(Slides) A Method for Sharing Traffic Jam Information Using Inter-Vehicle Communication

A Method for Sharing Traffic Jam

Informationusing Inter-Vehicle

Communication

Naoki Shibara, Takashi Terauchi*, Tomoya Kitani*,

Keiichi Yasumoto*, Minoru Ito* and Teruo Higashino**

Shiga University, JAPAN*Nara Institute of Science and Technology

(NAIST), JAPAN**Osaka University, JAPAN

[ Invited Paper ]

The 2nd International Workshop on Vehicle-to-Vehicle Communications 2006 (V2VCOM 2006), 21 July, 2006

2V2VCOM 2006 - N. Shibata et al. July 21, 2006

Background

$100 billion/year of economic loss by traffic jam

Existing services for alleviating traffic jam VICS (Vehicle Information and Communication

System) A service provided by Japanese government Provides traffic jam information of trunk roads

Cyber-Navi （ Pioneer ） An advanced car-navigation system Predicts traffic jam from information in the

past Weaknesses of the existing methods

Service area Operation cost Time lag / not up-to-date information


Purpose of the study

Autonomous collection of statistical traffic info.

Using GPS and inter-vehicle communication No need for costly infrastructures

Prediction of arrival time using the gathered info.

Provides basic car-navigation system functions Route navigation avoiding congested areas


A1 A2 A3

A6A5A4

A7 A8 A9

Overview of the method (1/2)

The map is divided into areas.

Granularity of area is decided according to the amount of traffic and road density.

Cars measure time to pass through each area using GPS.Traffic info. can be collected by exchanging info. between cars.


Overview of the method (2/2)

Arrival time can be estimated by summing up time to pass through areas

A1 A2 A3

A6A5A4

A7 A8 A9

1’20’’1’40’’

S

D

tA7

tA4 tA5

tA2

tA7’

tA8

tA5’

tA2’


Outline

Step 1. Collection of traffic info. Collecting time to pass through each

area Propagation and retention of collected

info. Avoiding redundant processing of same

data Exchanging data with priorities

Step 2. Estimating arrival time


Challenges for accuracy

Distinguishing time between turning right/left and going straight is crucial

Especially, time needed to turn right is largely influenced by the opposite lane


Problem of per-link measurement

• How can time to turn right/left and go straight be distinguished?

Collecting info. on a per-lane basis is hard Too much data by collecting on a per-link basis


Per-area measurement

Collecting data for each combination of incoming and outgoing link Time to turn at crossings is reflected

Area borde

r

24 sec

38 sec


Time to pass through area

Measuring time for each combination of two links crossing area border

G

EA

H

IB

D

C

F

a

e

d

c

b

Blue links cross area border

Red dotted lines are area borders

Links Measured time( a , b ) 150 sec( a , e ) 220 sec....

For the area at the center, time is

measured for each two combination of

blue links


Outline







Area border

Exchanging info. between cars

When a car crosses area border, it broadcasts its info

When another car receives this info, it adds the info into its memory

The car continues to broadcast data for some time


Adjacent areas The original area the info is generated at

Retention and disposal of data

• Info. for an area adjacent to the area a car is running at is retained.


Retention and disposal of data

Here, this car disposes

info.

• Info. for an area adjacent to the area a car is running at is retained.

• When a car goes off from these areas, it disposes the corresponding data


Outline







Redundant counting of same data

Average area passage time to be obtained

Data from multiple cars have to be collected

Data originated from one car is exchanged through many cars, and treated as multiple dataA

A

(A+B)/2

(A+C)/2

(A+A+B+C)/4 ?!


Avoiding the problem

Avoiding redundant processing of area passage time Measured time by each car is not

processed until a car gets a sufficient number of dataThen, data are converted to statistical data

Ignore received data if it has a same set of data as data retained.

Avoiding redundant processing of statistical data Distinguish redundant data by hash

value


Avoiding redundant counting

5 sets of data7 sets of data

AA


Avoiding redundant counting

AA

If a same set of data is included in the received data, it's ignored.


Exchanging data between cars

The case when threshold C = 10

5 sets of data 7 sets of data


Exchanging data between cars

The case when threshold C = 10

5 sets of data7 sets of data

C sets of data is converted to one statistical data

10

Remainder


AA

Avoiding redundant processing of stat. data

Each stat. data include hash value calculated from car IDs

Stat. data

A

A

Compare hash value, and discard if it has already the

same data


Outline







Exchanging information

All information cannot be exchanged due to bandwidth limitation

Data is prioritized based on where the car is running at, and how the areas are congestedMi

d HighHigh

High

Mid

Low

Low LowMid

Position of the car


Evaluation

Experiment 1 Gain of accuracy by avoiding redundant

processing

Experiment 2 Gain of accuracy by prioritized data transmission

Experiment 3 Overall accuracy of estimated arrival time


Common configurations

Area size 300 m×300 m Radio range 100 m Max speed of cars 16.6 m/s (60

km/h) Threshold C 5 Size of packet 1500

byte Max # of packets sent by a car

0.3 packets / sec

Duration of each packet 0.01 sec Duration of simulation1 hour Time to live of info. 30

minutes Number of cars 300 at

maximum


Traffic simulator ： NETSTREAM by TOYOTAMap size ： 1.2km×1.2kmThe number of nodes ： 21The number of links ： 78


Gain of accuracy byavoiding redundant

processing

0

20

40

60

80

100

120

A B C D E F G H ILink Pair

Pas

sage

Tim

e (s

ec.) No avoidance

Our method

Actual time

If no avoidance, obtained time is much closer to the mode


Gain of accuracy byprioritized data transmission

0

20

40

60

80

100

A B C D E F G H ILink Pair

Pas

sage

Tim

e (s

ec.)

No prioritizing

Our method

Actual time

Data is lost

Only two cars have data

Loss of information is avoided by prioritizing


0

20

40

60

80

100

120

140

(A,O) (B,P) (C,Q) (D,R) (E,S) (F,T) (G,U)

(Area 1, Area 2)

Pas

sage

Tim

e (s

ec.)

Estimated time vs actual time

Estimated

Actual

A1A2

A

O

B

C

P

Q


Conclusion

We proposed an autonomous collection method for traffic information

We evaluated our method using the traffic simulator NETSTREAM

Future works include Dissipating information to further area Making it works correctly with very few

cars on the road

32V2VCOM 2006 - N. Shibata et al.

Shibata, N., Terauchi, T., Kitani, T., Yasumoto, K., Ito, M., Higashino, T.: A Method for Sharing Traffic Jam Information Using Inter-Vehicle Communication, The 2nd International Workshop on Vehicle-to-Vehicle Communications (V2VCOM) (Mobiquitous2006 Workshop), pp. 1-7 ．DOI:10.1109/MOBIQ.2006.340428 [ PDF ]

July 21, 2006

http://dx.doi.org/10.1109/MOBIQ.2006.340428

http://ito-lab.naist.jp/themes/pdffiles/060725.shibata.v2vcom06.pdf

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