http://en.wikipedia.org/wiki/Roadrailer
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 specially-manufactured bogies that do double-duty, serving as articulation points between multiple trailers in a train. Each 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 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 1980’s located in West Chester Pennsylvania. The trailiers were built by the Budd Corporation 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 C&O’s Railvan used in the 1950’s. The railroad wheelsets attached to the aft portion of the trailer were lowed pneumatically by activating a simple valve controller on the left rear of the trailer. To transfer from highway mode to rail mode the trailer driver would position the trailer over tracks inlayed into a paved rail yard. First the operator would activate the valve to remove the air from the airbags that supported the trailer in the highway mode. In the fully lowered or squat position, hooks which held the railwheel set up above the road surface released. Then the operator would move the valve to inflate the two large airbags used for rail mode. These rail air bags were similar to those used in passenger rail cars at this time. After being fully transferred, the trailer would be fully level and ready for connection to the next trailer in the train.
Throughout the early 1980’s various railroads experimented with the RoadRailer concept to determine if the equipment would be durable enough to endure railroad use. The positive attributes of the RoadRailer were its exceptionally smooth ride, light weight and low capital costs to set-up a rail yard. Since no flatcars were involved, no crane systems were needed to transfer the trailers between modes. In fact during one demonstration test a train of RoadRailers was broken down in the middle of an industrial street in Portland Oregon which happened to have track in the street demonstrating the flexibility of the system. Another note was that a RoadRailer train did not have a caboose car which at the time was still required for freight trains. A simple box was designed with a yellow strobe light designed to be installed in the unused coupler of the last car. Later, as cabooses were phased out, railroads today use a similar strobe to mark the end of the train.
In 1982, Conrail operated a route between (Railports) Buffalo, Rochester and Highbridge New York in the Bronx called the Empire State Xpress operated by Bi-Modal subsidiary Road-Rail Transportation Company. The concept was to offer customers rapid freight service that would be competitive with traditional over the road service. Dedicated trains left Buffalo and Highbridge each evening arriving early the next morning. The line was eventually shut down after never establishing enough key customers to utilize the service.
The primary reason that the original RoadRailer concept did not catch on was the weight penalty imposed on the trailers because of the attached railroad wheelset. This was resolved in later designs which removed the integrated wheelset by having a dedicated rail bogie assembly that stayed in the rail yard as seen today.