What limits there are on the use of (a) non-road and (b) road heavy-duty diesel engines.

New diesel engines for use both in road vehicles and non-road equipment have to comply with mandatory emission standards specified in European Directives as part of the type approval process. In addition, on-road heavy goods vehicles have to pass an annual roadworthiness inspection. This inspection includes a smoke test as a check that their engines are properly maintained. There are no similar inspections for non-road machinery.