Ha - that question was neatly dealt with by Prof. Adrian Davis - he called it an "outlier question", not really worthy of consideration and then outlined the physics involved in vehicle collisions. I don't think we will be hearing that question again.
CityCyclingEdinburgh Forum » Infrastructure
20mph zones may go Scotland wide after Edinburgh trial
(797 posts)-
Posted 5 years ago #
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I’ve been watching this and the panel were very impressive. Some of the MSPs not so much. Mike Rumbles doesn’t understand averages.
Posted 5 years ago # -
That article makes no sense - the financial memorandum that accompanies the Bill estimates it will cost local authorities £9m-£10m per year in the first two years, i.e. £18m-£20m pounds. Which would seem about right, given the quoted figure of £0.5m for Aberdeenshire Council. Maureen Watt doesn't seem to realise that £16m is less than the estimated £18m-£20m - insert joke about "low watt" here.
Posted 5 years ago # -
There's something about Aberdeen that makes folk insane when it comes to cars.
And you'd think someone with Ms Watt's long involvement in public policy would have requested costings for leaving the speed limit at 30mph, with the attendant increase in injuries, illness and road surface maintenance.
Posted 5 years ago # -
There's something about
Aberdeenhumans that makes folk insane when it comes to cars.FTFY.
Posted 5 years ago # -
Yay! The Alliance of British Drivers (ABD) has submitted written evidence to the REC Committee about the 20mph Bill. This should be fun. Fact checking to follow...
Posted 5 years ago # -
ABD fun fact 1:
ABD say "Vulnerable road users are given the perception that 20mph zones are safer than 30mph areas and behave less cautiously in them, while actual speeds are typically reduced by perhaps 1-2mph”.
There is no research evidence that shows vulnerable road users are less careful where there are lower speed limits. Also - nice victim blaming.
Posted 5 years ago # -
ABD fun fact 2:
ABD say "A distracted driver striving to maintain 20mph is more likely to collide with a vulnerable road user at 20mph than an observant one travelling at higher speed". They quote a study (Bowden, Tatasciore and Visser 2017) to support this claim.
There is no research evidence that drivers have to look at their speedometer more where there is a 20mph speed limit. The 2017 study doesn't look at reduced speed limits. It considers changes to the "leeway" that police forces allow drivers travelling above the speed limit before taking enforcement action.
Posted 5 years ago # -
Keep up the good work.
Posted 5 years ago # -
ABD fun fact 3:
ABD say: "From the Ashton-Mackay curve, right, the average impact speed of UK RTAs involving pedestrians is already typically 20mph or lower".
What!? The graph shows something else entirely - namely the risk of pedestrian fatality in a collision by vehicle impact speed. Using data collected in Birmingham during the 1970’s by researchers Ashton and Mackay.
Posted 5 years ago # -
“There's something about Aberdeen that makes folk insane when it comes to cars.”
Well there were a whole lot of them on telly tonight saying how much time the bypass is saving them.
Posted 5 years ago # -
I was just looking at that and scratching my head, but then got distracted by the fact he's using bold; bold and underlined; and bold, underlined AND italicised to emphasise the particularly important bits. Plus square brackets because presumably they look a bit more serious and sciency than parentheses when you're talking gibberish
Posted 5 years ago # -
(my post in response to Morningsider's, BTW)
Posted 5 years ago # -
ABD fun fact 4:
ABD say: "It is often quoted that a 1mph in mean speed brings a 5% reduction in risk or number of collisions, or some similar figure. That is self-evidently invalid – it would mean that a reduction of mean speed from, say, 70mph to 50mph would remove all risk (20mphx5%=100%), which is clearly not the case. This claim stems from report TRL421".
Doh - if only those boffins at the Transport Research Laboratory had thought of this. Oh, wait...
"This relationship inevitably relates only to the range of road types and traffic conditions covered by the data included in the analysis. In particular, the effect on accidents of each 1mile/h reduction in average speed cannot reasonably be extended outside the range of speed reductions observed in the various studies."
The TRL report looked at urban and rural single-carriageway roads and the speed reductions considered by the TRL vairied between 0mph and 10mph.
Posted 5 years ago # -
"or some similar figure"
So he's just writing this off the top of his head without actually checking the documents he's misunderstanding?
When I think how I sweated bullets over the POP evidence to the committee on the climate change bill, to make sure it could all be defended and was all referenced, it's enough to make a cat laugh
Posted 5 years ago # -
ABD fun fact 5:
ABD state: "Forcing lower speeds introduces hazards which are never accounted for. Slower speed does not automatically imply safer – see Solomon Curve, left."
It's starting to get quite embarrassing now. The Solomon Curve does not show a relationship between any particular speed limit and number of collisions. It shows that drivers travelling at close to the average speed for a particular section of road have a lower risk of being involved in a collision than drivers travelling at higher or lower than average speed on that road.
Posted 5 years ago # -
ABD fun fact 6:
ABD state: "The recipe for an accident involves a hazard (or hazardous condition) AND a triggering event...Conclusion: 20mph does not remove hazards (or have any measurable positive effect on them)...Does 20mph remove triggering events? Simply NO."
The TRL report mentioned above makes it clear that the road safety benefits of slower speeds come from more time for drivers to react to a hazard, shorter stopping distances and (in the event of a collision) less energy involved in the impact.
Posted 5 years ago # -
The MSPs aren't going to believe any of this stuff are they? I mean, I know they're politicians but they're not completely stupid ...
Posted 5 years ago # -
Can submissions be rejected for being economical with the actualité.?
Posted 5 years ago # -
“I know they're politicians but they're not completely stupid ...”
I thought you were used to dealing with them?
Posted 5 years ago # -
ABD fun fact 7:
ABD says: "It is often claimed that the value of a life is nearly £2 million and that that is the cost if someone is killed on the road. It is then further claimed that prevention of a deaths leads to a saving of £2m. This is a specious and spurious argument. £2m is not the cost of a death on the road."
Really!? Just...really?!
Anyway, the value given to deaths and injuries on British roads is based on research conducted by the UK Department for Transport.
Ohhh, but here's the good bit. These same figures are used to calculate the economic benefits of accident reduction for all new transport projects. I doubt any major road scheme would ever return a positive cost/benefit ratio if these valuations were reduced to the "thousands of pounds" requested by the ABD.
Here's an example The A9 Dualling: Case for Investment, Table 6.19 shows that accident reduction accounts for £461.08m savings, that is 24% of all benefits attributable to the scheme. The cost/benefit ratio (including a scandalous £430m for "reducing driver frustration") is just 1.12. Reduce the accident reduction to say £5m and the ratio drops well below 1 - no A9 dualling.
Posted 5 years ago # -
Well there were a whole lot of them on telly tonight saying how much time the bypass is saving them.
Was talking to Stonehaven to Westhill commuters at New Year. They're delighted. An hour saved, easy.
Will last four years, as we all know. Their jobs are in the oil. Aberdeen is the lair of First Bus. Adults ride bicycles on the pavement. It's Mordor.
Posted 5 years ago # -
ABD fun fact 8:
ABD state "The recent 10kph limit reduction on French rural roads reduced average speed by 4.4kph, yielding no tangible casualty reduction improvement. It deflated the French rural economy by 3.8Bn€ per annum."
This relates to a reduction in the speed limit on French single carriageway rural roads from 90kmph to 80kmph. Okay, not really related to urban streets in Scotland - but lets just go with it.
Hmmm - that assessment was quick off the mark. The speed limit only changed on on 1 July 2018. Ahhh - the evaluation of the 80km/h limit (in French) referenced by the ABD is not an assessment of actual accident data, but a statistical prediction by "independent experts" working for the 40-million motorists group.
Also, the French Government issued statistics (in French) for the six months following the introduction of the new speed limit on 29 January 2019 which stated something along the lines of “116 lives were saved in the second half of 2018 on the network subject to the reduced 80 km / h speed limit”. (someone who actually speaks French might want to check that).
Posted 5 years ago # -
Re: ABD Fun Fact 3.
I spent too much time trying to figure out what they meant, but I think I got there.
The preceding point is that 2% of pedestrian-vehicle collisions result in a pedestrian dying. Since the graph shows that the fatality rate of collisions where the impact speed is >20mph is > 2%, they infer that most collisions are at < 20mph.
This ignores (presumably amongst other things):
* The difference between travelling speed and impact speed (most drivers will brake before hitting a pedestrian).
* The graph is purely for front-on collisions.I'm still not sure what their actual point is, either. Sure, maybe most collisions are already at <20mph, but it'd still be better if there were fewer collisions, and if impact speeds were reduced.
Posted 5 years ago # -
I mean, I know they're politicians but they're not completely stupid ...
Worth sending Mark Ruskell some notes, at least.
Posted 5 years ago # -
I can't take any more of the madness - all you really need to know is that the section on air pollution is supported by quotes from interviews on talk radio and Andrew Neil on the Sunday Politics. Not my specialist area, but that's enough for me to rate it as "I reckon this is off" from a quick sniff test.
@sally and chdot - My only concern, and why I have raised these issues, is that anti-20mph MSPs could jump on this nonsense as being sufficient to cast doubt on the proposal and reject the Bill. Anyone who wants to tweet these out - please feel free.
Posted 5 years ago # -
@Morningsider - applause
I suppose they'll bring up frustration? Motorists forced to travel at 20mph will get frustrated and cross and start accelerating dangerously? I have heard this put forward by a Councillor about long light sequences.
She taunted me, your honour, which is why I strangled her.
Posted 5 years ago # -
Frenchy - if you were being super generous, you could infer that from the wider text.
However, a single bullet point does say "From the Ashton-Mackay curve, right, the average impact speed of UK RTAs involving pedestrians is already typically 20mph or lower." The graph just doesn't show that - and I'm not disposed to being generous to the ABD.
Posted 5 years ago # -
The twitter army has been roused from its slumbers under Tintagel. I hope it won't end up with a dogpile on the chairman again, but it should at least mean that some of the arrant nonsense is being loudly countered.
Posted 5 years ago #
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