There are just three four-level stack interchanges in the UK, a type of junction where sliproads connecting two motorways are piled up four levels high. The first of them, opened to traffic in 1966, was Almondsbury Interchange, connecting the M4 and M5 near Bristol.
It would be hard to overstate just what a pioneering achievement this was considered to be, at the time it was opened, or just how remarkable and new this kind of junction was. The UK had seen nothing like it before; it was the first time two motorways had crossed each other and the first time a structure of such complexity had been built. No wonder its designers though that the junction itself - not the roads it connected, which were built as part of the same contract - was worthy of a commemorative booklet of its very own.
This booklet was published when the interchange first opened to traffic, at which time it wasn't yet complete and only made connections between three approaches. It linked the M4 near Bristol to a short length of M5 heading southwards towards the Avon. The M5 to the north was still in planning, so while the junction was designed to allow its connection, it didn't yet exist. The rest of the interchange was completed, using earthworks and structures already in place, in 1971.
- "The Almondsbury Interchange" (1966) was subject to Crown Copyright, now expired. Scans appear here courtesy of Ian (@lccmunicipal).