You will be able to get on the train, but it is somewhat unpredictable whether you will get a seat in Los Angeles or you will have to stand at first and wait to sit down later (after someone gets off). For example, sometimes, a Metrolink commuter train is late so the Metrolink passengers (who mostly have monthly tickets) get on the first train to their destination instead of waiting for their regular train. As a general rule, the trains that have numbers starting with a 5 tend to be less crowded than trains with numbers that start with 7. (Southbound 700 series trains start in San Luis Obispo, Goleta, etc., but Southbound 500 series trains start in Los Angeles.) The worst crowding I saw was when a Metrolink train hit someone and they made all the Metrolink train passengers get off that train and onto an Amtrak train so it had two trainloads of passengers in one train.