How policemen, roundabouts and the lights conspire to create traffic jams

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

10 August 2008

Dan Wambua has been wondering about the roundabouts on our roads. He writes “I read somewhere that there are three ways of controlling vehicles at an junction. These are; a traffic policeman, a roundabout or traffic lights. The article also said that only one of the methods should be used at any one time”.

Dan continues: “But in Nairobi, I see roundabouts with traffic lights and policemen controlling the movement of vehicles. Isn’t this contributing to the chaos that we have on the roads nowadays? And, by the way, why are there lights at the centre of the roundabout?”

If the traffic density at a junction is very low, there is no need of control. The Highway Code demands that drivers give way on a first come, first to cross basis. When the number of vehicles increases, a police officer (or a marshal) may be assigned to control the flow – especially during peak hours. Alternatively, a roundabout may be built if there is there is enough space for it.

Further increase in the number of vehicles will require traffic lights at the roundabout. However, in some countries (like the USA), they go straight from no control to traffic lights!

But to have police controlling the traffic at a junction that has lights defies logic! Drivers learn to ignore the lights and eventually that habit is carried to other junctions. The Bunyala roundabout on Uhuru highway is a good illustration of this – the lights have never been allowed to do their work and motorists hoot angrily at any car that stops when the lights are red!

Lights are installed “inside” the roundabout in order to give room for pedestrians crossing the road. Suppose you were walking from Nairobi city centre to Uhuru Park along the left hand side of Kenyatta Avenue. When you get to Uhuru Highway, you can’t cross if the cars from the city are on green. This is because some of them will go down the highway at the point you intend to cross.

Next, when the cars from the Westlands side are on green, you still can’t cross the road and neither can you when those from Serena Hotel direction are moving. Your opportunity only comes when the vehicles coming from Mombasa Road start moving.

The only problem is that some of these motorists may wish to do a “U” turn at the roundabout. That will leave you very little time (about three seconds) to make a dash to the safe island in the middle of the road.

To avoid this, traffic lights are installed inside the roundabout to stop cars from doing an uninterrupted “U” turn. Thus those from Mombasa Road side will be stopped at the Kenyatta Avenue point before completing the circle.

This gives you enough time to walk (without running) halfway across the Uhuru Highway to the safe island. There you wait for the cars from Mombasa road to be stopped and then you cross into to Uhuru Park.

The only problem is that, thanks to the action by our police officers, many Kenyan drivers do not obey traffic lights at all, let alone those inside roundabouts. So might still have to run!