New Hampshire Route 123

New Hampshire Route 123 (abbreviated NH 123) is a 63.055 mi secondary north–south state highway in southwestern New Hampshire. The southern terminus of the route is at the Massachusetts state line in Mason where, as Mason Road, the road continues as an unnumbered local road in the town of Townsend. The northern terminus, as signed, is at the Connecticut River, where the highway continues west for 0.313 mi to U.S. Route 5 in Westminster, Vermont, as Vermont Route 123 (VT 123). Route logs, however, place the terminus at New Hampshire Route 12 in Walpole.

In Walpole, NH 123 runs in a wrong-way concurrency with NH 12 north–south alongside the Connecticut River, the water body that represents the border between New Hampshire and Vermont. For the entire length of the NH 12/NH 123 concurrency, NH 123 South is, in reality, heading north on the compass while NH 123 North is traveling to the south.

History
In October 2005, heavy flooding in the New Hampshire area forced the closure of NH 123 in two different locations. The first was at the intersection of NH 123 and Cold River Road near Drewsville, where a bridge was destroyed from high water in the Cold River, approximately 5 mi east of North Walpole. The second closure was approximately 3 mi south of the junction with New Hampshire Route 123A in the town of Alstead, where a section of roadway was completely washed away by the water. Both sections were subsequently rebuilt and reopened.

New Hampshire Route 123A
New Hampshire Route 123A (abbreviated NH 123A) is a designation held by two separate state highways in New Hampshire, United States. Although the two segments are not directly connected, they are linked by their parent route, New Hampshire Route 123.

Southern segment
The southern segment of NH 123A is a 4.216 mi secondary rural road that runs from the town of New Ipswich to the Massachusetts border.

The southern terminus of this segment is at the Massachusetts state line in New Ipswich. At this location, the road is locally named Ashburnham Road. The road continues into Massachusetts and becomes West Road in the town of Ashby. The northern terminus is at NH 123 and New Hampshire Route 124 in New Ipswich. At this location, NH 123A is locally named Main Street.

Northern segment
The northern segment of NH 123A is a 10.070 mi secondary rural east–west highway in western New Hampshire, running between the towns of Alstead and Marlow. The eastern terminus of this segment of NH 123A is at New Hampshire Route 10 in Marlow. The western terminus is at NH 123 in Alstead. The road is the only numbered state highway in the town of Acworth, and is the main road through the village of South Acworth.