This has appeared on news group uk.transport: and was nicked by me
Transport Committee session on road pricing, evidence from Highways Agency and Department of Transport Wednesday 2nd February.
Alistair Darling (DoT)
David Lamberti (DoT - Road Charging)
Frank Kelly (DoT - Scientific Adviser)
Gwyneth Dunwoody (Chair)
The Chair challenged the DoT team to explain why road tolling should not
be implemented with immediate effect, since the technology in the form
of microwave and GPS systems was already available.
David Lamberti answered that unfortunately trials have established that
satellite based systems cannot distinguish parallel roads with
sufficient accuracy to determine which pricing structure to apply.
Furthermore studies have also shown significant problems in obtaining
accurate distance run measurements using GPS systems.
Mr Lamberti concluded that satellite systems are profoundly unreliable
in this application.
The Chair then challenged the team to explain why road tolling was being
considered for lorries using similar technology. Mr Kelly and Mr Darling
responded by stating that the proposal for lorries will involve a system
primarily dependent upon tachograph records as well as GPS data. The
tachograph giving operators an independent source to confirm GPS data.
The final implementation will be a box which will take input from
microwave sensors, GPS and the tachograph and store this information to
be transmitted when the vehicle is turned off.
Sad thing is they'll probably try and implement it anyway even though they know about the parallel roads issue. There is some talk about microwave transmitters or somesuch going into lamposts to track vehicles. Seeing as there is uproar every time a mobile phone transmitter goes up I wouldn't fancy their chances of persuading the great british public to have these transmitters everywhere.
The implementation with german lorries has been a bit of a disaster but the IT company in charge seems to be the german equivalent of EDS...
teabelly
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Its likely GPS would be accurate enough if the Americans allowed civilian users access to the military accuracy their satellites are capable of, as I understand it the wider market is prevented from having access to the military precision intentionally, I guess to lower the chances of Bin Laden sending a cruise missile up Santa Monica Boulevard with the GPS ripped out of his Toyota dashboard
As far as I understand it Europe plans to put up some competing satellites to end the US domination of GPS, and I'm not so sure they would prevent it being used for big brother sorry I mean road safety and charging measures
What's the timeline on the European satellites being up there? not that far away in the big scheme of things
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"Its likely GPS would be accurate enough if the Americans allowed civilian users access to the military accuracy their satellites are capable of"
It is. Jitter (the way of making it inaccurate) was removed by Clinton.
The GPS we use is the GPS the American Military use.
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im not going to accuse you of being wrong, but i dont think this is correct, if i get some time ill find out for sure, im fairly sure military gps reciever has greater accuracy that civillian ones, i could probably find the exact techie reasons quite easily too
if im wrong i appologise in advance
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www.wsrcc.com/wolfgang/gps/accuracy.html
i.e. not *quite* as accurate but damn close.
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think RF is right believe they can block certain areas out as they did in iraq during the main events so to speak...cheers...keo
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Back to the point. With GPS accurate to within 1.5 to 5 metres, how do they come up with this "its not accurate enough" rubbish
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Because the problem is determining the road, not the position.
So there is a 5m error in determining position. Now you need to match that to a digitised map showing the roads, and decide which road. What is the error in the map data?
The overall error will be a combination of both - in this case probably the sum total as I guess there isn't a relationship between them.
You also have to get it right all day, every day, everywhere in the UK.
You only have to watch a satnav system to see that they do get it wrong. Not often enough to be a problem, unless you're going to charge people tolls automatically.
Or apply the brakes for them, for that matter.
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I think because it forces your position to a map. Presumably that could make it up to 3.0 to 10.0 metres inaccurate. And presumably that would sufficient for the courts to be buried in appeals.
There are situations where the Sat Nav in my car will make an error on parallel roads although it normally sorts it out as soon as there is a turn one wayr another.
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Could be interesting on the A4/M4 elevated section out of London.
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My guess is that road charging will be implemented without GPS.
Motorways will be first, using much simpler and cheaper RFID technology at each junction, followed by arterial dual carriageways (A1, A19, A34 etc.)
The system will then be thrown open to individual local authorities to expand as they see fit.
Kevin...
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Could be interesting on the A4/M4 elevated section out of London.
How does the current generation of Satnav work in that location?
i.e work out if you are on A4 or M4.
For those who don't know the area, the A4 runs directly under the elevated section of the M4 for quite a distance. The A4 has a major roundabout which is junction of A406 & A206.(North and South Circular)
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welll.....as it happens..... On a VDO MS5000.
If you have set a route it assumes you are on that road (A4 or M4) until it realises you aint. If you set M4 Eastbound then drop off the M4 onto the A4 its quite happy until you hit the chiswick roundabout (at this point its seperated from the M4 by about 10 yards width) The woman gets all shirty and quickly recalculates telling you to take the third exit (to get back on the now A4 at the other end of the flyover.
If no route is set, on its maximum (or is it minimum - the one that gets you down to drain cover level!) the little curser follows all the exits and slips and changes faithfully
EXCEPT when you are under the M4 - no sats visible, so its running on accelerometers and speedo pulses. gets a bit wavery then.
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