Abstract: A security barrier is disclosed for controlling the passage of vehicles along a vehicle throughway (16). The security barrier comprising upper and lower barrier members (20, 22, 120, 122, 220, 222, 320, 322). The upper barrier member (20, 120, 220, 320) is pivotally mounted for movement between a closed configuration, in which a barrier portion of said upper barrier member (20, 120, 220, 320) extends across the vehicle throughway (16), and an open configuration in which the barrier portion is raised to permit passage of a 10 vehicle along the vehicle throughway (16). The upper and lower barrier members (20, 22, 120, 122, 220, 222, 320, 322) are operably linked so that pivoting of the upper barrier member (20, 120, 220, 320) to the open configuration causes the lower barrier member (22, 122, 222, 322) to be lowered, and pivoting of the upper barrier member (20, 120, 220, 320) to the closed configuration causes the lower barrier member (22, 122, 222, 322) to be raised.