The obvious solution to this doubling up of regulation is to harmonise emissions and testing standards in EU and US. At the same time, environmental requirements could be harmonised at a global level on the basis of UN/ECE proposals. Indeed, the UN/ECE should be encouraged to develop a fully Global World Harmonised Duty Cycle (G-WHDC).
Harmonised standards would boost development for manufacturers by providing predictability- and simplify matters for customers too.