Most of the stuff for semis is in fmvss 108.
The big reason that Pete and older trucks still HAVE doors installed is because they are separate structure from the cab.
The Volvo's, macks, Freightliner and other unibody designs went this way without doors because there were direct and solid cab/sleeper assemblies as one unit.
The cab would not separate or partially separate from the sleeper obstructing egress.
As separate components, the sleeper must have exits on it other than the direct egress to the drivers compartment.