1 package org.opentrafficsim.road.gtu.following;
2
3 import org.djunits.unit.AccelerationUnit;
4
5 /**
6 * The Intelligent Driver Model by Treiber, Hennecke and Helbing.
7 * <p>
8 * Copyright (c) 2013-2015 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
9 * BSD-style license. See <a href="http://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
10 * <p>
11 * @version $Revision: 1408 $, $LastChangedDate: 2015-09-24 15:17:25 +0200 (Thu, 24 Sep 2015) $, by $Author: pknoppers $,
12 * initial version 19 nov. 2014 <br>
13 * @author <a href="http://www.tudelft.nl/pknoppers">Peter Knoppers</a>
14 */
15 public class IDM extends AbstractGTUFollowingModel
16 {
17 /** Preferred net longitudinal distance when stopped [m]. */
18 private final Length.Rel s0;
19
20 /** Maximum longitudinal acceleration [m/s^2]. */
21 private final Acceleration.Abs a;
22
23 /** Longitudinal deceleration [m/s^2]. (Should be a positive value even though it is a <b>de</b>celeration.) */
24 private final Acceleration.Abs b;
25
26 /** Safe time headway. */
27 private final Time.Rel tSafe;
28
29 /**
30 * Time slot size used by IDM (not defined in the paper, but 0.5s is a reasonable trade-off between computational speed and
31 * accuracy).
32 */
33 private final Time.Rel stepSize = new Time.Rel(0.5, SECOND);
34
35 /**
36 * Mean speed limit adherence (1.0: mean free speed equals the speed limit; 1.1: mean speed limit equals 110% of the speed
37 * limit, etc.).
38 */
39 private final double delta;
40
41 /**
42 * Construct a new IDM car following model with reasonable values (reasonable for passenger cars).
43 */
44 public IDM()
45 {
46 this.a = new Acceleration.Abs(1.56, METER_PER_SECOND_2);
47 this.b = new Acceleration.Abs(2.09, METER_PER_SECOND_2);
48 this.s0 = new Length.Rel(3, METER);
49 this.tSafe = new Time.Rel(1.2, SECOND);
50 this.delta = 1d;
51 }
52
53 /**
54 * Construct a new IDM car following model.
55 * @param a DoubleScalar.Abs<AccelerationUnit>; the maximum acceleration of a stationary vehicle (normal value is 1
56 * m/s/s)
57 * @param b DoubleScalar.Abs<AccelerationUnit>; the maximum deemed-safe deceleration (this is a positive value).
58 * Normal value is 1.5 m/s/s.
59 * @param s0 DoubleScalar.Rel<LengthUnit>; the minimum stationary headway (normal value is 2 m)
60 * @param tSafe DoubleScalar.Rel<TimeUnit>; the minimum time-headway (normal value is 1s)
61 * @param delta double; the speed limit adherence (1.0; mean free speed equals the speed limit; 1.1: mean free speed equals
62 * 110% of the speed limit; etc.)
63 */
64 public IDM(final Acceleration.Abs a, final Acceleration.Abs b, final Length.Rel s0, final Time.Rel tSafe, final double delta)
65 {
66 this.a = a;
67 this.b = b;
68 this.s0 = s0;
69 this.tSafe = tSafe;
70 this.delta = delta;
71 }
72
73 /**
74 * Desired speed (taking into account the urge to drive a little faster or slower than the posted speed limit).
75 * @param speedLimit DoubleScalarAbs<SpeedUnit>; the speed limit
76 * @param followerMaximumSpeed DoubleScalar.Abs<SpeedUnit>; the maximum speed that the follower can drive
77 * @return DoubleScalarRel<SpeedUnit>; the desired speed
78 */
79 private Speed.Rel vDes(final Speed.Abs speedLimit, final Speed.Abs followerMaximumSpeed)
80 {
81 return new Speed.Rel(Math.min(this.delta * speedLimit.getSI(), followerMaximumSpeed.getSI()), METER_PER_SECOND);
82 }
83
84 /** {@inheritDoc} */
85 public final Acceleration.Abs computeAcceleration(final Speed.Abs followerSpeed, final Speed.Abs followerMaximumSpeed,
86 final Speed.Abs leaderSpeed, final Length.Rel headway, final Speed.Abs speedLimit)
87 {
88 // System.out.println("Applying IDM for " + follower + " headway is " + headway);
89 // dV is the approach speed
90 Speed.Rel dV = followerSpeed.minus(leaderSpeed);
91 Acceleration.Abs aFree =
92 new Acceleration.Abs(this.a.getSI()
93 * (1 - Math.pow(followerSpeed.getSI() / vDes(speedLimit, followerMaximumSpeed).getSI(), 4)),
94 METER_PER_SECOND_2);
95 if (Double.isNaN(aFree.getSI()))
96 {
97 aFree = new Acceleration.Abs(0, AccelerationUnit.SI);
98 }
99 Acceleration.Rel logWeightedAccelerationTimes2 =
100 new Acceleration.Rel(Math.sqrt(this.a.getSI() * this.b.getSI()), METER_PER_SECOND_2).multiplyBy(2);
101 // don't forget the times 2
102
103 // TODO compute logWeightedAccelerationTimes2 only once per run
104 Length.Rel right =
105 followerSpeed.toRel().multiplyBy(this.tSafe)
106 .plus(dV.multiplyBy(followerSpeed.toRel().divideBy(logWeightedAccelerationTimes2)));
107 /*-
108 Calc.speedTimesTime(followerSpeed, this.tSafe).plus(
109 Calc.speedTimesTime(dV, Calc.speedDividedByAcceleration(followerSpeed, logWeightedAccelerationTimes2)));
110 */
111 if (right.getSI() < 0)
112 {
113 // System.out.println("Fixing negative right");
114 right = new Length.Rel(0, METER);
115 }
116 Length.Rel sStar = this.s0.plus(right);
117 if (sStar.getSI() < 0) // Negative value should be treated as 0
118 {
119 System.out.println("sStar is negative");
120 sStar = new Length.Rel(0, METER);
121 }
122 // System.out.println("s* is " + sStar);
123 Acceleration.Rel aInteraction =
124 new Acceleration.Rel(-Math.pow(this.a.getSI() * sStar.getSI() / headway.getSI(), 2), METER_PER_SECOND_2);
125 Acceleration.Abs newAcceleration = aFree.plus(aInteraction);
126 if (newAcceleration.getSI() * this.stepSize.getSI() + followerSpeed.getSI() < 0)
127 {
128 // System.out.println("Limiting deceleration to prevent moving backwards");
129 newAcceleration = new Acceleration.Abs(-followerSpeed.getSI() / this.stepSize.getSI(), METER_PER_SECOND_2);
130 }
131 // System.out.println("newAcceleration is " + newAcceleration);
132 return newAcceleration;
133 }
134
135 /** {@inheritDoc} */
136 @Override
137 public final Time.Rel getStepSize()
138 {
139 return new Time.Rel(this.stepSize);
140 }
141
142 /** {@inheritDoc} */
143 @Override
144 public final Acceleration.Abs maximumSafeDeceleration()
145 {
146 return this.b;
147 }
148
149 /** {@inheritDoc} */
150 @Override
151 public final String getName()
152 {
153 return "IDM";
154 }
155
156 /** {@inheritDoc} */
157 @Override
158 public final String getLongName()
159 {
160 return String.format("%s (a=%.1fm/s\u00b2, b=%.1fm/s\u00b2, s0=%.1fm, tSafe=%.1fs, delta=%.2f)", getName(),
161 this.a.getSI(), this.b.getSI(), this.s0.getSI(), this.tSafe.getSI(), this.delta);
162 }
163
164 }