(a) A carrier may transport migrant agricultural workers only in a:
(1) bus;
(2) truck to which a trailer is not attached; or
(3) semitrailer attached to a truck tractor.
(b) A carrier may not:
(1) attach a trailer to a semitrailer described by Subsection (a)(3); or
(2) use a closed van that does not have windows or a method to ensure ventilation.