Barrier transfer machines, also known as zipper machines, are heavy vehicles used to transfer Jersey barriers or other concrete lane dividers used to relieve traffic congestion during rush hours.
The vehicle contains an S-shaped channel in its undercarriage which lifts the barrier segments (which may weigh over a thousand pounds) off the road surface and transfers them over to the other side of the lane, reallocating traffic lanes to accommodate increased traffic for the currently dominant (tidal) direction. These barriers are linked together with steel connectors to create a formidable but flexible safety barrier.
Moveable barriers are in permanent use in such cities as Auckland (Auckland Harbour Bridge); Philadelphia, Pennsylvania; New York; Honolulu, Hawaii; San Juan, Puerto Rico; Boston, Massachusetts, Washington, D.C., Dallas, Texas; and Sydney, Australia; while many other cities use them temporarily during construction work.
A variant of the machine uses two narrower machines running in tandem. This setup tends to be used in reversible lanes when the movable barrier is used to divide two directions of traffic--the narrower machines are less of an impediment to traffic in either direction. The lanes created by the machine are sometimes referred to as zipper lanes.