Public transportation in Nouakchott are taxi, bus, donkey chart, what else??. I dont really used it since my company provides me with company's car + driver.
Well, if i were to drive on my own, i will sure opt for 4 wheel drive since the road condition are not really good and you may need to go offroad (sand) for shortcut + safety (4WD supposed to be harder & tougher i guess). The road here is really small so hardly u can drive very fast.