A concrete solution which would have avoided &quot;Dieselgate&quot; is if the EPA had made urea NOx removal tech mandatory on all diesel vehicles. Saying &quot;cars in the future must be X% cleaner&quot; is needed, but it&#x27;s not a complete solution.<p>Plus, more often than not, the technology to make cars cleaner is available, but expensive and so manufacturers don&#x27;t use it.<p>Water-methanol injection, for instance, is well proven tech (since WW2), but not adopted at large scale because it requires changes to gas pump infrastructure etc. The only way to overcome a chicken-and-egg problem like that is governments making it mandatory.