Thru the Tunnel is an Accident mini-game in Sonic Shuffle. It can randomly occur by accident in Riot Train.
This mini-game is similar to Sky Bridge. Everyone starts on the last car of the train and the object is to run to the first car as the train passes through a series of tunnels. Players should press to move forward and to duck under obstacles; and press to jump to grab overhead Rings. As the race continues, the back cars start to come off. Hitting an obstacle will set a player back a few feet. If a player is hanging off the end of a car, they should repeatedly press to climb back on.
The player who reaches the front car first wins 20 Rings. Anyone still in the race at that time will win 10 Rings while anyone that fell off loses 10. If everyone falls off, no one loses Rings.
||The train cars are being separated! Get to the lead car, but watch your head!
— Instruction displayed when the mini-game begins