First of all let me say how much I'm enjoying using cycle.travel - its been the most easy to use routing software I've used. Secondly I think this topic relates more to Open Street Maps - the data used rather than cycle.travel software but I'd like to use this forum to gather some opinions on this idea.
I'm essentially a touring cyclist - I hate main roads & typically ride on 28/32mm tyres and I'm always on the lookout for usable back roads/bridleways. I realise there is a tracktag but it seems it is likely to be precise rather than accurate and clearly getting local knowledge is going to slow going. My question is could we use some grading of usability rather than surface, my suggestion would be
Road bike (narrow tyres - corresponing to ashalt, paved, concrete, tarmac & maybe paving stones
Hybrid , I've sen the term A to B bike on a German web site which I rather like - corresponding to the above plu scompacted, gravel
MTB - all the above plus the rest.
Clearly usability will depend on weather & the map user would need to bear that in mind
It would need a quick way of classifying the routes but a simple system should make it practical for local cyclist to quickly assess their patch for the benefit of visitors. I hear Cycling UK is keen to promote better use of bridleways and this information would tie into that.