Roundabouts are more efficient than intersections – that’s according to numerous studies

In the article PSVs, Private Vehicles, decongesting Nairobi’s traffic and the right to access CBD, I argued that the Government (both National and County Government of Nairobi) have willingly ignored the root cause of the never ending traffic jams in Nairobi and have embarked on implementing cosmetic measures to address the problem. The biggest cosmetic measures being implemented is getting rid of roundabouts in high ways leading to Nairobi’s CBD. This implementation started in the middle of last month and heightened during the Easter holidays, and as a result a traffic nightmare has greeted Nairobians the first day of work after the holidays.

There is a myth in Kenya that our traffic problems are caused mainly by the roundabouts. I have heard of this myth from almost every single driver I have had a chance to talk with about the traffic problems and possible solutions. Top of every driver’s suggestion include getting rid of roundabouts, constructing overpasses and/or underpasses, ensuring proper functioning of intelligent traffic control systems and getting rid of traffic police.

In the run up to the implementation of measures to decongest Nairobi roads, the County Government of Nairobi set up a task force to study the traffic problems and come up with a plan to sort out the problems. In the plan unvelied last month, the top priority in short term solution is to get rid of almost all roundabouts in highways leading to Nairobi’s CBD by April 2015. This tells me that that the task force’s finding was sourced from opinions of Nairobi drivers. One such opinion by Arthur Buliva, as posted by BBC, explained the roundabout problem in Nairobi in these words;

 The worst thing that the British colonialists left us with were the roundabouts. These are the main source of traffic problems in Nairobi since the place to which you are headed may be very clear, but because the cars already in the roundabout have the right of way you are forced to wait.

Unpredictable traffic is the way of life here. Even if a place is only a kilometre away, you are safer leaving your house an hour ahead of time or even just walking. But laziness and pride makes walking to be frowned upon. The worst traffic jams are every Friday – when it rains even a little, you can even sleep in the road.

The removal of roundabouts (UK system) is meant to allow Kenya adopt the four way signal intersections (US system). This, according to the joint statement issued by the Nairobi Governor and the Transport CS, would “improve the [traffic] flow by about 30-40 per cent”. In the short to mid term, the statement says that “five (5) roundabouts will be removed and substituted with signalized intersections.”

The immediate question one would ask, in the realization that the Government intends to abandon one system for another, is whether the system being adopted is superior. The best place to get such information, if available, is from the user of the system to be adopted. What does US think of their signal intersections? The Washington State Department of Transportation has the following words on the benefits of roundabouts over signal intersections.

Studies have shown that roundabouts are safer than traditional stop sign or signal-controlled intersections.

Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS). Studies by the IIHS and Federal Highway Administration have shown that roundabouts typically achieve:

  • A 37 percent reduction in overall collisions
  • A 75 percent reduction in injury collisions
  • A 90 percent reduction in fatality collisions
  • A 40 percent reduction in pedestrian collisions

One such study concluded as follows, “In general, the results are consistent with numerous international studies and suggest that roundabout installation should be strongly promoted as an effective safety treatment for intersections”

It’s not just in the safety department that roundabouts reign superior to signal intersections. The infamous Mythbusters also carried their own demonstration to find out whether the myth that roundabouts allow for greater traffic flow than intersections is true, and surprisingly, their results was that roundabouts are 20% more efficient in traffic flow than the signal intersections that Kenya wants to adopt. Watch this video for details of the demo. Washington State Department of Transportation explains the increased traffic efficiency in the following words,

 Contrary to many peoples’ perceptions, roundabouts actually move traffic through an intersection more quickly, and with less congestion on approaching roads. Roundabouts promote a continuous flow of traffic. Unlike intersections with traffic signals, drivers don’t have to wait for a green light at a roundabout to get through the intersection. Traffic is not required to stop – only yield – so the intersection can handle more traffic in the same amount of time.

Studies by Kansas State University measured traffic flow at intersections before and after conversion to roundabouts. In each case, installing a roundabout led to a 20 percent reduction in delays. Additional studies by the IIHS of intersections in three states, including Washington, found that roundabouts contributed to an 89 percent reduction in delays and 56 percent reduction in vehicle stops.

 Roundabouts do not require traffic light

I can’t believe it either. We have traffic lights (non-functional) in almost all roundabouts in Nairobi. The way roundabouts are designed to function is that drivers are “not required to stop – only yield”. This then leads me to conclude that it is not roundabouts that’s the problem, the drivers are.

If the typical Kenyan driver cannot do any good on the good old roundabouts, what do we expect of them once the signal intersections are here? The signal intersections in US could be functioning because generally the drivers over there are more disciplined and obey traffic rules almost to the letter. We should be very stupid to expect that our reckless ruthless drivers will suddenly be saved from recklessness by magically removing the roundabouts and inserting the signal intersections.

Dear Dr. Evans Kidero, please let the roundabouts be but invest in instilling discipline in our drivers. The traffic in Nairobi today should already tell you that we are headed to complete failure. My other recommendation is, limit public vehicles from accessing CBD. Dear Nairobi driver, please be disciplined.


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