Ideally, you could get something like the motor vehicle emissions model - the federal government passed restrictions only after California, and they were less s

Ideally, you could get something like the motor vehicle emissions model - the federal government passed restrictions only after California, and they were less strict, so the California Air Resources Board got dispensation to set stricter standards. Individual states could then decide to follow the EPA restrictions or the stricter CARB ones; this has led to a gradual convergence of EPA regulations to the stricter CARB standards.