:: Quite right. I'll try to check Eric Partridge's 1936 Dictionary of Slang when I have the chance; but all my books are in store. It has kinda fallen out of fashion because deliberately in the UK they have been getting rid of these extremely dangerous roads: as I put in the stub, I think, they changed the British A507 Baldock-to-Woburn road from a "my side, your side, suicide" road to having two very wide lanes, you can still see the old road markings for the three lanes (because the UK has been cutting back a lot on road maintenance out of short-term economical reasons that make no damned sense in the long term but still charge me £250 a year for my road fund licence). I'm with you, it is hard to source reliably. Perhaps we should try at WikiProject:Roads? 

 ::But then on the other hand I tried about four years ago to edit left and right hand traffic and was pretty much always undone/reverted because I wanted to change from always saying "right hand drive" meaning "left hand traffic" and "left hand drive" to "right hand traffic" which I think is confusing to readers, but got nowhere with that one.