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), (July 2006) , pp. 1-7, DOI:10.1109/MOBIQ.2006.340428 (invited paper). http://ito-lab.naist.jp/themes/pdffiles/060725.shibata.v2vcom06.pdf

1. A Method for
Sharing Traffic Jam Information
using 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

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

3. 3July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

4. 4July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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.

5. 5July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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’

6. 6July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

7. 7July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

8. 8July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

9. 9July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Per-area measurement
Collecting data for each combination of
incoming and outgoing link
 Time to turn at crossings is reflected
Area
border
24 sec
38 sec

10. 10July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Time to pass through area
Measuring time for each combination of two
links crossing area border
G
E
A
H
I
B
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

11. 11July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

12. 12July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

13. 13July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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.

14. 14July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

15. 15July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

16. 16July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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 data
A
A
(A+B)/2
(A+C)/2
(A+A+B+C)/4 ?!

17. 17July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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 data
Then, 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

18. 18July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Avoiding redundant counting
5 sets of data7 sets of data
AA

19. 19July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Avoiding redundant counting
AA
If a same set of data is included in the
received data, it's ignored.

20. 20July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Exchanging data between cars
The case when threshold C = 10
5 sets of data 7 sets of data

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

22. 22July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

23. 23July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

24. 24July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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 congested
Mid High High
HighMidLow
Low Low Mid
Position of
the car

25. 25July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

26. 26July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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 simulation 1 hour
 Time to live of info. 30 minutes
 Number of cars 300 at maximum

27. 27July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Traffic simulator ：NETSTREAM by TOYOTA
Map size ：1.2km×1.2km
The number of nodes ： 21
The number of links ： 78

28. 28July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Gain of accuracy by
avoiding redundant processing
0
20
40
60
80
100
120
A B C D E F G H I
Link Pair
PassageTime(sec.)
No avoidance
Our method
Actual time
If no avoidance, obtained time is much closer to the mode

29. 29July 21, 2006 V2VCOM 2006 - N. Shibata et al.
Gain of accuracy by
prioritized data transmission
0
20
40
60
80
100
A B C D E F G H I
Link Pair
PassageTime(sec.)
No prioritizing
Our method
Actual time
Data is lost
Only two cars have
data
Loss of information is avoided by prioritizing

30. 30July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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)
PassageTime(sec.)
Estimated time vs actual time
Estimated
Actual
A1
A2
A
O
B
C
P
Q

31. 31July 21, 2006 V2VCOM 2006 - N. Shibata et al.
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

32. 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 ]
32July 21, 2006 V2VCOM 2006 - N. Shibata et al.