Diesel Particulate Filters.

[oil pan 4]

Unless big changes are made the current design of DPF is pretty bad for fuel economy.
Modern diesels don't make much smoke unless someone puts in a retard program to purposely make lots of black smoke.

[redpoint5]

Yeah, lets start with getting the morons who roll coal, or drive around with a failed turbo off the road.

[chefdave]

When a dpf does a regen it actually pumps out all the soot/carbon that has built up. So the law is law but in this case is seems so wrong. Dumps in one go instead of being spread out in time.

[oil pan 4]

It uses fuel to burn the captured diesel soot, then it does produce soot that is 1 to 2 micron which is most hazardous.
My old diesel, what soot it makes is big 100 to 150 micro. You can see it and smell it and that's a good thing, our bodies can stop almost all of that before it gets into our lungs.
The problem with the 1 to 2 micron size, that's the size chemical weapons manufacturers are going for, so it gets inhaled deeply into the target's lungs.

[cRiPpLe_rOoStEr]

Originally Posted by JockoT

It would appear that many UK motorists are driving about without Diesel Particulate Filters.

AFAIK some truckers are running a bypass system that re-routes part of their exhaust flow to a straight pipe while a smaller amount goes through its aftertreatment system, but that's mostly for the sound of a straight-pipe. I'm sure any attempt to "roll coal" would not be worth the risk of ruining the DPF and the SCR core.