Like most Southern California cities, San Diego is built around the car — distances are deceptive on a map and the freeway network is the main arterial system. A rental car makes most things easier, especially if you're heading to the beach districts or up to La Jolla. Parking downtown and at the beaches gets tight on weekends.
The MTS Trolley has three light-rail lines that cover downtown, the Mexican border at San Ysidro, Old Town and the eastern suburbs out to Santee — useful if you're staying near a station, less so otherwise. The Coaster commuter train runs north along the coast to Oceanside in rush hour. City buses cover most neighbourhoods but slowly. The Coronado Ferry between downtown and Coronado runs frequently and is a pleasant 15-minute crossing.
San Diego is one of the better cycling cities in California, with protected paths along Mission Bay and the Pacific Beach boardwalk. Bike rentals are easy in the beach districts.