Midnight Special - blues or?
 

I found a nice little (and free) transcription of Merle Travis's version of the Midnight Special traditional:

http://www.michel-lelong-music-house...hel-lelong.pdf

It certainly sounds like a blues to me, but it doesn't look like the 12-bar version which is the only kind I'm (let's say formally) acquainted with. Is that just because it has been condensed? The recording of Travis playing this is different enough, and a lot longer too.

You could call it an 8-bar blues, I guess. It's actually quite a common folk-blues form, which is like a 12-bar blues with the first 4 bars cut. I.e., it starts on the IV.
"Folk-blues" is a nice catch-all term for traditional songs which would have been in the repertoire of blues and folk-country singers alike. Leadbelly, after all (not first to record Midnight Special, but the one who popularised it) was a "songster", who knew a wide range of stuff, beyond blues.

Other folk-blues songs with similar form are Richland Woman Blues:

and the Memphis Jug Band's You May Leave (But This'll Bring You Back).

Midnight Special is probably older than either of those, but it's quite likely both were based on some other source.

There are other blues tunes in (more or less) 12-bar form which also begin with IV. I.e., the changes are IV-I for both the first two lines, not just the second. You Don't Love Me (Willie Cobbs, Bo Diddley) and Meet Me in the Bottom (Howlin' Wolf) are examples.

Long history of the song here:
https://en.m.wikipedia.org/wiki/Midnight_Special_(song)

A guy did that song at a local open mic last night and related a short version of the history because one of the versions is reported to have been based on happenings at a prison not too far from the open mic, in a town where I worked for a few years, Sugar Land (TX).

I'll have another look with a set of brand-new eyes, thanks :) I'm guess that the regular 8-bar blues isn't just a 12-bar blues without the first 4 measures, normally?

I had already scanned through the wikipedia article but that didn't help me much for the problem at hand. I like the song, and have a nice interpretation of it by Eric Bibb and Jean-Jacques Milteau on a disc called something like Leadbelly's Gold (heard them live last summer with that programme).

True. That's just one way of looking at this particular 8-bar sequence.

Other kinds of 8-bar blues begin on I and have other sequences. (Key to the Highway, Trouble in Mind, etc.)