------s--------------) (--h--)|___| ))) vTar
 

Here, s is the distance to the target speed, and h is the desired headway if the vehicle would drive at the target speed vTar.

In this way car-following models will first underestimate the required deceleration, as the virtual vehicle is actually stationary and does not move with vTar at all. Because of this underestimation, strong deceleration is required later. This behavior is not in line with the sensitivity parameters of the car-following model.

To correct for the fact that the virtual vehicle is actually not moving, the speed difference should be larger, i.e. the speed of the virtual vehicle vTar' should be lower. We require:

• if v = vTar then vTar' = vTar, otherwise there is an incentive to accelerate or decelerate for no good reason
• if vTar ~ 0 then vTar' ~ 0, as car-following models are suitable for stopping and need no additional incentive to decelerate in such cases
• if 0 < vTar < v then vTar' < vTar, introducing additional deceleration to compensate for the fact that the virtual vehicle does not move

These requirements are met by vTar' = vTar * (vTar/v) = vTar^2/v.

Furthermore, if v < vTar we get vTar' > vTar leading to additional acceleration. Acceleration is then appropriate, and possibly limited by a free term in the car-following model.

The virtual vehicle is thus placed with speed vTar' at a distance s + h' where h' is the desired headway if the vehicle would drive at speed vTar'. Both vTar' and h' depend on the current speed of the vehicle, so the virtual vehicle in this case actually moves, but not with vTar.

This approach has been tested with the IDM+ to deliver decelerations in line with the parameters. On a plane with initial speed ranging from 0 to 33.33m/s and a target speed in 300m also ranging from 0 to 33.33m/s, strongest deceleration is equal to the car-following model stopping from 33.33m/s to a stand-still vehicle in 300m (+ stopping distance of 3m). Throughout the plane the maximum deceleration of each scenario is close to this value, unless the initial speed is so low, and the target speed is so high, that such levels of deceleration are never required.

Parameters:

carFollowingModel - car-following model to use

parameters - parameters

speed - current speed

speedLimitInfo - info regarding the desired speed for car-following

distance - distance to the location of the target speed

targetSpeed - target speed

Returns:

acceleration acceleration based on the car-following model in order to adjust the speed

Throws:

ParameterException - if parameter exception occurs

NullPointerException - if any input is null

IllegalArgumentException - if the distance or target speed is not at least 0