A wheel chock for use over a ground-anchored base plate in a restraint system to prevent a parked vehicle from moving away in an unauthorized or accidental manner in a departure direction when the wheel chock is in a tire-blocking position on the base plate , the base plate having a plurality of spaced-apart blocking elements and each blocking element having opposite first and second sides, the wheel chock having a tire-facing side to be positioned directly in front of a tire of a wheel of the parked vehicle , the wheel chock including: a main body ; a plurality of spaced-apart first teeth provided underneath the wheel chock to engage the first side of at least one of the blocking elements of the base plate in a latched engagement when the wheel chock is in the tire-blocking position on the base plate ; and a locking mechanism including: - a positioning unit located inside the main body and movable between an unlocked position and a fully locked position, the positioning unit having at least one second tooth provided underneath to engage the second side of a corresponding one of the blocking elements in a latched engagement when the positioning unit is in the fully locked position, the at least one second tooth being out of engagement with the blocking elements when the positioning unit is in the unlocked position; - first means for moving the positioning unit from the unlocked position towards the fully locked position; characterised by - second means for selectively holding the positioning unit in the fully locked position, the second means being located inside the main body . a main body ; a plurality of spaced-apart first teeth provided underneath the wheel chock to engage the first side of at least one of the blocking elements of the base plate in a latched engagement when the wheel chock is in the tire-blocking position on the base plate ; and a locking mechanism including: - a positioning unit located inside the main body and movable between an unlocked position and a fully locked position, the positioning unit having at least one second tooth provided underneath to engage the second side of a corresponding one of the blocking elements in a latched engagement when the positioning unit is in the fully locked position, the at least one second tooth being out of engagement with the blocking elements when the positioning unit is in the unlocked position; - first means for moving the positioning unit from the unlocked position towards the fully locked position; characterised by - second means for selectively holding the positioning unit in the fully locked position, the second means being located inside the main body . - a positioning unit located inside the main body and movable between an unlocked position and a fully locked position, the positioning unit having at least one second tooth provided underneath to engage the second side of a corresponding one of the blocking elements in a latched engagement when the positioning unit is in the fully locked position, the at least one second tooth being out of engagement with the blocking elements when the positioning unit is in the unlocked position; - first means for moving the positioning unit from the unlocked position towards the fully locked position; characterised by - second means for selectively holding the positioning unit in the fully locked position, the second means being located inside the main body . <EOS>