Speeding through average speed camera zones - What gives?

[Adam Ansel]

Bonefish Blues said:

I tghink your muddling this up with the ACPO Guidelines, aren't you. The speed will be accurate.

No.
When they send you the summons they deduct the appropriate amount, to allow for speedometer error.

[xRIEx]

Adam Ansel said:

Bonefish Blues said:

I tghink your muddling this up with the ACPO Guidelines, aren't you. The speed will be accurate.

No.
When they send you the summons they deduct the appropriate amount, to allow for speedometer error.

You're thinking about this the wrong way round: they have no idea what it says on your speedo so they don't deduct anything. They measure the speed accurately in the first place, your speedo does not.

[WD39]

Hoofy said:

Far Cough said:

Have no idea how "average" speed cameras work

Because they see it doesn't flash at 55mph, they just blitz through at 70 perhaps thinking it's fine.

Or they think "average" is used to describe its design.

Average speed cameras don't flash.

They are totally automatic and controlled by computer.

There is no human involvement.

Your 'ticket' arrives courtesy of Microsoft (or similar.)

Why do drivers speed through them? It's all part of the current I don't give a sh*t style of motoring, with a dash of self entitlement.

[LankyLegoHead]

Speaking from someone whos been through the M25 Gantries for several miles at warp factor 7, and watched as the flashes went off behind me... I can tell you they only are active when a speed is shown. The flashes are ANPR.

For the record, it was silly o clock in the morning and I was rushing back from London to a relative that was in hospital. I didn't give two fks if I got banned from driving that night. As it happens, nothing came from it. Maybe just coincidental luck but

[TeaNoSugar]

Pesty said:

TeaNoSugar said:

A colleague of mine was caught on the section between J28 and J25 of the M1 while the widening and new gantries were going in a few years ago. He was recorded averaging just over 60mph as far as I remember.

I drive from J34-J26 and back 3 days a week. Speed limiter always set to 57mph. Thats fast enough to keep me out of the way of the HGVs, and in the last 3 years while those works have been ongoing I haven't had a ticket. I wouldn't want to risk any more, but do see the odd car barrelling through overtaking everything else, I just assume they're not legit and don't give a f***.

On a related note, does anyone know exactly why all the new "Extrudakerb" central barriers were ripped out a few months back after only being in place for a year or so??

EDIT: I'm thinking of the yellow cameras in the roadworks, not the smart-motorway gantries (they're not average speed cameras are they?)
Also, on the M1 near J27 there are some new cameras which are cantilevered off the outside of the new gantries, so overhanging beyond the hard shoulder. Are they a new speed camera as well, or something else entirely??

Edited by TeaNoSugar on Thursday 11th February 12:09

Im up and den the m1 and 62 all the time. Also other roads with average cameras all the time. I drive about 30k miles a year for work. How I haven't been done by these or in the dash camera thread I have no idea. I set the cruise at around 54 which is about 50-51. What my specific issue is if they are long enough like the fking m1 has been for years after miles and all of a sudden the road opens up I automatically just floor it forgetting I'm in an average zone. Then drive for miles and remember them think oh fk. So if you see a dick driving like he stole it it's probably me. No tickets yet.

I've done exactly the same thing a few times. Sat on the M1 with the speed limiter on 56-57, then road opens up and you put your foot down, forgetting about the average speed cameras for a few seconds then sudddenly you wonder why everyone else is dawdling along and realise its still 50mph, but like you, I've been up and down that stretch for the past 4 years and so far, no issues.

[3xpendable]

1Addicted said:

That be Diesel power :-D. Agreed, in seriousness, my brute of a V8 is driven with care comparatively but at least the 2.0TDi drivers can tell their friends that they minced a C63.

Haha yes. My DD is a manky (but loved) 2001 Mondeo 2.0 Petrol. I've had more than one comment from from people that I drive "Like a Granny". Ironically, one of the very same people moaned that his Golf GTD wasn't doing the economy it says in all the magazines and it was, and I quote "Eating front tyres"...I had a lift off him once and every accelleration was like a traffic light Grand Prix, I said to him "And you wonder why your car is guzzling fuel and eating front tyres, yet my granny driving sees me get more MPG than you and tyres that last 5 times as long?"

[Bonefish Blues]

xRIEx said:

Adam Ansel said:

Bonefish Blues said:

I tghink your muddling this up with the ACPO Guidelines, aren't you. The speed will be accurate.

No.
When they send you the summons they deduct the appropriate amount, to allow for speedometer error.

You're thinking about this the wrong way round: they have no idea what it says on your speedo so they don't deduct anything. They measure the speed accurately in the first place, your speedo does not.

Adam, you're wrong, some forces use the ACPO Guidelines to set thresholds for prosecution (some don't, also), which is what you're muddling this up with. Your summons will state an accurate speed.

[monthefish]

Good thread OP, I've often wondered this myself.

sicasey said:

KTF said:

sicasey said:

So why do modern speedometers err on the side of caution?

Calibration costs money.

That cant't be the reason.

If a speedo was under-reading, then in theory a driver could blame the vehicle manufacturer for them breaking the speed limit as they would unknowingly broken the law (not sure how well such a challenge would stand up however, but that's a different topic altogether)

In all components in all car manufacture, there are tolerances; Component tolerances, system tolerances, production/assembly tolerances, tolerances due to environmental factors etc etc. Particularly in mass-production, these can be quite wide when summed up*.

The tighter the tolerance control, the higher the manufacturing cost.
Say there's a potential total tolerance of 4% in a certain system (e.g. speedo) when all factors are at their extreme. A manufacturer can either spend a lot of money tightening up that tolerance (but they can't eliminate it altogether), or they can set the 'nominal' to a value so that a +/-4% tolerance becomes -0/+8, meaning the speedo will never under-read, but it quite likely to over-read.



(* off topic, but I believe Nissan 'cherry pick' various engine components at various end of tolerance on their GTR so that, when assembled as a system, the tolerances counteract each other so that the total tolerance is minimised)

[mattdaniels]

The_Burg said:

I know these supposed to be average speed cameras but is there any sort of overide?
For example if you went tearing through at 150mph then slowed down enough to average under the limit would it register anything? I would have though there must be some sort of check.

sicasey said:

If a person has no understanding of what an average (average of anything) means, should they really be issued with a driving licence?

[speedking31]

[quote=sicasey]So why do modern speedometers err on the side of caution?[quote]Tyre wear can amount to a couple of % of rolling circumference = 1 mph at 50.

[AJordan]

Presumably all these people sailing through at 50+ aren't causing multiple accidents, endangering other road users, running over baby ducklings ect? (I'm sure this does occasionally happen, but personally I've never noticed it)

If this is the case, then it proves surely proves that the cameras are solely there to generate revenue, or that the set variable limit is bks (or both)

[jshell]

sicasey said:

xRIEx said:

I've heard claims that they will trigger at 90 even when not illuminated - I've not tested that myself, but I have been travelling at, ahem, something over 70mph and had people passing me under the gantries and still no flash; I would estimate that 85 on the clock (depending on car) wouldn't trigger anything, even if they are active in those situations.

I love all of these urban myths, proper pub talk

Thread on here in S,P & L attesting to the fact that they do trigger over 90. For this guy it was WELL over 90 I remember.

[xRIEx]

AJordan said:

If this is the case, then it proves surely proves that the cameras are solely there to generate revenue,

IIRC the 50mph limit is because the barriers used between the carriageway and the roadworks are type approved up to 50mph.

[jshell]

aero93 said:

Does anyone know anyone that has actually been caught by these?

Yup. Me. Cameras on North side of the Forth Road bridge last year. Going through every Monday morning for weeks and the cameras had "Cameras Under Test" signs beneath them. 6 o'clock one Monday, no sleep, missed that the signs had been removed. 53 in a 40. bd!

[forzaminardi]

I've been up and down the M1 a lot over the past 6 months. I set my cruise control at 54 and generally find myself passing everyone else at a steady rate. I've not had anyone except those properly 'going for it' pass me that I can recall, nor (so far) had a ticket. It's worth noting that in both the 50 average zones Southbound around Nottingham and Northbound before Sheffield, the first camera is quite some way after the 50 zone begins, so that's a bit of a free for all for anyone who realises.

I recall just after New Year heading south being overtaken at a huge speed by an Infiniti saloon thing (only time I've ever seen one on the road). As we came up to a camera he braked, cut in close behind a truck, went past the camera then pulled out and carried on at 70+. Seemed like a rather foolish/brave tactic to me.

I find it annoying when people are going along at 48-50ish (fair enough) but then slow to 40-45 (why!?!) as they pass the camera.

[xRIEx]

speedking31 said:

sicasey said:

So why do modern speedometers err on the side of caution?

Tyre wear can amount to a couple of % of rolling circumference = 1 mph at 50.

Possibly a separate debate, but I did read that tread depth makes minimal difference to rolling circumference, as the steel belt is the limiting part of the tyre construction. From here: http://www.carbibles.com/tyre_bible_pg4.html

"STATIC LOADED RADIUS, OUTER DIAMETER AND ROLLING CIRCUMFERENCE
[rolling circumference]
These three measurements are all important to consider when talking about wheels and tyres. They're all interlinked. Straight from the manufacturer, a tyre is circular and it's outer diameter (OD) is based on this unladen, perfectly circular condition. Because tyres deform under load (flatter on the bottom than they are on the top when taking the weight of a car), the vertical radius of a tyre under load is not half the diameter. It's typically about 44% of it (from the centre of the wheel to the road). In addition, a tyre doesn't roll like a solid wheel; the steel or fabric belt 'rolls along the ground' like a caterpillar tank tread does. Because of this, the rolling circumference of the tyre isn't quite what you'd expect. The closest approximation for this value can be calculated by taking the outer diameter, subtracting twice the tread depth and multiplying by PI. Roughly speaking, that's 0.96 x OD x PI."

Edited by xRIEx on Thursday 11th February 14:26

[ashleyman]

forzaminardi said:

I've been up and down the M1 a lot over the past 6 months. I set my cruise control at 54 and generally find myself passing everyone else at a steady rate. I've not had anyone except those properly 'going for it' pass me that I can recall, nor (so far) had a ticket. It's worth noting that in both the 50 average zones Southbound around Nottingham and Northbound before Sheffield, the first camera is quite some way after the 50 zone begins, so that's a bit of a free for all for anyone who realises.

I recall just after New Year heading south being overtaken at a huge speed by an Infiniti saloon thing (only time I've ever seen one on the road). As we came up to a camera he braked, cut in close behind a truck, went past the camera then pulled out and carried on at 70+. Seemed like a rather foolish/brave tactic to me.

I find it annoying when people are going along at 48-50ish (fair enough) but then slow to 40-45 (why!?!) as they pass the camera.

Heard this lots and lots, using the truck to cover the plate from the camera. Just have to make sure you can get through each camera covered or your done!

[xRIEx]

ashleyman said:

forzaminardi said:

I've been up and down the M1 a lot over the past 6 months. I set my cruise control at 54 and generally find myself passing everyone else at a steady rate. I've not had anyone except those properly 'going for it' pass me that I can recall, nor (so far) had a ticket. It's worth noting that in both the 50 average zones Southbound around Nottingham and Northbound before Sheffield, the first camera is quite some way after the 50 zone begins, so that's a bit of a free for all for anyone who realises.

I recall just after New Year heading south being overtaken at a huge speed by an Infiniti saloon thing (only time I've ever seen one on the road). As we came up to a camera he braked, cut in close behind a truck, went past the camera then pulled out and carried on at 70+. Seemed like a rather foolish/brave tactic to me.

I find it annoying when people are going along at 48-50ish (fair enough) but then slow to 40-45 (why!?!) as they pass the camera.

Heard this lots and lots, using the truck to cover the plate from the camera. Just have to make sure you can get through each camera covered or your done!

As each camera is paired with another (I think they still are), you only have to make sure half of the cameras are covered - although, it has to be the correct half.

[speedking31]

And the modern cameras seem to all be rear facing so much harder to get a truck into the correct position

[speedking31]

xRIEx said:

Possibly a separate debate, but I did read that tread depth makes minimal difference to rolling circumference, as the steel belt is the limiting part of the tyre construction. The closest approximation for this value can be calculated by taking the outer diameter, subtracting twice the tread depth and multiplying by PI. Roughly speaking, that's 0.96 x OD x PI."

Hardly makes any difference to the sums.

For a 215/45/17 the diameter is 625 mm. Say 7 mm of tread wear (x 2) = 2.2%.

For 2 mm tread the rolling circumference is (625 - 2 x 2) x π = 1952 mm.
For 9 mm tread the rolling circumference is (625 - 2 x 9) x π = 1908 mm.
Difference = 44 mm = 2.3%.