I feel a lot of commenters are simply focusing on what signs can do or what sort of junction to build, rather than focus on the fact that on high speed primary country roads, bicycles shouldn't be sharing the road with the cars. In Denmark, a lot of high speed roads (excluding motorways, of course) out in the country have separate dual-way bicycle lanes near it but not attached to it. (Example: https://i.imgur.com/dS…
Strong disagree with Svip. Training doesn't make good drivers. Who is going to ensure the trainers are good? Who is going to test that the training is being effective? More restrictive licensing, with more consistent requirements, might make a difference, but is politically nearly impossible. As long as many people will be inattentive and unreflective humans, there will be bad drivers. Unless you're going to support a policy of refusing to allow a large percentage of the population to drive (like, say, how we restrict most people from performing surgery), you'll have bad drivers.
Bez's proposed solutions have the benefit of being politically palatable, and aligning actual driver behavior with public safety.