On Fri, 30 Jul 2010 03:40:11 -0700 (PDT)
Andy wrote:
You seem to miss the subtle detail that the distances are massively long
for any even remotely competent and roadworthy vaguely modern vehicle.

I don't think that they're massively long. If you look at the table in
the highway code, it gives the distances in terms of car lengths
(being 4m):

Frankly who cares and why do they bother anyway. Its not possible to accurately
gauge distance from behind the wheel of a car so its all a waste of time.

B2003

Andy gurgled happily, sounding much like they were
saying:

You seem to miss the subtle detail that the distances are massively
long for any even remotely competent and roadworthy vaguely modern
vehicle.

I don't think that they're massively long. If you look at the table in
the highway code, it gives the distances in terms of car lengths (being
4m):

20mph = 3 car lengths, 50mph = 13 car lengths, 70mph = 24 car lengths
(=96m) with the other speeds in between.

75m, actually - we're talking about the stopping distance. Whether the
average driver's reactions accord to the guesstimates in the HC is
another question entirely.

And, yes, they are - hugely so.

A quick google tends to bury actual road test information under swathes
of HC related stuff, but here's one...

http://www.insideline.com/subaru/imp...t-2002-subaru-
impreza-outback-sport.html

So that's a roughly 8yo test of a fairly heavy non-performance-oriented
car, with drum brakes on the rear and "all-season" tyres (virtually
unknown in the UK, being a compromise between the tyres we see (known as
"summer" elsewhere) and winter tyres).

127ft from 60 to a stop. 38m. HC quotes 55m. 45% further.

In article , d
scribeth thus
On Fri, 30 Jul 2010 11:05:56 +0100
Bruce wrote:
Of course the easiest way to 'defeat' the cameras is to stick to the
speed limit. Boring, I know, but it also helps save fuel.

Actually the easiest way to defeat them is to drive a foreign registered
car of which there are plenty around. If road safety was really the concern
then they'd have traffic plods patrolling the road, not revenue raising
"safety" cameras.

B2003


Quite.. I just wonder where they are most all of the time. I have to use
the A14 in Cambridgeshire quite a bit of the time . The driving
standards are very poor but where is Mr Plod?. Tucked away in the police
canteen somewhere not being able to afford the petrol?. Or filling lotsa
forms and paperwork?.

OK sure they can't be everywhere all of the time but it does have an
influence on driver behaviour a patrol car ....
--
Tony Sayer

Adrian wrote:

Chris Tolley (ukonline really) gurgled happily,
sounding much like they were saying:

This may come as a shock to you, but the tables never had anything
to do with real performance. They are a simple mathematical model
linking the speed in mph with the stopping distance in feet. Anyone
with GCSE maths should take no more than 2 minutes to deduce the
formula that is used..

Sure. But the formula was based on a roughly representative family
car of the period - the 105E Anglia, allegedly.

The formula is far too simple to be based on anything real.

No, but the formula would have been worked so that the resulting
stopping distances are approximately correct for "something real".

Perhaps you should offer some evidence for this contention.

Put it this way - I didn't bother to memorise the distances for my
driving test. I memorised the formula, and as I say, it links mph to
feet. The only way in which it would have any resemblance to reality is
if there were some universal driving constant whose value happens to lie
in the region of 1/5280, being the conversion factor from miles to feet.

So did this formula get plucked from thin air for a totally random result?

I see mathematics is not your strong suit. Formulas do not give totally
random results. (And no, I'm not going to enter into a debate about
chaos theory.)

Why 75m from 70mph?
Why not 200m or 20m?

The thinking distance is merely the speed in mph expressed in feet. The
stopping distance is merely the speed in mph squared and divided by 20,
then expressed in feet.

vmph v ft thinking + v*v/20 stopping

20mph --- 20 ft thinking + 20*20/20 stopping ---- 40ft
30mph --- 30 ft thinking + 30*30/20 stopping ---- 75ft
40mph --- 40 ft thinking + 40*40/20 stopping ---- 120ft
...
70mph 70 70*70/20 ---- 315ft

Your "75m from 70mph" is merely the stopping part of that - 245ft. It
should be 315ft. Manifestly, you are driving without thinking.

As for your Ford Anglia allegation, the Highway Code predates Ford
Anglias by several decades. The same figures were included in the 1946
HC, and may have been in versions before that; I can't be bothered to
look them up.

I respectfully suggest that you could have looked this up just as easily
as I did, and if you had done so you would not have gone on to make it
look quite so much as if you don't know what you are talking about.

It no doubt gives and always gave a safety margin. But until every
relevant vehicle has ABS

Which doesn't actually make the slightest difference to stopping
distances, since it does absolutely nothing at all unless the driver
cocks up in a way that would have failed them their driving test.

Never having had a car so fitted, I wouldn't know. The only evidence I
have to go by is that the continuous rubber smears on the road tend to
be longer than that dashed ones, from which I infer that ABS reduces
stopping distances.

Did you miss the "unless"?

No. I did not.

I explained that I would not know from personal experience what
difference ABS makes, and then went on to present information that I can
glean about ABS. Could you not tell that from what I wrote?

Personally, I drive according to the two second rule. That's much more
straightforward. I observe that many of my fellow road users think they
are considerably better drivers and can get away with a 0.5 second rule.

I don't think anybody's said anything to contradict that.

But if these figures purport to be a typical "stopping distance", do you
not think it might actually be useful if they were?

They purport to be a "thinking and stopping" distance. There are some
who believe that the thinking element is insufficient, and that overall
the distances quoted in the HC are reasonable as they are. For example -
here's one guy who claims to have *proved* it.

http://www.peterjackson.org.uk/Stopp...0distances.htm


--
http://gallery120232.fotopic.net/p9683753.html
(142 083 at Lancaster, Mar 1991)

Chris Tolley (ukonline really) gurgled happily,
sounding much like they were saying:

So did this formula get plucked from thin air for a totally random
result?

I see mathematics is not your strong suit. Formulas do not give totally
random results. (And no, I'm not going to enter into a debate about
chaos theory.)

I do apologise - I thought it relatively clear that I was not referring
to the precise formula and the precise figures, but the ball-park figures
and the meaning they convey.

Why 75m from 70mph?
Why not 200m or 20m?

The thinking distance is merely the speed in mph expressed in feet. The
stopping distance is merely the speed in mph squared and divided by 20,
then expressed in feet.

Once again - why that particular formula resulting in figures in that
particular ballpark?

Your "75m from 70mph" is merely the stopping part of that - 245ft. It
should be 315ft. Manifestly, you are driving without thinking.

sigh No, but you do appear to be posting without thinking or reading...

It no doubt gives and always gave a safety margin. But until every
relevant vehicle has ABS

Which doesn't actually make the slightest difference to stopping
distances, since it does absolutely nothing at all unless the driver
cocks up in a way that would have failed them their driving test.

Never having had a car so fitted, I wouldn't know. The only evidence I
have to go by is that the continuous rubber smears on the road tend to
be longer than that dashed ones, from which I infer that ABS reduces
stopping distances.

Did you miss the "unless"?

No. I did not.

I explained that I would not know from personal experience what
difference ABS makes, and then went on to present information that I can
glean about ABS. Could you not tell that from what I wrote?

So I can only presume, then, that you have not taken a driving test? If
you lock the brakes on the emergency stop, you would fail the test - as
well as massively extending the stopping distance.

But if these figures purport to be a typical "stopping distance", do
you not think it might actually be useful if they were?

They purport to be a "thinking and stopping" distance.

sigh I'm not sure why you're being so obtuse about this.

Look at the chart in the HC. For each speed there is a thinking distance
and a stopping distance.

Clearly, humankind has not evolved in the last half century, so we can
assume that the thinking distance has remained relatively static. So the
stopping distance is what we are discussing.

d wrote:

some sanctamonious do gooder

ITYM, "a concerned citizen who had observed somebody breaking the law".
Would I be a "sanctamonious do gooder" if I reported somebody breaking
in to your house?

Cheers

mark-r

On 30/07/2010 07:23, Charles Ellson wrote:
On Thu, 29 Jul 2010 14:28:53 -0700 (PDT),
"jonporter1052@btint ernet.com wrote:

On 29 July, 15:15, wrote:
On Thu, 29 Jul 2010 15:01:56 +0100


Paul wrote:
In , David Walters
writes

On Thu, 29 Jul 2010 14:08:34 +0100, Paul Terry wrote:

Added to which, it has been widely reported (and confirmed by the
cameras' manufacturer) that drivers can defeat a SPECS camera by the
potentially unsafe practice of lane-hopping during the measured section
of road.

That hasn't been the case since sometime in 2007.

http://www.theregister.co.uk/2008/07...d_camera_myth/

Ah, glad to hear that that loophole has been closed.

Did anyone believe it worked anyway? Why would anyone writing the software
make the cars lane part of the database key in the first place? It makes
no sense whatsoever.

Possibly for the sake of simplicity to allow for e.g. the difference
in speed between two vehicles remaining in parallel in lanes 1 and 4
where there is a significant curve between measurement points. If the
usual 10% etc. tolerance is ignored and speed limits applied strictly
then in theory it would be possible for the two vehicles to stay
together with one under and one over the speed limit.

Do the maths... the standard lane width on a motorway is 3.65 m, so the
maximum extra distance, even assuming the motorway does a 90 degree
turn, is 3 * PI/2 * 3.65 or about 18 metres. Assuming the average speed
cameras are fairly close, say 1/2 mile (or 800 m), this is only 2% of
the distance (and hence a difference in speed of 2%).

In practice, there aren't many (any?) motorways that do a 90 degree
curve in 800 metres, so the difference in speed would in practice be
less than this.
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/

On Fri, 30 Jul 2010 13:02:34 +0100
Mark Robinson wrote:
wrote:

some sanctamonious do gooder

ITYM, "a concerned citizen who had observed somebody breaking the law".

Concerned about what exactly? That the biker could get away with speeding
and he couldn't?

Would I be a "sanctamonious do gooder" if I reported somebody breaking
in to your house?

Please do explain how the motocyclist was effecting or doing any harm
to anyone or any property or business. Though no doubt he deprived the
treasury of some tax , sorry fine, revenue. Oh cry me a river.

B2003

On 30 July, 11:54, Adrian wrote:
Andy gurgled happily, sounding much like they were
saying:

You seem to miss the subtle detail that the distances are massively
long for any even remotely competent and roadworthy vaguely modern
vehicle.
I don't think that they're massively long. If you look at the table in
the highway code, it gives the distances in terms of car lengths (being
4m):

20mph = 3 car lengths, 50mph = 13 car lengths, 70mph = 24 car lengths
(=96m) with the other speeds in between.

75m, actually - we're talking about the stopping distance. Whether the
average driver's reactions accord to the guesstimates in the HC is
another question entirely.

But as the thinking distance is probably under estimated in the
Highway Code for a real life situation, . The whole of the time from
recognizing the danger to being at a stop is the important
consideration (and not really covered in the HC) when actually
stopping from 70 mph in real life, whether you've traveled 15m less
than the calculated number for the braking distance doesn't really
matter.


And, yes, they are - hugely so.

A quick google tends to bury actual road test information under swathes
of HC related stuff, but here's one...

http://www.insideline.com/subaru/imp...t-2002-subaru-
impreza-outback-sport.html

So that's a roughly 8yo test of a fairly heavy non-performance-oriented
car, with drum brakes on the rear and "all-season" tyres (virtually
unknown in the UK, being a compromise between the tyres we see (known as
"summer" elsewhere) and winter tyres).

127ft from 60 to a stop. 38m. HC quotes 55m. 45% further.

And do you honestly think that these distances are representative of
real life situations (with passengers, luggage etc), in a range of
cars with normal drivers who don't do brake tests as part of their
job? Remember, if you get it wrong on the road, you've hit the vehicle
in front, better to have the number in the HC erring on the safe side
than trying to be an accurate representation of the latest and
greatest cars on the road.

Adrian wrote:

Chris Tolley (ukonline really) gurgled happily,
sounding much like they were saying:

So did this formula get plucked from thin air for a totally random
result?

I see mathematics is not your strong suit. Formulas do not give totally
random results. (And no, I'm not going to enter into a debate about
chaos theory.)

I do apologise - I thought it relatively clear that I was not referring
to the precise formula and the precise figures, but the ball-park figures
and the meaning they convey.

Why 75m from 70mph?
Why not 200m or 20m?

The thinking distance is merely the speed in mph expressed in feet. The
stopping distance is merely the speed in mph squared and divided by 20,
then expressed in feet.

Once again - why that particular formula resulting in figures in that
particular ballpark?

Because the numbers are easy to do. Before people had little computers
in their pockets, they could do v*v/20 in their heads. Some (inc me
still can). Back in the day there were many of these things. We called
them "rules of thumb". Simple approximations that were sufficiently
accurate when answers were not presented to eight or more decimal
places.

But the point is that it's all a very theoretical thing anyway. There
are going to be astonishingly few people who have the talent, in a
moving frame of reference, to place their vehicle at any precise
predetermined distance behind the one in front. The HC is for reading
before you go out on the road, not while you are driving. On the road,
other mechanisms, like the 2 second rule, experience of conditions, and
empathy for other road users, come into play.

It no doubt gives and always gave a safety margin. But until every
relevant vehicle has ABS

Which doesn't actually make the slightest difference to stopping
distances, since it does absolutely nothing at all unless the driver
cocks up in a way that would have failed them their driving test.

Never having had a car so fitted, I wouldn't know. The only evidence I
have to go by is that the continuous rubber smears on the road tend to
be longer than that dashed ones, from which I infer that ABS reduces
stopping distances.

Did you miss the "unless"?

No. I did not.

I explained that I would not know from personal experience what
difference ABS makes, and then went on to present information that I can
glean about ABS. Could you not tell that from what I wrote?

So I can only presume, then, that you have not taken a driving test? If
you lock the brakes on the emergency stop, you would fail the test - as
well as massively extending the stopping distance.

Oh dear, considering that elsewhere you accuse me of posting without
reading, you've clearly overlooked the previous post in which I told you
about my test. Early HCs talked about these in the context of an
emergency, which is the situation I imagine ABS comes into its own. The
commentary in the 1946 edition starts "DO YOU REALISE how long it takes
to pull up in an emergency?"

But if these figures purport to be a typical "stopping distance", do
you not think it might actually be useful if they were?

They purport to be a "thinking and stopping" distance.

sigh I'm not sure why you're being so obtuse about this.

I can only work with the material that is in front of me. If you want me
to stop pointing out the flaws in what you are writing, stop writing
them.

Look at the chart in the HC. For each speed there is a thinking distance
and a stopping distance.

Clearly, humankind has not evolved in the last half century, so we can
assume that the thinking distance has remained relatively static. So the
stopping distance is what we are discussing.

That would be an irrational and unwarranted assumption. I would argue
for assuming the opposite. Back when this thing was dreamed up, there
were far fewer vehicles on the roads. The emergencies envisaged might be
such things as a child rushing out in front of the car, and because
there are no other cars around, it's the one thing the driver focuses
on. The ball game is completely different when the emergency arises from
the erratic behaviour of another road user who is also moving, and one
is surrounded by a lot of other moving things too, as well as a forest
of signs and other distractions.

Either way, any discussion of stopping distances that ignores the amount
of time it takes to size up the situation and decide what to do about it
isn't going to produce a worthwhile answer.

In terms of general stopping distances, I personally drive in a manner
which means the HC understates how long it takes to slow down. I am not
one of those who dashes from place to place slamming brakes on. Indeed,
I often point out to SWMBO how many times other drivers are applying
their brakes while I am not doing so at all, since I've thought ahead
about what is in front of me. I had my previous car 6 years and never
replaced the brake pads, my current one is approaching that landmark,
and I haven't done so with that either.

--
http://gallery120232.fotopic.net/p9633098.html
(55 011 at Peterborough, 3 Sep 1979)