Why dont cars use GPS technology to give an accurate speedometer reading?

Question

I have yet to own a car that has an accurate speedo reading. As you reach higher speeds most cars are upto 10mph faster on the speedo than you are actually doing. Yes, a backup 'normal' speedo would prob be needed as the odd time you may lose your signal but GPS speedos that are 100% true are the future? Lots of cars have sat navs built in so the technology is already in the car. Any ideas??

Surely mfctrs dont make their speedos show an artificially slow reading to keep the speed down?

Answer 1

Hi
The system you ask about is on it's way and guess what, every time anyone goes over the speed limit by even one m.p.h, they'll get a fine through the post, just wait and see.
Ray. West York's. U.K.

Answer 2

10% is the worst, normally a differance of between three% and 5% is recordable. The worst offenders for this are Audi's. The situation is that If everyone was fined who strayed over the restrict, lovely quickly there can be nobody left on the roads. Every person would become with a ban. Speed digicam's are callibrated to incorporate a 10% speedo differance. I;E 77mph in a 70 zone will outcome in a quality. Police comprehend there's a differance in producers speedo's. What would occur if all drivers had been fined for going 1 or 2 mph over the restrict? Finally there would be no drivers to power emergency vehicles. The science is in situation to use the approach you mention, however truely it isn't functional.

Answer 3

10% is the worst, normally a differance of between 3% and 5% is recordable. The worst offenders for this are Audi's.
The problem is that If everyone was fined who strayed over the limit, pretty soon there would be nobody left on the roads. Everyone would end up with a ban.
Speed camera's are callibrated to include a 10% speedo differance. I;E 77mph in a 70 zone will result in a fine. Police know there is a differance in manufacturers speedo's.
What would happen if all drivers were fined for going 1 or 2 mph over the limit? eventually there would be no drivers to drive emergency vehicles.
The technology is in place to use the system you mention, but in reality it is not practical.

Answer 4

10% is the worst, often a differance of between 3% and 5% is recordable. The worst offenders for this are Audi's. the problem is that if each and every physique grow to be fined who strayed over the decrease, surprisingly quickly there may be no one left on the roads. each and every physique might finally end up with a ban. velocity digital camera's are callibrated to comprise a 10% speedo differance. I;E 77mph in a 70 zone will effect in a great. Police understand there's a differance in manufacturers speedo's. What might happen if all drivers have been fined for going a million or 2 mph over the decrease? finally there may be no drivers tocontinual emergency vehicles. The technologies is in place to apply the equipment you point out, yet surely it particularly is no longer sensible.

Answer 5

A GPS-based speedometer is only accurate on the flat. On a gradient it under-reads, as the surface distance (and therefore speed) is greater than the horizontal distance). Also, it cannot work if it cannot see the satellites (e.g. in a tunnel).

The regulations that car manufacturers must adhere to in order to sell their cars in the major markets do not allow speedometers to under-read, but do allow them to over-read by up to 10%. This is so that if there is a 30mph limit, and the driver assumes the car speedometer is accurate and sticks to an indicated 30mph or less, the driver is not exceeding the limit. It also must work at all times. A GPS-based speedometer cannot meet these regulatory requirements.

Therefore, to err on the side of caution and keep their cars legal, most manufacturers develop speedometers that over-read by about 3% with a tolerance of about ±1% on new tyres (as the tyres wear, or if the pressures are too low, the amount of over-read increases).

Answer 6

because it violates peoples privacy rights, it would mean a Big Brother culture where people can be tracked at all times. Takes away a person right to live a private life. This is why the pay-as-you-go insurance option never took off as predicted. The car would have to be fitted with a tracker which can effectively work Speed by putting distance/time. A persons privacy is the only thing which they own and have total control of. this is taking that away from them.

Answer 7

Well I for one can say I will never own a car with a built in GPS or Onstar or anything similar to that.

It is just another way for your life to be taken away.
Privacy is about the only thing we can still say as American we still have, seeing how freedom is now gone, and most people live in fear - since 9-11.

I will not have some GPS or other tracking devise letting anyone that can hack know where I am how fast I am going and what is being said in my vehicle.

Answer 8

most gps only accurate up to 2meters. thats why factory sat nav's have a speed sensor input to give more accurate readings. and sometimes the us army (who own gps) switch it off sometimes (less now than a few years ago) .
give it a few years, speed will be from gps

Answer 9

what is with these civil liberty people?
if the security services can tell if i am in ASDA or robbing a bank, whats the big deal ?
there are many good applications to knowing where a car is , for instance ,a hill walker lost or overdue. find the car and you know near enough what hill the persons on.
if you ain't up to any bother , whats to fear

Answer 10

hmmmm interesting point you have. I think i agree with you on that one because the technology is already there it will just need tweaking. I think some tachographs are designed about 2mph slower to make sure if youre doing the speed limit so you wont get caught speeding.