Barrier Gate Arms / parking lot gate arms (also called booms) are the long metal, wood, or PVC horizontal bar that blocks the road. The boom or arm is typically 8' to 12' long but longer parking lot gate arms are available. Longer gate arms may require supports and heavy duty motors, etc. Barrier gate arms are available in either straight lengths or folding type. Folding gate arms allow for arms to be used in limited height applications such as the inside of a garage.