Road signage decisions (1)

Until the 1970s, Exeter was known for the regular congestion on the by-pass every summer.  Because the main roads to the south-west of England converged on the city, and the by-pass was constricted by a narrow bridge over the Exe and the Exeter Canal, traffic queued for hours.  Today, the congestion and queues are not so severe, and generally there is good flow of traffic. 

One section of the “old by-pass” (as many people know it) is blocked by a roundabout (at Countess Wear, for UK readers).  There traffic is controlled by lights, to ease the flow of commuters.  There are two lanes from the north-east, one for traffic going left and ahead, one for traffic going right.  (Remember, we Brits drive on the left!)  A couple of hundred yards before the lights, there is a sign advising motorists of this division of the lanes.  Unfortunately, most evenings, the traffic backs up for a greater distance.  Regular users of the road know that they must get in the correct lane as soon as possible, but the stranger does not have this knowledge, and often there are scenes where a driver has to force his or her way into the other queue, when the error is discovered.

So here is a planning or decision problem.  Where should the advance signs for traffic lanes be placed?  And how many should there be? 

And there is a deeper question.  Many road signs are only relevant to a minority of road users.  Regular users of a stretch of the highway will know which lane to use, and what is ahead of them.  They will concentrate on driving, because the route, and its condition, are familiar.  The visitor, the stranger, the newcomer, these are the people who need the information.  But, the regular user needs to be told when there is a change.  So how do you communicate information to those who need it?