Freeways and highways
Due the automobile being the primary means of transportation for the majority of residents, San Diego is served by an extensive network of freeways and highways. This includes Interstates 5, which runs south to Tijuana and runs north to the Canadian border through Orange County, Los Angeles, Sacramento, Portland, and Seattle; I-8, which runs east to Imperial County and Arizona; I-15, which runs north to the Candian border through Riverside County and Salt Lake City; and I-805, which splits from I-5 at Sorrento Valley and rejoins I-5 near the Mexican border. Notable state highways are CA-94, which connects downtown with I-805, I-15 and east county; CA-163, which connects downtown with the northeast part of the city, intersects I-805 and merges with I-15 at Miramar; CA-52, which connects La Jolla with east county through Santee and CA-125; CA-56, which connects I-5 with I-15 through Carmel Valley and Rancho Peñasquitos; and CA-75 (San Diego-Coronado Bridge), which spans San Diego Bay.
Several regional transportation projects have been undertaken in recent years to deal with increasing congestion problems on San Diego freeways. This includes a massive expansion of Interstates 5 and 805 around "The Merge," a notorious rush-hour spot where the two freeways meet. Also, an expansion of Interstate 15 through the North County is underway with the concept of high-occupancy-vehicle (HOV) "managed lanes" in the freeway median. A tollway (The South Bay Expressway) connecting CA-54 and Otay Mesa, near the Mexican border, is also under construction and is expected to open in 2007.
(Source: Wikipedia.org)
