(This article is about the section of Interstate 5 in California. For the entire route, see Interstate 5.) Interstate 5 (I-5) is a major north–south route of the Interstate Highway System in the U.S. state of California. It begins at the Mexico–United States border at the San Ysidro crossing, goes north across the length of California and crosses into Oregon south of the Medford-Ashland metropolitan area. It is the more important and most used of the two major north-south routes on the Pacific Coast, the other being U.S. Route 101, which is primarily coastal.