It serves as part of the primary route from the Monterey Peninsula to either the San Francisco Bay Area or the California Central Valley.

Along with US 101, it is the quickest route from the San Francisco Bay Area to the Monterey Peninsula.

Route 156 joins U.S. 101 for the next 8 miles (13 km) before splitting off as an expressway east to San Juan Bautista.

[4] The route is eligible for the State Scenic Highway System,[5] 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,[6] 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.

Highway 156 experiences heavy truck traffic as it serves as a primary route for moving people and goods between the Monterey Peninsula and the rest of the state.

It directly links with Highway 152, one of a small number of passable routes across the Coast Ranges between Monterey Bay and the Central Valley.

Environmental studies are underway to upgrade this 5-mile (8 km) section to either a 4-lane highway or fully controlled access expressway.

The Transportation Agency for Monterey County and Caltrans have narrowed the list of upgrade alternatives to one freeway and one expressway option.

The entire segment may be upgraded to freeway status to eliminate delays caused by numerous traffic lights currently present in the Hollister area.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.