What’s used to reduce traffic bunching on a motorway?
A: Variable speed limits
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B: Contraflow systems
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C: National speed limits
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D: Lane closures
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Congestion can be reduced by keeping traffic at a constant speed. At busy times, maximum speed limits are displayed on overhead gantries. These can be varied quickly, depending on the amount of traffic. By keeping to a constant speed on busy sections of motorway, overall journey times are normally improved.
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Traffic bunching and variable speed limits
In an Exeter University study reported in the Independent:
They discovered that under certain conditions, when cars are bunched in a specific density and travelling at a specific speed, a single driver over-reacting can set off a braking shockwave that will build momentum and travel back along a motorway for miles.
Variable speed limits, which can be controlled manually or automatically, can help reduce this type of effect which can be quite significant. Below is a very short video in which scientists recreate traffic bunching on a circular road.