Tony Lockhart
Avoiding Stress, at Every Opportunity
No such thing as zero emissions. The energy comes from somewhere, and could be used for something else.
Is it time for all motor vehicles to be fitted with a black box?
- Thread starter S-Man
- Start date
No such thing as zero emissions. The energy comes from somewhere, and could be used for something else.
@Tony Lockhart - that’s it, and more succinctly than I’d written.
There are other factors too: tyre wear increases dramatically above 120 km/h, producing lots of nasty microplastic particles that pollute waterways.
There are other factors too: tyre wear increases dramatically above 120 km/h, producing lots of nasty microplastic particles that pollute waterways.
20mph zones is the only significant lowering. Smart motorways reduce speed when there is congestion or accidents. Cars keep getting faster & bigger but we have not evolved into better drivers. Whenever a safer/greener method of transport is mooted car drivers always kick up a stink. Our entire transport infrastructure is geared around cars it’s not too much to ask for a little restraint when it comes to speed. Other forms of transport are available.
Looks like the claims of SafeSpeed are not as valid as some here would suggest :- https://en.wikipedia.org/wiki/Safe_Speed
It even says here that the originator of the site was "a crank" :- https://www.monbiot.com/2005/12/22/paul-smith-and-safe-speed-the-self-exposure-of-a-crank/
CHE
It even says here that the originator of the site was "a crank" :- https://www.monbiot.com/2005/12/22/paul-smith-and-safe-speed-the-self-exposure-of-a-crank/
CHE
Tony Lockhart
Avoiding Stress, at Every Opportunity
Speedometers aren’t calibrated to be accurate under 30mph. There has been a challenge on Pistonheads over the years for someone to prove they’ve been collared for exceeding 20mph, I don’t think it has ever happened, unless maybe they were being silly and doing 50 for example.
Funk
pfm Member
Fair comment - it was one of the upper results when I searched. The messenger may be dodgy but the message isn't - here's a couple of government documents discussing it:
http://data.parliament.uk/Deposited...DfTCircular01-2013SettingLocalSpeedLimits.pdf
Page 11: "34. Mean speed and 85th percentile speed (the speed at or below which 85% of vehicles are travelling) are the most commonly used measures of actual traffic speed. Traffic authorities should continue to routinely collect and assess both, but mean speeds should be used as the basis for determining local speed limits.
35.For the majority of roads there is a consistent relationship between mean speed and 85th percentile speed. Where this is not the case, it will usually indicate that drivers have difficulty in deciding the appropriate speed for the road, suggesting that a better match between road design and speed limit is required. It may be necessary to consider additional measures to reduce the larger than normal difference between mean and 85th percentile speeds or to bring the speed distribution more in line with typical distributions. The aim for local speed limits should be to align the speed limit to the conditions of the road and road environment."
35.For the majority of roads there is a consistent relationship between mean speed and 85th percentile speed. Where this is not the case, it will usually indicate that drivers have difficulty in deciding the appropriate speed for the road, suggesting that a better match between road design and speed limit is required. It may be necessary to consider additional measures to reduce the larger than normal difference between mean and 85th percentile speeds or to bring the speed distribution more in line with typical distributions. The aim for local speed limits should be to align the speed limit to the conditions of the road and road environment."
https://www.standardsforhighways.co.uk/prod/attachments/8995b012-dac8-4ee3-a8a8-03da2e5c2ae4
Page 12: "85th percentile speed calculation
3.1 85th percentile vehicle speeds shall be calculated where designs are to be based on measured vehicle speeds. NOTE 1: 85th percentile vehicle speeds can be calculated using a variety of methods, including: 1) built-in functions in spreadsheet software; 2) statistical formulae; and 3) listing out the measured speeds in ascending order and counting down from the highest value until 15% of the values have been passed (the value that is arrived at is the 85th percentile speed). NOTE 2: The method of listing out the measured speeds in ascending order and counting down to establish the 85th percentile is only suitable for samples that include 200 or more vehicles."
3.1 85th percentile vehicle speeds shall be calculated where designs are to be based on measured vehicle speeds. NOTE 1: 85th percentile vehicle speeds can be calculated using a variety of methods, including: 1) built-in functions in spreadsheet software; 2) statistical formulae; and 3) listing out the measured speeds in ascending order and counting down from the highest value until 15% of the values have been passed (the value that is arrived at is the 85th percentile speed). NOTE 2: The method of listing out the measured speeds in ascending order and counting down to establish the 85th percentile is only suitable for samples that include 200 or more vehicles."
I'm not sure how recent the second link is and there may be a newer version of the first but 2013 was the most recent I could find.
P.S. Some would say Monbiot's also a bit of a fruitloop himself... 
I'm not sure about where you are but a significant number of roads near me that were once NSL (60 and 70) are now 50 limits, 50 limits are now 40.
Again, to be clear I'm not arguing against speed limits, I'm questioning the validity with which they're set. Our roads are some of the safest in the world already - where's the tipping point for drivers to say "That's absurd..." when limits reduce again and again?
Also some here may be of the opinion I'm a speed-crazed loon - I'm very much not, although I will admit to some tomfoolery in my younger days...
Speed limits are generally lowered in line with changes to urban environment or accidents. It is perfectly conceivable for limits to be brought down due to the spread of urban hinterland. Things change.Fair comment - it was one of the upper results when I searched. The messenger may be dodgy but the message isn't - here's a couple of government documents discussing it:
http://data.parliament.uk/Deposited...DfTCircular01-2013SettingLocalSpeedLimits.pdf
Page 11: "34. Mean speed and 85th percentile speed (the speed at or below which 85% of vehicles are travelling) are the most commonly used measures of actual traffic speed. Traffic authorities should continue to routinely collect and assess both, but mean speeds should be used as the basis for determining local speed limits.
35.For the majority of roads there is a consistent relationship between mean speed and 85th percentile speed. Where this is not the case, it will usually indicate that drivers have difficulty in deciding the appropriate speed for the road, suggesting that a better match between road design and speed limit is required. It may be necessary to consider additional measures to reduce the larger than normal difference between mean and 85th percentile speeds or to bring the speed distribution more in line with typical distributions. The aim for local speed limits should be to align the speed limit to the conditions of the road and road environment."
https://www.standardsforhighways.co.uk/prod/attachments/8995b012-dac8-4ee3-a8a8-03da2e5c2ae4
Page 12: "85th percentile speed calculation
3.1 85th percentile vehicle speeds shall be calculated where designs are to be based on measured vehicle speeds. NOTE 1: 85th percentile vehicle speeds can be calculated using a variety of methods, including: 1) built-in functions in spreadsheet software; 2) statistical formulae; and 3) listing out the measured speeds in ascending order and counting down from the highest value until 15% of the values have been passed (the value that is arrived at is the 85th percentile speed). NOTE 2: The method of listing out the measured speeds in ascending order and counting down to establish the 85th percentile is only suitable for samples that include 200 or more vehicles."
I'm not sure how recent the second link is and there may be a newer version of the first but 2013 was the most recent I could find.
P.S. Some would say Monbiot's also a bit of a fruitloop himself...
I'm not sure about where you are but a significant number of roads near me that were once NSL (60 and 70) are now 50 limits, 50 limits are now 40.
Again, to be clear I'm not arguing against speed limits, I'm questioning the validity with which they're set. Our roads are some of the safest in the world already - where's the tipping point for drivers to say "That's absurd..." when limits reduce again and again?
Also some here may be of the opinion I'm a speed-crazed loon - I'm very much not, although I will admit to some tomfoolery in my younger days...
I am now one of those annoying people who stick to limits & often drive under them when I feel it’s appropriate.
Smart motorways are very dangerous. If you breakdown there is simply nowhere to go other than stop in the lane you are in.
Cars have had to get bigger to accommodate safety features such as 99 million airbags, TC, ESP, Lane Control, seat-belt tensioners, automatic braking blah, blah, blah.
A Ford Fiesta isn't massively faster than one from the 70s - aerodynamics contribute to higher top speeds. The cars are heavier but weight has no effect on maximum speed.
I agree that driving standards have not improved, in my opinion the 'me, me, me' attitude these days has made things worse.
I don’t mind smart motorways but fail to see why they do away with a hard shoulder; that is the opposite of smart.
I get why cars have got bigger to a point but now even vehicles which started big are getting bigger. 3 series BMW is the same size as a 90s 7 series, utterly nuts. Look at all the stupid 4x4s, I would like an X5 though
I get why cars have got bigger to a point but now even vehicles which started big are getting bigger. 3 series BMW is the same size as a 90s 7 series, utterly nuts. Look at all the stupid 4x4s, I would like an X5 though
Yep, passenger safety cages and crumple zones take up lots of room.
My local MOT guy is a BMW service specialist and loves X5s - for the revenue they bring in.
TheDecameron
Unicorns fart glitter.
Sorry this is unreferenced, it was presented at a conference on speeding organised by Edinburgh City Council in October. The rule of thumb I had heard previously was that at 30mph the majority of pedestrians survive, at 40mph the majority die.
TheDecameron
Unicorns fart glitter.
And they deliver more kinetic energy to the skeleton of the pedestrian/ cyclist they hit.
Thorn
pfm Member
Every cloud...
Darth Vader
From the Dark Side
Yes indeed but its relatively small compared to speed. The KE is proportional to the velocity squared so from your table above we have at 20mph 400units at 30mph 900 units whilst at 40mph 1600units. So a car with 10% extra mass would add add 10% to those figures and so on.
Its that velocity squared that causes the damage. You can see why 25mph is often chosen as a speed limit in areas likely to have pedestrians from the above figures.
DV
Tony Lockhart
Avoiding Stress, at Every Opportunity
Where?
TheDecameron
Unicorns fart glitter.
Thanks for putting it in context DV. The other issue with speed is that it’s a futile method of making progress through urban centres- traffic light sequencing and bottlenecks see to that. It doesn’t stop some drivers racing away from a light for 200yds ( at 45mph in a 20mph zone as I saw yesterday) till they reach the next obstacle and slam on the breaks. For me it’s a balance of safety and keeping traffic flowing and from what I’ve actually experienced in Edinburgh 20mph looks reasonable as a limit.
