Bringing a car to campus is extremely helpful but not necessary. For students without cars, cabs are easy to get, but they can be expensive; campus trams go to Old Town every hour, and Zipcars are available to rent for a few hours or for a full day. If you think you'll be using public transportation often, the San Diego Metropolitan Transit System sells monthly passes that can be used on buses, Coaster trains, and trolleys. The best advice for freshmen who didn’t bring their cars to campus is to make friends with those who did. This enables spontaneous trips to Target or the mall, and is cheaper and more convenient than public transportation.
There are trams that run from East Campus to Main Campus and around West Campus. These trams can be really convenient when you’re running late to class, but they can be unreliable. There is an app for iPhones that tells you where trams are at a given time, but there’s almost no telling how long the driver will wait at a stop or if he’ll go on break before coming to your stop. Most students find that it’s easier to walk across campus than it is to wait for the trams.