We're unfamiliar with the expressions 'transit/vehicle code(s)' and with what is being referred to by use of these terms.

<<Are you referring to road rules (speed limits; school zones etc)?

Are you referring to rules relating to vehicle permits and registration of vehicles? (the mechanical and engineering quality of vehicles? Expert certificates of roadworthiness? the type of vehicles that are able to be registered and driven on public roads? Presence of rust, condition of tyres, functioning indicators etc>>

<<Does this relate to rules applying on public transport systems - Trains? Trams? Buses?>>

Since most but not all trains, trams, buses usually have or depend on a fuel-powered, piston-explosion motor or machine component to run, then yes, it does.

<<As with so many aspects of English language usage what seems immediately apparent and self-explanatory in one context or geographical area is obscure and opaque in another sphere of use.>>