Re: GPS is bad at measuring height
"If you lose the signal you lose the signal, what's the difference whether it's up, down, left, right?"
Because it could lose the signals just as you get on. End result, it doesn't know which deck you entered. Murphy's Law. Like I said, most satnavs I've tried (including Google Maps) get mixed up simply by going into a reversible lane.
"No. Short of a bridge with vertical a car elevator (which would be freakin' awesome) you're still coming in on a physically different road, which is easily distinguished with sufficiently precise data, which this is."
I still haven't gotten a clear answer to just HOW precise the thing is at motorway speeds. It needs to be within 2m while driving 100km/h to not get mixed up, especially if the ramps involved are very close to each other (which actually happens at those two bridges; I used to live on Long Island). Other complicated interchanges like Bruckner and Washington's Springfield Interchange create similar mixups.