Back in the summer of 1967, when I was 11, my parents and I traveled across the USA by car from Fort Wayne, IN to visit my mother's brother & family in San Buenaventura, CA (better known as Ventura). The Interstate System as we know it today was only about 1/3 to 1/2 way completed, so we used both freeways and U.S. Highways to cross the country. Roughly, we took US 30 to the Chicago area, then I-80, US 30 & US 6 to western Nebraska, & then I-76/US 6 to Denver, where we visited friends of my parents and spent half a day doing touristy things (such as visiting the Denver Mint). From there, we took the then-tolled Denver-Boulder US 36 route up (literally) to Boulder & Rocky Mountain National Park. After cresting the Continental Divide, we exited the park on US 34 and then picked up US 40 in Granby, CO. Following highway 40 for the next two days, and what was then built of I-80 from east of Salt Lake City on, we eventually spent night five of the trip in Auburn, CA. On day six we entered Sacramento and picked up old US 99 (which was still being converted into CA 99, after the Great CA renumbering of 1964).
Driving south on the 99 through the Big Valley, I noticed a lot of signage for "Frontage Road" throughout that day's journey. My 11 year-old brain thought, "This must be one LONG road!" Of course, as I later learned, these signs were just referring to the freeway's local service/access roads that paralleled the highway. But to me, ALL such paralleling roads will always and forever be FRONTAGE roads, no mater what the FHWA, State and/or local DOTs, and local residents prefer to call them!