Nuvi 765 routing funny- I think..

Okay, so Saturday I planned a route in basecamp. It started from a point just off the A3, a few miles away from home. Preview was fine (both before and after transferring). When starting device and importing route etc, I got the normal, "Do you want to navigate to start of route" To which I reply yes. Garmin plots the route. All good, it sets me off down the A3 towards my start. About 3 junctions before my start of the route I planned, it tells me to take the exit off the A3. I do so. It tells me to take exit 2 on the roundabout and rejoin the A3. I do so then continue on merrily to the correct junction whereby I exit and meet the start of my route.

Great. For no reason was I asked to exit and rejoin same m way in same direction. But I was really curious why it told me to exit and then rejoin. This was a navigation that the nuvi plotted for me. My route even started off of the the A3, and was further ahead than the junction it asked me to leave and then rejoin from! All my avoidance's are turned off in both BC and device.

Yesterday, I rode a very similar but new route. Again, same start point down A3. Again it asked if i want to navigate etc , again I said yes, and again I got told to take the exit and rejoin (of course I wasn't caught the second time!).

So this morning, I manually plotted a route on BC from my house to the start point. Guess what , the "take exit and rejoin" instruction is missing... so it appears that manually creating a route to start from has avoided this...?

So curiosity is piqued....what happened, any ideas? Not a train smash this time just a waste of riding time to exit and rejoin...

I suspect that the answer lies somewhere in your 'preferences' settings.

However, you do occasionally get the glitch when the distance between two points is marginally shorter, so the clever device will route you that way. There used to be a point on the A2 when it happened, routing you off the dual carriageway, up to a roundabout, straight across the roundabout and back down to the dual carriageway; all to save a yard or a second.

Hi, your explanation of a gremlin makes more sense. My preferences are set to fastest routing and cutting off and then back down is not really going to be quicker. Oh well, no trainsmash. (I have been caught out in the past with shortest -that goes all behind the shops and through lanes that think are private!)

The routing algorithm makes no consideration for stopping or slowing for give ways, roundabouts, traffic lights, sharp corners etc. To aid the speed of calculation, and work with the limited processing power available, I guess that the number of factors considered are pretty minimal. The fact that it preferred a 60mph segment of the route as opposed to a 70mph segment over a similar distance does seem a bit odd, or is the A3 at that point a lower limit.

I have encountered this anomaly myself a few times, where the instructions defied logic. I guess that not being correct 100% of the time isn't acceptable in this day and age... The vast majority of the time if does get it right though.

Well, again it happened today 2 different routes! Getting bloody annoying now, as this time I did not know the area, so followed the "take the exit to roundabout" and rejoin same carriageway just behind the caravan and car I had overtaken a while ago. twice! so third time I got the "take exit" I ignored it. And of course that one was the first exit off roundabout, not the rejoin on second exit! Will be looking into it but cannot fathom this, as they were again plotted by the device. My preferences say fastest route (not shortest). And most other settings are unticked. This has only started happening recently, and I have not updated device that I am aware of...maybe un ticking all my routing preferences (to make basecamp and device the same when transferring?) has inadvertently, has caused this? I'll post what I figure out but any ideas welcome. Nuvi 765T. Out of date maps as well, but the roads haven't changed recently!

I still suspect some slight glitch in the preferences set-up and / or in the device's inability to calculate a route EXACTLY where the rider expects it to go.

Whilst it is different, in that I created the routes on a computer and then sent them to my Nav V device (where they were re-calculated on import) I had just two what I call 'Garmin features' in about 1000 miles of routes. Both were the inexplicable leaving of a main road in order to ride parallel for three hundred yards of B road and then rejoin the highway. Another was the cutting of a corner, using 20 yards of farm track.

I re-checked where it was on the route that the routing error occurred, comparing my track with the error, aginst the 'correct' version held on my computer. Both were 'correct' on the computer, so the routing error can only have been created when the route was imported into the device.

Mildly frustrating when it happens, though a few hundred yards in one thousand miles of quite complicated routes is maybe acceptable.

I sometimes spot them coming up on the screen, so can avoid them by ignoring the routing instruction. Sometimes I don't. When I don't I just accept them and laugh.... The alternative being to write out a thousand miles of detailed routing instructions by hand.... Something I used to do.

back handers?

Motorway services giving Garmin back handers for extra custom? probably not. I must admit that when the pc maps are not identical to the device maps oddities appear to occur more often (still not as much as tot tom units)

The routes I created for the Easter Wander included about 50 miles of motorway in Belgium.

They were created in BaseCamp on my Mac, exported to a Nav V running indentical and fully uptodate mapping. Both ran perfectly.

The same routes shared with bods on the ride, who displayed them on their PC's running Mapsource (map versions unknown) and then imported into their 660's, mapping unknown. Both reported that their routes asked them to deviate into the motorway service areas, then back to the motorway. Bizarre and not something I had ever seen happen before. Easy enough to ignore of course.

Could it be a fuel thing if they were using the fuel tool on the 660? I don't use it so not sure if it uses map data.

You may well be right.

There are so many possible variables as to why a specific bit of routing instruction goes awry, it's difficult to guess.

My only suggestions are:

To turn as many of the device's functions off as possible. These include: auto-recalculate, masses of 'must do' waypoints (as opposed to viapoints or shaping points), routing help (like twisty roads). In short, make it as basic as possible.

Take a bit of care when placing via and shaping points. If you happen to place it far enough up a side road by mistake, it WILL take you that way, because that is where you have asked the route to take you.

Match whatever maps you have on your computer to those on the device

Match whatever preferences / avoidances you have on your computer, to those on the device. Preferably reducing the preferences / avoidances to as few as possible or limited to those that really do have some real value to you. Seasonal closures is a common one. Yup, the device knows that some roads are closed in the winter, so it will avoid them. Unfortunately, the software is not so clever that it knows that Augurst is not winter. U-turns is another; some very popular hairpin bend routes are read as u-turns. So, the device may well route you around the very hairpins you have ridden hundreds of miles to enjoy.

Okay, so I have just unticked "avoid unpaved roads" on device and in software. This is the only change I have made. All other functions seem normal and remian set as plan a faster route - not a shorter route.

To turn as many of the device's functions off as possible. I only have faster time and avoid unpaved roads selected (on device and in basecamp)

These include: auto-recalculate, I cannot see where to turn this feature on/off (i have an old nuvi so it must be set automatically)
masses of 'must do' waypoints (as opposed to via points or shaping points). All routes were plotted by the device where I simply said navigate to "home" or to start of a route so waypoints were not included by me (not even sure any would be set by device. Naturally, missing a portion of ITS route would just recalculate the new route between start and end point.

routing help (like twisty roads). - dont have this feature available to me either

Take a bit of care when placing via and shaping points. If you happen to place it far enough up a side road by mistake, it WILL take you that way, because that is where you have asked the route to take you. - again, the device plotted it so no user input

Match whatever maps you have on your computer to those on the device - Basecamp takes its maps from the device so cannot be this

Match whatever preferences / avoidances - as above
U-turns is another; not selected as an avoidance either. Not really sure where to go and will only know if anything works the next time I drive past those same places with the device selecting the route. Mildly irritating but seems to be a start of some irritation as it never did this previously (well not as frequently!). Will update as I figure it out