I was only able to detect this because I've spent hours watching and listening to Freedom Highway while cutting it up to use as appropriated footage in a video project that may or may not ever be finished. But anyway...
In Alice Doesn't Live Here Anymore, Ellen Burstyn tells her son to go in the other room so she and Harvey Keitel can talk. Her son complies, and soon we hear (presumably from the TV) a faint voice intoning "Gone are the dark days of the War between the States..." from about 54 seconds into Freedom Highway.
Derek, oddly enough, appropriates the visual from roughly the same passage; at some point in the film (I forget where, since I was taken by surprise) we see the rolling wheel of the bus and then a clip of the bus in its entirety.
Surreal in the way that only 50s educational films can be, Freedom Highway is, um, a film that tells us about American history or something. It features the bizarre combo of Angie Dickinson, Tex Ritter, Bill Roberts of the Philadelphia Eagles, and all kinds of other people, crammed aboard a Greyhound bus crossing the country and learning about life, romance, how to love their country, and stuff like that. The rest of it's kind of hard to explain, but it's worth watching. Make sure to get a load of the conversation between the mysterious stranger and "Fred Schroeder of Portland, OR".
I've embedded the YouTube version for the sake of the visual, but the incomparable Prelinger Archives at archive.org has a better version.