Research Trends and Results

Congestion countermeasures by road-vehicle
cooperation using automobile technology
KANAZAWA Fumihiko, HeadSAKAI Koichi, Senior Researcher
SUZUKI Kazufumi, Researcher
IWATAKE Koichi, Guest Research Engineer
Intelligent Transport System Division, Research Center for Advanced Information Technology(Key words) Expressway, sag, congestion countermeasure, ACC
1. Introduction
Approximately 60% of congestion on inter-city
expressways in Japan occurs in sections called sags
where the road gradient is gradually changing to arising gradient, a problem demanding urgent measures.
This division is cooperating with auto makers on
research and development of expressway congestion
countermeasures based on road-vehicle andvehicle-vehicle cooperation of the road infrastructure
and automobiles. This report introduces initiatives
concerning research and developments of thesecongestion countermeasure services.

Road state clarification sensor
Information provision device[2] Maintaining appropriate
following distance with ACC
turned on[1] Urging use of thenearside lane

[3] Traveling without fallingbehind, even on the inboundlane with ACC turned on

Figure 2. Congestion Loss Time According to the Smooth
Traveling Vehicles Mixing Rate
2,500
2,000

Congestion
loss time※(rightaxis)
渋滞損失削減率(右軸)※※
渋滞損失時間Congestion
loss time(左軸)(left axis)

23.6%

2,085

2,080

1,500

1,968
1,592

1,000
500

30%
25%
20%
15%
10%

0.0%

0.2%

5.6%

05%
0%

0%

5%
10%
20%
Smoothtraveling car mixing rate(%)
円滑化走行車の混入率[%]

Congestion loss reduction
rate (%)

Congestion loss time(vehicle-hours)
渋滞損失時間[台時]

3,000

渋滞損失削減率 [%]2. Outline of the service and its expected congestion
mitigation effectivenessThis service provides information from the roadside about traveling methods which effectively
mitigate congestion according to traffic conditions inorder to maintain smoother and more stable traffic
flows by having drivers operate their automobiles
based on this information, using a system that consistsof roadside information provision antennae called ITS
Spots, which are already installed at more than 1,600
locations on expressways as part of the roadinfrastructure, and an automatic control system thatcontrols following distance between vehicles andvehicle speeds at fixed levels called ACC (AdaptiveCruise Control) and which has spread in recent years
as automobile technology (Fig. 1).
To confirm the effectiveness of these congestion
countermeasure services, based on the results ofvarious test drives conducted on test courses, vehicle
behavior models were built and simulation
calculations performed on computers to trial calculate
effectiveness. Hypothesizing a case of relatively
small-scale congestion (congestion of about 15km/h)
with occurrence frequency accounting for about 70%
of all congestion on the Yamato Sag on the outboundTomei Expressway, the rate of decrease of congestion
loss time was trial calculated according to the mixing
rate of vehicles receiving the service and cooperatingwith any one of the driving operations in [1] to [3] inFigure 1 (smooth traveling vehicles) (Fig. 2). The

Figure 1. Image of the Congestion Countermeasure Service
based on Road-Vehicle Cooperation※ Congestion loss time means the time obtained by subtracting the actual traveling time from thestandard traveling time (assuming speed of 70km/h) required when traveling in a certain section.
It was assumed that the average following distance of a smooth traveling vehicle was about 1.75
seconds before the sag and about 1.5 seconds on the rising slope, and that on the rising slope, itfollows the leading car alertly so it does not fall beyond it.

Figure 3. Showcase at the ITS World Congress Tokyo2013

 View of preliminary explanation at thebooth before the participants get in thecar View inside the car during thedemonstration drive (lower right is atable terminal screen displaying
vehicle information)

results indicated that at a mixing rate of smoothed
traveling vehicles of about 20%, the congestion loss
time can be cut by about 24%.

Research Trends and Results
3. Application of the results and future
development
Based on this research, in the showcase event of theITS World Congress held in Tokyo in October 2013,
in cooperation with five domestic auto makers, theworld’s first demonstration drive providing experienceof the service was held, showing off Japan’s advanced
initiatives in this field (Fig. 3).
In the future, we will study advertising and publicawareness-raising methods to increase the social
acceptability of these services and methods ofproviding drivers with easy to understand informationby carrying out questionnaire surveys and performing
testing using test subjects, and at the same time,
perform simulations to clarify the road-vehicle
cooperation system development goals and thecongestion mitigation effectiveness at the nation-widelevel.