DavidR ) gurgled happily, sounding much like they
were saying :

Though it is an oddity of the regs that, rather than having blanket
regulations for particular classes of vehicle, that it distinguished
between different fuel types.

It's an oddity in that it says "This is what you do to the exhaust" rather
than "This is what you should be shoving out the exhaust" - legislating the
means not the target.

A hint of lobbying from the precious metal miners, p'raps?

Oh, and LB can't meet the NOx regulations specified for petrol engines.

It can't... at the state of development it was left in when compulsory cats
killed it.