Interstate 5 (Wikivoyage) Interstate 5 (I-5) is a United States interstate highway that starts at the border with Mexico in San Ysidro, California and runs 1381 miles (2223 km) north through the states of California, Oregon and Washington to the border with Canada in Blaine, Washington. It serves as an important north-south transportation corridor along the U.S west coast connecting the major cities of San Diego, Los Angeles, Portland, and Seattle; the three state capitals of California (Sacramento), Oregon (Salem) and Washington (Olympia); and two additional major cities in neighboring countries (Tijuana & Vancouver) just over the international borders.