●Research Trends and Results
Empirical study of traffic smoothing service at sag sections on
expressways by means of vehicle to infrastructure communication
KANAZAWA Fumihiko, HeadSAKAI Koichi, Senior Researcher
SUZUKI Kazushi, Researcher
IWASAKI Ken Guest Research Engineer
Research Center for Advanced Information Technology, Intelligent Transport System Division(Key Words) Sag or ascending slope, road-vehicle links, adaptive cruise control, traffic smoothing, traffic simulation

Road situation
clarification
Basedon gradient 道路状況把握sensor
勾配情報、交通センサ
information and
状況を踏まえた
traffic situation,
走行速度・車間provides
travelingspeed,
headway etc.
時間などの提供

Information
provision
情報提供用
antenna
アンテナ
Clarifying
macroscopic
マクロな交通traffic
situation
状況の把握
Existing
既存のtraffic
counter
トラカン

Sensing
traffic situation
きめ細やかな交通状況（交(trafficflow) in detail通流）のセンシング

Road-vehicle
路車間通信
communication

I 適切な車間を維持し、
will follow maintaining an
追従走行
appropriate
headway.
I適切な車間を維持し、
will maintain a suitable
headway to prevent
減速波（ショックウェー
transmissionof a shockブ）の伝播を抑制
wave.

：ACC車両
ACC vehicle
None ACC vehicle：非ACC車両

Figure 1. Image of the Service Linked to ACC Vehicles
25120
100%24.7 24.4

100

22.5
20.4

97%

2080

79%
13.3

1560

46%

1040

5.2
520

17%

1%

9%

0.8

070%

100%

0Reduction rate (%)

Congestion loss hours (at1,000 vehicles)
渋滞損失時間（ 千台時）

30削減率（％）

1. Introduction
Approximately 60% of congestion on inter-city
expressways in Japan occurs at sags or ascending
slopes. The Intelligent Transport System (ITS)Division is conducting a series of research projects
intended to develop a new service for mitigating
traffic congestions by means of vehicle toinfrastructure (V to I) communication at sags orascending slopes1). Congestion at sags or ascending
slopes occurs as a result of drivers unconsciously
slowing down at the points where gradient changes
and driving aimlessly after encountering congestion. It
is possible to restrict or prevent these negative humanfactors by taking advantage of ACC vehicles’(Adaptive Cruise Control equipped vehicles)characteristics, which can control their speed andheadway, so this service would contribute to mitigate
congestion at those points.
A microscopic traffic simulator was built to clarify
the congestion mitigation effects of the inclusion ofACC vehicles. This paper will report the results of aseries of trial calculations of congestion mitigation byusing the microscopic simulator.
2. Congestion mitigation measures by means of
ACC vehicles to Infrastructure communication
Figure 1 shows an image of the service which uses
V to I communication, and which was the object of theestimation of congestion mitigation effects based on
inclusion of ACC vehicles. In response to information(for instance: appropriate traveling speed, headway,etc.) provided from ITS Spots (road side units), ACCvehicles activate their ACC function to maintain apreset speed or headway.
3. Trial calculation of congestion relief effects of
ACC vehicles
To clarify the congestion mitigation effects ofincluding ACC vehicles, the microscopic traffic
simulator capable of reproducing the unique vehicle
behavior on sag sections and ascending slopes alreadyclarified by past research2) was built to trial calculatecongestion mitigation effects. Figure 2 presents thecongestion loss hours according to ACC vehicles
inclusion rate and the rate of reduction from thepresent situation (ACC vehicles inclusion is 0%). The
results of the trial calculation have clarified that themore ACC vehicles are included in traffic flow, the00%

3%

5%

10%

30%

50%

ACC
vehicleの混入率Mixing Rate
ACC車両

Figure 2. Results of Trial Calculation of Congestion Loss
Hours by ACC Vehicle Mixing Rate
more congestion mitigation rate is improved.
4. Summing up
In this report, the results of a trial calculation of themicroscopic traffic simulation show that congestion
mitigation effects increase according to the ACCvehicles inclusion rate. In the future, more detailed
estimations will be made by performing simulations
under different conditions at the same time as theresearch will be conducted to realize the services byconducting feasibility studies.
[References]
1) NILIM ITS Research web site: Congestion
countermeasures based on roadside information –vehicle control technology links
http://www.nilim.go.jp/lab/qcg/kadai/acc/acc.html
2) Jian Xing, Koshi Masaki: Research on thecongestion phenomenon and vehicle following
behavior on expressway sags, Journal of the Japan
Society of Civil Engineers, No. 506, IV-26, pp. 4455, 1995.