Connecting between terminals at Los Angeles Airport has historically been a modern day nightmare. With each terminal being constructed and operated separately, each terminal has historically had its own security and transferring airlines has required re clearing security. This has historically been true, even with connecting between codeshare partners such as Alaska and American or United and US Airways (who are no longer codeshare partners). The good news though is LAX has realized the hassle this has caused for travelers and the airport is slowly opening up more connection options between terminals.
In the current state, passengers traveling on United, Alaska, Delta, American, US Airways, Great Lakes, and Copa Airlines, along with all other airlines operating from airports on the south side of the airport (Terminals 4-8) can connect to each other via a mix of underground tunnels and airside termine bridges. By year end, there will also be a connection open between Tom Bradly International Terminal and terminal 4 which will allow customers to easily connect to international flights/carriers at LAX.
If you are flying through Los Angeles and are connecting airlines, just follow the signs that are located near the far southern end of each terminal to connect via underground tunnel to the other terminals. This is especially useful when connecting to Alaska airlines from a Delta/AA codeshare or when Delta is operating out of terminal 6 gates instead of terminal 5. Furthermore, US airway flights currently operate out of terminal 6, so instead of waiting for a bus to shuttle you, stretch those legs and get walking!
The access point from Terminal 6 is near Alaska Airlines’ gates, across from the Alaska Airline Board Room and near the Ruby’s diner. The tunnel ends at terminal 6, so you must exit the tunnel and access terminal 7 & 8 by above ground walkways which are near the terminal exit and security screening center.