Phase 1 of the Los Angeles Metro E Expo Line opened on April 28, 2012 with the last two stations (Culver City and Farmdale) of this phase opening on June 20, 2012. Phase 2 of the expo line, that completed the Expo Line to within blocks of the Pacific Ocean and Downtown Santa Monica opened on May 20, 2016. The line (from Expo Park/USC onwards) uses the ROW of the Santa Monica Air Line that was the Pacific Electric trolley route from Santa Monica to Downtown Los Angeles and last saw passenger service on September 30, 1953. The line though was kept in service for local freight traffic until 1987. Luckily the ROW was purchased by Metro and preserved instead of getting divided up piecemeal.

Phase I of the line mostly runs in the median of Exposition Blvd and many stations have split-platforms with the platforms for each direction completely offset from each other on the near or far sides of an intersection with the namesake street crossing between the platforms. Phase 2 of the line also follows Exposition Blvd but more sections of it are grade-separated and include a number of stations on arterial structures. Every new station on the line also has a unified design that is unique to the expo line. The fencing and steel framework of the stations are all a similar Aqua Blue to the line's color. Stations have unique wavy steel canopies along the entire platforms. These don't deflect rain but more diffuse the California Sun. Every platform also has about two more solid steel canopies that provide plenty of shelter from rainstorms.

The line represents a few firsts for Metro:
It is the first line that shares tracks with another line. The line enters downtown Los Angeles on the two tracks shared with the Blue Line terminating at 7th St/Metro Center, stopping at Pico Station shared with the Blue Line before finally going straight and continuing south on Flower Street after the Blue Line curves east on Washington Street (just before the Blue Line's Grand Station). Phase 1 of the line was built without a train yard line (one will be built in Santa Monica with Phase 2) and Expo Line trains use the Blue Line's in Long Beach. This also means that the line's entire fleet is shared with the blue line consisting mainly of Metro's oldest cars, the P865s and P2020s supplemented by some P2000s (that are also running on the blue line) that have been relocated from the gold line with Metro's newest cars (the P2550s) all staying on the Gold Line. The strip maps in the Blue Line fleet now show the routings of both the Blue and Expo Lines since their fleets are unified. There are tons of sings at 7th St/Metro Center telling to passengers to look at the destination signs ("Long Beach" or "Culver City") to make sure their boarding the right train.

The line is the first to be represented by a name and not just a color as the Expo Line for Exposition Blvd that it runs along. It is aqua-blue on maps but station bullets for the line are an aqua dot with a black E in the middle of them. (I actually just used the NYC Subway bullets font sent to make the bullet used on this website for the station pages). It seems from a few surviving bullets without E's that the line was originally supposed to be represented by a simple aqua dot like every other metro line but this aqua colored dot was seen as looking to similar to the darker blue of the Blue Line. The Expo Line name for the route will be short lived, Metro is currently beginning to build the Regional Connector Tunnel through downtown that will connect the Blue and Expo Lines with the Gold Line through downtown. As part of this lines are also getting letters, with the Expo line becoming formally the 'E; line.