So Cal Metro found and posted this tired Checker Aerobus. I can well imagine it led a long and hard life. Not all of these were used strictly as airport shuttles, but its name does rather suggest that as its primary market. This was of course in the day before van-based shuttle buses were invented, or at least popularized.
I found one in a more scenic setting a few years back:
I found this one sitting in front of the historic Glacier Park Lodge. That one was still in use, shuttling guests from the nearby train station to the lodge. And because it had also been used to take folks up on the steep ans scenic Going to the Sun Road, it had a four speed manual. Full story on the Aerobus and this particular one here.
These weren’t just “stretched” Checker Marathons; they had unique heavy duty frames and suspensions, and used different drive trains too. As in a Chrysler polysphere V8, until 1965, when Chevy 327 and then 350s took over.