At locations such as downgrades, curves, and switches, the same signals additionally serve to enforce speed limits. A system called "grade timing" regulates speeds, and is indicated by an additional "lunar white" light below the one or two coloured lights previously mentioned. The white light means that the next signal is red (or double red) only because of grade timing, and if the train approaches at the proper speed, the signal will clear to a less restrictive aspect before the train gets there. If the train goes too fast, it will pass the red signal and be stopped by the train stop.
