Air bag assembly providing adjustable cushion depth

An air bag assembly utilizing a releasable anchoring structure operatively connected to one or more extendible tethering elements and providing adjustable cushion depth. A displaceable support element selectively engages or disengages the anchoring structure during operation of the vehicle taking into account steady-state inputs such as vehicle velocity, occupant size, seating position, and seat-belt use. The displaceable support element may be automatically engaged or disengaged from the anchoring structure as occupant and/or driving conditions change prior to actual air bag deployment.