Speed limits, clear roadsides crucial in reducing accidents

Dickens Kwesiga Kakitahi 

What you need to know:

  • It is well established that two lane rural highways experience crashes several times higher than divided highways. The operation of two-lane highways involves a subject vehicle temporarily occupying the opposite side/direction of the road while passing (overtaking) slower moving vehicle/s. This constitutes a very high severity conflict that could end in head-on collisions.

We appear to be in yet another season of high severity crashes on our roads. I thought I should talk about one or two aspects of road safety that I always only discuss with my engineering colleagues. I will focus on two lane rural highways.

It is well established that two lane rural highways experience crashes several times higher than divided highways. The operation of two-lane highways involves a subject vehicle temporarily occupying the opposite side/direction of the road while passing (overtaking) slower moving vehicle/s. This constitutes a very high severity conflict that could end in head-on collisions.

Another common and severe form of collision is run-off road or roadway departure crashes. The severity of roadway departure crashes is determined by the roadside environment, among other factors.

Our major cities/economic centres like Jinja, Arua, Mbale, Mbarara, among others, are connected to the capital entirely by two lane highways.  A higher proportion of trucks on these highways coupled with limited passing/overtaking opportunities comes with lower speeds and quite often result in unsafe manoeuvres as drivers get impatient driving behind these “crawling trucks”.

But importantly I need to spend some time on the issue of desired speeds versus speed limits as is always the most cited cause of crashes. According to the Traffic and Road Safety Act statutory instruments supplement of June 2004, the speed limit is 80kph and 100kph for vehicles over and under 3.5 tonnes respectively unless indicated otherwise. In urban areas it is 50kph.

Speed limits are always chosen to be consistent with the geometry and to be accepted/complied with by majority drivers (at least 85 percent commonly). I think 80kph for all vehicles should be an appropriate limit considering the inherent risk associated with two lane highways. Additionally, because of several constraints including right of way and terrain, our road designs end up with consistency issues, and inadequately designed roadsides.

Our current two-lane roads do not allow motorists to drive at their desired speeds. I have not looked at the preliminary studies for the planned Kampala-Jinja Expressway but I am sure this argument is made in not very different words to justify the project.

Some countries have successfully implemented 2+1 roadways in which the road is built with three lanes consisting of two in one direction and one in the other alternating every few kilometres. This can be a more immediate solution.

The standard gauge railway could also provide relief to the corresponding corridors by reducing the number of freight trucks on roads.

Let me close with the issue of roadside environment. Drivers getting off the road can come from several causes including loss of control, distractions, impaired and fatigued driving, among others. When drivers go off the road, they may end up overturning or colliding with unyielding obstacles like trees, utility poles, roadside slopes etc. In these cases, proper design of the roadside may be as important as the design of the roadway itself. The roadside environment should be “forgiving” to errant drivers. 

Roadside design mainly involves two elements, (1) properly designing roadside slopes and (2) removing or shielding unyielding obstacles. Depending on the terrain you may need more land to design safer slopes than the land required for the roadway itself. On the second element, I believe a lot more can be done on our highways. There should be more efforts to remove obstacles like trees, utility poles, signposts/boards etc or at least shield them from errant vehicles.

Dickens Kwesiga Kakitahi is a traffic/transportation engineer at Gauff Consultants (U) Limited.

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