It should come as a relief that expansion of some of the major Kigali roads has begun, ostensibly to ease traffic congestion.

Concerns have been loud over the increasing time wasted commuting in the city. This is not to mention idling engines in the jam also mean incurring fuel costs which, incidentally, rose this week at the pump.

And yet traffic snarl-ups in Kigali are not as severe as, say, in Nairobi or Kampala. Congestion in these two East African cities can be several times more expensive and frustrating.

The Nairobi or Kampala traffic snarl-ups can be day-long in the worst of times – which is often in any given week. In Kigali, one mostly has to contend with the morning and evening rush-hour traffic clogged at bottlenecks at some particular roads, but moving.

Otherwise, more broadly, jams can be attributed to the load of heavy traffic and the human factor that accentuates traffic incidents, especially in the other two East African cities, as abrupt weather occurrences.

I would like to illustrate how the human factor plays a notable role, especially at the notoriously reckless hands of the matatu (Kenyan communal taxi) drivers, whose roads habits one finds in Kampala.

But, first, the weather factor: Let’s say a bit of rain shower suddenly falls. The rate of formation of a traffic jam in either city in the sudden change of weather – even in Kigali of late – is short of astonishing.

Researchers on the traffic congestion phenomena are yet to fully explain why this should occur. But they have what they describe as the butterfly effect, a concept first used with weather prediction but now widely adopted to illustrate how small causes can have large effects.

This is easily demonstrable with simulations of spontaneous traffic snarl-ups. First, there is the general acceptance that there are many and unconscionably bad – not poor – drivers anywhere who, for the sake of argument, we can take the matatu driver as an apt representative.

The typically notorious matatu driver will suddenly stop in the middle of the road to either pick up or drop a passenger. And, whether he is aware of it or not, it is then he triggers the cascading butterfly effect.

After the matatu stops, the vehicle behind must also stop, and the one behind it likewise, and on and on. Even after the matatu immediately begins to move again, the cars farther down the road will still be stopping in a backward trend until their turn finally comes for them to start driving again.

This is how the "small cause” – the brief stop by the matatu – causes spontaneous traffic congestion, or a "phantom jam”. Multiply this with any number of reckless matatus or other drivers causing vehicles to suddenly brake in heavy traffic and you have a full-blown snarl-up in your hands.

Reckless driving is however not really a Kigali problem, especially under the watchful traffic police. The concern is mainly in the increase in vehicles and roads that must be widened to ease traffic flow; which raises another conundrum described as the equilibrium effect.

Simply put, this effect describes how a sound decision can prompt change in behaviour with disastrous consequences. For instance, it makes absolute sense to widen the roads, yet the likelihood exists that commuters will see a de-congested highway and decide drive to work instead. Traffic goes up, and the situation is back where it was.

The Thika Superhighway in Nairobi is a case in point, which has spawned accelerated urban residential development, drawing the teeming middle class and their cars to the multi-lane freeway.

Various traffic congestion studies internationally show how building new roads and widening existing ones only results in additional traffic that continues to rise until peak congestion returns to the previous level.

So, what to do? There are various remedies such as instituting the congestion tax, a system of charging users of public goods subject to congestion due to excess demand at certain peak times.

But while we are yet to reach that point, infrastructural development is necessary. It is incontrovertible that Kigali needs the infrastructure as it gears to modernise. Other concomitant considerations will always come later, as any policy mandarin will concede.