[pessimizer]

No safety steps are needed. The criteria should be whether the cost of the intervention results in more benefit than if that cost was spent elsewhere. If you're going to have no defined ceiling on additional safety measures, the obvious step is to stop bicycling and choose a safer form of transport, or to stop traveling.

Virtually everything can be made safer, including sleeping and breathing. You don't have to prove it. You have to prove its cost-effectiveness.