[yontherubicon]

Sure, but emissions testing after you've got the car would be utterly useless.

[londons_explore]

The solution to this is to mandate that the car have built in emissions modelling.

The car itself must keep track of how much Nox it has produced and how many miles it's driven. The ratio must stay below some legal limit (or you pay an extra pollution tax to go over it)

[inferiorhuman]

How so? Roadside emissions testing is very much a thing, as are annual emissions checks.

[HeyLaughingBoy]

Not in all states. I haven't had to do it in 20 years.