Main thing is no one keeps a safe distance, your supposed to drive so you can stop safely if the vehicle in front stops and likewise the vehicle behind should keep that safe gap so if you come to 60mph to 0mph they shouldn’t be a collision but this isn’t the ideal world unfortunately.
I think hard shoulder should be for emergency only if speeds are above 50mph anything less you can have it as a running lane and the information display can help but 9 out of 10 times there misleading