It is a 2 lane road with some passing lanes, with the highest altitude being 2000 ft. It rivals US 101 for traffic, but it goes through the Los Padres National Forest and the San Marcos Pass. It starts in Los Olivos as a spur from US 101, goes through the town, and then the end of SR 246 at Santa Ynez. It then reaches Lake Cachuma and passes through the Los Padres National Forest, and across the Cold Spring Canyon Arch Bridge, where Cold Spring Tavern is on Stagecoach Road which passes below the bridge. Nearby it crosses Camino Cielo Road to the East and West, then the intersection of Painted Cave Road and Old San Marcos Road before descending to Santa Barbara. It then briefly becomes four lanes and passes an offramp for SR 192 (named Foothill Road to the East and Cathedral Oaks Road to the West of SR 154), before stopping at Calle Real and a Southbound onramp to US 101 and ending at the point where State Street to the East becomes Hollister Avenue to the West.
The highway from Santa Barbara through San Marcos Pass to what was Route 2 was added to the state highway system in 1931.[10] The route renumbered to SR 154 by the 1964 state highway renumbering.[11]
Major intersections
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. R reflects a realignment in the route since then, M indicates a second realignment, L refers to an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see California postmile § Official postmile definitions).[12] Segments that remain unconstructed or have been relinquished to local control may be omitted. The entire route is in Santa Barbara County.
^"Article 2 of Chapter 2 of Division 1". California Streets and Highways Code. Sacramento: California Office of Legislative Counsel. Retrieved February 6, 2019.
^Federal Highway Administration (March 25, 2015). National Highway System: California (South)(PDF) (Map). Scale not given. Washington, DC: Federal Highway Administration. Retrieved September 24, 2017.
^Natzke, Stefan; Neathery, Mike & Adderly, Kevin (June 20, 2012). "What is the National Highway System?". National Highway System. Washington, DC: Federal Highway Administration. Retrieved July 1, 2012.
^California Department of Transportation (2012). Scenic Highway Guidelines(PDF). Sacramento: California Department of Transportation. p. 5. Retrieved June 8, 2017.
^ abCalifornia Department of Transportation. "State Truck Route List". Sacramento: California Department of Transportation. Archived from the original(XLS file) on September 5, 2015. Retrieved June 30, 2015.