A RoadRailer is a trailer or semi-trailer that can be hauled on roads by a tractor unit and then by way of a fifth wheel coupling, operate in a unit train on railway lines. The RoadRailer system allows trailers to be pulled by locomotives without the use of flatcars, instead attaching trailers directly to bogies. Overview The advantage of using roadrailers is their ability to be used 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 one fifth wheel at one end and a connector plate at the other end. The connector plate slides into a female receptacle on the rear of the trailer in front and is secured with a steel pin. At the head of a Road Railer train 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. RoadRailers were built by the Bi-Modal Corporations in the early 1980s located in West Chester, Pennsylvania. The trailers were built by the Budd Company locally with the integration of the wheelsets and railroad braking system done at the nearby Bi-Modal factory. This was a modern up-date of Chesapeake & Ohio Railway's RoadRailers introduced in 1955. The railroad wheelsets attached to the aft portion of the trailer were lowered pneumatically by activating a control valve on the left rear of the trailer. To transfer from highway mode to rail mode, the trailer driver would position the trailer over tracks laid into a paved rail yard. First the operator would activate the valve to exhaust air from the airbags that supported the trailer in the highway mode. In the fully lowered or squat position, hooks holding the railwheel set above the road surface released. Then the operator would move the valve to inflate