On Thu, Nov 01, 2018 at 05:46:47PM +0000, Graham Harrison wrote:

Probably not BUT where do you set the limit?

I don't have access to the detailed journey data needed to do a sensible
analysis.

In any case, this is
not about raking in money (even though it might do so). It's about
air quality and therefore keeping as many "polluting vehicles" out
is/should be the aim.

Wrong. The aim should be to reduce *pollution*, not to reduce polluting
vehicles. What's worse, a hundred polluting vehicles entering the zone
once a year each, or a single polluting vehicle entering every day?
Obviously the latter.

--
David Cantrell