Earlier this week I was driving a couple of cars behind an older BMW 3 series, on a 'B' road, passing through a '30' speed-hump urban area. The BMW caught my attention as it was emmiting big 'puffs' of thick black smoke every time the driver accelerated between the humps. Once the road became NSL the BMW accelerated and belched out an incredible plume of this thick black smoke which obliterated any forward view of the road (coverage between the verges and about as high again) and all cars behind had to slow dramatically to cope with the zero visibility. I am guessing this was a diesel BMW but wonder what would cause such volumes of black smoke to be emmited and surely this car cannot be long for this world? Looking into the distance as the smoke dispersed I could still see the car up the road, still smoking but had morphed into a sort of grey haze trailing behind the car. Next time I see it I'll grab the number and report.