the two airbags used for rail mode. These air bags were similar to those used in passenger rail cars at the time. After being fully transferred, the trailer would be fully level and ready for connection to the next trailer in the train. A similar system was trialed in the UK, though the concept proved unsuccessful, partly due to the reduction in load volume required to fit inside the UK's smaller loading gauge, and also due to objections by the powerful rail and road transport unions. Throughout the early 1980s various railroads experimented with the RoadRailer concept to determine if the equipment would be sufficiently durable to endure railroad use. The positive attributes of the RoadRailer were its exceptionally smooth ride, light weight and low capital costs to establish a rail yard. Since no flatcars were involved, no crane systems were needed to transfer the trailers between modes. 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, which at the time was still required for freight trains. A box was designed with a yellow strobe light, and equipment for monitoring air pressure through the brake line was designed to be installed in the unused coupler of the last car. Later, as cabooses were phased out, railroads moved to their current use of an end-of-train device to mark the end of the train. In 1982, Conrail operated a route between Buffalo, Rochester and Highbridge in New York State, 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. In 1992, Amtrak began a trial of RailRoaders to carry mail attached to passenger trains. It was deemed unsuccessful. In 1991, the RoadRailer concept was purchased by Wabash National Corporation. The primary reason that the original RoadRailer concept was not viable 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