Abstract: A pit disposed between an unsecured area and a secured area is normally bridged by a generally flat platform which normally forms a continuation of a roadway. The plate is pivoted at the unsecured side of the pit and is normally supported at the protected side by a weight-responsive removable or frangible support so that an unapproved vehicle will cause the support to give 'way and let the platform swing down and thereby entrap the vehicle in the pit. A plate at the protected side of the pit normally lies in the plane of the platform and functions as an extension thereof. When the weight-responsive support gives 'way and the platform swings down, the plate swings up and forms a blast shield across the path of the force of an explosion of a bomb in the entrapped vehicle. When an approved vehicle is to cross into the secured area a normally inoperative support is engaged with the platform so as to bypass the weight-responsive support.