50mph on motorway due to road works

Car_54

PhilStation wrote: »

Speedometers are not calibrated and so not completely accurate but I disagree that GPS would be more accurate. There is a delay in sending and receiving the information and they are never more accurate than around 6 metres so when travelling at any speed, that offers a considerable margin of error.

The position info is sent from the satellites and received by the satnav. It travels at the speed of light for a negligible distance. There is no delay there. There may however be a delay in the satnav processing the info.

bigadaj

Jackmydad wrote: »

If you look at rule 268 of the highway code, which I have now, but hadn't when I originally posted, it does say not to move into the LH lane to overtake. . .

This is where the correct terminology is critical, a bit like settling finance rather than cancelling it.

If I'm in the left hand lane and continue past a vehicle in an outside land I haven't changed lane and so haven't undertaken. If I've cut under the vehicle and then popped back out again then I've definitely undertaken, largely a function of the amount of traffic but a definite difference.

GwylimT

caprikid1 wrote: »

"50mph on your speedometer is not 50mph, probably closer to 45mph."


Really ? maybe on a morris minor but most car Speedo's are very accurate up to 80 at least.


There are lots of "You are doing" "30 / 40 / 50" signs "happy", "sad face" by me and even my old cars are accurate enough that I would never play the dangerous 10% game. What if they are reading 10% under ???

Brand new honda

Speedo GPS
30 28
40 37
50 45
60 54
70 64

unforeseen

Car_54 wrote: »

The position info is sent from the satellites and received by the satnav. It travels at the speed of light for a negligible distance. There is no delay there. There may however be a delay in the satnav processing the info.

Since the satellites are at around 12500 miles altitude, I wouldn't call that negligible. You can add to that height because it's distance from you is the slant range rather than just the height.

That was equates to an error of 4-5 metres at 60MPH


However at a constant speed this error can be ignored as the satnav uses two position fixes to determine the speed so the same error exists in both and any speed error is down to the algorithm used to calculate speed. As the sats now all work at the 'military' accuracy setting they are capable of pinpointing position to the metre.

Some people claim that going up and down hills affect it due to the change in altitude. Bower as the sample rate is so high the vehicle has only travelled one or two metres between samples so will have little appreciable effect.

Car_54

bigadaj wrote: »

This is where the correct terminology is critical, a bit like settling finance rather than cancelling it.

If I'm in the left hand lane and continue past a vehicle in an outside land I haven't changed lane and so haven't undertaken. If I've cut under the vehicle and then popped back out again then I've definitely undertaken, largely a function of the amount of traffic but a definite difference.

Correct terminology is indeed critical, and the correct term is "overtake on the left" . As pointed out earlier, overtaking does not ne cessation imply a change of lane.

PhilStation

Nodding_Donkey wrote: »

This may be true regarding accelerating/decelerating where there will be a slight lag but at a steady speed on flat ground they are more accurate than a speedo.

Sorry but that is just inaccurate. If that was the case, why would the police rely on fixed points and calibrated speedos when they could simply use GPS at a significantly reduced cost.

unforeseen

Because nobody issues calibration certificates for the GPS system that a court would accept

Nodding_Donkey

PhilStation wrote: »

Sorry but that is just inaccurate. If that was the case, why would the police rely on fixed points and calibrated speedos when they could simply use GPS at a significantly reduced cost.

Reason number one is in the previous post. Reason 2 could be that the positioning satellites are owned by the American military and could be turned off any time they want.

facade

Nodding_Donkey wrote: »

Reason 2 could be that the positioning satellites are owned by the American military and could be turned off any time they want.

That will be a surprise to GSA and ESA, the whole point of the (13 so far) Galileo satellites is to stick 2 fingers up at the American military and their "selective availability";)

https://www.gsa.europa.eu/european-gnss/galileo/galileo-european-global-satellite-based-navigation-system

RichardD1970

facade wrote: »

That will be a surprise to GSA and ESA, the whole point of the (13 so far) Galileo satellites is to stick 2 fingers up at the American military and their "selective availability";)

https://www.gsa.europa.eu/european-gnss/galileo/galileo-european-global-satellite-based-navigation-system

Galileo is the global navigation satellite system (GNSS) that is currently being created by the European Union (EU)

Will we still be allowed access after Brexit? :eek: