Sandbag

V. In roller coaster operation: To delay the dispatch of a train for as long as possible without causing a cascade effect. Usually done after adding and empty train after it has been at rest. A fresh train will not move as fast because the wheels are cold and need to move to generate the friction required for maximum speed. For this reason the "hot" fully loaded train behind it may catch up to it during the ride. different types of Coasters require some trains to be sandbagged more than once to allow for the preceding unit to achieve maximum velocity.