Yesterday, I was travelling clockwise on the M60 at J17, when I saw the Matrix stating " Oldham 6 Miles 6 mins". Now to accomplish that, you would have to do 60mph, but you can’t, because the speed limit up to just past J 20 E/B is 50mph. So, are they encouraging you to break the speed limit. if not, then shouldn’t the distance time be based on 50mph ?
I’m puzzled as to why they put that advice up on the sign .
They get these times by clocking a car number plate and seeing how long it takes to get between the two points. Iirc any car travelling at an average higher than the posted limit is disregarded. Obviously I may have this completely arse about face and will be subjected (quite rightly) to public humiliation and vilification.
I think those signs give car times
Yep, that’s why I said CAR number plate 
. Lets face it, if they took the times from a supermarket lorry most motorists would conclude that the carriageway was blocked somewhere ahead and so seek an alternative route!
ROG:
I think those signs give car times
It could give rocket ship times, if the limit is 50 its 50 and should show 50 times.
the maoster:
Yep, that’s why I said CAR number plate
Or, take it from my Bandit & they could half the Journey time.
But you’ve already ruined that theory by saying that they don’t take average times from Speeding Motorists. Aww Shucks !
Wouldn’t you come off at J22 for Oldham giving you 2 junctions at 70 to bring your average up a bit ?
From j17 there’s only a mile or so of restricted motorway on the M60. Don’t forget that to take the M60 you drop off at Simister Island (j18) and turn right at the roundabout continuing on the unrestricted M60.
Carrying straight on from j17 will take you onto the M62 where the restrictions continue
ROG:
I think those signs give car times
They do give car time but in a 50mph zone you cannot keg sly go 6 miles in 6 minutes, which was the OP’s point. At a steady 50moh it’s going to take you 7 minutes 12 seconds to cover 6 miles so by stating you can do it in 6 minutes they are saying you need to drive faster than the posted limit, 60moh.
Coffeeholic:
which was the OP’s point.
The M60/M62 crossover at j18 is a strange one, a driver would only be in restricted limits for about 1 mile from M60-j17 before coming off at Simister and turning right at the roundabout to continue on the M60 unrestricted.
Staying on the same road from M60-j17 turns into the M62 where the restrictions continue.
Edit to add
I believe the OP was thinking the M60 continued straight through the roadworks, this would be the M62 to Oldham…
Whenever I see those signs I always think - “Challenge accepted.” 
To much maths going on here for me (head hurts), I am only going to travel anti clockwise on the M60 next week 