There is a universal rule of self-preservation that applies to visitors to non-Western countries. You do not drive. Period.
One reason is that you do not have the skills to survive in the mayhem that passes for road rules in many of those countries. A second is that if something goes wrong, there is a chance that the locals will kill you if the accident does not.
If you have a local driver, the risk of an accident is lowered. If you are not driving, the probability of your surviving an accident scene increases. It is standard advice to leave the scene of an accident immediately.
In some countries, the simple fact of your not being a local makes you guilty of all crimes associated with the accident. An aid organisation working in Kenya should know these things. The local driver certainly knew them, and it is unimaginable that he allowed a young visitor to take the wheel.
I know them because I survived five years, three accidents, and hundreds of close calls in Africa and elsewhere. Caution, management, a dose of luck, and refusing to drive.
They all made a difference.
Accidents such as these are far more common than are ever reported, and are a key risk for any humanitarian effort.
Our hearts go out to the survivors, the families of those lost, and the well-intentioned young man for whom things went so desperately wrong.

Ian McLean, Tauranga.