The police have taught Kenyans to disobey traffic lights

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

22 December 2019

I drove from the Jomo Kenyatta International Airport to the city centre on Monday 25th November and had a fairly smooth journey. I started off at 2:31pm and reached the Kenyatta Avenue roundabout at 2:58pm. That is, 27 minutes to travel 16km on one of the most congested roads Nairobi.

My journey was interrupted for 9 minutes by a traffic police officer manning that junction. We were allowed to move on at 3:07pm. I reached my final destination (the Lifestyle parking lot) at 3:10pm.

A 17km-trip took me 39minutes, out of which the final one kilometre took 12 minutes. To put that in proper perspective; the last 5 percent of the journey took 30 per cent of the time!

After parking the car, I looked back and thought about my trip. There are four major intersections along the route: the roundabouts at Lusaka and Bunyala roads, and at Haile Selassie and Kenyatta avenues.

There were no police officers controlling the traffic at the first three roundabouts (Lusaka, Bunyala and Haile Selassie). Motorist snaked their vehicles through and passed fairly easily. But at the Kenyatta avenue junction, an officer stopped us for a full nine minutes.

Now, I have always wondered why anyone would stop the movement of vehicles on a busy city road for such a long time. Furthermore, why the authorities invest so much (time, effort, money, human skills, etc.) on the installation and maintenance of traffic control lights and then post police officers to direct the movement of vehicles.

I suspect that the extended stops are result of lack of understanding of traffic dynamics. I think the police officers aim to open the flow from each direction for about three minutes. Unfortunately, this means that each approach has to wait for the other three to go before moving.

Three approaches each getting three minutes makes a total of nine minutes of waiting. To improve the flow, the “go time” for each stream of vehicles should never be more than 30 seconds. With this timing, the waiting vehicles are stopped for a maximum of 90 seconds. Thus, a full cycle lasts for 120 second.

Since the numbers of vehicles approaching the junction from each direction is not the same, the traffic control timing is adjected so that the approach with the heaviest density gets more time. However, the total cycle time must be maintained at 120 seconds.

I think this is part where our traffic control officers make a big mistake. Instead of keeping the cycle period constant, they increase it to give more time to the stream that has more vehicles. The result is that the other streams are kept at a standstill for very long times.

Finally; why do we install traffic lights and then post officers to direct the flow? The usual explanation is that Kenyan drivers do not obey the lights. I think that is a lame excuse. In my view, the reason Kenyans don’t obey traffic lights is that they have been taught by the police to ignore them!