David Ross - Guild of Motoring Writers
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'I don't see health benefits - massive increase of pollution at tailpipe'
CityCyclingEdinburgh Forum » Infrastructure
20mph zones may go Scotland wide after Edinburgh trial
(797 posts)-
Posted 9 years ago #
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The WAR and Harry Lauder can properly be described as arteries - built for lots of things travelling quickly, with a few junctions but without anything for carless humans to interact with and therefore without the need to cater for carless humans. Arteries have thick walls at the side. Anything without Armcos at its edges is a normal city street which has been co-opted as a multi-lane transport corridor, but the streets (and all the doors and things for people to interact with along the side) were there first.
Posted 9 years ago # -
Then there's the simple thought of, why is someone entitled to safety around their house or flat, but that same person when going shopping, or working, or sightseeing, is no longer seen as important enough to warrant protection?
I think the 20 mph round residential is a limited think of the children mentality. Obviously a child would never run out on an arterial road so no need for speed limits. In fairness kids are more likely to be playing football on a small street in a council estate than Lothian Road.
Posted 9 years ago # -
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David Ross Motoring contributor to many titles including the Sun. Also an expert on motoring and motorsport history.
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Posted 9 years ago # -
Obviously a child would never run out on an arterial road
Is Mayfield Road / the QBC arterial enough? I had a very young girl run straight out into the middle of the road there. (She survived. We stopped in good time. She ran back off the road again.)
Posted 9 years ago # -
The QBC is clearly not an arterial road its a quality bike corridor...
Posted 9 years ago # -
Caught the end of that. Truck driver saying "you can only do 20mph now, so can you imagine if there was a 20mph limit - you'd not get anywhere!"
Some serious cognitive dissonance going on there.Posted 9 years ago # -
"Some serious cognitive dissonance going on there."
Perhaps in fact he understands the concept of average speed. So he accelerates to 30 for some stretches, but is caught in congestion for others and travels well below 20. It averages out at 20 across his journey?
Nah. He's just a c0ckwomble.
Posted 9 years ago # -
All this misguided talk about 20mph causing more congestion reminds me that in fact the safest speed to drive is exactly 164mph
Posted 9 years ago # -
BBC report Five drivers caught speeding at over 140mph in 2014 (but none at 163mph, that would be deadly)
Posted 9 years ago # -
but just Imagine how good the traffic flow would be if everyone drove at that speed
Posted 9 years ago # -
I really don't understand the anti 20 logic of it increasing congestion at all. All I've been able to come up with is:-
If one allows 3 seconds between each car ("only a fool breaks the 3 second rule" *), then traveling at a constant 20mph you can get 60 cars in a 1 mile stretch of road.... traveling at 30mph there's only 40... so less "congestion"... the missing 20 cars are where? **
At 164mph there's space for 7 and a bit cars per mile.
Following the above "logic", at 240mph *** there is less congestion as only 5 cars in a 1 mile stretch....
Conclusion = We should all drive Bugatti Veyrons / Road-going LeMans Sports Cars (i.e. Porsche 962 / 965, Ferrari 512 etc.)!
* This doesn't apply to the average EEN commentator as their driving is so good!
** Queuing up to get onto the 1 mile stretch of road?
*** And because the brakes are so good the car can stop from this speed in just under 500m!.... I haven't found data on what speed a Veyron can be doing to stop in the 23m quoted in the highway code for stopping from 30mph... EEN commentators seem to ignore the fact that regardless of how good car brakes are now, then if you hit something at 30mph you are still hitting them at 30mph regardless of your braking technology?!?!Posted 9 years ago # -
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Next year, we plan to introduce 20mph speed limits to urban roads, which will not only reduce the likelihood of accidents, but will create a more comfortable, relaxed atmosphere for those riding bikes.
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Posted 8 years ago # -
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'No plans for national 20mph limit' -Transport Scotland
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Posted 7 years ago # -
@chdot, shame, having 20mph zones all over the country would increase safety and I think decrease congestion. Fewer accidents clogging up the roads, more cars contained within an area but still moving rather than accelerating to the next pinch point. Feels less congested if traffic is moving.even if slower.
Not sure where we could find people willing to look at things this way within the SNP?
Posted 7 years ago # -
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08/03/2016 2:14 PM
Tiredtaxpayer
Nightwing: "Slower Speeds = Higher Revs = More fuel used, by more people."
Absolutely correct, unfortunately the vast majority of environ-mentalists like samlang have probably never actually driven a car before (except maybe on an x-box). The majority of cars/vans/lorries on the road will have a manual gearbox set up with gear ratios leaning towards maximum efficiency (have to con the idiot emissions experts every way possible) at standard speeds like 30 and 60.
One of my cars is an automatic with a 6 speed zf auto box and at 20 it's constantly hunting between 2 lower gears, resulting in higher revs and consumption than at 30. The other one is a 1950's classic with a 4 speed manual and widely spaced ratios - it needs to stay in 2nd gear for flexibility at 20 - noisier and less fuel efficient than 3rd gear at 30.
The idiotic assertion that less speed means less fuel consumption is the kind of asinine nonsense spouted by people who think that the trams are a low-carbon emission form of transport. Whilst it's true that the nuclear power plant that supplies their leccy has low emissions, we mustn't forget the hundreds of thousands of tonnes of CO2 generated by the steell mills and concrete factories used in setting the damned thing up, never mind the diesel burnt by the thousands of construction vehicles that clogged up the centre of town and thousands of litres of fuel wasted by vehicles stuck in the construction-generated traffic snarl-ups.
This toxic legacy will take many many, many decades to recover from but that's conveniently been forgotten..........
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Posted 7 years ago # -
Yeah, lets set the road policy around folk with 1950's classic cars... both of them. I wonder how often he uses this for work.
I really don't understand the grear/rev argument, my car will sit around 1500 rpm in 4th at 30 and same engine speed at 20 in 3rd.
Posted 7 years ago # -
"This toxic legacy will take many many, many decades to recover from but that's conveniently been forgotten"
And he doesn't think over-use of cars is a toxic legacy?
(my car has a little thing that indicates what gear you should be in for maximum efficiency, and at 20 it puts me in third, which means lower revs. As for the "I have to be in 2nd at 20 for 'flexibility', well for all of his assertions that environmentalists must never have driven, he clearly has, and is very poor at it if he's unable to change between gears for maximum efficiency and, actually, more flexibility that remaining in one gear).
Posted 7 years ago # -
@steveo, @wc good points. This particular pseudo-science argument infuriates me. Revs don't purely determine emissions. Engine load, injected quantity and rpm determine emissions - and that's before cats, dpfs etc..
In reality driving at 1500 rpm in 3rd uses more fuel than driving at 1500 rpm in 2nd as the engine load us greater due to increased resistance - especially wind resistance. This resistance increase is not inconsiderable even at those speeds - we who cycle all know that. I think the increase is logarithmic in speed but I can't remember - someone else will no doubt know.
Modern cars have injection cycles determined by maps. For example here's the driver's wish map of a typical automatic. On account of resistance the accelerator position will be greater at 30 than at 20 - you can see that with the same rpm the injected quantity is greater.
This argument about greater emissions at 20 is nonsense.
Posted 7 years ago # -
@algo
Nice graph.
Although when I first saw your graph, I thought you'd plotted something mocking the driver's IQ versus their perception of engine speed :)
Seriously though, it all assumes a constant speed...
City driving though, is more like: accelerate; coast for 100yds; brake; accelerate hard; brake hard; repeat ad-infinitum...
Most of the fuel is used, and pollution created, during the acceleration process. It doesn't take a genius to work out that it takes more fuel to accelerate to 30 than it does to accelerate to 20. Sadly, that is too difficult* a concept for Mr Tiredtaxpayer.
*Or simply a concept that he doesn't want to entertain, as it invalidates his argument.
Posted 7 years ago # -
@edd1e_h - my graph is not very scientific - it's just an example of an automatic driver's wish map - there are loads of others of course. Good points about your acceleration too - I was just responding to the usual argument that rpm alone determines the emissions.
Posted 7 years ago # -
I think what has been conclusively proven here is that EEN commenters talk nonsense. I mean, we knew that anyway, but it's always good to have it in black and white (and multi-coloured graphs).
Posted 7 years ago # -
@algo, that's a nice graph, so basically the higher your revs the further down you have to press the accelerator before you will get any increase.
One small point, air resistance increases approximate to exponential not logarithmic. I think it's roughly a square function, ie double in speed and you'll have 4 times the resistance. A logarithmic increase would slow the rate of increase the faster you went.
Posted 7 years ago # -
"I mean, we knew that anyway, but it's always good to have it in black and white (and multi-coloured graphs)"
Yes, but this 'making my car/traffic go slower causes more pollution' keeps coming up. Urban myth it may be, (not helped by the inability to believe 'manufacturers' figures'!), must be having some influence - if only on those who want to believe the convenient.
Posted 7 years ago # -
@acsimpson - thanks indeed of course you are right about my misnomer - I should have said exponential. I was being lazy and indicating it as non-linear. I think what you're suggesting is quadratic rather than exponential. When I said logarithmic I was trying to loosely refer to the notion of exponential and logarithmic functions - one being the inverse of the other.
Posted 7 years ago # -
"... must be having some influence..."
Absolutely. But it's difficult to see how it can actually be completely shot down. See also 'cyclists don't pay road tax', and 'immigrants are here for our benefits', etc etc. Ideas get into the public consciousness, and are blinkin' stubborn to get rid of.
Posted 7 years ago # -
@algo, yes you are right, quadratic it is.
Posted 7 years ago # -
@acsimpson - ta. In future I should not be so lazy and actually look stuff up before I type...
Posted 7 years ago # -
The kinetic energy of an object at 30mph is more than double that at of the same object at 20mph. All that energy has to come from burning fuel and all of it is lost to friction when it has to stop*.
So, even for a spherical car in a vacuum*, it takes twice as much fuel to accelerate to 30pmh as it does to 20.
* unless you have regenerative braking
* i.e. ignoring tricky stuff like drag and friction.Posted 7 years ago #
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