The impact assessment assumes no change in pollution because 70% of >7.5tonne already travel at or near the proposed increased speed limit.
The modelled increase in casualties is on the low side (5.5-7.5% (ish)), modelled from accidents featuring >3.5 - <7.5 T which already travel at 50.
An interesting assumption given that they already state that most >7.5 travel at between 43-49 on sc roads.
And that they assume that the drivers will not do what they state they do at the moment.....travel within the 10%+2 figure.
Personally, having read their rather rambling assessment report, I consider it a quite nice way of making/altering law.....if an accident is caused by a driver overtaking a vehicle travelling at the legal maximum the adopted approach is to increase the speed limit applying to the slower vehicle. Given, as stated, that the majority of >7.5 travel at the lower proposed increase (5mph) already.
And the figures from vehicles having bad-overtake accidents involving trucks is not collected since they are collected as collision stats and not why....
I think, having assimilated the philosophy of the report, that it is safe to assume that the speed limit of 40mph is going to be raised, and that the only question remaining is to what: 45 or 50mph.
We can doubtless expect the same approach to other vehicles/accidents....if a motorcyclist is killed overtaking a car travelling at 70mph, we then raise the speed limit of the car.
I also note an initiative by Leics police:
http://www.bbc.co.uk/news/uk-england-leicestershire-20643725