The routes that passengers take through the bus are defined in a file called something like "paths.cfg" (there may be several of these for different variants of the bus). This is done with a series of path nodes followed by a series of path links between those nodes. Some of these nodes are defined as places to enter the bus and some as places to exit the bus. This is done in a file called something like "passengercabin.cfg" (again there may be several for the same reason), using [entry] and [exit] entries. These are followed by the zero-based index of the path node that should be an entry or exit. To stop passengers entering where you don't want them to, you should remove the [entry] definitions other than the ones you actually want.