Suggested OSM Tagging for very poor roadside cycleways

This is the A34 between Oxford and Bicester.

The path on the left looks deeply unpleasant to ride on (narrow, bumpy, and inches away from roaring 70mph traffic), but because it's signposted to allow cycling, it's (correctly) tagged as bicycle=designated on OSM.

Thus, cycle.travel includes 3 miles of this path on it's suggested cycle route from Oxford to Cambridge. If I hadn't checked out this bit of the route in advance, I'd have been in for a nasty surprise I think.

Are there any tagging improvements I can make to steer CT away from picking this route? I've added accurate "width" and "smoothness" tags, but I'm curious how much these will help. There's also an existing "adjacent=trunk" tag, maybe this could be useful?

I appreciate it's a tough balance to make on your side: if this path was a meter wider, a little smoother, and seperated from the roadway by a grass verge this would be perfectly fine to ride on!

"surface=bitmac" handling

I recently travelled to an area where a number of paved cycle routes were showing as "unpaved" on cycle.travel

On digging into the streetmap data, it seems this was because they were tagged with the "bitmac" surface type, instead of the more common "asphalt".

Could this be added to the list surface types cycle.travel considers to be paved? From what I can tell, bitmac/bitumen is merely a specific type of asphalt/tarmac, and the difference is immaterial to a bicycle.