It doesn't always have to be that. When the A23 was upgraded and dualled, over a large section an entire new roadway was constructed, and the old A23 was de-trunked, reclassified as a B road and left as a service road running parallel to the new road, about 200-300 yards west of it. This makes an excellent cycle route. See here.Chiz wrote:For me, cyclists being prohibited from any particular road will only be acceptable when a practical alternative is offered. By that I mean quite literally a segregated cycle/pedestrian route running alongside the road in question.
Having said that, cyclists are not barred from the new A23. I see no reason why they should be, but if they had been, maybe Marie Vesco might still be alive today...