Rail Racer is the combined form of the MicromasterRailbots. His relationship to the other known Rail Racer is currently unknown.
Rail Racer was never sold as a complete set; he could only be obtained by buying all six individual Railbot components (Overload, Midnight Express, Railspike, Rapid Run, Swindle, and Tankor). He requires a large amount of combiner kibble to form a complete robot mode. These parts form little "battle train" stations to be towed by the individuals' train modes when separated. He is physically identical to the 2003 Takara reissue of Sixtrain, who was also available only by purchasing the individual team members.
The Railbots were originally a Kay-Bee stores exclusive, but later made their way to other outlets, most notably drugstores like CVS.
Rail Racer and the rest of the Universe Micromasters were released in the "main" line in Europe (Energon or Cybertron). Presumably this is because the Universe line was never released in the European market. Why the Micromasters were the only part of the Universe line to get a European release in unknown, but it probably had something to do with their sub-Basic class size and previously being Japanese-exclusive molds.