James Drake visited both Germany (Organisation Todt hosted him and several other highway planners in 1938) and the USA after the war where he experienced the PA Turnpike (opened in 1940), which was America's first true intercity route. The influences were there for him, and he took on board the best bits. Other counties didn't seem to get the memo so whilst Lancashire pressed ahead with plans for a D3M motorway across the county with elegant interchange design, Worcestershire designed the M5 as if it was a 1930s autobahn (down to the straight sections and sharp curves) with single carriageway slip roads at most of its interchanges. Kent went ahead and did similar with the M2 and A20(M).booshank wrote: ↑Fri Oct 16, 2020 15:18 Hasn't this been going on for many decades now, this "not invented here" attitude? For example the USA had already developed quite a bit of experience with freeways (and regional equivalents) when Britain started building its first motorways, such as the first part of the Hollywood Freeway opening in 1940. Yet rather than learning from and developing that experience, it seems Britain decided to reinvent the wheel, maybe even inventing entirely new terms. Not everything they came up with was bad or inferior of course, but it seems that a big opportunity to build on existing experience was missed. Other countries obviously took that experience on board and adapted it to local conditions, making improvements or compromises based on budget/space/traffic volumes etc.
The exception was the M1, which was designed more akin to an Italian autostrade, ignore the hills, just go in a straight line over each one.
Motorway design wasn't really codified into a single national document until the mid 1970s - and that's where it's stubbornly remained since.