Middle English barrere, from Anglo-French, from barre bar
- 1a : something material that blocks or is intended to block passage <highway barriers> <a barrier contraceptive>
- b : a natural formation or structure that prevents or hinders movement or action <geographic barriers to species dissemination> <barrier beaches> <drugs that cross the placental barrier>
- 2plural often capitalized : a medieval war game in which combatants fight on foot with a fence or railing between them
- 3: something immaterial that impedes or separates : obstacle <behavioral barriers> <trade barriers>
Automatic full barriers are a set of four half-barriers closing a road at a railway level crossing.
Typically the barriers on the approach side to the crossing are lowered first with those on the exit side following shortly after. The sequence timing is set to allow enough time for a vehicle or pedestrian on the crossing to exit before the exit barriers come down. There are no examples of these in the UK. All full barrier level crossings in the UK are manually operated and not automatic.