I read this in the Guardian and it was also posted on http://www.theguardian.com/uk-news/2014/jan/07/stretch-m1-limited-air-pollution – a proposed speed limit reduction in rush hours. Since I have mild Environmentalist inclinations my automatic reactions are to welcome such a move. However I believe that most pollution is caused by traffic jams. There is a tendency for people to want to drive at the same time – ‘rush hour’. We should really be encouraging drivers to use the motorways when they are quiet – between midnight and 6am. Clearly drivers would be very encouraged to drive at these antisocial hours if the speed limit was raised to 80mph during that period. This will reduce traffic in daylight hours and cut pollution.