Ir. Bernat Goñi Ros, Dr. Victor Knoop, Prof. Bart van Arem, Prof. Serge Hoogendoorn
Delft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Transport & Planning Tel. 015 27 84912 / b.goniros@tudelft.nl
Impacts of Car-following Behaviour on
Traffic Flow Capacity at Sags
Introduction
Congestion frequently occurs at sags:
Capacity decreases on the uphill section.
Congestion generally forms first on the fast lane(s) and then it spreads to the slow lane(s).
The factors triggering congestion on the fast lane(s) have not been clearly identified yet.
Research objective
To determine whether changes in car-following behaviour or lane changes are the main factor reducing the capacity of the fast lane(s) at sags.
Data characteristics
2284 vehicle trajectories (including lane changes) collected by means of 10 video cameras located 120 m apart from each other along a 3-lane sag of the Tomei Expressway (near Tokyo, Japan), during the morning peak hour. Sample:
Change in gradient (sag) 1. Changes in car-following behavior Capacity reduction 2. Lane changes High traffic demand Congestion
Findings
Finding 1. Drivers tend to keep longer time headways on the
uphill section than on the downhill section at similar speeds:
Finding 2. Most traffic flow disturbances (89%) are triggered
by car-following instabilities instead of lane changes (11%):
Speed disturbances propagating upstream
Cause of speed disturbance formation and growth: Car following instabilities Lane changes
Conclusions
The results show that car-following behaviour changes on the uphill section, which reduces capacity.
Furthermore, these changes in car-following behaviour are the dominant factor reducing the capacity of the fast lane(s) at sags. Lane changes are a less important factor.
21.0 22.0 20.0 23.0 km Eleva ti on +2.4% -0.5% -1.9% Bottleneck 1000 1010 1020 1030 1040 1050 1060 1070 1080 1090 1100 400 500 600 700 Time (s)
Location from the sag bottom (m)
Median lane 30 40 50 60 70 80 90 100 110 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Vehicle speed bin (km/h)
Average time headway (s)
Median lane Downhill section Uphill section 06:40:00 06:45:00 06:50:00 06:55:00 07:00:00 07:05:00 50 km/h, C2 50 km/h, C3 50 km/h, C4 50 km/h, C5 50 km/h, C6 50 km/h, C7 50 km/h, C8 50 km/h, C9 50 km/h, C10 Time (h:min:s)
Speed, Camera number
