Someones not played L4D then?
Can't remember the name of the mission but the ending is in some car yard and you get into a DIY armoured van with teeth painted on it and drive off at the end.
You need to start a generator to get the lights on then halfway through the generator dies and you need to get back over there and restart it while the hordes keep trying to rape you.
that's CC, it was added much later during development of L4D2 to fulfil their DLc promise.
it's a one off and not the norm for l4d1.