The JRX Store called -- they're running out of bullet trains. JRX was the Japanese name for this combined form of Team Bullet Train. In North America, he was known as Rail Racer. The three members of team (Midnight Express, Rapid Run and Railspike) could link up in train modes (though they're all engines), or connect as a larger 'bot. This helps explain while Midnight Express had such large legs; they're scaled to work as a third of a larger robot.
An Online Amateur Sketchpad