Self righteous cameramen

Commuting, Day rides, Audax, Incidents, etc.
BakfietsUK
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Re: Self righteous cameramen

Post by BakfietsUK »

So the debate, if I am right, which I am probably not, Includes:

Cameras being used to trap the most subtle and inconsequential misdemeanours, leaving others unchallenged.
Tackling bad habits by extra infrastructure rather than enforcement and education.
prioritisation of speed enforcement away from the upper end say 70 to 80 and concentrating on 20 to 30 and 40.

I wonder what the difference in consequences of collision are with 70 compared to 80. I also wonder how this compares with the difference between 30 and 40. Presumably whether you are doing 70 or 80 a collision is going to be life threatening anyway, but 30 rather than 40 is a different matter. Seems that at 30 you are less likely to kill someone. With the speed at 70 or 80 that boundary is well passed anyway and catastrophe is probable. All the more reason to limit motorways to 50 or 60. Given most of the M27 around my way moves at 15 for a major part of the day, the difference and argument is purely academic. Thankfully I have made my lifestyle incompatible with motorways. Yes I am what some may pejorativly call a "self righteous" eco warrior and I'm proud of it.
Vorpal
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Re: Self righteous cameramen

Post by Vorpal »

This only goes up to 70 mph, but you can see that it doesn't make much difference.
speed vs risk of fatality graph.jpg


Richards, D. (2010), Relationship between Speed and Risk of Fatal Injury: Pedestrians and Car
Occupants
, Prepared for the Department for Transport by TRL Limited, Wokingham, Berkshire,
available from http://www.dft.gov.uk/publications/rsrr ... -report-16
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom
AdamS
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Re: Self righteous cameramen

Post by AdamS »

Did you post the right graph? What is the relevance of pedestrian fatality risk to motorway speed limits?
Vorpal
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Re: Self righteous cameramen

Post by Vorpal »

For car occupants, the risk of fatality is more dependent upon the sudden change in speed, and the location of impact makes a different, too.

A head-on collision is less likely to result in a fatality because there is a large chunk of metal at the front to absorb energy, at least until that capability is exceeded.

Otherwise, the change in speed has a similar outcome for vehicle occupants as the speed does for pedestrians. There is little difference between a 70 mph crash and an 80 mph in terms of severity, although I would expect a slightly higher incident rate, due to reaction times, stopping distance, etc.
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom
BakfietsUK
Posts: 220
Joined: 4 Jul 2015, 10:35am

Re: Self righteous cameramen

Post by BakfietsUK »

Very interesting Vorpal and thank you. Seems the lines are tending to converge around 70 suggesting that differentials at that speed are not so significant. I am sure however that at 80 mph, reactions to the events on the road would need to be faster. So arguing for faster speed limits may need to take into account the limits of human perception and reaction. Thinking distance and braking distance would be increased which leads to an increasingly inefficient use of road space. The speed differential between the fastest and slowest vehicles would be increased, giving rise to greater potential for fatality, notwithstanding some vehicles having superior crash worthiness.

It is possible to calculate the traffic speed which results in the most efficient use of road space, but I have not done it myself. I did see an OU programme where they did this calculation and it turned out to be about 15 mph. So again raising the speed limit to 80 would waste a lot of the capability of the infrastructure to provide the extra stopping space needed. This could mean that more roads may be needed to accommodate higher speeds if no other variables change. To me there are so many arguments against upping the speed limit that it just does not make any rational sense. There would be a compromise needed to balance realistic journey times with potential capacity and this may be better pegged at say 55 mph. This would increase road capacity, save fuel, reduce pollution and possibly save lives. Considering the current limit is 70 I would suggest that this is already way too high.
landsurfer
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Re: Self righteous cameramen

Post by landsurfer »

Slightly off post but .....
I find the levels of concentration to comfortably drive at 70mph jump up considerably at 75mph.
The 75mph cruise is not pleasant compared with the the 70mph one.
I use Garmin gps to log my speed as well as the vehicle speedometer.
70 mph on my Isuzu Speedo is only 66 on Garmin ....
30 mph on my Isuzu Speedo is only 27 on Garmin ....

My experience is that the Garmin is the accurate one.
However.
My comfort zone, with the long distance milage i drive, has led me to set my cruise control to 70mph, vehicle indicated, when appropriate.
“Quiet, calm deliberation disentangles every knot.”
Be more Mike.
The road goes on forever.
thirdcrank
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Re: Self righteous cameramen

Post by thirdcrank »

I've heard it suggested that the speed cameras on "smart" motorways only operate if a speed limit is displayed on the associated matrix signs. I've no idea if this is true and it may be an urban myth, of which there seem to be many on the subject. I do know from observation that as well as lower limits being displayed with a number in a red circle, the national speed limit sign - white with black diagonal - is shown to indicate when a lower limit ends but is not otherwise displayed.

Lower limits may be set for safety reasons, eg broken down vehicle, or to ease congestion. I get the impression that the cameras do not enforce the 70 limit. ie If there's no safety reason to impose a lower limit, they aren't particularly bothered about safety above 70.
MikeF
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Re: Self righteous cameramen

Post by MikeF »

landsurfer wrote:Slightly off post but .....
I find the levels of concentration to comfortably drive at 70mph jump up considerably at 75mph.
The 75mph cruise is not pleasant compared with the the 70mph one.
I use Garmin gps to log my speed as well as the vehicle speedometer.
70 mph on my Isuzu Speedo is only 66 on Garmin ....
30 mph on my Isuzu Speedo is only 27 on Garmin ....

My experience is that the Garmin is the accurate one.
However.
My comfort zone, with the long distance milage i drive, has led me to set my cruise control to 70mph, vehicle indicated, when appropriate.
What's your evidence? Garmin devices can't track your position accurately.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
landsurfer
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Joined: 27 Oct 2012, 9:13pm

Re: Self righteous cameramen

Post by landsurfer »

MikeF wrote:
landsurfer wrote:Slightly off post but .....
I find the levels of concentration to comfortably drive at 70mph jump up considerably at 75mph.
The 75mph cruise is not pleasant compared with the the 70mph one.
I use Garmin gps to log my speed as well as the vehicle speedometer.
70 mph on my Isuzu Speedo is only 66 on Garmin ....
30 mph on my Isuzu Speedo is only 27 on Garmin ....

My experience is that the Garmin is the accurate one.
However.
My comfort zone, with the long distance milage i drive, has led me to set my cruise control to 70mph, vehicle indicated, when appropriate.
What's your evidence? Garmin devices can't track your position accurately.


Good point.
In December 2016 I was a passenger in a South Yorkshire Police car travelling on the M1 from Junction 30 to Junction 36.
During this period I and the 2 officers logged and compared the readings from the BMW 5 series speedometer, the calibrated speedometer and my Garmin Edge Touring.
We left the M1 at J36 and carried out lower speed comparisons on Derne Valley Parkway.

2 days later.

I compared the readings, as a passenger, in my Isuzu D Max 2.5 ltr driven by TFJ.
Which is where my comments came from ...
“Quiet, calm deliberation disentangles every knot.”
Be more Mike.
The road goes on forever.
MikeF
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Joined: 11 Nov 2012, 9:24am
Location: On the borders of the four South East Counties

Re: Self righteous cameramen

Post by MikeF »

landsurfer wrote:
MikeF wrote:
landsurfer wrote:Slightly off post but .....
I find the levels of concentration to comfortably drive at 70mph jump up considerably at 75mph.
The 75mph cruise is not pleasant compared with the the 70mph one.
I use Garmin gps to log my speed as well as the vehicle speedometer.
70 mph on my Isuzu Speedo is only 66 on Garmin ....
30 mph on my Isuzu Speedo is only 27 on Garmin ....

My experience is that the Garmin is the accurate one.
However.
My comfort zone, with the long distance milage i drive, has led me to set my cruise control to 70mph, vehicle indicated, when appropriate.
What's your evidence? Garmin devices can't track your position accurately.


Good point.
In December 2016 I was a passenger in a South Yorkshire Police car travelling on the M1 from Junction 30 to Junction 36.
During this period I and the 2 officers logged and compared the readings from the BMW 5 series speedometer, the calibrated speedometer and my Garmin Edge Touring.
We left the M1 at J36 and carried out lower speed comparisons on Derne Valley Parkway.

2 days later.

I compared the readings, as a passenger, in my Isuzu D Max 2.5 ltr driven by TFJ.
Which is where my comments came from ...
Thanks. Interesting comparison. Vehicle speedos also probably vary slightly according tyre wear and pressure.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
Vorpal
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Re: Self righteous cameramen

Post by Vorpal »

MikeF wrote:
landsurfer wrote:
MikeF wrote:What's your evidence? Garmin devices can't track your position accurately.


Good point.
In December 2016 I was a passenger in a South Yorkshire Police car travelling on the M1 from Junction 30 to Junction 36.
During this period I and the 2 officers logged and compared the readings from the BMW 5 series speedometer, the calibrated speedometer and my Garmin Edge Touring.
We left the M1 at J36 and carried out lower speed comparisons on Derne Valley Parkway.

2 days later.

I compared the readings, as a passenger, in my Isuzu D Max 2.5 ltr driven by TFJ.
Which is where my comments came from ...
Thanks. Interesting comparison. Vehicle speedos also probably vary slightly according tyre wear and pressure.

Motor vehicle speedometers have to read between the actual speed and 110% + 6.25 mph. The UK law is aligned with an EC directive.

Tyre size and wear can affect this.
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom
old_windbag
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Re: Self righteous cameramen

Post by old_windbag »

Vorpal wrote:Motor vehicle speedometers have to read between the actual speed and 110% + 6.25 mph


For very good reason too. An under reading speedo would be a liability so they have to err on the safe side to guarantee you are never over the limit when reading it visually.

But on the GPS measurement of instantaneous speed I've always thought the errors dependent on update rate versus speed of travel and change in direction( bends and gradients ). In other words a bicycle gps updating at 1 update per second will be more accurate when travelling in a straight line and on bendy roads when travelling more slowly so the bends are seen as bends, not cut corners.

In a car I'd have thought this would get worse but not sure what the update rate is in a satnav. I know my garmin edge 510 instaneous speed is not great compared to a trusty cycle computer with a fixed wheel size entered. As vorpal states about tyre pressures etc the speedo in the car has further errors, this should be remembered when people change tyre sizes radically to pimp up the car. Can result in a change in gear ratio and speed measurement. One car I had with a digital dash had a jumper on the back for selection of one of two factory fitted tyre sizes( hard to access as it was for factory use at production time ).
MikeF
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Re: Self righteous cameramen

Post by MikeF »

Vorpal wrote:Motor vehicle speedometers have to read between the actual speed and 110% + 6.25 mph. The UK law is aligned with an EC directive.
That's what Wikipedia states but I cannot find the source for + 6.25mph. EC directive is 110% + 4 kph.

Edit - Seems it's here but obviously somewhat different from the EC directive.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
old_windbag
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Re: Self righteous cameramen

Post by old_windbag »

It seems an odd coincidence that 6.25kph is 4mph............ is there an accidental switch in units by the person who entered it? Instead of +4kph should it not be +6.25kph in EU but uk has +4mph?
Vorpal
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Re: Self righteous cameramen

Post by Vorpal »

MikeF wrote:
Vorpal wrote:Motor vehicle speedometers have to read between the actual speed and 110% + 6.25 mph. The UK law is aligned with an EC directive.
That's what Wikipedia states but I cannot find the source for + 6.25mph. EC directive is 110% + 4 kph.

Edit - Seems it's here but obviously somewhat different from the EC directive.


Yes. I didn't remember that they differed.

The Road Vehicles (Construction and Use) says
Instead of complying with paragraph (1) a vehicle may comply with Community Directive 75/443 or with ECE Regulation 39.


I'm not sure why there is any difference at all. But maybe one of the British manufacturers, such as McLaren or Rolls Royce asked (lobbied?) for it, intending to make it easier to get approval, especially for a wide range of tyres sizes without calibration changes.
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom
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