Junction design and traffic management

Fashions for road junction design differ greatly across the country. In some towns such as Milton Keynes the roundabout is king with scarcely a traffic signal in sight. In others such as Northampton Traffic signals appear at every opportunity.

In both cases it is nearly always the junction capacity that is the limiting factor. Are the current designs sensible?

In rural areas dual carriageways with two lanes in each direction often have roundabouts offering no more than two lanes at the stop lines. That ensures that the capacity of the road between the junctions can seldom be used to more than half its potential since the traffic at the junction may have to give way half the time. The solution is to provide either double the number of lanes at the junction as are on the approach, or a flyover.

However, instead of doubling the number of lanes we often find road markings assigning each of the existing lanes to a particular turning movement. That reduces capacity if one of the movements is relatively small compared with the others. The reason for the markings is both to direct motorists and to reduce accidents. There is also a belief that a multi-lane, widened approach will cause accidents. The same arises at traffic signals where, particularly in Northampton, the town is being brought to a near standstill by allocating a “phase” to each and every movement. Consequently queues now abound where none previously existed.

A good design with the exit double the width of the approach.	Prescriptive road markings on the roundabout approach at centre guarantee the queue.	More prescriptive road markings to the right guarantee unnecessary queues.

Probably the answer lies in designs, which reduce speeds through the junctions to 10-15 miles per hour, so that motorists have eye contact, and to remove the road markings.

Then there are one-way systems and the banned turn - forcing motorists to drive miles further than necessary. Often those banned turns and one-way systems impose greater delay and cause more accidents than the apparently more dangerous and congested original layout. Illustrations from Northampton include:

1. Banned right turns at:
   
   (a) The access to a new development (Canterbury Court). There those wishing to turn right on leaving the development have a 2.5 km round trip via a large signal controlled gyratory or the option of U-turning via intermediate garage forecourts etc. Those wishing to turn right into the development have a round trip of at least 1 km via a set of signals and a roundabout, or the option of turning left and U-turning in a side road opposite the development.
   
   (b) Quorn way – the access to a small industrial estate. There a lorry wishing to turn right into the estate would have great difficulty in reaching the destination without driving several miles.
   
   
2. Banned left turns. These are quite extraordinary, forcing peculiar detours upon those wishing to make a movement which would otherwise be simple.
   
   
3. One-way systems, in the town centre and on housing estates, which force miles of unnecessary driving.

Such layouts increase accidents and pollution as well as wasting valuable time across the nation. Transport Watch invites others to provide similar examples.