It is quite a few years since I was there, but I remember the dualling of the A55 between Conwy and Bangor.
Round the headlands of Penmaenmawr and Penmaenbach the road was a single carriageway through tunnels, and cyclists shared it.
New tunnels were bored to make a continuous dual carriageway and cyclists were banned and routed on to a much older, superceded road.
It seemed odd that we were evicted from a much more spacious road, than the previous confined route.
especially since our new route involved crossing both carriageways a short distance from the tunnel exit.
As I remember this was the only non-motorway road that we were banned from.