Once you have the necessary portable emissions testing equipment, how much work is it to test a vehicle?

I've been wondering why the researchers at WVU who found the VW cheating have not gone on to test a larger set of vehicles to see who else is cheating.

Do we know the researchers haven't tested other vehicles? If VW were cheating to a greater degree than other manufacturers, that might explain why they were the first to be caught.

Yes, they weren't doing this on their own initiative, they had a contract to test 4 specific vehicles of which 3 were VW TDIs, I think. They didn't initially think they'd found cheating, and it took a year or two for CARB to get interested and things to develop.

You'd think someone would fund broader testing...

they are all cheating and the punishments won't be equivalent (I assume you mean to the amount of damages and money they made during the cheating period on the cheating vehicles)

But you're right, we don't have proof right now. I think the logical proof, that other companies are selling similar vehicles at similar price points that are "passing" the emissions testing is proof but obviously not of the legal variety.

"If you're not cheating, you're not trying" and it's easier to ask for forgiveness and to pay the fine after the fact.