Captain Blackadder: Baldrick, what are you doing out there?
Private Baldrick: I'm carving something on a bullet, sir.
Captain Blackadder: What are you craving?
Private Baldrick: I'm carving "Baldrick", sir.
Captain Blackadder: Why?
Private Baldrick: It's part of a cunning plan, sir.
Captain Blackadder: Of course it is.
Private Baldrick: You know how they say that somewhere there's a bullet with your name on it?
Captain Blackadder: Yes?
Private Baldrick: Well I thought that if I owned the bullet with my name on it, I'll never get hit by it. Cause I'll never shoot myself...
Captain Blackadder: Oh, shame!
Private Baldrick: And the chances of there being two bullets with my name on it are very small indeed.
Captain Blackadder: Yes, it's not the only thing that is "very small indeed". Your brain for example- is brain's so minute, Baldrick, that if a hungry cannibal cracked your head open, there wouldn't be enough to cover a small water biscuit.
Assume N is the total number of buses. Where N=1 your solution works. For N>1 the engineers can still be hit by a bus. This also ignores all other vehicles such as garbage trucks, semis and stealth bombers, all of which can take out your bus.