Research Trends and Results

Field Operational Tests to Examine the Driving Practicefor Congestion Mitigation at Sag Sections
Research Center for Advanced Information Technology, Intelligent Transport System Division
KANAZAWA Fumihiko, HeadSUZUKI Kazufumi, Researcher
IWASAKI Ken, Guest Research Engineer(Key words) expressway sag sections, traffic congestion mitigation program, Field Operational Tests
1. Introduction
About 60 percent of the traffic congestion on highways
occurs at an upslope of sag sections. It easily causes achange on the inter-vehicle spacing by involuntary speed
reduction at sag sections which gently changes the gradeof the road from down to up. It is also considered that an
unstable traffic flow due to the excessively long or shortfollowing time gap is a factor of traffic congestion.
Therefore, information providing services have beendeveloped: (a) information providing service for drivers
to recommend the driving practice which leads smoothtraffic flow before traffic congestion occurs via ITS Spotscompatible car navigations and/or other devices, and (b)services integrated with ACC (Adaptive Cruise Control)vehicle which is able to maintain a certain vehicle speed
and/or following time gap that has been commerciallyavailable in recent years as a vehicle advanced
technology, in order for preliminary detection of traffic
congestion by road side sensors1). This article reports asummary of the field operational test (FOT) for (a) thatwas conducted on the public road to carry on a basic
study to find possibility of the service actualization anddrivers’ acceptance and effects on traffic flow.
2. Driving practice for traffic congestion mitigation at sag
sections
This service expects traffic congestion mitigation interms of realizing smooth traffic flow by adjusting
excessively long or short inter-vehicle spacing by
requesting drivers to maintain a certain inter-vehicle
spacing at traffic congestion-prone point such as sag
sections described on Figure 1. For actual drive practice
to keep a certain following time gap, the drivers’ ease ofacting is considered while remaining smoothness andsafety, thus it was targeted to maintain as fixed for thefollowing time gap (time interval from the passing offront vehicle to the driver’s vehicle at a certain spot) as 2
seconds.
3. Summary of driving test on public road
The driving test was conducted at Yamato sag section
Tomei highways (20.0kp~23.0kp) and was conducted in
the early morning on Saturdays and national holidays atwhich traffic demand excess in November and January
2012. To conduct the experiment at a higher traffic
volume before occurrence of traffic congestion on thepassing lane to confirm the effects of a certain control ofinter-vehicle spacing time, it was chosen at 120 vehicles
or more / 5 minutes as a condition of the experiment start.

Fig. 1 The inter-vehicle spacing optimization service by roadvehicle coordination.

It was prepared 8 passenger vehicles as experimentvehicles.
At the FOT to maintain the following time gap 2
seconds, subject drivers (collected from general drivers)
were asked to count the following time gap by verballycounting“0102(zero, ichi, zero, ni, pronunciation of zero,one, zero two in Japanese)”2) while driving, in order toconfirm possibility of actualization and acceptance tomaintain a certain following time gap. Also, to analyze
the change of the traffic flow rate, change of eachfollowing time gap by putting vehicles that maintain acertain inter-vehicle spacing, occurrence and propagation
status of deceleration shockwave, driving behavior datasuch as the vehicle location of latitude and longitude,speed, acceleration and deceleration speed were acquiredby GPS logger mounted on the test vehicles in addition tovideo image of the roadside cameras.
4. Conclusion
Utilizing the data collected from this driving test, thetraffic congestion mitigation effects by mixing ratio of
vehicles that maintain a certain following time gap willbe identified by the traffic simulation and the more
effective information service method for drivers will bestudied.
【Reference】
1) Intelligent Transport System Division web site
Traffic congestion mitigation program integrated withroad information and vehicle control technology
http://www.nilim.go.jp/lab/qcg/kadai/acc/acc.html
2) "For expressway users" (Metropolitan Police
Department web-site)
http://www.keishicho.metro.tokyo.jp/kotu/kousoku/osirase1.html