It’s too expensive to use police for traffic control

 By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

19 June 2011

Sarah Wainaina feels frustrated by the police officers manning various junctions in Nairobi. She asks a straightforward question: “Why waste money installing traffic lights if we are going to control the movement of cars manually? Is it an attempt to save electricity? If so, then it is not working because the lights are not switched off when the cops are controlling the traffic!”

This got me thinking about the costs of controlling traffic manually compared to using the lights. The main cost of using human police officers is their salaries while in an automated system, the biggest expense is the electricity bill.

The salary scales of the police force are graded from PG 1 through to PG 10. Officers in grade PG 1are paid Sh11,010 per month while those in PG 10 get Sh61,000. We can use the middle of grade PG 5 as an average for the present calculations. This corresponds to a monthly salary of about Sh29,000.

Four officers are needed in a typical roundabout during peak hours – 6am to 9am and 4pm to 7pm. The total duration is equal to almost one working day (8 hours), therefore, we can use the full salary to get the total cost. This comes to Sh116,000 per month.

In the traffic light system, each stream approaching the roundabout has two poles with lights. In addition, there are four poles with pedestrian control lights. There are also two more poles inside the roundabout, adjacent to the incoming lane.

Now, while there are very many bulbs in total, they are never all on at the same time! The Kenyan switching sequence is: red – red+amber – green – amber – red. Thus at any moment, there is only one bulb on – except the red+amber which lasts for one second every cycle. This simplifies the calculation because we don’t have to count the bulbs – just the poles. In total there are 32 poles at a typical roundabout

So, what is the cost of running 32 bulbs continuous from 6am to 9pm (15 hours) every day? The bulbs are rated at between 75W and 100W; that’s an average of 90W. Therefore, they consume about 43kWh (units) of electricity daily.

After 9pm, something interesting happens: the vehicular control lights switch to “amber flashing” mode (on for one second, off for one second) while the pedestrian lights are switched off permanently. The energy consumption for the flashing ambers during this period is at half the rate of the normal operation.

In the 9h amber flashing period, there are 16 bulbs consuming at half-rate; that is, 6.12kWh. Therefore, the total daily consumption is about 49kWh. That is about 1,470kWh in a month.

How much does this cost? The basic charge is about Sh9 per unit which comes to about Sh13,230. But there are additional adjustments, levies and taxes. These vary from month to month but it is fair to assume that the bill almost doubles as a result. Therefore, the total cost comes to about Sh25,000 per month.

Clearly then, this is yet another reason why the police should be removed from traffic control duties. They should concentrate on policing the traffic; that is, arresting motorists who disobey the lights.