Proactive Traffic Merging Strategies
for Sensor-Enabled Cars
Ziyuan Wang, Lars Kulik and Kotagiri Ramamohanarao
Department of Computer Science and Software Engineering
The University of Melbourne, Australia
VANET 2007, September, 2007
Outline

Introduction

Problem Statement

Progress So Far

Future Directions
2
Traffic Congestion

Some facts on traffic congestion

Total amount of delay: 3.7 billion hours in 2003

Wasted fuel: 2.3 billion gallons lost

Congestion cost: $63 billion
Source: Texas Transportation Institute, 2005 Urban Mobility Report.
3
Major Causes of Congestion
5%
5%
Bottlenecks:
•Intersections of on-ramps and main roads
15%
40%
•Blockage due to obstacles
10%
25%
Bottlenecks
Work Zones
Special Events
Traffic Incidents
Bad Weather
Poor Signal Timing
Source: Federal Highway Administration. Traffic Congestion and
Reliability: Linking Solutions to Problems - Executive Summary.
“slinky type” effect
4
Emergence of VANETs

Sensor-Enabled Cars

Spatial information
Position
Speed

Dedicated Short-Range
Communications (DSRC)



Acceleration
Deceleration
Vehicle-to-Vehicle (V2V)
Vehicle-to-Roadside (V2R)
Vehicular Ad hoc Networks
(VANETs)


Safety: less accidents
Efficiency: higher road utility
5
Problem Statement

Goal


How



Optimize traffic throughput
Proactive traffic merging algorithms
Technology available: sensor-enabled cars + VANETs
Applications


Intersections at the ramp and the main road of highways
(Highway merge assistant)
Lane changing when there are obstacles on the way
6
Existing Approaches

Traffic signal timing





Fixed
Traffic-responsive
Ramp metering
Traffic conditions
are highly variable
and unpredictable
Real-time information
Limitations

Adaptive

Flexible

Robust
Automation


Fully: Platoon (tightly grouped cars)
Partial: Adaptive Cruise Control (ACC)
7
Contributions

Proposed proactive traffic merging algorithms that
aim to use the current road facilities efficiently

Designed a controlled simulation environment
intended to test various traffic merging strategies

Investigated what criteria are significant to evaluate
the performance of traffic merging algorithms
8
Proactive Merging Algorithm
A
B

Highway
bottleneck
X
Y

Regular
strategy

Local decision

Distance-based

Velocity-based
A
B
Y
X
A
B
Y
X
9
Outline of Our Algorithms
Comparisons of the proactive merging algorithms
Information Right of Way
Assumption
Strategy
Distance-based Position
The car that is
closest to the
merging point
Velocity does
not vary much
Velocity-based
The car that
arrives to the
merging point
first
Acceleration
does not vary
much
Position
Velocity
10
Outline of Our Algorithms


Sliding decision
point
Adjust speed
appropriately
Input
{c, d, e}
{x, y}
Merging strategy Output
{c, d, x, e, y}
Distance
{c, x, d, y, e}
{x, c, d, y, e}
11
Evaluation Metrics

Delay


Throughput


The time to fill up the main road with a certain number of
cars from the ramp
The number of cars that complete merging over a period of
time
Flow

The product of density and velocity
12
Simulation

Intelligent Driver Model (IDM)


Microscopic traffic model
Safety distance
Parameter
Value
Maximum velocity
Safe time headway
Maximum acceleration
Maximum deceleration
100 km/h
1.5 s
1m/s^2
3m/s^2
Exit ramp
Decision point
Merging point
13
Experiments and Results
Experiment settings
Main road
Ramp
Light Medium Heavy
5
3.6
10
--
Delay (min)
cars/km
cars/km
∞
30
25
15
7.2
Unit
∞
∞
∞
Regular
Distance-based
20
Velocity-based
15
Platoon-Velocity
10
5
0
100- 110- 120- 130- 140- 150- 160- 170- 180- 190- 200- 210- 220- 230110 120 130 140 150 160 170 180 190 200 210 220 230 240
Number of Cars
14
Throughput (cars)
Experiments and Results
280
260
240
220
200
180
160
140
120
100
Regular
Distance-based
Velocity-based
Platoon-Velocity
1
3
5
7
9
11
Flow (cars/h)
1800
13
15
17
19
21
23
25
27
Time (min)
1600
1400
Regular
1200
Distance-based
1000
Velocity-based
Platoon-Velocity
800
1
3
5
7
9
11
Velocity (m/s)
30
13
15
17
19
21
23
25
27
17
19
21
23
25
27
Time (min)
25
Regular
Distance-based
Velocity-based
Platoon-Velocity
20
15
10
1
3
5
7
9
11
13
15
Time (min)
15
Summary

Traffic merging strategies benefit from sensorenabled cars

Proactive merging algorithm outperforms regular
strategy in terms of throughput and delay

Achieved at the cost of slightly lower velocity
16
Robustness of Algorithms

Human factors

Imperfect information


Unreliable communication medium


Sensor accuracy
Studies* show only 50-60% of cars in range will receive a
car’s broadcast
Penetration rates

Initially, only a small number of sensor-enabled cars
* Source: J. Yin, T. EIBatt, and S. Habermas, Performance evaluation of safety
applications over DSRC vehicular ad hoc networks, VANET 2004
17
Higher Degree of Realism

Obstacles


Traffic patterns


Different distributions
Multiple lanes


Blocking
Lane-changing
Heterogeneity

Different types of vehicles
18
Thank you!
Questions,
Suggestions,
&
Comments
19