young driver insurance specialists?

[hugh]

Guidance based on the false belief that the 10% tolerance on a speedo is symmetrical.

[Doctor D]

Kingscroft Volvo in Leatherhead managed to do something similar for a mate of mine some years ago. Put their own plates on a second hand car he bought from them: OBD on the front and ODB on the rear.

I noticed it when I was looking around it. He'd had it a fortnight by then!

[Doctor D]

Quite. 80k so far in an automatic with original pads and discs all round. Last service said they were about 60% worn, so I'll be gutted if they don't last the 100k.

[dennis]

Only if you know where all the cameras are, they are not required to be visible.

[John Williamson]

The GPS, by cross referencing with the NavTeq or Teleatlas databases. That's also how they can tell you've been speeding.

For accurate carbon emissions, they'd also need a fuel flow meter.

[Andy Burns]

There are plenty of places where roads with different speed limits parallel each other, close enough to be within the GPS margin of error.

It could be estimated from the CO2 rating of the car, combined with the speed & distance from the GPS and some sort of fudge factor (the rating on paper for mine is 179 g/km, but based on actual fuel consumed over

6,500 miles it works out something like 233 g/km).

[John Williamson]

My (Phone-based) satnav will tell me which carriageway of a motorway I'm sitting in a traffic jam on. It'll also notice I've taken a Motorway slip well before I get to the roundabout. Ten metre uncertainty? It will certainly tell me whether I'm on the service road or the main road where the housing estate has that arrangement. It can't tell whether I'm on the M4 or the A4 underneath it in Brentford, and it tends to assume I'm in the tunnels in Brussels, not on the road above them, as that's the way it told me to go. Do you know of any roads less than ten metres apart?

The Green Road trip recorders we use at work give similar results.

[Andy Burns]

But satnavs (as opposed to pure GPS units) tend to "manipulate" the displayed position, based on known location of roads, e.g. when a new bypass is built and maps haven't been updated, it's not uncommon for the display to follow the old route (for a hundred yards or so) on the assumption you haven't driven across the fields

I can think of some 1' apart. (e.g. 50mph dual carriageway with 30mph residential service roads each side of it, separated only by a metal fence).

[Chris Whelan]

[...]

What percentage of the total road network do you think that would represent?

Chris

[John Williamson]

Offhand, I can only think of a couple of miles of road like that in Nottingham. Much less than 1%, and I expect that the insurance company would give you the benefit of the doubt if you mentioned it to them if they accuse you of speeding on that stretch. Of course, there's an equal chance that doing 50 along the service road would show you on the dual cariageway. There are also a couple of miles of a similar layout with a slightly wider gap on the A3 near Tolworth.

The carriageway centres are still far enough apart that my satnav discriminates between them with better than 90% reliability.

And, yes, I do know about the fudge factors applied by most satnavs, and one navigation program I use from time to time for it excellent journey logging feature lets me turn off the "Snap to road" feature, in which case, it has been known to place me on the wrong carriageway of a dual carriageway for a moment or two. Whether the error is on my unit or in the mapping, I'll leave as an exercise for the user, as it uses Open Street Map. The most consistent error I've ever seen was when the satnav insisted I was driving along halfway up the hill to the North of the M25 for quite a few miles near the M23 junction. It happened every time I used that road until the maps were updated. Navigon version 5 about 5 years ago, for what it's worth.

[Chris Whelan]

[...]

That's currently considered to be within seven metres; the first stage of the Galileo project, EGNOS, is accurate to with two metres and is already being used in trials as the sole system for aircraft landing guidance at one airport.

When Galileo is fully functional, it will be accurate enough to guide someone on foot to the correct platform to catch their train.

Chris

[Andy Burns]

Oh, tiny. But it depends if the insurers box counts the total distance you've spent "speeding" or tallies the number of times it "catches" you speeding, and whether you live near to such a road ...

[tony sayer]

Umm what's wrong with current landing systems?..

So it's going to penetrate a station roof then?..

[Chris Whelan]

[...]

They are not as accurate as EGNOS will be. They do not have the same levels of redundancy. It doesn't have the capability to cope with expected levels of traffic in the future. More here:

>When Galileo is fully functional, it will be accurate enough to guide

I don't use public transport, so I was unaware that all railway stations have roofs.

Chris

[ARWadsworth]

I used the sat nav to calibrate my speedo.

[Rob]

they do now and its not just vertical the signals will come in sideways as well.

[tony sayer]

U should get out more Chris.. thats if you can afford the train fare;!...

[tony sayer]

Well if its that transparent but not all are..

Yes -if- you can get a decent triangulation but I can imagine NXEA cocking this one up if they are running the trains when its operational...

[Andy Champ]

I'd like to see it do that at Birmingham New Street.

Or indeed any other station with a covered roof - like all the big London ones.

Andy

[dennis]

My GPS worked for about 25 yards into a tunnel in Brum (Queensway IIRC). Even then it indicated lost signal but continued to plot my position all the way through the tunnel. My S2 works indoors in most buildings.