Played Zombies Tranzit most the night on Black Ops 2.
I now actually have the courage to go down the roads without the bus with little worry, as long as I keep moving and have my knife handy I'll be fine. In fact I may do this everytime I get out of the building you start in, just to get that handy rifle that is along the way, the first time I did I had some saving up to do first because I can't kill zombies in the start without my precious shotgun, but I did so with ease.
I don't know how to upgrade the bus with the ladder, but when others do it I love going on the roof of the bus, it's one of my favourite spots to kill zombies from, better than inside the bus I think.