Highway grade crossing warning systems are generally divided into two main categories: passive warning systems and active warning systems.
Passive warning systems rely on signs and roadway markings to warn drivers and pedestrians about the presence of railroad tracks. These systems do not detect trains or activate automatically when a train approaches.
Common passive warning devices include crossbuck signs, STOP signs, yield signs, pavement markings, and advance warning signs placed before the crossing.
Passive systems depend on road users remaining alert, recognizing the signs, and deciding when it is safe to cross the tracks.
Active warning systems use electrical and mechanical devices that automatically activate when a train approaches or occupies the crossing. These systems are controlled by train detection circuitry.
Common active warning devices include flashing red lights, audible warning bells, and automatic gates that block roadway traffic when trains approach.
Active systems provide stronger and more direct warnings than passive systems and significantly improve crossing safety by clearly alerting drivers and pedestrians of an approaching train.