By plane
Fly via John Wayne/Orange County Airport SNA and Irvine is across the street. Alternatively, Los Angeles International LAX is about an hour's drive away without traffic via freeway 405, or Long Beach Airport about 30 minutes away, also via 405.
Greyhound
(http://www.greyhound.com/...) +1-714-542-2215 has a station in Santa Ana, a neighboring city.
Amtrak
provides rail service via Metrolink and the Pacific Surfliner with a stop right in Irvine. (http://www.metrolinktrain...) OCTA bus #86 connects to the train station. (http://www.octa.net/)
By car
Irvine is at the intersection of the 5 and 405 freeways. One does have to consider, though, that these freeways have a significant amount of traffic and may be slow during rush hour. If traveling from San Diego and you wish to avoid some traffic, you may consider using the 73, which splits off from the 5 in Laguna Nigel. Be aware that this is a toll road, however.
The 55 state freeway may be used to get to destinations in the northwest of Irvine; north of the 55 is Santa Ana.