Question (stacked roadways)

My 765 gives me elevation so it would be possible to determine whether I was on the upper or lower roadway.

However, getting the elevations mapped and into the map would be a real exercise.

If motionless, I think it'd not know. But I also imagine that when it's moving, it'll assume you're legally traveling with traffic and that you're not drunk and traveling against traffic, then would assign you to the correct level (with the appropriate exits/entries).

It's probably like existing roadways with traffic lanes very close together--once it determines your direction of travel, the "snap to" feature of most GPSes will show you on a roadway even if it calculates you be be 5-25 feet off and will put you on the correct side of the roadway.

http://www.gpsreview.net/snap-to-roads/

Your position would not be calculated after you entered the lower roadway. You will almost certainly hear from Jill, "Lost satellite reception..."

dobs108

would this not depend on the number of satellites the unit could see?

Travel on a level is in a single direction and as the GPS knows the direction of travel it would know which ramps are usable.

I would think that it depends on which level you entered the roadway along the route you are following. If it tells you to take the top level, then it will continue on the top level.

Likewise, if it told you to take the bottom level, then it will continue to route you along the bottom level and proceed from there.

20 some years ago, there were lots of stacked highways in San Francisco area. One day, a little earthquake caused lots of lives lost on the collapsed highways. People got sandwiched to death. After that, California are trying to demolish or replace these double-decker highways. Earthquake is not the only natural disaster that can bring down a double-decker highway.

Sitting at my computer and simulating routes looking for junction views means that I do not have to be under a clear sky to get reception to navigate calculated routes.

This makes be think that being on the lower level of a stacked freeway should not be a reason to lose reception.

This is to report that my unit somehow keeps pseudo satellite contact while I am traveling under the water in the Baltimore Harbor Tunnel.

If it can do it there --- it can do it anywhere

even in New York, New York.

Gary Hayman

My experience indicates that the Garmin just keeps you moving along the road at the same speed you were travelling when satellite contact was lost.
Mark

You can try it in Toronto. Drive on the Gardiner Expressway where it is elevated above Lakeshore Blvd. Then take an exit that allows you to drop down to Lakeshore. The GPS will still show you driving up on the Gardiner, until you exit Lakeshore Blvd or the Gardiner and Lakeshore separate horizontally far enough that it knows you have changed roads.

As others mentioned, while navigating a route it will assume you are on the road it sent you on.

I know Garmins can determine elevation, but I have heard it is not very accurate, so don't know if that could be used to determine which road level you are on.