were all told how speed kills etc… i just passed a sign on the m6 nr j4 4 that said… junction8 15miles in 12mins… 
my maths tell me that you need to be doing 75mph to achive this, and i always thought the legal limit was just 70mph…
these signs most the time have fiction on them… go up the a1m south of peterbro in the nite… (4am,ish) just after alconbury it warns of queing traffic in the roadworks area, and ques after next junction… so the signs warn you not to travel above 60mph… thro the roadworks… now this is also strange as the roadworks limit is just 50mph… oh and for the record, ive still to see the traffic the signs are warning me about…
This sort of thing applies to sat-navs and Autoroute, average speeds way above what can be legally achieved. The problem is that some drivers try to get to their destination in that time.
The signs that advise your time to the next junction are simply relaying what time it actually took the average vehicle to do that distance in the past few minutes. It uses anpr so if the average vehicle is doing 75 mph then thats the time it sticks up. Its an excellent system and about the only decent idea to be used on motorways in the past 20 years. Its the only accurate way of knowing whether the road ahead is clear or not.
maurice:
The signs that advise your time to the next junction are simply relaying what time it actually took the average vehicle to do that distance in the past few minutes. It uses anpr so if the average vehicle is doing 75 mph then thats the time it sticks up. Its an excellent system and about the only decent idea to be used on motorways in the past 20 years. Its the only accurate way of knowing whether the road ahead is clear or not.
I’m sure one of HATO’s on here posted about this a while back. IRC it uses sensors in the road, not ANPR and also is set to ignore vehicles (on motorways anyway) doing over 70MPH.
Colingl:
I’m sure one of HATO’s on here posted about this a while back. IRC it uses sensors in the road, not ANPR and also is set to ignore vehicles (on motorways anyway) doing over 70MPH.
We are both kind of right and wrong.
You are correct that it should be capped to 70 mph so I was wrong, but it does use anpr.
http://www.highways.gov.uk/traffic/15756.aspx
I’m guessing its just under 15 miles and just over 12 minutes which would probably bring the average to 70 mph.
It is unlikely you would see a sign showing those figures on the M25 during daylight hours. More likely 20 miles in 60 minutes.
I would like to see these signs displaying
LANE 1 … YOU CAN USE IT IF YOU DRIVE A CAR TOO YOU KNOW !!!
LANES 2 & 3 ARE FOR OVERTAKING ONLY , YOU THEN RETURN TO THE LEFT … ITS THE ■■■■■■ LAW AND IT HELPS THE TRAFFIC FLOW AS IT’S MEANT TOO , YOU ■■■■■■■ THICK , IGNORANT , DOCILE FOOLS , PLEASE READ THE HIGHWAY CODE , GOONS .
but I don’t think there’s enough space 
I was driving up the M2 at Sittingbourne one day, and the matrix sign said “Delays, M5 J28-29”.
Harry Monk:
I was driving up the M2 at Sittingbourne one day, and the matrix sign said “Delays, M5 J28-29”.
Going by the length of some of the closures on that section, it might still have had delays by the time you got there.
When i see that on a matrix sign i take it as the HA are setting down a challlenge for anyone to see if they can beat that time 
“So how how long did it take me then to cover those 15 miles, please tell me you set your stopwatch orficer?..or i’ll have to to do it again”
On the M42 between J3 and 3a the matrix usually gives the time to M40 J15. I find this strange since most traffic - and most problems - are on the M42
maurice:
The signs that advise your time to the next junction are simply relaying what time it actually took the average vehicle
They don’t work very well then as last week I was sat in 3 lanes of stationary traffic (handbrake on, engine off) and the sign in front of me said something like “To J18, 12 miles, 12 minutes”. I didn’t even get as far as the sign in 12 minutes…
Paul
repton:
maurice:
The signs that advise your time to the next junction are simply relaying what time it actually took the average vehicleThey don’t work very well then as last week I was sat in 3 lanes of stationary traffic (handbrake on, engine off) and the sign in front of me said something like “To J18, 12 miles, 12 minutes”. I didn’t even get as far as the sign in 12 minutes…
Paul
That’s on a par with 40mph matrix and sitting twiddling your thumbs.
Ok, the 15 miles in 12 minute type signs do use a type of anpr, and as been said it may be 15+ miles. These register a set of number-plates and time them between the 2 specific points (ignoring those above 70 mph) so if there’s been an incident that stops the traffic, there’s the problem of showing this incorrect information for at least 12 minutes, more like 15 mins until the system realises that traffic is stopped. In this type of scenario I like to set over the top of this type of message sign (we have priority) with a more relevant message.
The 40 mph signals that you see along with “Queue caution, or Queue ahead” are automatic signals set by the sensor wires set in the road surface. 40 is the minimum these will show unless the HDS (highest displayable speed) has been set lower. Each pad is auto checked approx every 4 minutes, if an reasonable amount of traffic has flowed over it faster than the posted limit, it will either switch off, or go up in speed.
These can be triggered by anything going slower than the set limit, ie slow moving large load, ambulance under ■■■■■■, or where there are sensors in the H/S as well, by a vehicle stopped on top of the wires. when roadworks are put in place, the crew are supposed to call in with the marker-post locations for start & finish of the lane closure, we then switch off the sensors so that their vehicles, signs, equipment doesn’t trigger them, now and again the foreman might forget to call in and we only find out when a HATO patrol goes through and calls up.
Through roadworks where there is a mandatory speed limit, the HDS should be set 10 mph lower than the speed limit. (ie normally roadworks have 50 mph limits, so HDS is set at 40 mph. If they show incorrect then it’s more than likely an operator error.
I always see those signs as a challenge
The real Biffo:
Ok, the 15 miles in 12 minute type signs do use a type of anpr, and as been said it may be 15+ miles. These register a set of number-plates and time them between the 2 specific points (ignoring those above 70 mph, Paddy and the like) so if there’s been an incident that stops the traffic, there’s the problem of showing this incorrect information for at least 12 minutes, more like 15 mins until the system realises that traffic is stopped. In this type of scenario I like to set over the top of this type of message sign (we have priority) with a more relevant message.
quote edited
M1 London -Leeds 60 minutes But in ze Fazerland zey find zat it’s cheaper not to bozzer viz zem.
Pointless info as they never show the junction i want.