Wednesday, January 30, 2013

When the logical road solution isn't always the right one.

Water pipe replacement work is being carried on in Stourport at the moment necessitating a set of controlled traffic lights to allow traffic through as these sit at a three-way junction it would seem logical to put up a set of three way traffic lights. Instead a set of two-way were placed at the junction itself; yesterday they were switched out for a three-way set and this morning back to a two-way. The question is why?

The junction itself in simplistic terms is a straight North-South run with a West side junction. While a two-way set of lights were in effect proceedings were as follows:

Traffic heading South on the main road continued only while the light was green; if they wished to make a turn West they did so at the end of the roadworks just before the stopped Northbound traffic. Traffic heading North on the main road were also required to wait for green; however should they be at the head of the queue and wish to turn West it was easily accomplished on a red light provided no Southbound traffic prevented them. For traffic from the West the rules were a little more complicated.

To head North was only possible on a green light, but would require beating or merging with any other Northbound traffic on the main road. To head South, however, could be accomplished on either a red or green light provided no traffic on the main road prevented it.

The lights were controlled but even with a timing switch the two main streams of traffic would have to wait perhaps a maximum of 2 minutes before the lights changed.

With the alteration to a three-way set of lights all traffic could only move on green. Traffic turning West from the South was now unable to reach the junction to turn on red and must wait also. If the lights were on a timer the wait now doubles as each take their turn. The natural flow of traffic from the West junction is halted. Logically the queues forming at this point should be reduced as they now have an absolute right to proceed at intervals, but the cost is extended queues on the main road. How extended?

Stourport has always had problems with its road network. Consider it a crossroads with the junctions connected by a narrow one-way system. In the mornings the majority flow is from the North, South and West exits outward to the North and East; while in the evening the flow reverses from North and East to North, South and West. In essence the lights blocked the South exit. In theory this should have no effect on the other exists, but as I said it's connected by a one-way system.

Traffic from the North wanting to travel West was unaffected. Traffic from the North to South or East to South of course was. However traffic from the East to North became blocked by the traffic trying to travel South. In turn this prevented lesser traffic from the West travelling either South or East.

This simple change resulted in evening rush hour traffic shifting from a queue stretching 0.1 miles along a single stretch of road into a a multi-tailed queue stretching out to at least 2 miles.

The lesson to learn is to understand and appreciate the traffic flows of wherever is being disrupted.