Some of the parts of the route have been incorporated into Interstate 40 and some go through business districts. At least that's how it is from Amarillo to Barstow-ish.
I missed the 4 least guessed answers. Never even heard of the bottom one. My cousin and I drove along portions of historic route 66 when I was moving back east from California, though we started in Sacramento, then detoured through San Francisco, Yosemite, Death Valley, Las Vegas, and the Grand Canyon before going along I-40 most of the way. Picked up I-88 after Knoxville and went toward DC. We stopped in or passed through Flagstaff, Albuquerque, Amarillo, and Oklahoma City. Overall much more enjoyable than the drive out when we passed by Chicago and stayed on I-80 west most of the trip - the midwest states along this route were brutally boring.
Normal is called that because universities set up to train teachers were originally called normal schools for whatever reason. Hence the town that was developed around the Illinois State Normal University (now just Illinois State) was renamed Normal.
Pasadena, Upland, Rancho Cucamonga, Fontana, Rialto, Hesperia, and Victorville all clock in with higher populations.
...and Arcadia, depending on if you want to use the 2010 census or the 2018 estimate
(I still can’t)