There's been a lot of trying to build a train to the airport, but there are a lot of challenges to this, and it would be incredibly expensive even if it could be made to work. Why not try bus-only lanes on the main arteries to the airport, particularly on the 405?

Allow all buses and shuttles, public or private, to use the lane if they have a capacity over 10 or so. People can bus from the Valley, Westwood, Culver City, and all the places that currently offer slow, expensive shuttle service along this route, and have a fast, dedicated lane to the airport.

This would be far faster and cheaper to implement than a train, and it would be a lot more flexible in the future if routes or schedules need to be changed.