I think you'd have to face four regulations that are the same, but the operating principles of propane and natural gas are a little bit different. Propane is typically a couple of hundred psi versus natural gas, which is 3,000 psi or greater. Propane is heavier than air and settles. Natural gas evaporates but rises to higher points. So there are some safety precautions that would be unique to each, but I think the regulations could be discussed by looking at the commonalities between them and start there, then looking at the unique differences and then craft a policy around those unique differences.
In the United States today there are some states that allow natural gas vehicles in tunnels, but they don't allow propane vehicles in tunnels. I'm not sure why. It goes back to education. For example, in New York State they didn't allow propane vehicles in the tunnels. They now do because we provided them the documentation showing them that it's safe and that there's no reason not to allow them.