Change in routing

Hmm, the big question is: did your route get you to your destination each time?

I had my GPS set for shortest route and the Garmin had me leave the main highway for a secondary road because it was shorter distance wise. But timewise you lose out going on the secondary route.

You might want to reset for the fastest route.

Good point. I never tried any setting other than fastest route. I can see where a bicyclist or pedestrian may prefer shortest, but for motor vehicle use, my goal is to reach the destination in the shortest time.

Fastest route always takes me on Interstate highways, which I avoid when I can.

Yep. Just wondered why the routing between the same 2 end points would be different between map versions.

I'm just guessing here but to me, it seems reasonable that Garmin has to make a trade off between finding the actual shortest/fastest/etc. route and the amount of time the nuvi takes to make the calculation. Since we're not dealing with supercomputers here, Garmin may be making a decision that we prefer faster route calculations rather than spend 50% extra calculating time to result in a 5% shorter/faster route.

This is not only a problem with shortest route, but it's something I see with my faster route choices as well.

The longer the route and the more road options open to the nuvi, the more error that can be introduced. I've found on cross country trips that it's better to pick 1-2 expected pass-through cities and divide the route into smaller pieces.

One last thought: I think your nuvi in Avoidances can be set to avoid Highways. If so, it might be worth experimenting with fastest route & avoid Highways rather than shortest route with Highways not avoided.

Good luck, have fun, and arrive at your intended destinations...

You don't want to pick shortest in Missouri unless you want to drive on a lot of gravel roads.

This weekend I had MapSource set me up a couple of routes that I loaded into the 855 unedited. In both cases the 855 slightly changed the routes. When we got home I loaded one of the routes back into MapSource just to check the change and found instead of keeping me on a main two lane highway the 855 took over and routed me on a county road that was as good a road as the main highway and cut 1.5 miles off the trip. Normally I route with MapSource only if we are on a long trip using several different interstates and have never had the 855 take over, so it kind of surprised me that it didn't agree with MapSource or MapSource didn't agree with the 855 seeing as they are both a Garmin product.

As to why your GPS receiver would make different choices with different revision levels of the maps, I think the most likely candidate for the element of map data that changed was the average rate of advance carried for at least some segments of the roads in your comparison. I have definitely seen that change between versions, and seen it to cause changes in routing. By comparison the actual length of the roads seems less likely to be changed between versions.

Separately, I think most of the Garmin GPS receivers have a setting to avoid toll roads. I believe on at least one or two of my units I have observed use of that setting also to avoid interstate highways which have no toll. Perhaps the person posting in this thread who dislikes interstate highways might try using that setting instead of "shortest".

To the person who dislikes getting routed on non-paved roads when using "shortest", I suggest checking whether your unit supports an option to avoid non-paved roads. At least some of them do.

It could be you have unpaved roads not checked off in avoidances, Perhaps putting a check mark there will prvent the gravel roads.

Gravel road avoidance is hit and miss in Illinois & Iowa using shortest route preference.

I suppose Navteq map makers are not sure of what roads are paved or unpaved. I rarely use shortest distance so I've never been directed to a dirt road.

I have a TomTom, not a Garmin, so my comment may not be accurate, but whenever I have compared the two brands I have found that they seem to be essentially equivalent.

With my TomTom, one of my menu choices is whether or not to avoid unpaved roads. You may want to check your menu system to see if that option exists on your device. If it does, and you check that option, you may find that it helps your device select a more optimum route as *you* define an optimum route.

- Tom -

I agree et, insuring that the avoidance "unpaved roads" is checked ON would help in this kind of situation. AFAIK, all Nuvi devices have the Unpaved Road avoidance.

I have been complaining about Garmin's routing problems for the last couple of years. Every time a new map comes out, they seem to fix one thing and break another.

New routing algorithms come with the new map. Maybe they should start over and build some new ones from scratch.

I have that option checked and have had it checked on the last four Garmins I've owned and they all still routed me onto gravel roads. I also have no U-turns checked and they have all at one time or another wanted me to make a U-turn. All of those options are at the mercy of the map makers and are hit or miss.

Not only the map makers but remember if the Nuvi can't get you from A to B without breaking one of the avoidances then it has no choice. Also if you pass a destination on your route the "fastest" or "shortest" way to recalculate and correct your mistake could be a U-turn or a trip down an unpaved road. That may have nothing to do with the avoidances set, just getting you back on the right track.

Just to make an example, if you've made a mistake and a U-Turn is the ONLY way to get back, the U-Turn avoidance has to be broken. Otherwise it would just silently fail, leaving you stranded to figure your own way out.

As an aside, I've never had my 360, 760, or 2555 break the initial avoidance settings on the initial route. Only on a recalculation. I almost always use Fastest, unless I'm doing the Blue Hiway thing. Then, I use Shortest.

There are probably some subtle changes in the maps that you can't see. If Navteq updates a speed limit on a road, a new secondary road gets added, perhaps a 'road type' definition got updated. Changes like that would not be very noticeable when looking at the map, but could trigger a different routing decision.

Updates in maps definitely can change the routing; I've seen that a couple of times.

And I definitely take routing as a suggestion, reviewing the proposed route before I start off on it to see if it makes sense.

As others have pointed out, some preference settings will have it directing you to take a freeway offramp and get right back on as a "shorter" route.