San Diego isn't particular known for it's public transportation system, and getting between the UTC area and more interesting parts of town can be problematic. Nevertheless, it certainly is possible to use the buses to get around San Diego, particularly once one gets downtown. There's a LimitedFreeBusZone in which students can ride for free on many city buses.
Here are the routes that go through the UTC area:
Route5 (UTC_Mall south to Clairemont, OldTown, downtown, then east)
Route30 (From MiraMesa through UTC south to downtown LaJolla, PacificBeach, and downtown, WEEKDAYS)
Route34 (UTC and campus south through downtown LaJolla, PacificBeach, and OldTown)
Route41 (UTC and campus south through Clairemont to MissionValley)
Route50 (UTC_Mall south through Clairemont to downtown, WEEKDAYS)
Route101 (UTC and campus north to TorreyPinesStatePark, DelMar, SolanaBeach, Encinitas, Carlsbad, and Oceanside)
The official Metro Transit System (MTS) website.