Road expansion not the solution to traffic jams

Every transport engineer knows that you cannot reduce traffic jams by building bigger roads! One wag put it in a more dramatic way: “Building bigger roads to reduce traffic is like buying larger clothes to reduce weight!” If you doubt it, check out the Thika Superhighway.

In December 2007, I wrote a piece here arguing that it would be a waste of money to expand the Mombasa highway into a dual carriage way. I arrived at that conclusion after driving down to the coast and counting the number of vehicles in a 100km section of the road – it was so deserted that I could drive and count at the same time!

Over the last 20 years, I have been driving down that road at least once a year; all except 2013 and 2014. So I was shocked when I did the trip two weeks ago after the two-year break: the number of lorries is simply unbelievable.

You can hardly drive for one kilometre before pulling up behind a convoy of five trucks crawling along at 45km/h. Consequently, the average speed for a personal car has gone below 50km/h. I started off my journey at 5am and arrived in Mombasa at 4 pm!

ONE CONTAINER AT A TIME

Upon arrival, I saw a promotional billboard by the Kenya Ports Authority and immediately realised the source of the problem. It proudly proclaimed: “One million containers handled in 2014.”

Obviously, that meant 500,000 were loaded onto ships and 500,000 were off-loaded. 500,000 per year works down to about 13,700 per day or 570 per hour. That is; every hour, 570 containers entered the port and another 570 left.

I estimate that 70 out of the 570 carried goods for Mombasa and its environs and the remaining 500 were for upcountry and export destinations. Furthermore, I guess that the old railway carried 100 containers leaving 400 for the lorries.

The challenge of carrying containers this way is that a lorry can only carry one container at a time! Therefore, there were 400 trucks leaving Mombasa every hour in 2014 and another 400 arriving.

Now, as a former truck driver myself, I know that most have a top speed of 80km/h (I can’t understand why the government insists on speed governors!) and they normally cruise at between 50km/h and 60km/h.

If we “inject” lorries into a highway and they move at 50km/h, the first one will have gone 50km in one hour. “Injecting” at the rate of 400 per hour means that this 50km stretch will have a queue of 400 trucks.

400 trucks in 50km of road works down to 8 per kilometre. Turning this up-side-down, we find that there will be one truck after every 125m.

These are just trucks: now add buses and private cars in the remaining space and you will see that we are soon going to break the world record for the longest traffic jam!

For that reason, the construction of the standard gauge railway is a step in the right direction. We need it urgently.