A cantilever rail is the structural backbone of a cantilever sliding gate. It's a heavy section (commonly an 80x80x6 SHS or a proprietary cantilever profile from suppliers like Comunello or Combi-Arialdo) that runs along the bottom of the gate panel and extends past the gate by 30 to 50% as a counterweight tail.
The rail rides over a pair of top rollers fixed to the receive post. Because the gate hangs off these top rollers, no ground track is needed. The driveway stays clear of any rail, channel, or trench.
CAD60 sliding-gate models compute rail length from the opening width plus the counterweight overhang, and place the roller positions on the side-elevation drawing.