We could probably go a long way in making trunk roads safer without lowering speed limits on them if we had some (cultural, technical, or legal) means of enforcing the dictum "drive at a speed from which you can stop in the distance you can see to be clear".
My take on this is that the potential-but-not-actual cyclists who want to commute on trunk roads are far outnumbered by the potential converts in city centres: in terms of bang-for-buck we would do better concentrating on the urban environment. The numbers say that there are more people in cities, and that journey lengths are shorter, so I would be quite surprised if this were not the case. I hope, further, that once everyone who ever strays into a city centre is used to the idea that they share the roads with cyclists, it will be less of a mental stretch for them to support cycle provision on or adjacent to inter-urban trunk roads.
My take on this is that the potential-but-not-actual cyclists who want to commute on trunk roads are far outnumbered by the potential converts in city centres: in terms of bang-for-buck we would do better concentrating on the urban environment. The numbers say that there are more people in cities, and that journey lengths are shorter, so I would be quite surprised if this were not the case. I hope, further, that once everyone who ever strays into a city centre is used to the idea that they share the roads with cyclists, it will be less of a mental stretch for them to support cycle provision on or adjacent to inter-urban trunk roads.