Disappointed & perplexed Nuvi user.

Hi David,

I think we have met!

You have to develop a sense with your unit of when it is being stupid and when it is smarter than you. You can't blindly trust your unit to always make the right choices. Mine sent me on an abandoned road once and I could not turn around. Mine often says to drive 1 -2 miles and make a U-turn when I could just make a left turn. It is because it tries to avoid making left turns because right turns are safer.

A good rule of thumb is that if the GPS doesn't sound right it most likely isn't! Try letting it pick on the way back and see if it comes up with the same route but don't follow it. Take I-20!

Hill

Curiosity had me try your route several times using mapsource, and got the same route as you. I went south from wilmington trying various points until I got the more direct I-20 route. I had to go to Five Fathom Creek before I got the I-20 route.
I don't know why it selects the 85/385 route.
However, we need to remember we are a bit more logical than these electronic gizmos. We can reason. If we know something to be true and the gizmo says false, who do we trust?

I applaud you for at least trying the unreasonable route. I have tried a route that was suggested with all the doubts in the world...I was surprised. So, I suppose sometimes it works both ways.
Sometimes we must let our own common sense take over and ignore the machine.
I suggest giving it another try, to win back your trust...just not on that particular route..lol
I do know that sometimes the fastest route is not always the shortest and the shortest route is not always the fastest.

I'm sure someone will be along with the technical reasons.

I plotted it in MapSource (which presumably uses the same or similar algorithm) and here's what I got.

I-75 to I-285 to I-85 to SC-8 to Hwy 418 to I-385 to I-20 to I-95 to US-74 to Sam Potts Hwy

543 miles 8 hours 21 minutes

The only explanation that I can come up with is that fastest does not always mean best. It means taking the average speed of the roads involved, the route plotted will take the least amount of time.

I always check the route before I go. As I have said before, if you know a better route, then take it (you don't need the GPSr). I like to stick to interstates so I plan my trip ahead of time and figure out which ones I want to go on. Then I use my GPSr to get me from one interstate to another and locally. I guess what I am saying is that I use the GPSr for the detailed turns, not the over all travel route (unless it is locally)

I would not loose faith in your little friend!!! I love mine even when she does wrong (sound like a child I am talking about)

Thanks for the input and affirmation that the Nuvi has flaws that are best tolerated. I was hoping to better understand its algorithm -- or the method to the madness. I guess like anyone who has ever given me directions -- some work out fine and others would have been better left unsaid!

So far, and I emphasize "so far", after playing with the settings on my 350, I've always been able to determine what it was "thinking" when it came up with a silly routing. What I do when I'm not satisfied that it's given me the best route, is to keep changing the settings and let it recalculate based on the changes. So far, there's that disclaimer again, with a little patience and fidgeting I've always been able to get a useable route.

That said, it does sometimes eventually determine that a better route is available which to me indicates that it initially made a mistake on the routing. What I'd like to know is which algorithm does it use to determine when is the best time to inform you that it's found a better routing? Is it the algorithm that provides the least chance of you picking it up and throwing it into oncoming traffic?

See this post for the "A Better Route Found" mystery: http://www.poi-factory.com/node/7229

Does anyone know what specific factors go into the Nuvi 350 algorithm, differentiating its route selection from Mapquest, Google Maps, Streets & Trips, etc?

I have the Nuvi 680 and have found some issues with the directions given. For instance, sometimes it sends me off the freeway to just get back on immediately. That direction doesn't seem to make sense and seems to be an example of a silly child. One time I gave it an address and I found it was sending me through a new gated community. This seems to be an example of the the information is only as good as what has been put in. At best, the maps in my Nuvi is probably a year old. So, the lesson is to be aware of your surroundings and to keep a backup map available, just in case of problems. That make sense, just in case of a mechanical failure with the device.

Hi Goldie,

I try it my Nuvi 760. It gives me the right direction. The one you want Goldies. Dont forget to choose higways and fastest route. Your problems seems to be your none exclusions. You have to choose somes exclusions. Try it.

Best regards

Thanks. You are correct, sort of...
If I chose to AVOID highways, the Nuvi uses the correct Interstate from I-95 to I-20 to I-75. However, it has me exit I-75 in Resaca GA and take a very strange detour to Chattanooga -- going about 50 miles on secondary roads, instead of just staying on I-75.

Why should I have to chose to AVOID highways, when I really want to travel on highways???? Very strange!!

I seriously doubt anyone around here knows the Algorithms unless they actually work for Garmin or one of the others. Even so, I'd think they would some how attempt to safeguard that information as it might be of interest to competitors. We can all speculate and maybe even try and reverse engineer speculations but that's probably about it.

You may be right. I'd really like to understand why it routed so poorly...

Call me old fashioned, but when I know the route, and have traveled it numerous times, I don't use my Garmin to second guess me! I have realized, by trial and error, that if I have found the shortest/fastest route possible, my Garmin 360 os off.

The thing always gets me there, may not be the most direct/fastest/ shortest route, but it gets you there, that's it's job, and it does it well.

Very well said!!! Like you, if I know a better route, I take it and my 350 finally catches up with me. If I don't know where I am going, it doesn't get me lost (unless you are in boston...lol)

From my understanding, each road is given a 'weighting' value in the routing engine based on what kind of road it is, ie: Interstate vs. Freeway vs. US Highway vs State highway vs county road and each also comes with an average speed. Then, your unit uses the "user selected" preferences and avoidances, and then calculates the best route between your starting point and destination. If one selects "shorter distance" in the preferences, it will give you exactly that - even if it means getting off an interstate for a short time to go a shorter distance. May seem illogical to a human, but the GPSr is merely doing what it's programming tells it to do....and whether that is good or poor is more of a value judgment that electronics are not capable of....yet

This is an excerpt from "Don't Buy the Wrong GPS on Black Friday" - #7 "Routing Quality": http://www.gpsmagazine.com/2007/11/dont_buy_the_wrong_gps_on...

"Even if two GPS units have identical maps installed, they may choose very different routes. That’s because there’s a lot of math and algorithms behind how GPS devices figure out the “best” route to your destination. Is a particular street closed after business hours? Will you arrive only to find your destination is on the left side of a busy street, and you have to make a U-turn or go around the block? Is a given highway known to be congested at this time of day? Is a slightly longer route actually a shorter drive time? These are all factors that GPS manufacturers must tackle and some do a decidedly better job than others. This is the least well understood aspect of GPS devices and not something advertised on the box ... In general, Garmin does the best job routing, followed by Magellan and then TomTom."

Your post mentioned you had no advoidances set. That might be part of the problem. With my Nuvi 350, I have it set to avoid Traffic, U-Turns, and Unpaved roads. You might try turning on some of the advoidances and then reviewing the proposed route by tapping on the green bar at the top. Most of the time, my 350 pretty much takes me the way that I myself would have picked if consulting a map. Not always, of course.

I HAVE noticed that the Nuvi's propensity to avoid left turns will sometimes have me go past or around something and then U-turn back so that I can make a right turn at the destination. Turning off U-turns greatly reduced that behavior. Setting the navigation preferences to Faster Time works best for me. It will give preference to bigger roads like interstates and highways. I learned the hard way with a previous GPS system that "shortest" will very often route you through back roads and side streets that might make you nervous.

I have used several GPS units, and I learned with all of them to take a moment first to review the proposed route to check for the occasional "what the heck?" routing decision. I've had the 350 for around a month now and took it on two trips besides daily work travel and I am very pleased with the overall accuracy.

I tried every combination of settings. The closest I got to the most reasonable route (I-20 to I-75) was when I turned highways off in 'avoidances'. After routing me for 400+ miles on interstates, the Nuvi had me get off I-75 in Resaca Georgia to follow secondary roads for the remainder of the trip. Very strange.

Lessons learned:
She's just not perfect - PERIOD!
Trust -- but verify.

... a better route, but the general direction, it may work well for you. Last night we bumped into a congestion. We were a few miles from the destination. I knew the general direction to the place and took an exit, after which I continued on a parallel to the highway street. My nuvi plotted a new route after trying to tell me to turn around and get back on the highway a couple of times and I ignored it. If we kept going on the highway, we would have ended up 1/2 hour later.

I can't speak for your particular route, but sometimes the map (even though "up to date" may still have some details from a few year ago. Therefore, maybe the road was not complete at the time, so they make you take an exit. I have seen this happen as the major highways have had new construction in my area over the past several years and I remember when there was a forced exit.

A fellow co-worker recently bought a gpsr. One dark night it routed her onto a dirt road, in the middle of nowhere in a big truck. Needless to say, she was scared.

After she got herself onto a decent route, she called me and asked what good is the gps if it's going to get her into trouble.

My only advice was: Trust the gps into the city (to destination), and out of the city. Everything else is up to her and a paper map.

Most time the gps will do a good job. But sometimes the sattelite signals are not right, or countless other possibilities arise. You do need to know where you are going to be able to use the gps.

One thing for sure is, gps technology is still in its infancy.

I used to live in the Atlanta area. That is a very common shortcut for people traveling that stretch of road. I used to use it myself all the time.

The technology is quite solid - it's use among the general population is what's in its infancy.

David,

I think it is quite common for new owners to feel a bit disappointed (remorse)in their GPSr after owing it for a short time. I went through this and others have too because we expect the technology to do more at the consumer level than it does right now. In time I and others have developed a sense that the GPSr is just a tool that we use to help us to get from point A to B more efficiently. But it is not the all knowing box that always makes the correct judgement in every case. But rather it tries to make a good judgement a high percentage of the time based upon techniques that try to fill in for incomplete data like the actual speed of the highway at the time you travel it.

I have the traffic receiver and use it to help me make decisions on traffic all of the time. In Atlanta where I live, the traffic map can help me make a better judgement with the information I have from it but it rarely can make as good a judgement as I can based upon the data from my experience. I've learned not to expect too much and I'm happier with my 680 now. I think as I went this process I felt some grief over learning my unit doesn't do as much as I think it should and I felt some fear that perhaps I can't trust it at all. But I've learned that sometimes it is smarter than I am and sometimes it just plain stupid in the choices it makes and that I have to just ignore and override it and let the GPSr catch up to me. When you develop this kind of sense, you may be a lot happier with your GPSr.

Do you have the traffic receiver? Perhaps it was trying to route you around traffic at Ringgold. I went to Chattanooga where I used to live) twice over the Holiday ( and there was about a 10 mile backup at Ringgold. I went up HY 76 to east ridge to avoid it.

Since you and I have talked about technology face to face before, I know you are pretty tech savvy and are trying to understand how your 350 works. Although it may seem random, as other's have said it is following the programming but there are many parameters (including settings) it takes into account so it's hard to isolate the effect of each one of them. But over time you will see the effect of some of them clearly and if you go up north and set avoid tolls, you might get routed hundred of miles out of your way!

Happy GPSr.

Hill

BTW,have you tried geocaching?

My wife has not taken to my nüvi very well. She would rather have it muted and have me relay the instructions to her (I navigate, she drives).

More than once, when Emma says "turn right in .x miles" Colleen turned right, one ramp or exit too soon!

She can't visualize the mileage and would probably prefer "turn right soon" and "turn right NOW!".

simply solution ... you take over driving!!

I couldn't imagine not being the one behind the wheel. My wife NEVER drives when we are together, and we've driven cross country a number of times. For one, I'm a control freak, but ... two, she doesn't want to drive - she rather read and sleep!(though this may have something to do with #1)

When I'm driving I can't play with the GPS (without complaints) and I have a back seat driver to deal with. This arrangement solves both those problems.

Though, wrong turns are still my fault

no matter what it is!

... every man should have figured that out long time ago
I believe in most of the families "we know who is the boss", no matter what we say!

I love to drive, but when we take a driving trip, my wife drives 95% of the time. She is the world's worst back seat driver and I inevitably get irritable from all the constant warnings and frequent stomping of her imaginary brake pedal. We enjoy the trip - and each other - so much more if I just let her do most of the driving.

That's when I offer to take my wife to the nearest airport. It's the deal we make before we leave home. The GPS can always tell me where the nearest airport is located and how long it will take to get there.

Bill