Variable Speed Limits and Smart (Dumb) Motorways

The UK is in the middle of a program to implement Smart Motorways on various M and A roads. The intent of these is to allow the hard shoulder to be used as a normal lane except in the event of an accident whereby the variable speed limit signs will mark the lane as out of operation. This seems like a smart idea until you realise the competence of the current variable speed limits.

Variable speed limits can only work if the traffic is capable of travelling faster than the proscribed speed. They can only slow the traffic down. If the variable speed limit is set above the current speed of the road then it is wasting it’s time. This is the majority of uses of the variable speed limits. In addition these limits are kept in place far longer than the problem exists. I have frequently travelled through speed restrictions on the M25 where no broken down car or lose animal was visible. I call the problems these cause artificial traffic jams.

We have an organisation controlling the speeds on motorways that seems unable to reliably determine that a problem has been resolved. Given that this is a similar problem to detection when a breakdown has happen we will have no hard shoulders and traffic just breaking down on the roads.

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