I consistently see during highway driving that the speed that waze shows is 2 mph slower than what the speedometer shows. Has anybody noticed this or know which of the two is the accurate one?

 

I think its very common in all cars, motorcyclists are very aware of the error. I think the logic is to err on the side of caution with the displayed speed. Imagine if it was the other way around, manufacturers would be on the hook for all sorts of liability. At highway speeds, say 70mph, a 2 mph difference is pretty darn accurate considering there is probably some error in Waze too, though I would consider it the more accurate measurement.

 

I always found my car to be about 1-2 mph slower than radar signs. I think it's manufacturer being "safe".

 

If I recall correctly, there was a very contentious lawsuit against BMW many years ago on this issue. I don't remember too many specifics, but the end result was, it was deemed to be okay if speedometer registers a little high, however, the odometer must be pretty much spot on.

With the above lawsuit in mind, I believe there was another suit brought against Honda and/or Acura regarding the odometers registering a bit high as well, and as such, some models qualified for something like an additional 5% extension on the mileage portion of the warranty.

Keep in mind, the above is all off the top of my memory and should not in any way be deemed 100% accurate; said another way, if you need more specifics, hopefully I've given you enough information to research the issue further.