Those "Average 50mph" speed zones are nasty

MarkDavis · 26 Dec 2007 at 17:40

I've noticed that quite a few of them have sprung up on the M1 near London and also on the M4 heading towards Bristol.

Previously I thought they were just there to slow traffic due to roadworks but they've installed multiple yellow SPECS cameras hanging over the lanes to measure the speed you enter the zone, and the speed you exit the zone. No flash or radar appears being used, and it doesn't seem to show up on the TomTom POI camera database.

Over a 2 mile stretch of the M1 there must have been at least 4 entry/exit camera points and the M4 is even worse.

Anyone else notice these or been caught out by them? Presumably they don't work at night? Anyone know if there's a tolerance above 50mph that they allow?

GT3 · 26 Dec 2007 at 17:43

They do work at night iirc, infa red.

Just change lanes

MarkDavis · 26 Dec 2007 at 17:51

There are two cameras that seem to cover all 3 lanes. I can't imagine that changing lanes would fool the system since presumably the images from both cameras are downloaded and compared/analysed centrally by some sort of computer?

http://www.a77safetygroup.com/content_files/soEdit_images/A77 Sandyford 4 (Camera Head).JPG

Mr Joshua · 26 Dec 2007 at 17:52

I saw some temporary ones on the A1 north of Doncaster in roadworks. There's 2 sections on each carriageway I'd imagine one for each lane so they seem to be getting about a bit more, it's the first time I've seen them that far north.

georges · 26 Dec 2007 at 17:54

I hate these. My car is pretty hard to keep at a constant speed, so you keep having to look at the speedo. :/ Makes it less safe if anything.
In urban areas (as this article suggests) I could see this being much more important, since you need to be looking about constantly to make sure you don't miss someone in between cars about to walk out, instead of looking at the dashboard.

http://news.bbc.co.uk/1/hi/magazine/7048645.stm
seems to think changing lanes doesn't work too well (unless it's trying to con people).

Whenever I've been in one of these zones, the congestion has been ridiculous, so you'd be hard pushed to speed. They always seem incredibly dangerous to me, since cars tend to be within 3m of each other at 50mph or 70mpg (depending on zone).

Ev0 · 26 Dec 2007 at 18:26

GT3 said:
Just change lanes

Had a chap who is quite high up in Devon and Cornwall Police tell us this nugget of info when some average speed cameras went up near our work, no reason why he would say that if it didn't work

DannyW · 26 Dec 2007 at 18:34

if you go through the 1st half of the 2 mile stretch at 60 mph then the 2nd half at 40mph they dont catch you (average speed still 50 mph

)

all speed cameras work at night

Ben M · 26 Dec 2007 at 18:41

MarkDavis said:
to measure the speed you enter the zone, and the speed you exit the zone.

umm no... they just time how long that stretch takes you... to work out your average speed...

qwerty · 26 Dec 2007 at 18:59

DannyW said:
if you go through the 1st half of the 2 mile stretch at 60 mph then the 2nd half at 40mph they dont catch you (average speed still 50 mph )

all speed cameras work at night

Actually that gives an average speed of 48mph.

EDIT: I fyou wanted, you could go at 66.66mph for the first mile and 40mph for the second mile and average 50mph over the two miles.

Peter Diffey · 26 Dec 2007 at 19:14

qwerty said:
Actually that gives an average speed of 48mph.

EDIT: I fyou wanted, you could go at 66.66mph for the first mile and 40mph for the second mile and average 50mph over the two miles.

Which wont work anyway because the cameras are not placed at just the beggining and exit, they are inbetween.

PinkFloyd · 26 Dec 2007 at 19:20

qwerty said:
Actually that gives an average speed of 48mph.

EDIT: I fyou wanted, you could go at 66.66mph for the first mile and 40mph for the second mile and average 50mph over the two miles.

AM I completely missing something here. :confused:

Your logic is baffling me.

The average of 40 + 60 is clearly 50.
40+60 = 100
100/2 = 50

thewanted · 26 Dec 2007 at 19:40

MarkDavis said:
Ialso on the M4 heading towards Bristol.

Which side of Bristol? Cardiff or London?

Like you said, I thought they only used them for roadworks *sigh*.

DannyW · 26 Dec 2007 at 19:43

i think it was once said on TG, you could go through the 1st camera at 100 mph, pull over for 5 minutes, then go through the 2nd camera at 100mph. quality

MarkDavis · 26 Dec 2007 at 19:45

PinkFloyd said:
AM I completely missing something here.
Your logic is baffling me.

The average of 40 + 60 is clearly 50.
40+60 = 100
100/2 = 50

Don't forget that you're travelling at different rates.

For the 1st mile, you'd be travelling at 60mph. Therefore it takes you 1/60th of an hour to travel that distance ie 0.0166 (recurring) hours

The 2nd mile, you'd be travelling at 40mph, so it take you takes you longer - 1/40th of an hour to travel that distance ie 0.025 hours

Total distance is 2 miles which takes you 0.0416 (recurring) hours to travel that distance,

Therefore you're average speed over that distance is:-

2 miles / 0.0416 recurring = 48mph

Mulder · 26 Dec 2007 at 19:47

This thread is pretty funny. They just time how long it takes you to cover the set distance between the cameras and works out the speed from that?

DannyW · 26 Dec 2007 at 19:50

Mulder said:
This thread is pretty funny. They just time how long it takes you to cover the set distance between the cameras and works out the speed from that?

1st camera takes a pic of you
then 2nd camera takes a pic, computer works out the speed on how long it took you to get to cam 2

Ultra_Extreme · 26 Dec 2007 at 20:14

DannyW said:
if you go through the 1st half of the 2 mile stretch at 60 mph then the 2nd half at 40mph they dont catch you (average speed still 50 mph )

all speed cameras work at night

Vans and other video based cameras dont work in the night or in the rain or fog.

Durzel · 26 Dec 2007 at 20:25

Ev0 said:
Had a chap who is quite high up in Devon and Cornwall Police tell us this nugget of info when some average speed cameras went up near our work, no reason why he would say that if it didn't work

I find it hard to believe that a system that probably cost hundreds of thousands of pounds in deployment costs is fooled by doing something that people do all the time anyway on the motorway, etc.

Ultra_Extreme · 26 Dec 2007 at 20:42

Durzel said:
I find it hard to believe that a system that probably cost hundreds of thousands of pounds in deployment costs is fooled by doing something that people do all the time anyway on the motorway, etc.

I find it hard to believe it works at all, the logistics are mental, i'd say that of all the traffic that passes through them only about 10% can possibly meet prosecution worthy standards

SoliD · 26 Dec 2007 at 20:43

Durzel said:
I find it hard to believe that a system that probably cost hundreds of thousands of pounds in deployment costs is fooled by doing something that people do all the time anyway on the motorway, etc.

Its something to do with the law I believe that doesnt give them the right to track over changed lanes, some stupid little loophole. I dont mind these zones as long as work is being done just really ****'s me off when you go past every day and nothing happens, much like on the a27 between portsmouth and havant for the past 6 months.