Neither the Federal Motor Carrier Safety Administration (FMCSA) nor the DOT has a walking-working surfaces equivalent. There are vehicle requirements for manufacturers, but no specific DOT guidance on preventing slips, trips, and falls. There are a range of best practices to prevent injuries depending on the type of trailers, but nothing mandated by FMCSA.
OSHA governs the safety of working around and on trucks when the trucks are in yard areas not open to public travel by means of prohibitive signs or gates.