Roundabouts cause a lot of agony for Kenyan motorists, with many advocating for the removal of this “colonial relic” in major Kenyan cities. They have been pinned as a major cause of traffic jams in most Kenyan towns.
But why do they exist in the first place?
Roundabouts were invented in the United States to solve the issue of the cross road. A cross road is a plain intersection where two roads meet. While a cross road works for small roads, and might work well for busier roads with traffic lights, the cross road becomes an issue when handling significant traffic. By modifying a cross road and placing a circle in the middle, we are able to reduce vehicular conflict, including the crashes.
A roundabout makes driving easier for motorists. In Kenya, where we drive on the left, a motorist joining a roundabout will find that all traffic is flowing to the left, and they do not have to worry about traffic that might be flowing across their path.
In addition, a single rule is meant to eliminate gridlocks in roundabouts, you should not join the roundabout until it is clear. Joining a roundabout while other vehicles are using it might lead to a circular wait, where you block a motorist who was taking the next exit, who in turns blocks a motorist who was taking the exit that you came in through and who in turns block other motorists (probably who were taking your exit) who now blocks you. Such is particularly common in cities like Nairobi, and at times can be observed beneath the Globe Flyover in the redesigned Thika Highway.
Another shortfall of roundabouts is that they introduce a wait time especially during peak hours. For traffic to continue flowing through a roundabout, they must wait for those already in to exit. However, the amount of traffic getting to a roundabout, say at 7 A.M. may be more than that leaving the roundabout. This means that motorists have to queue and use the roundabout in intervals. As long as more vehicles continue arriving at the roundabout than are leaving, the queue to join the roundabout gets longer. As peak hour comes to an end, more vehicles are leaving the roundabout, thus the queue to join the roundabout gets shorter and eventually is eliminated.
Ideally, a roundabout should function well, with few delays, say a five to 10 minute delay during peak hours. In Kenya, though, this does not seem to work, and delays in roundabouts often take an hour or two.
But have roundabouts reached their maximum utility in Kenya, or can we change our habits and squeeze more life out of them?
Looking at current roundabouts, the long delays seems to be caused by two busy roads crossing each other. Motorists thus have to queue longer as they await their turn. In addition, the roundabouts tend to be inefficient by allowing traffic flow from a single side out of four possible sides. Can roundabouts be used in such a manner that traffic is flowing from two or even the four sides.
Let’s take the Nyayo stadium to Museum Hill series of roundabouts. We can then assume that the dominant direction is Uhuru Highway and that most motorists are looking at getting to town. Motorists joining the roundabout will be barred from cutting across the roundabout. A motorist coming from Langata Road onto Lusaka Road towards City Stadium would be required to use the roundabout at Bunyala Road, instead of cutting across Uhuru Highway right into Lusaka Road. The motorist will thus join CBD bound motorists and gradually change to the inner lane, before taking the Bunyala Roundabout and again gradually drive to the outer lane before joining Lusaka Round at the Nyayo roundabout again.
Likewise, Bunyala road users would repeat the same manoeuvres at Haile Selassie and Nyayo Stadium roundabouts, depending on which direction they are are headed.
Haile Selassie avenue users would use the GPO (Kenyatta Avenue) roundabouts and the Bunyala Road roundabouts.
Those crossing from the University of Nairobi hostels (State House Road) into town can use the Museum Hill Flyover, or drive back through Nyerere road into Kenyatta Avenue, then back to the University Way roundabout.
An extra slip lane would have to be added near South ‘C’ to account for lack of an extra roundabout for those crossing from Lusaka road into Langata road.
Why the extra, sort of complicated manoeuvres? The aim here is to reduce traffic by eliminating or greatly reducing the amount of time motorists queue to join roundabouts. This is done by allowing traffic from all lanes to join the roundabouts and flow in parallel directions. Motorists can then use the next roundabout, by which time they should have gradually joined the innermost lane.
For the slight inconvenience of covering an extra hundred meters, motorists no longer have to spend an hour or two waiting to join the roundabout.
However, the design will have a few flaws. First of all, there is the assumption that motorists will gradually join the inner lane and maintain smooth traffic flow. This though may not be the situation, and motorists trying to join the inner lane might still drastically slow down Uhuru Highway traffic, probably by attempting to almost cut across the three lanes.
Another setback arises from the driving habits of Kenyans. Assuming that the above suggestion works well, a good number of motorists will still attempt to “save time” by cutting across the roundabouts, instead of using the next one. Their assumption is that a single motorist doing this will not cause much harm. However, though, such single motorists will cause a lot of harm and may even see the new system achieving little improvement from the current flow.
A single motorist cutting across traffic brings all lanes they cut across to a stop, and subsequently, every motorist in these lanes has to stop. Every motorist then takes some time to continue with their driving. For every motorist that cuts across, the above scenario is repeated till the tailback is several kilometres long, and takes a good amount of time to get through.