Just future planning for the Colorado Trail. Most likely will be solo going from Denver to Durango.
For the CT this year I drove to Durango and lefty truck at a friend's house. Flew to Denver, assembled my bike in the baggage claim area and then hopped on the metro train to the last stop, 12 bike path miles from Watertown canyon. Perfect warmup. Hardest part of the scheme was finding a bike box when no shops were getting new bikes. Flight was easy and cheap, something like $30 plus $75 bike fee.
For AZT 300 I self shuttled using moto since I didn't start with the grand depart. If you do, there is a shuttle service or you might be able to carpool with someone else.
For AZT 750 I flew to Tucson with bike, and Mark at Sun and Spokes in Sierra Vista picked some of us up at the airport. He gave me a ride to the start line. At the end, I hitch hiked to Kanab and then to St George, caught a shuttle to Vegas and rented a car home. Again the hitch there was needing a bike box for the Vegas shuttle, complicated only because Id lost my phone.
For local shuttles I use the moto to self shuttle. It has a bike carrier on it now which makes shuttling very easy.
Hitch hiking can work but it's harder when you have a bike.
Sure you could turn around and ride back to the start, but why not finish the route first?