[mikeash]

Scale matters a lot, though.

The EPA's goal is to regulate the overall quality of the atmosphere. To the extent that they regulate individual machines, it's just because of their contribution to the total.

When something is done by a few idiot hobbyists, it's just not worth trying to enforce. The effort would be better used elsewhere.

Individual cars are tested for emissions not so much to catch illegal modifications (although I'm sure they're happy to do so when they can) but to detect failures due to age or broken equipment.

"Rolling coal" is obnoxious and ought to stop, but it shouldn't be surprising nor upsetting that there isn't much enforcement effort against it.

[knorby]

If the EPA had to tackle the problem standalone, then, sure, the scale wouldn't make it sensible. It could end up influencing whatever regulation goes into cars to prevent this sort of dishonesty in the future. Perhaps cars will need to start logging to a black box of sorts to track engine related settings, or emissions will need active monitoring and logging.

It is also worth noting that the hobbyist solution has the potential of becoming widespread. If VW merely does a software fix, more than a few owners with suddenly sluggish cars might look into the devices. There is nothing specific about 'rolling coal' by trucks...most uses of the devices are purely for performance tuning.