You get more MPG at 50 than at 60mph... Using less fuel = less emissions. That is the logic.If all the traffic is going through these areas more slowly , won’t they be there longer so the effect on emissions will be approximately Zero ?
Yup. The smart motorway is about increasing capacity not about reducing speed or emission. The speed limit is about safety due to the lack of a hard shoulder.As far as congestion is concerned I know that on the M42 around Solihull/ NEC area which was always a car park before the smart motorway it made a considerable difference to journey times when they introduced the 50 limit smart thingy. Whether that was purely down to speed limits or combined with lots of cameras I’m not sure.