In theory, the EPA could still include the number of lives saved in how it considers the upside of a regulation without attaching a dollar value to it. But experts say that in practice, leaving the dollar costs of compliance in the equation and ignoring the economic value of the health benefits will likely skew the balance toward less regulation.

For more than five decades, the Clean Air Act has prevented millions of premature deaths, hospitalizations, and lost work and school days. “I don’t think anyone wants to go back to ... not being able to see anything,