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Speeding Tickets Issued Against Guidelines
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sussamb
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PostPosted: Wed Jun 01, 2016 10:12 am    Post subject: Reply with quote

Yes, hardly the 'negligible amount' someone mentioned Rolling Eyes

JimmyTheHand wrote:
So how much more longer does it take to stop at 33mph than 30mph - I'd suggest it is almost negligible ...

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M8TJT
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PostPosted: Wed Jun 01, 2016 12:02 pm    Post subject: Reply with quote

Oh, and BTW, the distances mentioned by Duddy and me do not include 'reaction distance' which is reckoned by HC to be approx 0.7 second = 1 foot/MPH i.e. 3 feet extra at 33MPH and 5 feet extra at 35MPH which makes the overall at 30MPH 12 feet extra and from 35MPH an extra 21 feet. (Getting on for nearly double the overall stopping distance compared with 30MPH.)

As suss says, so much for "insignificant" and just goes to demonstrate the total miss-understanding of the effects of speed on stopping distances shown by some people.
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DennisN
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PostPosted: Wed Jun 01, 2016 4:24 pm    Post subject: Reply with quote

Question Surprised Not Worthy

My dear old granny says if I stay under the speed limit I'll live another five years. Absolute bargain, being as how I've already well had my three score and ten!
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DennisN
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PostPosted: Wed Jun 01, 2016 4:25 pm    Post subject: Reply with quote

By the way, all you geniuses have forgotten that the quicker you brake, the faster you go slower. Cool
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MaFt
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PostPosted: Wed Jun 01, 2016 9:35 pm    Post subject: Reply with quote

Regardless of stopping distances, advances in car technology, increases in gadgets, weather conditions etc etc etc - the law's the law whether we agree with it or not.

You may think it's safe to travel at 33mph on a 30mph road - that's fine, but the simple fact it it's breaking the law. Yes, chances are it might end up safe and not hurt anyone.

Stealing a chocolate bar doesn't really hurt anyone - but it's still illegal.

So until the government revise how road speeds are decided (probably never) then we just have to make do with it. Your new car might mean you don't feel like you're going as fast as you are (extra padding, quiet/smooth ride etc) so surely that's all the more reason to use a camera database as a reminder?

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JimmyTheHand
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PostPosted: Wed Jun 01, 2016 9:35 pm    Post subject: Reply with quote

Duddy wrote:
Just picked up this tread. Without going into the ins and outs of exceeding the speed limit a question was asked what the stopping distance difference was between 30 and 33 mph.
It is of course variable dependant on road condition but using the figures from the highway code (Not admissable in law) i.e. deceleration rate of 0.68g the stopping distance from 30 mph would be 13.47m (44ft 2.5 inch) and from 33 mph 16.31m (53ft 6inch). Difference 2.84m further.


Sure if your car's braking is cable operated drum brakes all round, no abs and emergency brake assist and running on 1950's tyres - the chances are you car has at least front disks, hydraulic operated and assisted along with ABS and tyres, i.e. has improved.

However the one thing that hasn't changed the driver and I suspect for a lot of younger drivers have never driven cars without ABS etc, so I suspect are less likely to plan ahead (I think you can see that on motorway everyday) and thus average thinking distance will increase.

Interestingly this Video has braking distances at 60kph (37.5 mph) of 42 metres which is 24 metres thinking distance (highway code 9m * 37.5/30 = 11.25 metres) and 18 metres stopping distance (high way code has 14 metres at 30mph at 24 at 40) so thinking time is greater than twice what the highway code.

sussamb wrote:
Yes, hardly the 'negligible amount' someone mentioned Rolling Eyes

JimmyTheHand wrote:
So how much more longer does it take to stop at 33mph than 30mph - I'd suggest it is almost negligible ...


Now how much time does it take to check your speedometer I'd suggest by the time you have glanced down, processed the display and decided how to react and returned attention back to road it is somewhere close to the highway code thinking distance (because of the way the brain works you will mainly beware of speedometer and road not the gaps/processing ) i.e. about 0.7 seconds or 9 metres at 30mph, so at one point you will add 9 metres to your thinking distance. Now how often do people check their speed, every 100 metres if they are paranoid about being caught speeding? What triggers people to check their speed? Does anything the anti-speed campaign do make people check speedometers when they should just slow down.

Personally I think we could do much more to improve safety but it involves driver education, unfortunately it seems to be the authorities are only interested in speed, which I suspect is well into the diminishing returns part of the curve.
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MaFt
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PostPosted: Wed Jun 01, 2016 9:38 pm    Post subject: Reply with quote

JimmyTheHand wrote:
Personally I think we could do much more to improve safety but it involves driver education, unfortunately it seems to be the authorities are only interested in speed


Totally agree!
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sussamb
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PostPosted: Wed Jun 01, 2016 9:50 pm    Post subject: Reply with quote

JimmyTheHand wrote:

sussamb wrote:
Yes, hardly the 'negligible amount' someone mentioned Rolling Eyes

JimmyTheHand wrote:
So how much more longer does it take to stop at 33mph than 30mph - I'd suggest it is almost negligible ...


Now how much time does it take to check your speedometer


Fraction of a second, same for checking mirrors. Part of the information gathering process that makes a good driver .... Google IPSGA Smile
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Kremmen
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PostPosted: Thu Jun 02, 2016 4:42 am    Post subject: Reply with quote

As MaFt said, I use the database as a reminder to check my speed. I try not to speed but it's easy to drift over with modern cars.

I certainly don't use the database as a warning system to temporarily slow down as has been posted here a few times.
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claireswares
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PostPosted: Fri Jun 03, 2016 8:37 am    Post subject: Reply with quote

NukeThemAll wrote:
Time for some science regarding speed, stopping distance and 'damage'.

Assuming a car has a constant deceleration... blah blah
[/i]


... and that's where the pseudo-science falls down. Rolling Eyes
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M8TJT
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PostPosted: Fri Jun 03, 2016 9:15 am    Post subject: Reply with quote

So, are you are implying that because the car does not exhibit absolutely constant deceleration (-a), the all the above calculations can be totally ignored, and increasing the speed has no effect on the stopping distance and stopping distance is not proportional to velocity squared? Rolling Eyes Rolling Eyes I have no doubt that it could also be argued that as an exact 'straight line' stop is unlikely, then that makes a total mockery of the car's speed being considered to be its velocity (v).
Presumably then, along the same lines, its kinetic energy does not go up with velocity squared as it is unlikely that the car will be going in an exact straight line.
HERE'S a little light reading.
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Kremmen
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PostPosted: Fri Jun 03, 2016 11:20 am    Post subject: Reply with quote

Isn't is easier to just obey the speed limits and if you are unfortunate to have an accident (can you call it an accident if you are speeding) then you have no concience if you maim someone.
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M8TJT
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PostPosted: Fri Jun 03, 2016 11:42 am    Post subject: Reply with quote

Yes.
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NukeThemAll
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PostPosted: Fri Jun 03, 2016 12:09 pm    Post subject: Reply with quote

Having a dash cam (as I do) is another incentive to obey the speed limits. Why? Because if I'm unfortunate enough to have an accident and wish to demonstrate to the Police and/or my insurance company that it's not my fault, my GPS-equipped dash cam will have been recording my speed.

To answer some of the other points that have been made.....

The wonderful thing about science is that it's true whether you believe it or not. The physics of kinetic energy is simple. My exposition of the science of braking is indeed simplified but nonetheless is (I'm sorry) correct. I didn't factor in driver reaction time, but that's easy to do - it's generally assumed a constant at about 2.3 seconds (but note the 'average' - it varies hugely according to predictable factors)

Regarding modern cars' deceleration capabilities..... even a standard family hatch can brake from about 60 mph (about 27 m/s) to 0 in about 35 metres on a grippy dry road with good tyres, ignoring driver reaction time. This is an average deceleration of (27x27)/(2 x 35) = 10.4 m/s**2 (and yes, a modern car can exceed 1g braking - there's lots of papers out there which will explain why)

The reality is of course much more complicated - roads might be wet, reaction times longer, drivers are generally reluctant to 'emergency brake' until it's screamingly obvious they're heading for trouble (again, do some basic research and all of this is explained) so the Highway Code assumes a lower deceleration.

But the fact (basic physics) remains - the faster you go, the less likely you'll stop in time when The Very Bad Thing happens, and if you don't stop and you hit something/someone, the probability of death or serious injury rises rapidly with residual velocity.

Even if you disagree with all the above - as has been said, none of your protestations will work in court if you get caught speeding. It's The Law and it may be a very blunt instrument but, well, there it is.
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Kremmen
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PostPosted: Fri Jun 03, 2016 12:21 pm    Post subject: Reply with quote

I'll bet these inner town 20mph limits have been implemented because to some the old 30 = 35+ = a fatality that could have been an injury.

I wonder what speed the Stirling Moss brigade do under 20mph limits ?
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