A vertically folding barrier gate arm has a proximal first segment and a distal second segment connected by a pivot hinge allowing them to fold. An extension set pivotally affixed to an outer offset bracket on the housing for the motor of the gate arm is connected to an outer offset bracket on the distal gate arm segment by a multi-articulated compound hinge formed by a plurality of links attached to each other by hinges providing a constrained range of rotation relative to each other. The gate arm translates from a fully extended position where the proximal and distal gate arm segments are parallel and co-linear along a horizontal longitudinal axis, to a vertically folded position where the proximal and distal gate arm segments lie substantially against each other within the plane of rotation of the first segment.