“Dualising” Mombasa highway would be a waste of money

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

30 December 2007

Would it make economic sense to upgrade the Nairobi-Mombasa highway into a dual carriageway?  That was the question that I pondered to kill time while driving the 500km distance recently. I was somewhere between Voi and Mariakani when the thought came to mind. Then it suddenly occurred to me that this road is not busy – it is actually deserted.

Consequently I embarked on a little experiment. I timed how long it would take to count twenty vehicles (not just cars, but lorries and buses as well) coming from the opposite direction. The result was about five minutes. That done, I concentrated on the road ahead: when cruising at 120km/h, you don’t want to entertain distractions from your driving!

At the end of the journey (and after a well deserved rest), I got down to crunching the figures. The objective is to find out the average vehicle density on the highway. To get that, we start by finding out what distance I travelled in the five minutes of my experiment.

At 120km/h, I was covering 2km every minute. This is obvious if you bear in mind that one hour has 60min. Thus 120km/h means 120km in 60min; which is 2km in one minute. Therefore, in five minutes at that speed, I had covered ten kilometres.

Now, if the twenty vehicles in the other lane were stationary, this calculation would end here and the final result would be two per kilometre, or one every 500 metres. That is a very low density – picture one car at Nyayo house roundabout and the next one at the university way junction…

But these vehicles were also moving, so we need to adjust the calculations accordingly. I estimate that the private cars were cruising at 120km/h (like mine – the road is so smooth that you don’t realise when you go above the speed limit) and the big lorries and buses were doing 80km/h. This means an average speed of 100km/h. (Ideally, I should have counted the numbers of the various sizes of vehicles and weighted their speeds in order to get a more accurate average. But remember, I was driving – at 120km/h!)

When I am driving at 120km/h and there are vehicles approaching me at 100km/h, the net result is that they appear to be hurtling at 220km/h. In five minutes at that speed, each vehicle in from will have travelled 18.3km. And in that distance, there are 20 vehicles.

Therefore, the true distance between these vehicles was about 900 metres. Clearly, this is a ghost highway! Making it a dual carriageway would be a waste of money.

If it is that deserted, why is there so much talk about “dualising” this road? Well, many travellers take this journey on the night buses and fall asleep a short distance from either city. Thus they don’t realize that 400km of the 500km drive is a deserted ghost highway. And the politicians harping on the idea either fly or travel in convoys of their own vehicles!