The reason why highway roads have fly-overs is to avoid getting hit by fast moving cars.
Unfortunately Kenyans make their own rules and they cross on highways without fear. Accidents continue to happen since a moving car does expect a normal citizen to be moving on such a busy road.
See this video of this two men who were thieves and forced to cross the busy Thika highway to avoid beatings from angry mob but one gets hit by a car. You will be shocked to the bone.