I have been mulling this one one for a while. This is quite a bold claim, I realise, but if we press ahead with the reduction in the National Speed Limit (NSL) to 50mph then people are going to die as a result.
In case anyone needs clarification, the NSL is a default speed limit. Unless some other rule applies, then the limit is the NSL - currently 60mph. A different limit of 50, 40, 30 or 20 can be signposted, or a 30 limit can be assumed from the presence of lamp-posts, or a 70 limit can be assumed when on a motorway. In all other locations, the NSL applies.
So the discussion is clearly limited to non-urban roads; urban streets will default to 30 unless signed otherwise. Non-urban roads will typically be very variable, but generally break down into three types. The most common type is fairly straight, not so straight that you see to safely overtake, but not so bendy so as to cause concern. These sections are typically interspersed with shorter sections that either require a much slower speed to negotiate, or which offer an excellent view and allow an overtake if the vehicle in front is not making progress.
First, let's deal with the slow bits - the danger points. At the moment, these are marked. Some will have 30 or 40 limits posted, some will have other signposts. Many, however, have signs indicating a 50 limit. All of these signs will, over time, be removed. This means, in effect, that less warning will be given to drivers of the forthcoming hazard. Drivers will receive information from officialdom that the forthcoming stretch is no more dangerous than the one they have been negotiating for the last few minutes; this information will be false. There will be accidents as a result.
If you have a hazard ahead, it is not difficult to realise that reducing the palette of information for drivers is not going to help.
Then there is the question of the quick bits - the overtaking sections. Human nature is such that drivers who have been negotiating these same roads for years (decades, even) at 60 will not be pleased to be stuck behind someone firmly sticking to an indicated 50mph - often equal to an actual 45mph*. So they will be keener to overtake. When an overtaking section arrives, there will be more pressure to go for it. I have also observed that there is a class of driver who always drives at "limit minus x". Their speed on NSL roads seems to drop from 45-50 to 35-40 when the limit drops from 60-40. This is frankly ridiculous; a road section that is objectively safe at 60 then has a queue sitting at 35 - this is often the source of a perfectly reasonable desire to overtake. I have, in fact, noticed more overtaking manoeuvres now that many formerly NSL roads have a 50 limit. There will also be some drivers that will accept more marginal overtaking locations; create a slow-moving roadblock and you create a queue of people who want to get past. Not all of them will have time to do so at the safe spots.
Overtaking can be safe, and can be wise. It can also be very dangerous. It is not difficult to realise that placing more pressure on some drivers to get past is not going to help.
I'm not making this up, either. A long open road near to me used to be NSL, but about three years ago - upset at the rate of deaths on the road - they put up a big yellow sign telling us to be careful because 60 people died or were serously injured over the 5 mile stretch over the previous 3 years. They also dropped the limit to 50. The sign has just been updated again. 93 died or were seriously injured** over the last 3 years. That is, roughly speaking, an additional death (or serious injury) every month or so.
I'll just repeat that, because it frightened me. An additional death (or serious injury) every month or so. Somehow, I don't think it was the big yellow sign that caused this.
*Speedometers are allowed to be up to 10% optimistic, but must not under-read. Engineering-led manufacturers therefore set them to over-read by 5%. Marketing-led manufacturers set them to over-read by 10%.
**The original version of this post simply said "died"; Steve Jones commented that this would be very surprising and, on that point, I have to agree with him. I'll go back and check; the sign may well have said deaths or serious injuries, rather than just deaths. In my defence, I was driving past (!) and therefore my attention was (and needed to be) elsewhere. Nevertheless, I should have spotted that. Until I can check it, I think it would be best if the post referred to the more likely of the two possibilities.