Monday, December 3, 2012

The Phantom Traffic Jam - An Explanation

They appear from out of nowhere, cause chaos for hours on end, and then disappear without a trace. They are the 'phantom traffic jams' - queues of stationary cars that develop for no apparent reason - and they seem to happen very frequently on Rande bridge.

They have the power to completely ruin a bank holiday. It has been revealed that phantom traffic jams can be caused by the actions of just one driver: under the right conditions, one individual's bad driving can create 'a traffic tsunami which can affect traffic up to 50 miles away.

The major cause of congestion was nothing more sinister than sharp braking, unnecessary lane changes and lorries overtaking one another: Under the right conditions, any one of these innocuous events can create the 'perfect storm' which can lead to 'traffic chaos'. A minor event such a car's lane change can cause the all the vehicles around it to slow down slightly. This very small difference in speed is magnified as each vehicle behind the original car slows down a little more.

This process creates 'stop and go waves', whereby huge sections of motorway traffic are forced to travel slower than they should. The stop-and-go waves are generated by very small events at the level of individual vehicles. In certain situations a tipping point is reached that magnifies small effects to create large changes that can involve hundreds of vehicles and which may be a couple of miles long. If there is just one error than this can usually be absorbed by the surrounding vehicles, but if others are forced to swerve, brake or change lanes suddenly this has a ripple affect. Then when drivers travel through the jam, they are confronted by open road and are on their way again.

Oddly enough, drivers may be able arrive at their destination faster if they travel slower. There is a real benefit if you can get people going at a constant 50mph rather than stopping and starting at 70mph. If you slow cars down you get better fuel economy and faster journey times.

No copyright infringement intended. For educational, non-commercial purposes only.


  1. Butterfly effect… I hate when some cars persist in driving along the left lane instead of moving to the right one when overtaking is over. Anyways, I wouldn’t mind being stuck for some time at Rande Bridge so I could admire the amazingly beautiful landscape there ;)

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