Route 15, consisting of the contiguous segments of State Route 15 (SR 15) and Interstate 15 (I-15), is a major north–south state highway and Interstate Highway in the U.S. state of California, connecting San Bernardino, Riverside, and San Diego Counties. The route consists of the southernmost 289.24 miles (465.49 km) of I-15, which extends north through Nevada, Arizona, Utah, Idaho, and Montana to the Canada–US border. It is a major thoroughfare for traffic between San Diego and the Inland Empire, as well as between Southern California, Las Vegas, Nevada, and the Intermountain West. South of its junction at I-8 in San Diego, the highway becomes SR 15, extending 6.13 miles (9.87 km) to I-5, about 12 miles (19 km) from the Mexican border. This segment was initially signed as a state route instead of an Interstate, but it is being upgraded to Interstate standards so it would become part of I-15 in the future. Including this segment, the entire length of Route 15 is 295.37 miles (475.35 km) in California. I-15 has portions designated as the Escondido Freeway, Avocado Highway, Temecula Valley Freeway, Corona Freeway, Ontario Freeway, Barstow Freeway, CHP Officer Larry L. Wetterling and San Bernardino County Sheriff's Lieutenant Alfred E. Stewart Memorial Highway, or Mojave Freeway.
