In railroad terminology a Roadrailer or RoadRailer is a highway trailer, or semi-trailer, that is specially equipped for use in railroad intermodal service.

The advantage of using roadrailers is that due to their construction, the trailers can be pulled directly behind other freight (or even passenger) equipment without the use of trailer flatcars.

Roadrailers first appeared on American railroads in the 1950s. The trailers were built with integrated railroad wheelsets that could be lowered into position when the trailer was pulled behind a train. More modern roadrailers do not include integrated railroad wheels, but ride on regular trucks that do double-duty, serving as articulation points between multiple trailers in a train. Each regular truck is equipped with two fifth wheels and at one end (or both ends) of a convoy there is an adaptor truck equipped with one fifth wheel and one regular AAR Type "E" or Type "F" automatic coupler. Each semi-trailer has one king pin at each end. Because the truck (bogie) is significantly lighter than a rail flatcar or well-car, roadrailer freight trains are much lighter and therefore are more energy efficient than traditional intermodal trains.