Rooftop Rail Grind is the third Challenge Act of Rooftop Run Act 2 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the modern era and is playable only as Modern Sonic.
The player is given a Snowboard throughout the whole Act, and they simply need to make it to the goal in the given time limit. The Act is also slightly altered with Ramps and Springs in order to make the Act's layout more friendly towards board riding.
The player begins the Act just after the normal starting point and continues on through the stage normally from there. The Goal Ring can be found just before the area where the player would normally use the Homing Attack on Balloons to get onto the aqueduct.