Isn't the issue that some people work around MOT decibel limits? After all they only need to pass the decibel limit on the MOT test, and not on the road in regular use.

The engineering solution approach doesn't seem to be fundamentally different to speed cameras.

What would be a better solution in your view?

Motorcycle exhausts are easy to swap out so people could easily take the MOT with the stock exhaust then swap the loud exhaust into place when they get home.

I used to live in downtown Chicago, where the worst violators where high end sports cars, though we did get the occasional quartet of motorcycles ripping down the roat at 3am.

Illinois doesn't require vehicle inspections, so there's no opportunity for exhaust modifications to be discovered.