smart51
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| posted on 14/8/12 at 10:41 AM |
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20 MPH speed limits and emmissions / fuel consumption
I'm going to a conference in a few weeks and one of the topics of discussion is 20 MPH speed limits. Do any of you have any links to studies
about the change in MPG or emissions in reducing speed limits from 30 to 20? I'm vaguely aware that only a few cars (mostly small cars with
small diesel engines) have their peak MPG at 20 or 25 MPH and that most cars are in the 30 MPH range or a little higher. I need a few hard facts
before I go.
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Mr Whippy
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| posted on 14/8/12 at 11:09 AM |
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I thought 20mph speed limits were about reducing fatalities rather than saving the planet, surely concentrating on car emissions is completely missing
the point by a long way, or how much of an increase in Co2 justifies a life lost?
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smart51
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| posted on 14/8/12 at 11:17 AM |
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Yes, the primary aim is safety but pressure groups are trying to add weight with an environmental arguement.
Safety can be targetted at specific places. The environment is everywhere. Plus ISTR that pollution is worse at 20 and there is evidence to show it.
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Mr Whippy
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| posted on 14/8/12 at 11:28 AM |
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totally agree with the extra emissions and most 20mph zones in my city are more to do with keeping bus noise levels down plus doing 20mph in a modern
car is a ball ache
however if someone is going to start arguing that above a certain level the extra emissions generated are worth the extra risk, especially regarding
kids, then they'd have to justify this is worth killing someone over and at what point that is the case
A lost cause really as no one will ever agree and the government will just go for what option gives them more chance of fining people for speeding 
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chillis
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| posted on 14/8/12 at 11:50 AM |
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The eu drive cycle is above 25mph if you run lower you need to be in a lower gear so the engine revs are higher and thus emissions in all probability
are worse than at 25 - 30 mph as that is where the industry has been designing their cars to run. Only the prius is better at 20 because it runs on
electric only but then thats the worlds most unenviromental car to make so the environment still loses out. Also it has been statistically proven (see
RoSPA) that drivers concentrate less at speeds below 30 so they are likely to both use more fuel and have more accidents through poor concentration,
thus more injuries and more pollution.
Speed is not really the issue its just a band wagon, education and good driving standards are the way to solve both problems and always have been.
[Edited on 14/8/12 by chillis]
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Doctor Derek Doctors
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| posted on 14/8/12 at 11:52 AM |
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It was on Radio 4 (the today programme I think) that injuries and fatalities in 20mph zones had actually increased. No definite reason was given but
it was suggested that the low speed caused people to not concentrate. Might be worth a google search or a trawl through the BBC website.
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Slimy38
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| posted on 14/8/12 at 12:19 PM |
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I don't seem to have a lack of concentration in a 20 zone, unfortunately I do find that concentration is firmly locked on my speedo rather than
the outside world! It's the same with 'safety' cameras, I spend more time checking my speed than monitoring what is happening.
With regards to emissions, my car has just about enough torque to rumble through in fourth, but it's not happy. Anything less than fourth and I
watch my mpg plummet. OK, for me around 30mpg is considered frugal, but to see it drop to 10 just because I'm trundling round at push bike speed
is not what I would describe as a win for the environmentalists.
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AllWeatherDan
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| posted on 14/8/12 at 12:24 PM |
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I would need to be in 4th gear to travel at 20.
= More pollution.
Although there is DEFFINATELY a call from me for 20 limits in housing estates etc.
I would be the first to ask for a 10 limit on my street!!!!
Dan
There is no such thing as a stupid question.
Just the ones I ask!
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russbost
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| posted on 14/8/12 at 12:28 PM |
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Went through a 20mph zone recently, except at that time the speed limit was 30mph, the signs said "20MPH when lights are flashing" if
we're going to have 20mph zones outside schools - which would seem a good idea as we are apparently incabaple of teaching kids to cross the road
sensibly any more - why can't they all be like this, what's the point in doing 20mph past there at midnight, there really shouldn't
be any kids around at that time!
But would agree with the above comments - the environmental argument is irrelevant (it is also rubbish as decelerating to 20 then accelerating to 30
in any car is going to increase fuel consumption & emisions, not reduce them)
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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hughpinder
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| posted on 14/8/12 at 12:29 PM |
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Have a lookat this document produced for the European commission, pages 54 to 58
http://publications.jrc.ec.europa.eu/repository/bitstream/111111111/22474/1/co2_report_jrc_format_final2.pdf
Regards
Hugh
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smart51
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| posted on 14/8/12 at 12:34 PM |
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Decelerating to 20 then accelerating to 30 is not the problem. Various groups are pushing for blamket 20 MPH speed limits on all residential roads.
In any case, I want to debunk the emmissions part of the arguement using authoritative sources. If you want 20 MPH for safety reasons, argue it on
safety reasons.
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bartonp
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| posted on 14/8/12 at 12:51 PM |
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quote:
Originally posted by smart51
Decelerating to 20 then accelerating to 30 is not the problem. Various groups are pushing for blamket 20 MPH speed limits on all residential roads.
In any case, I want to debunk the emmissions part of the arguement using authoritative sources. If you want 20 MPH for safety reasons, argue it on
safety reasons.
...and Bristol council have just voted this through:
http://www.thisisbristol.co.uk/20mph-limits-round-2015/story-16605044-detail/story.html
Can't do more than about 15 MPH avg during commute anyway
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whitestu
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| posted on 14/8/12 at 01:20 PM |
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I mostly drive within London. 20mph would be nice - I typically average 12.
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David Jenkins
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| posted on 14/8/12 at 03:34 PM |
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About 10 years ago I worked in the City of London... every day there were queues everywhere, and no-one got anywhere fast.
Then, one morning, all the traffic lights failed due to power failure or something and... you guessed it... there were hardly any queues! To be
precise, there were queues on junctions where a traffic policeman was on point duty...
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black fingernail
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| posted on 14/8/12 at 06:48 PM |
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since the 20mph zones have got more widespread, has anyone else noticed the annoying and dangerous new habit developing, whereby stop and give way
signs are completely ignored, and cars will just stop halfway out of the junction and into into the road, to try and force you to stop and let them
out...............or is it me?
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JoelP
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| posted on 14/8/12 at 07:17 PM |
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20 zones wouldnt annoy me as much as 40 zones in the countryside - on a good day you can happily ignore the 20 signs and you dont tend to get stuck
behind some wally doing 20, however in the countryside you do often get stuck behind morons going too slow, and this increases the chance of an
inappropriate overtake happening, IMHO the most dangerous situation on the roads - frustrated drivers overtaking at silly moments.
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MikeRJ
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| posted on 14/8/12 at 08:24 PM |
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Road deaths increase in 20 mph zones
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NigeEss
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| posted on 14/8/12 at 09:22 PM |
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Apart from increased fuel consumption there would be an increase in journey times, which as a
self employed person will cost me time. So I will spend more time collecting mterials and less time
on jobs.
Time is an illusion. Lunchtime doubly so.................Douglas Adams.
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02GF74
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| posted on 16/8/12 at 08:16 AM |
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quote:
The number of people killed or injured on roads in built up areas with a speed limit of 20mph totalled 2,262 in 2011, up by 24% from 2010.
Meanwhile casualties on 30mph roads were down by 1% from 2010, recorded at 125,494 in 2011, according to data from the Department of Transport.
... but is that because there are more 20 mph roads and fewer 30 mph roads in 2011 than in 2010?
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