From its southern terminus with SR 1 in Santa Cruz, Route 17 begins as a five-lane freeway (narrows to four lanes after Pasatiempo Drive).

At the north end of Scotts Valley, it becomes a four-lane divided highway, with access at various points without interchanges, and begins a winding ascent of the Santa Cruz Mountains.

The road crosses the Santa Clara/Santa Cruz county line through the Patchen Pass, commonly referred to as "The Summit", at an elevation of 1,800 feet (549 m), where there is an interchange with SR 35.

Just north of the summit, a winding descent of the mountains begins, again with access at various points, mostly without grade separations, as far as Los Gatos.

It has a combination of narrow lanes, dense traffic, slow trucks, sharp turns, blind curves, sudden changes in traffic speeds, and wandering fauna such as deer, wild turkeys, and mountain lions, which has led to a number of collisions and fatalities.

[citation needed] Efforts to improve safety have included adding electronic speed monitoring signs and warnings lights on curves, removing trees to improve visibility around blind curves, and increased patrol and enforcement of traffic laws.

In addition, barbed wired fencing and retaining walls were added after the route suffered landslides in the Loma Prieta Earthquake.

[citation needed] Gillian Cichowski Memorial Overcrossing Bridge, over SR 17 near Los Gatos at Lexington Reservoir, was named by California Senate Concurrent Resolution 32, Chapt.

The overpass was in response to a campaign by friends of Gillian Cichowski to make the intersection (with Bear Creek Road) safer.

SR 17 in Santa Cruz County is named after California Highway Patrol Lieutenant Michael Walker.

Walker was setting flares to direct traffic around an auto accident on New Year's Eve 2005 when he was struck and killed.

[11] Partly in response to this accident near the Glenwood Road intersection, Caltrans began work in 2008 to widen the shoulder to eight feet.

[14] The earliest connection between Santa Cruz and San Jose was an old Native American foot trail.

When the reservoir was built, the highway was rerouted to higher ground, and the two towns along its path (Alma and Lexington) were abandoned.

[19] When the reservoir levels are extremely low, the old highway pavement is visible as well as some stone and concrete foundations of buildings.

Both routes continued on 8th to Cypress Street which became an elevated viaduct entering the Bay Bridge Distribution Structure ("The Maze").

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.