How to make safety decisions - Wales urban 20mph

[dyqik]

We can do this rationally. That £4.6bn cost averages something like £3000 per household in Wales, where the average house (outside the social rented sector) is worth £213,000.

Since the £4.6bn cost is complete garbage, as it's based on an invalid calculation that integrates a non-integrable quantity, the £3000 per household is also garbage.

You can't proceed rationally from a completely irrational number.

[lpm]

Ivan, you started off the thread by pondering the safety saving - £110m p.a. cost vs safety saving being some portion of £400m. You forgot the non safety benefits.

You've now forgotten the safety saving and are effectively only comparing the £110m to increased enjoyment of homes.

You know you can't do this. List all the benefits and guess at a £ value for each, then compare the total to £110m p.a. (or whatever) cost.

[Sciolus]

People are talking about imposing costs on motorists in order to provide benefits to third parties. In fact, we are redistributing a fraction of the costs that motorists impose on third parties back onto the motorists. That seems rather harder to argue against (without going "waaaah, road tax!!11!").

But the motorists and the third parties are almost the same people.

No, because:

We don't need to ask people, because we already vote with our money. Collectively we pay a premium to live in a quiet cul-de-sac. And pay a discount to live on a busy road.

the people who live on roads that are both heavily-trafficked and have dense houses along them are considerably poorer than average and drive less than average. There is a strong social equity issue behind this policy.

[Sciolus]

Ivan, you started off the thread by pondering the safety saving - £110m p.a. cost vs safety saving being some portion of £400m. You forgot the non safety benefits.

You've now forgotten the safety saving and are effectively only comparing the £110m to increased enjoyment of homes.

You know you can't do this. List all the benefits and guess at a £ value for each, then compare the total to £110m p.a. (or whatever) cost.

Cough.

[lpm]

Your cough does not include these sorts of benefits. It also fails to highlight benefits to children.

It also doesn't see the policy as one of the necessary steps towards towns having cycling as a major transport method - Bristol expressly used 20 mph as a component of the wider steps that created a Cycling City. Obviously cycling measures require additional £ though.

[IvanV]

I believe I have been discussing both sides of the issue.

But we need to consider both sides of this a bit more carefully than the Welsh minister, who, in his explanatory note on the 48 page impact assessment, wrote in 3 lines that he believed the benefits justify the cost, without saying why.

The comparison of the two sides is - to a large extent - nicely summed up in the question that someone cleverly suggested, what do you prefer - that I drive at 20mph past your house and I drive at 20mph past (all your) houses, or that we all drive at 30mph past each others houses. There's the value from you driving at slower speed past my house, and the cost of me driving at slower speed past (all your) houses. I have not agreed the time savings from slower journeys are trivial, but maybe more complicated than application of single unit cost to a bulk of minutes extended.

People mentioned a lot of omitted benefits. I observed in my first post that there are omitted benefits, and people found some more, very valid benefits. A lot of those omitted benefits will be reflected in an increased house value. So I started talking about house prices, because that seemed a nice way of thinking about the value to residents of an environment with slower traffic, albeit always hard to quantify. But I asked, to motivate an order of magnitude debate, how much increase in house price might be more than the time cost of extended journeys that people experience. (And its 50 seconds per journey, not per day, and people typically make at least 2 journeys per day, if they make more than 0).

I have not acknowledged the value of time is trivial. I have said there are difficulties with multiplying a constant unit value by an aggregate total time, because a lot of those might be small. But many might be substantial. We don't even know if someone did detailed modelling to find that out. But if we could do that better, we cannot say that suddenly the value is approximately nothing, we don't have enough information.

I took that 4.6bn npv because it was a number to hand, because I wanted a capital value to compare with house prices. But that was indeed lazy, indeed wrong, of me, as that is actually a net figure, costs minus benefits. If we look at the RIA, the time cost side (30 year npv) has a 6.4bn central case, with low and high at 2.7bn and 8.8bn. The 4.5bn comes from deducting quantified benefits from the 6.4bn. My £110m per year back of the envelope, after multiplying it up for 30 years npv, was nearer, indeed a little below, their bottom end estimate. I had indeed been rather conservative when I made some Fermi estimates to quantify it quickly without everything to hand.

We have talked that adding up lots of small amounts of time might be a problem. But even if we can resolve that issue, I don't think is going to make a quantities like those disappear to nothing.

So, back to the question. If you have a choice between people driving past your house at 20mph, given you have have to drive past other peoples houses at 20mph, or the same with 30mph, which would people actually prefer?

Fwiw, where I live, in this county in SE England where people care a lot about property values, the county council did eventually decide, rather later than some neighbouring counties, that continuous residential areas should all be 30mph, with some exceptions on suitable major roads. That's been in place for maybe 10-12 years now, and the continuously inhabited part of my road, about a quarter of its length, was reduced from derestricted to 30mph in that section. As I drive along the local 30mph roads, pretty much nearly all of them, I do think of it as a social compact. I drive here at 30mph, you drive past mine at 30mph. But the way many people actually drive past my house, especially in the rush hour, they don't seem to think that a social compact even at 30mph is one they want to adhere to. Perhaps that is what in part makes me question whether they really would sign up to a social compact at 20mph. But if it was really enforced, I wonder what they really would prefer. I suspect, given the great extent of 30mph suburbia in this part of the world, that journey time extensions might be larger.

Btw, the DfT has been commissioning broader 20mph studies on places where they have been implemented - many have been quietly implemented over the years, with relatively little fuss. Here's one from 2018. There's over 200 pages of it. At a glance, it notes large evidence gaps on the size and value of many of the impacts; no evidence of any casualty reductions in 20mph areas, though needs reassessing after being in place for 5 years; but general broad support for them among residents who live in them. So to the extent there are loud objections, maybe it is just the usual cake-ism, people expect to benefit from 20mph zones where they live while driving everywhere else without being restricted by them, just like people expect to benefit from large public spending while paying low taxes. Perhaps the Welsh could have implemented most of this in quieter ways without attracting so much attention.

But this still leaves interesting questions of how to make safety decisions, which we don't seem to have got much further on.

[Woodchopper]

Thanks all for the discussion.

As a meta comment the thread seems to be a good example of the practical difficulties in implementing utilitarianism. While it may be an attractive principle, as this thread shows it quickly becomes very difficult to a) identify and reach a consensus on all the relevant consequences of an action, and b) to be able to compare those consequences with precision.

In theory the consequences of speed limit reduction should be an easier problem, as we can measure things like death and injury or average journey times. Other pressing social problems are much more difficult.

[El Pollo Diablo]

I think further to that, this may be a good case of the strategic case for the reduction being somewhat at odds with the economic case. The strategy is, "let's make roads safer so fewer people are killed or injured and communities can work better", in a nutshell. The economic case says, "yeah, but the total sum of the tiny cost to a lot of people is, by our calculations, greater than the monetisable benefits", if you follow the DfT's transport appraisal guidance and HMT's Green Book principles.

Without wishing to divert too much, HS2 has similar issues. The strategic purpose of the line (increasing capacity, allowing more bums on seats and freeing up the normal railway to run different services; in turn, driving wider economic investment in non-London cities such as we're currently seeing in Birmingham) isn't very well captured in the economic case, which largely focuses instead on the benefits of faster journeys. The level 2 and 3 wider economic impacts are poorly modelled, despite them being the point. And, much as it pains me to admit it, sometimes there needs to be a step of faith that something is the right thing to do, and the analysis be damned. But then, that leaves the door open to Boris Island and tunnels under the Irish Sea.

There have been increasing efforts recently to try to move away from the economic case being the be-all-and-end-all and towards the strategic case taking precedence. That would be good to see, but all the efforts come up against the big hulking monolith that is the Treasury, where investment goes to die.

[IvanV]

I think further to that, this may be a good case of the strategic case for the reduction being somewhat at odds with the economic case. The strategy is, "let's make roads safer so fewer people are killed or injured and communities can work better", in a nutshell. The economic case says, "yeah, but the total sum of the tiny cost to a lot of people is, by our calculations, greater than the monetisable benefits", if you follow the DfT's transport appraisal guidance and HMT's Green Book principles.

Without wishing to divert too much, HS2 has similar issues. The strategic purpose of the line (increasing capacity, allowing more bums on seats and freeing up the normal railway to run different services; in turn, driving wider economic investment in non-London cities such as we're currently seeing in Birmingham) isn't very well captured in the economic case, which largely focuses instead on the benefits of faster journeys. The level 2 and 3 wider economic impacts are poorly modelled, despite them being the point. And, much as it pains me to admit it, sometimes there needs to be a step of faith that something is the right thing to do, and the analysis be damned. But then, that leaves the door open to Boris Island and tunnels under the Irish Sea.

There have been increasing efforts recently to try to move away from the economic case being the be-all-and-end-all and towards the strategic case taking precedence. That would be good to see, but all the efforts come up against the big hulking monolith that is the Treasury, where investment goes to die.

I think you are right, although the analysis mustn't be totally damned. It should give us an idea of what this is costing us, and then we can say, so this stuff I believe in, can it really be worth the gap? And the gap should be not to break-even, but to remember that public money is in short supply and public money should to better than break-even.

A classic case was the introduction of motorways to Great Britain. The Treasury was against it, the economic case didn't stack up. But it was no white elephant, even remembering what it had cost. The M50 (Tewkesbury to Ross-on-Wye), we can see that is a white elephant.

An analysis of the tunnels or bridges from Kintyre to Northern Ireland clearly shows that in no plausible state of the world could that make any sense at all.

The Airports Commission looked at alternatives for expanding airport capacity in SE England, and reclaimed land in the Thames Estuary clearly made utterly no sense in comparison to alternatives. So this mode of analysis can make sense.

What can go wrong with safety projects in railways is that they are driven by a judge-defined concept, what ALARP should be judicially interpreted as meaning when someone says "but this costs too much". This only applies when it is a commercial entity making those spending decisions, so ALARP and that specific judicial interpretation of it is not the driving force for decisions made in the public sector when it affects health, life, and safety. That judicial interpretation of ALARP is not really the strategy we buy into in this country, it is just something that happened randomly because of one court case. This lack of a strategic view on safety/life/health expenditure badly distorts how we spend money with that aim, sucked into those bits of the economy where the judge says ALARP means this. If I was the government, I would repeal the law that created ALARP and in its place put a concept we can believe in and apply consistently.

And in the case of any specific large project that is proposed, the key to doing this well is deciding what it is for, and remembering what the thing is for. When it no longer makes sense for that idea, cancel it, don't soldier on. As Bengt Flyvbjerg, the great analyst of megaprojects that go wrong tells us, a consistent feature of the megaprojects that go wrong is when you revise what you think it is for as you go along. When that happens, your strategy is no longer consistent and you flounder, as you are no longer focused on achieving a clear strategic aim you believe in. And we agree that where we have now got to with HS2 is ridiculous. I would suggest we have got there because actually the story you tell is not a strategy that government really bought into and believed in at the time they pinned their colours to the HS2 mast, and considered justified the cost of it, which we all really knew were going to be a lot more than was first said. Good examples of realising you have reached a silly position and stopping are the Garden Bridge and the Metropolitan Line extension, which got cancelled even though a heap of money was tipped down each hole, even more in the latter case than the former, something TfL managed to keep quiet.

Meanwhile, some megaprojects that ended up costing a lot more than the costings that first justified them were the Channel Tunnel and the high speed railway from London to the portal. The cost overrun on the tunnel itself was substantially due to some new safety rules, that came in when the tunnel itself was nearly completed to the old standard, requiring a £5bn retrofit. Nasty trick, that, to play on the people who had to pay it, for it was taken from investors rather than the government. There were other issues, but that was the big one with the tunnel. HS1 cost about 3 times the original plans for the now usual British-can't-build-railways-at-sensible-cost-any-more reasons, and by then you couldn't steal from investors any more and the government stood that one. But we have them now and of course we use them a lot now we have them, though not as much as was originally forecast. (It doesn't help that post-Brexit immigration issues have substantially reduced their capacity, so that not even the disappointing-in-comparison-to-original-plans demand can't be carried at the moment). So are they worth what we ended up paying for them, in each case a lot more than they were intended to cost? Do they do at enough of what they were supposed to do to justify that money? There have been some nasty accidents, but did they need that £5bn safety upgrade? Did they actually achieve enough of what we thought they were for? There was a lot of noise at the time about economic development in Kent, which doesn't seem to have happened very much, but maybe that doesn't matter, maybe just getting from London to the continent and back is enough justification. The international trains never stopped at Ashford, though provision was expensively made for it, and now have stopped calling at Ebbsfleet. The domestic services were a kind of afterthought, and even those have underwhelmed in terms of economic development, though now much later there are at least to be some fairly big housing developments near Ebbsfleet station - but not much going on elsewhere. These are difficult questions and I really don't know the answer.

[Gfamily]

A classic case was the introduction of motorways to Great Britain. The Treasury was against it, the economic case didn't stack up. But it was no white elephant, even remembering what it had cost. The M50 (Tewkesbury to Ross-on-Wye), we can see that is a white elephant.

For some interesting thoughts on the justification for the M50 - https://www.pathetic.org.uk/current/m50/
Some of the comments are interesting too

[IvanV]

A classic case was the introduction of motorways to Great Britain. The Treasury was against it, the economic case didn't stack up. But it was no white elephant, even remembering what it had cost. The M50 (Tewkesbury to Ross-on-Wye), we can see that is a white elephant.

For some interesting thoughts on the justification for the M50 - https://www.pathetic.org.uk/current/m50/
Some of the comments are interesting too

It's a simple story. It's well known that original purpose of the M50 was to connect the Midlands to South Wales. It started construction before the M5/M4 route via Bristol and the Severn Bridge was complete. But as soon as it was, it became apparent the M50 was unnecessary, so they didn't finish it. Which they really should have realised in the first place.

[Sciolus]

Thanks all for the discussion.

As a meta comment the thread seems to be a good example of the practical difficulties in implementing utilitarianism. While it may be an attractive principle, as this thread shows it quickly becomes very difficult to a) identify and reach a consensus on all the relevant consequences of an action, and b) to be able to compare those consequences with precision.

In theory the consequences of speed limit reduction should be an easier problem, as we can measure things like death and injury or average journey times. Other pressing social problems are much more difficult.

I think it shows the limitations of technocracy and the need for politicians (yes, it hurts me to say that). It's hard to capture the various impacts of a proposed measure, and very hard to compare incomparable impacts. We can try to monetise them so they can be compared, but that is highly uncertain (we haven't gone into the problems with Willingness To Pay, for instance), so ultimately we need an informed but subjective appraisal that considers how a measure fits into the totality of policy.