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..... Its rather obvious really.

 

Oh, and a degree in Automobile Engineering comes in handy as well.

 

 

ahhhh silly me... fancy me not knowing that....

 

so why have a degree in automobile engineering and have the business you do (with such a big car park too) and then ride a bike??

 

:D

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Baz

 

Kinetic Energy at any speed is 1/2 mv2. So the energy required to reach 30mph is 2.5 times that needed to reach 20mph. Hence it takes 1.5 times as much energy to go from 20 to 30 as it does from 0 to 20mph.

 

Clever stuff Rod and I bet that baffled a few and maybe they are now googling. I didn't as I understand it. That's the thing that makes my other half know I'm annoyed when he asks me to throw him the remote when I'm busy. When I'm not busy and throw it gently it does not hurt him... when I am busy and throw it faster he screams when it hits him. I love kinetic energy :D:D

 

Anyway I do have some sensible(ish) comments to add or should I say ask.

 

So here's my questions as you say you have a degree in Car Engineering and I don't.

 

1...On a straight clear 2 mile road (ie no need to slow down from 20 then go up again and no other cars or obstacles) how much would this 1.5 increase in k energy cost me in pennies if I drove at 30 and not 20 ? I dont suppose you can anser that though but maybe you can.

 

(No point in asking for roads which are stop and start or have traffic lights, islands, junctions, crossings etc as we all know that slowing down and speeding up or stopping and starting used more fuel.)

 

2....Presumably aerodynamics come into it though as I'd have thought the increase in kinetic energy would differ between two cars of the same mass/weight if they have different aerodynmaics. I could be wrong but thought I'd ask you as I can't ask Issac N.

 

I've always know that kinetic energy has an impact on stopping distances and the force of impact should you be unlucky enough to have one. I'm suprised you didn't mention that though although we are talking about fuel consumption rather than that area.

 

I also know that KE is increased if you have your boot full of crap which you don't need to carry around or with more people in the car etc which is why motoring organisations always say not to drive your car with loads things in it that you don't need as it will use more fuel.

 

3..... Are 20's P also campaigning for car driver to drive with less unneeded items in their cars as clearly this does cause increases in emissions, fuel consumption and excess kinetic energy on impact.

 

EEK... there's a thought... if a car has 5 people in it rather than just one is it more dangerous :shock:

 

Bloody hell I hate it when I suddenly get a 'need to know' moment becasue someone says something intriguing. And I though Algy was the only one who got me in that state :oops::lol:

 

Back to the happy photo section for me I think :blink:

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By the way Rod..... did you see this?

 

http://www.newyorker.com/talk/2010/12/06/101206ta_talk_parker

 

Quite funny!

 

Baz

 

Yes, it amused me as well.

 

But I wonder if you saw this :-

 

 

 

or maybe this :-

 

http://www.streetsblog.org/2012/02/02/applications-for-20-mph-zones-pour-in-from-the-bronx-brooklyn-and-queens/

 

 

or maybe even this :-

 

http://www.thetimes.co.uk/tto/public/cyclesafety/article3313881.ece

 

 

Regards

 

Rod

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Dizzy

 

Thanks for your questions.

 

1...On a straight clear 2 mile road (ie no need to slow down from 20 then go up again and no other cars or obstacles) how much would this 1.5 increase in k energy cost me in pennies if I drove at 30 and not 20 ? I dont suppose you can anser that though but maybe you can.

 

Well it would only be the initial acceleration that used extra fuel. And that would depend upon the Mass of the vehicle. I suspect not much. And 20mph seems to use on average the same as 30mph at a steady speed.

 

2....Presumably aerodynamics come into it though as I'd have thought the increase in kinetic energy would differ between two cars of the same mass/weight if they have different aerodynmaics. I could be wrong but thought I'd ask you as I can't ask Issac N.

 

Aerodynamics does not really effect kinetic energy of a moving object. But once you get up to a speed you have to keep using energy to overcome the aero drag (as well as the frictional forces). The power required to overcome aeodynamic drag is 1/2 pv3ACd

 

Where

 

p is the density of air (fixed)

v is the velocity

A is the frontal area of the object (large cars will be have more drag)

Cd is the drag coefficient of the object (brick shaped cars have a higher drag coefficient than sleek sports cars)

 

The formula changes slightly dependent upon the speed and how smooth the surface is but it shows that energy consumed is proportional to the speed cubed. hence at 60mph you have 3x3x3 (27) times the aerodynamic drag than at 20mph.

 

But aero drag at lower speeds is far less than the power in most cars so it really isn't noticed. aero drag becomes more prominent at speeds above 30mph.

 

3..... Are 20's P also campaigning for car driver to drive with less unneeded items in their cars as clearly this does cause increases in emissions, fuel consumption and excess kinetic energy on impact.

 

EEK... there's a thought... if a car has 5 people in it rather than just one is it more dangerous

 

The mass of the car at 1-1.5 tonnes is usually far more of a factor than the few kgs of rubbish that maybe we all have in our boot.

 

However, I think that a car with 5 people in it is far preferable to 5 cars with one person in it.

 

Regards

 

Rod

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Dizzy

 

You said :-

 

I will be steering clear of speed bumps from now on though as fuel consumption and emmissions seem to rocket with them

 

The AA - 20 mph Lower limits can increase fuel consumption and CO2 emissions

 

That report was based upon speeding up between speed bumps and then braking for the next one. We responded to that in a press Release in 2008 as follows :-

 

28th Jan 08 AA spreads misleading information on 20 mph and CO2 emissions

 

The recently publicised report from the AA claiming that 20 mph speed limits increases pollution is laughable for both it shallow basis for testing and its failing to understand the wider environmental reasons for, and benefits of lower speeds.

 

The report suggested that rogue drivers who accelerate between speed bumps will emit up to 46% more CO2. Rather than condemning this illegal and fuel wasting practice, the AA claims that this questions the environmental benefits of lower speeds.

 

It also reports that when travelling at a constant 20 mph in 3rd gear a car uses 10% more fuel (and emissions) than a constant 30 mph in 4th gear. Had they done the 20 mph test in 4th gear they would have found very little difference.

 

The AA also misses the point that high vehicle speeds are the greatest deterrent to people walking and cycling instead of using the car. In Hilden, Germany, the percentage of in-town trips made by bicycle increased to 23% since the introduction of an 18.6 mph speed limit in all residential roads. Britain’s default speed limit of 30 mph is 60% higher than that throughout most Northern European towns where far more citizens enjoy the opportunity to walk and cycle in greater safety. At the same time UK pedestrians form a greater percentage of road fatalities (21%)1 than any other EU country.

 

The increase in CO2 emissions caused by "rogue" drivers and their anti-social behaviour is insignificant compared to the huge saving in emissions from reducing speeds and enabling people to switch from cars to cycling and walking.

 

The latest government guidelines on urban speed limits enable the implementation of 20 mph speed limits without physical calming. The AA report is therefore both misleading and irrelevant.

 

Rod King of 20’ Plenty For Us said:-

 

“This report seems to be a knee-jerk reaction to the increasing demand for 20 mph on residential roads not only from communities but also drivers. The AA report is not credible and fails to take into account the environmental benefits of modal shift which comes from lower speeds.”

 

 

Regards

 

 

Rod

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Arrgh I posted again and it refused me :evil: I tried to open your links Rod and they kept freezing on me but I saw your face on the first one before it did and was asking if you had been at bridge foot on monday morning blah blah. Can't be bothered to type all that again now.

 

So third time lucky and completely different post as my mind had gone awol now.

 

Rod.... in brief regarding your first reply to me where you kindly give all the calculations and formulas.

 

It seems to me that aerodynamics do make a difference to fuel consumption at any speed so the more aerodynamic you are the less difference it will make.... although kineticly speaking on impact there may be little difference.

 

I suppose a more aerodynamic car would take longer to stop too though, have you covered this yet ?

 

I recon you use your forumals and kinetics to back the impact arguement rather than the fuel consumption one :wink:

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Arrgh I posted again and it refused me :evil: I tried to open your links Rod and they kept freezing on me but I saw your face on the first one before it did and was asking if you had been at bridge foot on monday morning blah blah. Can't be bothered to type all that again now.

 

So third time lucky and completely different post as my mind had gone awol now.

 

Rod.... in brief regarding your first reply to me where you kindly give all the calculations and forulas.

 

It seems to me that aerodynamics do make a difference to fuel consumption at any speed so the more aerodynamic you are the less difference it will make.... although kineticly speaking on impact there may be little difference.

 

I suppose a more aerodynamic car would take longer to stop too though, have you covered this yet ?

 

I recon you use your forumals and kinetics to back the impact arguement rather than the fuel consumption one :wink:

 

Dizzy

 

The fuel used to overcome the aero drag is proportional to the cube of the speed. At high speed almost all of the fuel is used for pushing the air out of the way.

 

But at low speeds the major use of fuel is for re-accelerating after braking and overcoming friction in the tyres and drive train.

 

If you look at impact speeds then the energy needed to be lost is the kinetic energy in the vehicle and is therefore proportional to the square of the speed. hence a 30mph car colliing with an object has to lose 2.5 times more energy than one at 20mph. That is why damage to vehicle and object it collides with are very dependent upon impact speed.

 

Also you need to take into account the fact that the braking time available before impact is less at 30mph than 20mph. Even if you do get a braking reduction of 10mph to reduce impact speed from 30mph to 20mph (impact speed is now 20mph) if the car had been driving at 20mph then if you applied the same braking reduction then impact speed would be 10mph. In such a case the car with the initial speed of 30mph (20mph impact speed) would have 4 times the kinetic energy just before impact of the car with an initial speed of 20mph (10mph impact speed). Rememeber that kinetic energy is proportional to the square of speed.

 

No wonder that pedestrian and cycle injuries (as well as car damage) reduce substantially with lower speed vehicles.

 

 

Regards

 

 

Rod

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Blummin' heck Rod I can't keep up with you at all as you type and reply very fast. SLOW DOWN WILL YOU :P

 

Surely you too must have a cup of tea to drink or tomorrow's packed lunches and kids stuff to sort but at least you don't have to read, check or join in with all the other interesting topics on here too though eh? :lol:

 

So how about gear ratios as they make a difference to fuel consumption, drag and whatever else it was we were discussing.

 

Night Rod... maybe tomorrow re the rest of your info as I'm sure I'll have even more girlie questions once I have time to read and digest them :oops:

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I repeat

 

Reducing the speed limit from 30 to 20 will result in higher emissions and higher fuel consumption, so whatever the levels are in near gridlocked Warrington, we can looked forward to even higher levels.

 

:lol: Do you feel like you are stuck in a rut and being ignored Wolfie.

 

Maybe rather than 'repeat' you should 'howl' next time especially if there is a full moon :wink::lol:

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That is certainly true Wolfie as I can't really get out of 3rd gear in mine (1.6 manual) until after 20 mph so 4th and 5th gears are redundant. Our diesel guzzling 3L Turbo automatic 4x4 doesn't want to change either at lower speeds and revs stay high so fuel consumption is higher.

 

I feel like I have to add a formula now too as you are all doing it... errm

 

Higher gear = less engine revs (at speed) therefor far better fuel consumption.

 

I put at speed as obviously you can't drive in 4th/5th at 10mph as you would stall but you can at say 25 to 30mph

 

Right... time for me to read all the other posts now as I'm rather enjoying this physics lesson :D8)

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Dizzy

 

Whilst driving at any particular speed in a lower gear may use marginally more fuel than in a higher gear, there is no justification for believing that driving at say 3000rpm in a gear at 20mph will use any more fuel that driving at 2000rpm at 30mph.

 

The engine management systems measures and controls the amount of fuel being used in an engine and matches it to the speed of the engine, speed of the vehicle and the throttle position used by the driver. Soemeone using a light throttle at 20mph in 3rd gear will use less fuel than someone putting their foot to the floor in 4th gear at 30mph.

 

The fuel used is a product of the amount of fuel squeezed into the cylinder on each stroke and the speed of the engine. Because you are in a lower gear then the load on the engine is less because of the gearing and hence the amount of fuel squirted into the engine on each revolution is also less. However this is balanced by having mor revolutions and that is why there is little variation (about 10%) in fuel consumption at 20mph or 30mph, regardless of gearing.

 

Modern cars are surprisingly economic at low speeds. A Citroen C4 does 99mpg at a steady 20mph. Now, you and I know that 99mpg is almost impossible to achieve in normal urban and residential environments. By far the biggest consumer of fuel is that required for acceleration and which is repeatedly lost every time you brake. It is this which brings down the economic 99mpg at 20mph or even 30mph to the more realistic 20-40mpg that most cars get.

 

Hence if in any urban journey you can do a greater %age driving where you get 99mpg or such then this will reduce your overal fuel consumption. If at the same time you can reduce the amount of repeated acceleration (from 20mph to 30mph) then this will also reduce your consumption. And 20mph limits both enable steady speeds to be maintained longer and reduces repeated acceleration.

 

Thanks for trying to get your head around this.

 

Best regards

 

 

Rod

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front page news today.... decision being made by Exec Board tonight :unsure:

 

http://www.warrington-worldwide.co.uk/articles/12536/1/Final-approval-for-20mph-roll-out/Page1.html

 

You kept that quiet Rod :mellow::roll:

 

It says objections will be taken into consideration... does that mean we have to have objected by now even though we still don;t know which roads will be affected or does it mean there WILL now be full and proper consultations within each area or on a 'whole' scale and we can object then if need be ?

 

 

 

PS... Thanks for your other reply Rod :D I still think you need to drop the 'it will save on fuel and reduce emmissions' and give a more balanced view. I've had it all explained to me now although rather more indepth than you said and across a broader sense and yes apparently in some cars it may slightly reduce emissions based on vehicle, roads etc etc but in the mayority it definately wont reduce emissions or fuel consumption it will increase it. :cry:

 

And also somemething about hybrid cars flicking from electric to engine (and fuel) at around 30 mph as that is when an engine becomes efficient. Or something like that anyway :blink:

 

All irrelavant really though as it seems we're getting it anyway as the exec board wont understand any of it so you will clearly baffle them Rod.

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Ahhh I just found tonight's docs and yes at some stage in the future there should be a consulation.

 

All the areas and roads (well sort of) are listed on it.

 

See here... agenda item 7

Exec Board Decision Meeting 13 Feb 2012

 

Looks like Stockton Heath is not until year 6 anyway, although there are clearly roads round here that would benefit from being 20mph and which should be anywa ie those near all schools etc.

 

Anyway, for SH the big rollout table doesn't have the area in the box like the others it simply lists Fairfield Road and Ellesmere Road so does that mean none of the other side roads will become 20mph after all :unsure:

 

Clear as mud as usual :blink:

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....and re: enforcement the Police say there may be some but ONLY if there is a clear defiance of the limit on a certain road or area by a substantial number of drivers and then the police will intervene.

 

They also say

 

There is still a grey are in relation to enforcing 20mph that ACPO is presently working to resolve.

 

The issue is set around the agreed use of Driver Improvement schemes for minor speeding offences which is presently documented on all roads from 30mph and above.

 

At present there is no ‘buffer’ to allow drivers to be

guided to a course at 20mph with straight fixed penalty fines and points the only

enforceable option.

 

I hope all the 20's and non 20's are CLEARLY signed so as to avoid any accidental breaking of the 20 speed limit by people whoare not familiar with the areas etc :shock:

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All the formulas in the world ignore the fact that most cars need to be driven in a lower gear at 20mph than 30mph.

 

Lower gear = higher CO2 and higher fuel consumption. Forget the other formulas

And yet Rod still maintains that the (largely) impossible is perfectly possible. Even if a car is to be driven in 4th gear at 20mph, it will be labouring, and a labouring engine also uses more fuel. Amazing though for a man with his background that he insists on talking nonsense on this particular strand of the discussion.

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Thanks for the link Dizzy, so Cromwell Aveneue is "residential" is it and slated for 20mph?

 

 

I don't think it means that Fatshaft as the way I read the table and the other info.... I think means that all the residential roads which are inside the border/boundaries of the main roads ie "Cromwell Avenue (A574), Cannons Road, Hood Lane North, Burtonwood Road, Westbrook Way." will mainly become 20's etc .

 

....although I could be completey wrong of course but looking at the other boundaries and roads named they all seem to be the main key roads too but it takes some figuring out and is not clear at all.

 

It would have been far easier if they had just listed every road in Warrington and put 'yes', 'no' or 'possibly' next to them but I guess that would be too easy and people would understand that and realise ... hey even the exec board might understand it too then :lol:

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Not how I read it. As Cromwell has no houses on it and is a main trunk route (A574) then should be excluded. 20 acre and old hall road should also be excluded due to the bus issue (and that 20 acre doesnt have any houses) although 20mph around the school may be reasonable.

 

However they do have to stick to these rules and they have said that they wont necessarily. So no certainty at all then....

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