Advanced Driving Hub

http://www.standardsforhighways.co.uk

In particular: Design Manual for Roads and Bridges

and Traffic Signs Info

And of course everyone's favourite:

Traffic Signs Regulations and General Directions (TSRGD)

If anyone replies with equally nerdy (but potentially useful) road design websites. I'll create an index here.

Traffic Signs Manual

Edit: Just seen your link has this further down the page as a text link.

And of course the missing publication that allows councils to implement whatever bastardised road design they feel like is a good idea.