It is a western alternate route of U.S. Route 101 between Eureka and Arcata, routed via the three bridges over Humboldt Bay and Tuluwat Island and Woodley Islands, rather than motorists having to circumvent the entire northern section of the bay (known as Arcata Bay) to the road connecting the Arcata area to the Samoa Peninsula.

The original alternative was a relatively extensive route which took drivers north to Arcata and then around the bay to the northern peninsula before reaching the heavily industrialized area adjacent to Eureka.

Completion of the Samoa Bridge and the creation and designation of Highway 255, completed a circle around Arcata Bay by connecting to the New Navy Base Road (a portion now designated as 255), along the peninsula connecting Samoa to the Eureka shore of the bay.

However, one ferry, the Madaket, continues operating as a tour boat on Humboldt Bay.

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.