In response to 'why can't passengers know the speed?'

[jis]

Suffice it to say that the Speedometers installed in cars are not themselves that spectacularly accurate either. Use a stopwatch and mile markers to callibrate both while you are at it.

 

[MrFSS]

Suffice it to say that the Speedometers installed in cars themselves are not themselves that spectacularly accurate either. Use a stopwatch and mile markers to callibrate both while you are at it.

I know mine is off as I have timed it. When it says I'm going 70, I'm really only going 68.

Anyone know how accurate the radar signs they have to show your speed are. If one of those says I'm doing 55 is that pretty accurate?

 

[Oldsmoboi]

I think the point is that being off one or two mph in either direction isn't a big deal.

 

[jis]

That I agree with completely. As long as it is within say a +/- 3mph ballpark, who cares, unless of course you run into an anally retentive cop :help:

 

[Peter KG6LSE]

GPS can be very accurite in a line. Its curves and accels that are it's weekness

delta is the crux..

Mine show 79 MPh on many parts of the CZ and SWC in the past.

thats the FRA brick limit in most places of the LD system. sans a few places .

 

[Thirdrail7]

The Acela was supposed to to display speeds on the message board at the end coaches at regular intervals. I can't remember why they never put them in service.