Given your location, I'm not sure why you would choose to start from Union Station. You can avoid riding surface streets in downtown L.A. getting to the L.A. River trail by using the San Gabriel River bike path to Seal Beach from Encanto Park in Duarte. It also eliminates having to ride through Long Beach traffic on Ocean, 2nd St., and PCH. Just a thought if you are not comfortable riding in heavy traffic. The distance is about the same either way, and basically downhill to the beach, all 400 or so feet spread across 30 miles.