It is one of several routes which "dead-end" on the Atlantic coast at their southern ends.

The southern terminus of SR 129 is at Middle Road in South Bristol, a few miles north of Christmas Cove at the tip of South Bristol.

The northern terminus is located at U.S. Route 1 Business (US 1 Bus.)

In 2004, the route was truncated to the intersection with Middle Road, which remains its southern terminus.

No other major changes have been made to the route, except for the co-signing of SR 130 along its northern segment.