State Route 156 (SR 156) is a state highway in California, USA, running from State Route 1 in Castroville to State Route 152 near Hollister. It serves as part of the primary route from the Monterey Peninsula to either the San Francisco Bay Area or the California Central Valley.
The western terminus is at State Route 1 in Castroville. The eastern terminus is at State Route 152 near Hollister. It overlaps U.S. Route 101 for 8 miles (13 km) between Prunedale, and San Juan Bautista. Route 156 passes through Monterey, San Benito, and Santa Clara Counties. Along with US 101, it is the quickest route from the San Francisco Bay Area to the Monterey Peninsula. In addition, SR 156's connection with SR 152 allows direct access to the California Central Valley.
For its westernmost two miles (3 km), Route 156 is a freeway through Castroville, terminating at a Y-interchange with the Route 1 freeway. There is no direct access from Route 156 West to Route 1 North or Route 1 South to Route 156 East. Motorists who want to go from Route 1 South to Route 156 East can do so by using Route 183 South through Castroville. Traffic heading west on Route 156 can access Route 1 North by exiting at the Route 183 interchange and heading north. The route then truncates into a two-lane road between Castroville and Prunedale. Route 156 joins U.S. 101 for the next 8 miles (13 km) before splitting off as an expressway east to San Juan Bautista. Just after the intersection with The Alameda, Route 156 returns to a 2-lane road, then curves north by northeast, with several at-grade signal intersections, including one with State Route 25. Route 156 then crosses into Santa Clara County approximately 1/4 mile (300 meters) before a divided road and terminating at State Route 152 as a partial interchange. However, motorists wishing to use westbound SR 152 must exit at Casa de Fruita as there is no direct interchange between eastbound SR 156 and westbound SR 152.
SR 156 is part of the National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration. The route is eligible for the State Scenic Highway System, and from 1 mile (1.6 km) east of Castroville to US 101 is officially designated as a scenic highway by the California Department of Transportation, meaning that it is a substantial section of highway passing through a "memorable landscape" with no "visual intrusions", where the potential designation has gained popular favor with the community.
The original portion of the route was defined in 1909 and ran from U.S. Route 101 to Hollister. In 1933, the remainder of the route (between Castroville and US 101 and between Hollister and Route 152) was added. It was signed as Route 156 by 1963, but was not part of the original 1934 state signage of routes.