We currently have two very large categories - Bridges (1336 pages) and Junctions (2868 pages).
Roads is currently 8,320 pages!
The Bridges are currently also largely (although not completely) categorised under Arch, Suspension etc, and I would like in the longer term to do something similar with Junctions. As far as bridges are concerned, I think that the majority not in a sub-cat have [[Cat:Br..]] at the bottom anyway, so would it be possible to change the Bridges Infobox to read [[Category:All Bridges]] in place of [[Category:Bridges]] - the former could then be a Hidden Cat, and the latter would only (hopefully) have un-categorised bridges in.
Ditto, although maybe at a later date, for Junctions?
We could do something like that, yeah. What is possible is to auto-generate the categories (type=suspension or similar), but the big problem with that is that it involves extreme accuracy with the typing. I could probably do something with it so that if it didn't fit the exact wording it would fall through to a catch-all category.