Quote Originally Posted by Eric the Half a Bee View Post
How do you work that out? Car revs are roughly the same using 3rd at 20mph as 4th gear at 30mph. I find I switch down more to 2nd gear at 20mph, meaning higher revs and using more fuel.

A regular journey of mine has taken me 5 minutes longer both yesterday and today. I reckon that if I'm driving for 5 minutes more I'm using more fuel and creating more pollution.
I didn't work it out, there are various studies online about it, from the various other places around the world that have introduced a similar limit.

iirc the biggest impact on particulates generated is accelerating rapidly, and at 20 you get far fewer accelerations and breaking than at 30, as everyone drives along a lot more smoothly.
which makes sense, even with a clear road ahead of you, nobody is going to bother flooring it to get to 20.


as for using fuel, you'll remember from your GCSE physics that energy is proportional to the square of velocity, so even if the journey is taking longer it will use more energy to do it more quickly.