The problem of bottleneck that does not have to be neck breaking

One of the most common problems that traffic engineers have to solve is that of bottle-necks – or differential of capacity between two road sections or more. As a traffic engineer, I had to deal with this ‘Capacity’ problem but never asked myself:  Why does this problem occur in the first place.

On the surface, it seems that the cause is due to the difference in physical dimensions of converging roads. Take an imaginary example:  A cross road.  The east-bound road has 4 lanes, the other 3 roads have 2 lanes. Most traffic heads straight across the junction so the traffic travelling in 4 lanes has to pack themselves  into 2 lanes.
A queue is formed and delay experienced.

A classic engineer solution would be either:

a) Widening the east arm by add a flare to accommodate the traffic, allowing it to merge in row somewhere away from the junction, or

b) Adjust the traffic signal to increase the throughput capacity, or

c) Redesign the junction perhaps by creating a roundabout or, if space and budget allow, a grade separated junction.

Very well….

I have completed the design, checked the capacity, budgeted the cost, carried out accident analysis, written the report and handed it to the client.  Job Done.

Did I ever ask myself what are the causes of the problem in the first place? No.  It was not my scope, not part of the brief. As a young transport engineer I never questioned the brief.

But now I think I have the right to question.  As the money that will be used to build a roundabout is actually our tax money, I think I have a civic duty to ask: “What are the causes of this problem.  Why are there bottle necks?  Differential in capacity?  Why does it happen in the first place?”

This turning point came when I reading Prof. Knoflacher’s paper – “The Backside of the Coin”.

Differential in capacity occurs because somewhere someone decided it was a good idea to build a road to accommodate more cars.  To relief traffic jam, to increase capacity.  But isn’t it the capacity that creates the jam in the first place?  Hence more capacity – more cars – more jams and then… what next? Gridlock?

Congestion on the motorways is  not a signal for a too few capacity, but much more an indicator of too strong positive irritation to the public and the economy to use the car or truck – it is a clear signal for too much capacity and not too few” Knoflacher

Are we solving the cause or using a sticking plaster on a wound which requires major surgery?

It is not too late to ask this question before handing in that report to the client.   We, engineers, have been “solving” traffic problems the same way for too long. Perhaps it’s time to say to the client, the answer is not building more roads but increasing the efficiency of public transport on the routes affected and discouraging the use of private cars. Why not make the job more interesting for ourselves?


The backside of coin full paper here

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