There are a LOT of bikes used in Morogoro, and they use the road's shoulder to travel on. Unfortunately, that also where people have to walk.
It's not awful tho, because the bike riders will go along ding their little bike bells to warn of their approach. If you don't forget to listen for them, you'll be all right.
When you hear the bell, just step closer to the ditch and they will pass safely by.