Actually a lot of people die on the bus and this is really good tip for people attempting the bus challenge. You can but the knuckles and still do it by exiting the front door and entering the rear. This is really hepful when you need to revive friends on the bus.
It's tricky but not hard with practice. Zombies slow down when they're on the bus which gives you more time to reload. When you jump off for a second it confuses them and prevents you from getting swiped.
Try it out though, it's a really fun stragety for the bus chalenge.
And yeah the traps work really good if you have teammates helping you out with turbines.