Schwarzkopf Shuttle Loop

The Schwarzkopf shuttle loop used a weight-drop to power its catapult launch system.  One of the most famous Shuttle Loops was Thunder Looper at Alton Towers.  The riders operated with lap bars only.

More "recent" versions of Schwarzkopf shuttle loops used a flywheel to power its launch instead of a weight-drop.

Vekoma LSM Catapult Coaster

Using Linear Synchronous Motors, a catch car propels the train down the launch track.  The catch car then detaches and the train is sent around the track.  All current Vekoma LSM Catapult Coasters are clones - examples include the Rock 'N' Roller Coasters and Xpress at Walibi World. 

Arrow Shuttle Loop

Arrow's shuttle loop is very rare.  It involves two raised platforms seperated by a ground-level vertical loop.  A raised station platform propels the train forward at a fairly slow speed.  The train then travels down a hill, through a vertical loop, and up a hill, onto another flat launch section on the other side.  The train is then stopped and catapulted backwards, repeating the circuit.  An example is Irn-Bru Revolution at Pleasure Beach Blackpool.