Nothing that I've said contradicts either post #10 or Network Rail (though I could have elaborated that it was too wide
and too windy for a single arm barrier). If you could explain how it would be possible to fit a conventional crossing barrier pedestal in
this location without knocking down the signal box or narrowing a busy main road to allow the fitment of conventional two arm barriers on each side I'm all ears!
Fair enough. The reason for replacing the old gates was because they were worn out and unable to cope with the wind. Choosing a replacement Involved various factors - those two local ones of wind and restricted space, but also the safety requirements (then in the ORR guide
Level crossings: a guide for managers, designers and operators; withdrawn in 2021) and NR's own commercial practices (preferring standard items like BR843 barriers and machines, or approved suppliers, or catalogue items over custom-build).
I can't find any evidence of what alternatives, "conventional" or not, were considered and why they were not chosen. One of the few facts I have is that barriers supplied to BR843 only go up to 9.1m at most, and the road here needs about 10.7m. But here is some extra information that may be of interest.
Railscot has several pictures of the old crossing, which show that it was almost as peculiar as the new one. It had full-width gates driven by supporting wheels, so the crossing had to be longer (along the road) than it was wide. In fact both gates withdrew to the same side of the road, so it was twice as long. One question raised by seeing it is why those cumbersome full-width gates were chosen. Even the restricted space by the signal box (where there is a short length of fence) looks enough for a gate post, allowing half-width gates.
The new sliding barrier was supplied by edsUK (
here boasting about it), and is the sort of thing supplied for e.g. airports or other secure sites. It is described by NR as "bespoke", though I expect they always are designed to fit each location.