On 17/09/2020 07:41, alan_m wrote:
On 17/09/2020 07:01, harry wrote:
On Wednesday, 16 September 2020 22:46:38 UTC+1, Andy BurnsÂ* wrote:
If you travel at 60 mph instead of 70, you'll spend 16% longer time
covering a given stretch, will the NOx emission rate per mile be reduced
sufficiently to have much overall effect on the total emitted over a 4.5
mile stretch?

The main reason is that drag varies with the square of speed.
So going only a little slower causes a significant reduction in fuel
consumption.


I suspect that the question is related to a 60mph limit on 4 stretches
of UK motorways that is going to be imposed 24/365 to reduce local air
pollution. I suspect that it will not work because in my (limited)
experience of one of those sections traffic cannot travel at 70mph or
even 60 mph currently during much of the day.

But a continuous 60 limit should stop all the accelerating back up to 70
when the gaps open up. I'd still expect a net benefit, even if not the
"theoretical" number.