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GPS speedometer and tunnels?

I just read a Norwegian review of the Model S, and noticed that the speedometer is GPS based.

How will this work in a long tunnel? In Norway we drill an underwater tunnel under every fjord we can find. One close to me is 6 km long, and pretty steep both up and down. Construction will soon start on a 14 km long one.

Will the cruise control be able to keep the speed constant if set before entering the tunnel?

The main problem here is that there are speed cameras in these tunnels. Both regular ones, and average speed cameras that measure the speed all the way down...

- Erik

They have your main spring and they are winding....

Well - i don`t think it is legal to base the speedometer entirely and alone on GPS in a vehicle due to the inaccuracy and other problems associated with GPS-Reception (as mentioned above).
my 2c

One of my, "the government is out to get you" friends got his dog chipped. I jokingly suggested that the government used that to track people because dog lover take their dogs with them everywhere. He returned the dog until they removed the chip.

My wife actually likes that I track her phone. I did it because she is constantly losing it. It doesn't say, "it's under the couch" but at least we know if she lost it in a park, work, home, department store, etc.

Second part of the question was about tunnel reception. (aside from the notion that speedometer is GPS based)

I worked in the development of GPS and was very surprised, a few years ago, when I was driving a BMW in Switzerland that tracking was good thru their tunnels - one of which was about 35 miles long!!

First part - Using for instantaneous speed measurements in a slow moving vehicle is ludicrous.

An aircraft would be different.

Nominal accuracy of GPS is about half a microsecond - which translates to aporox 3 miles. This is fine tuned with the availability of multiple satellites in different directions. Using for speed measurements would rely on multiple satellites which may not always be visible.

Plus, each one is corrected once per day (or more). If using during that time it would throw you a curve.

We've all seen the occasional jump of the dot showing our location.

Bottom line - why do this when you have a perfectly good system in our cars?

@TV - you're a funny guy !!!

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