Garmin Nuvi40 Lost on The GW bridge

Well, at least it didn't try to route you *under* the bridge.

The Garmin Troll 2400 will be the next GPS series out and it'll offer that feature.

To the Original Poster: I see from Google that there are toll roads around this area. Make sure that your nuvi 40 doesn't have an Avoidance set for toll roads as that avoidance can create situations as you've experienced!

See p 19:

http://static.garmincdn.com/pumac/nuvi_30_40_50_EN_OM.pdf

The premium versions will be various iterations of Billy Goats with the Gruff being the top of the line.

My experience with a Garmin Nuvi is similar to what morpheus2013 experienced: the Nuvi is generally reliable but there are times when a person has to work with discretionary judgment.

When I generally know the area, I scroll through the route to see if it makes sense or not and then decide whether to follow it.

Too often people blindly follow the GPS expecting it to lead them to where they want to go, resulting in people dying in deserts or nearly dying in the wilderness.

The GPS is a navigation aid, not a replacement for common sense.

When you switch on your GPS, don't switch off your brain!

Suspension bridges such as the GW can be a nightmare for GPS designers (or they can provide a really hard test case).

In comparison to a tunnel, which just blocks the signal and the receiver goes deaf, in a bridge with all those (vertical) metal members, you get both signal blocking, and what's worse, multiple reflections of everything.

(here starts the nerdy, technical bit)
One of the reasons GPS uses circular polarization is that a simple reflection of the GPS signal will arrive at the antenna with the *reverse* polarization of the original signal from the bird, and so will be effectively ignored by the antenna. BUT -- on a bridge, with all those wires, closely spaced, and what's worse, moving a little, you get multiple sets of even-order reflections hitting the antenna at varying times. The poor little receiver can't figure out what's going on.
(end nerdy technical bit)

Harkening back to an old Wizard of Id comic strip, Rodney (the errant knight) asks the Wizard, "I saw a shooting star last night while riding back to the castle! Is it an omen?"

The Wizard replies, "Yes, you're going to have an accident!"

"What! How can you tell?" asks Rodney.

"You're not watching where you're going!" says the Wizard.

GPS is useful, but the most important part of any car is the loose nut behind the wheel!

I don't doubt you k6rtm, but please explain how my GPS maintains signal and position all the way throught the Holland Tunnel between NY and NJ, which is over a mile long. How do they do that? I've always wondered, and it seems you may know the answer!

Yes I would like to hear k6rtm explain tunnels.
In the meantime, I saved a link a long time ago.
http://www.boston.com/news/local/articles/2011/07/07/how_gps...

I have seen my Nuvi's do the same thing. They are just guessing and using our last known speed to continue you on the road you were on. In a one mile long tunnel in Zion National Park, we stopped briefly and the GPS kept happily motoring along.

With true "dead reckoning" you would also have a compass and motion/speed sensors so the system would be able to make a moderately accurate guess as to where you are. But our Nuvi's are just making the assumption that you are staying on the current road and continuing at your last known speed. If not in heavy traffic, try stopping sometime in the tunnel. Your arrow will happily continue down the road.

I see the same thing in "urban canyons" in metro areas, where large buildings block the signal, and in the tunnel gong across the Bay -- the little beastie will keep going with what it had for as long as possible, and then start barking about no signal. Even in some multi-story parking garages -- one I frequent, some times my Nuvi is complaining about no sat coverage before I get out to the street, and other times it doesn't seem to care.

High-end built-in car systems (Mercedes, I believe, for a few years now) can supplement with live data from the car, such as direction(compass) and speed.

That's one area where a really, really good built-in system could shine, by integrating multiple sensors including live vehicle data with the GPS solution. That's an inertial platform, and they used to be expensive because of the computation required to do it right. They're still expensive for the car companies who would rather put money into more cup holders, but quadcopters use them (using open-source software packages).

Rebroadcasting GPS signals is really, really frowned upon for a lot of reasons. So while solutions exist to propagate AM/FM radio signals in tunnels (leaky cables), and even some cellular connectivity (repeaters), it doesn't happen with GPS.

At least on my NUVI, it is easy to tell that it is simply faking the route by guessing where you should be. I can cruise through the Baltimore Harbor Tunnel (about a mile) and the GPS will show the correct position. But if there is slow traffic in the tunnel, the GPS still indicates the same speed. It then shows me existing when I would have if I had not slowed down. A little after it computes I should have exited (but didn’t), it then complains about a lost signal.

It would be interesting to use a NUVI in Switzerland. I wonder how it would predict the route when they have interchanges underground.