The conclusion that average vehicle speeds increased slightly with a raising of the speed limits on single and dual carriageways is clear enough---indeed might be characterised as self evident--- the safety and environmental data less so.
My take on it is similar: there is hard evidence that average vehicle speeds have increased; other than that it really falls into the "nothing to see here" bucket.
The fact that there's no evidence that safety has been improved or compromised is relevant though, because it gives the lie to the rubbish spouted by vocal pressure groups such as Brake that any increase in speed limits is automatically bad, and that every reduction in speed limit has positive benefits. The reality is far more nuanced, and - for them at least - often counter-intuitive.
But when HGV's hold up other traffic that can increase pollution just as all the green cyclists are increasing the pollution produced by the traffic that has to overtake them.
Spot on 190 ! This forms part of my argument concerning those selfish drivers who simply refuse to accelerate when joining a motorway or dual carriageway to match the speed of the traffic in lane 1 , you know the type ? never rev above XX rpm , no idea why there are red markings on their rev counter , etc..never mind the danger they pose to other road users in their mad attempt to save a thimble full of fuel the fact that they force HGV's to slow/change lanes/accelerate, which in turn causes countless other motorists behind them to do similar causing a waste of litres of (other peoples) fuel in the process.