Mainstream traffic flow control at sags using variable speed limits

Themes: Structural Engineering, Infrastructure & Mobility / Transport

Proof of principle

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Traffic congestion has negative impacts on the performance of freeway networks. In hilly countries (such as Japan), sag vertical curves cause many traffic jams. We are developing a traffic management concept aimed to reduce the severity of congestion at that type of freeway bottlenecks.


Variable speed limits are applied on a freeway section upstream of the sag vertical curve, keeping the traffic inflow to the bottleneck below its capacity. Consequently, traffic never becomes congested at the bottleneck. Traffic becomes congested on the variable speed limit section, but that congestion is less severe than if it occurred on the sag vertical curve.


We carried out a proof of principle using microscopic traffic simulation in 2013. Considering its potential benefits, we expect that this technology will be developed further. Traffic management services based on this technology could be ready for implementation in five years.

Ir. Bernat Goñi Ros


Dr. Victor Knoop

Prof. dr .ir. Bart van Arem

Prof. dr. ir. Serge Hoogendoorn