Although there are probably many who don't know their vehicle-specific limits.

Threre are quite a few who are not aware of the general speed limits either. The most common misunderstanding I encounter is those who believe a dual carriageway in a restricted area (i.e. one with a system of lighting) has a default speed limit of 40mph.

Going the other way, how many people do you see braking from 70 (say) to 60 or under when they come across a speed camera on a 'standard' (no lights) dual carriageway, which does have a speed limit (unless marked) of 70mph.

Where I live, the A505 from the A1 (Letchworth Gate) to the M11 (Duxford) has a BIG problem with this, and yet we see a multitude of serious and fatal accidents, most of which in the vicinty of the cameras (fixed and mobile). Some uniformed locals think its all about people 'speeding' - its not - those who do despite the cameras will still do so to the same extent if the limit is dropped to 60 or 50 at the danger points.

Its those idiots who wrongly believe the limit is 60mph as they pass the cameras and brake late/sharply and those driving too close behind that are part of the cause, as are those who have poor judgement when joining or turning across the flow out of/into small country lanes (though I have some sympathies as I'll explain), but also the poor design/layout of junctions which are I think the largest factor.

Most are effectively 'T' junctions onto 70mph roads - I've seen the same on 50mph dual carriageways and it barely improves things, as there's very little decent vision to spot traffic from either road, slip ons/offs are tiny and crossing points outright dangerous with insufficient waiting areas which mean larger vehicles especially (farm vehicles and trucks) have to turn sharply whilst trying to floor it to cross. Often, people get furstrated at having to wait for several minutes (especially at peak times) to get a gap, and often make the (sometimes fatal) mistake of crossing or pulling out onto the road when there isn't the gap to do so safeyly, especially when its dark and raining.

The fixed cameras are set too far away (as well as not having a speed sign far enough back to avoid people unnecessarily slaming on the anchors) to keep cars at whatever the limit is (or needs to be) as most just speed up again straight after, and the mobile camera 'favourite' locations again are not near enough (on the single carriageway 60 and 50mph sections) to the accident blackspots to make any meaningful difference. They are there purely (in my view) as a money-making exercise, as the high occurrance of accidents prove.

Personally speaking, if the cameras were positioned better, sometimes with average speed sections covering the dangerous junctions, and all revenue (including court cases) going towards road safety improvements in the area to the junctions etc as well as compensating/paying for rehab for victims, I'd have no problem in them being there. As it stands, they are more of a danger (as well as the revenue raiser) than a safety feature.

Speaking of which, why do so many 40 mph dual carraigeways not have repeater signs? The number of times I have slowed to 30 just in case on roads not familiar to me because there were no signs is not insignificant.