Garmin Routing

walkerx · Posted: Mon Apr 17, 2017 7:39 pm Post subject: Garmin Routing

So far these past couple of days, the Garmin has proved how bad it is at routing.

On A1 heading towards Kielder it told me to take a right turn onto a non existent junction. I later found that the junction we actually wanted was quite a distance prior to the one it notified me of yet never actually mentioned to take.

Next it was taking me of main a roads to go along b roads and county lanes, to only take me back onto the a road it had taken me off, which would have only taken 5 minutes instead of the 20 minutes.

Then today it took me down a road that became a private road to a dead end to a field.

And they wanting to use satnavs for driving tests... Big mistake........

sussamb · Posted: Mon Apr 17, 2017 8:43 pm Post subject:

You should try asking my wife to navigate Laughing Out Loud

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cjay2412 · Lifetime Member Joined: Jun 30, 2008 Posts: 102

having used both tomtom and Garmin for navigation whilst neither are perfect on all occasions tomtom is superior for a-b routeing although Garmin is slowly closing the gap with each map update there is still some catching up to do

walkerx · Posted: Mon Apr 17, 2017 10:55 pm Post subject:

Kremmen · Posted: Tue Apr 18, 2017 5:41 am Post subject:

I wonder why Garmin make these silly mistakes. They've been around long enough to have this sorted by now.
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Allan_whoops · Frequent Visitor Joined: Feb 18, 2006 Posts: 369

I've used both TomTom and Garmin recently as well as various smartphone apps. They all have the same problem. I think it is down to the maps now having speed limits attached to roads so the system 'sees' a 60 mph limit for a single track road as well as a major A road. Therefore the single track road appears quicker if it is shorter.

Even Mapfactor Navigator, which allows adjustment of speed for each type of road, doesn't handle this very well.

pcaouolte · Posted: Tue Apr 18, 2017 8:05 am Post subject:

Recently in the Lake District my Garmin tried to take me down exactly the same unsuitable road that a TomTom had tried to take me down previously.
I would never take a car down this road, it would be ok for a tractor, it is very narrow and full of large pot holes.

On the maps it is marked as a road and it doesn't have a speed limit so sat navs probably assume that you can do 60mph along it.

I think that I have seen a facility on the Garmin to set an area to avoid, I wonder if I can use this to make the Garmin avoid that road in future but I haven't tried this yet.
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Paul

Allan_whoops · Frequent Visitor Joined: Feb 18, 2006 Posts: 369

Yes, you can block off roads and whole areas. However, you will have to repeat the exercise if you do a master reset.

MaFt · Posted: Tue Apr 18, 2017 8:27 am Post subject: Re: Garmin Routing

M8TJT · Posted: Tue Apr 18, 2017 8:33 am Post subject:

The algorithm is simple. Don't route down B roads if there is an A road available even if it is a bit longer. Same for B/C road routeing.
Don't assume that NSL is achievable on a B road as invariably it isn't so revisit the satnav's assumption of speeds on B/C roads.
As Kremmen said, both Garmin and TomTom have years of experience and must have had thousands of complaints about this, so WTF haven't they got it sorted?
I'm sure it ain't easy, but I'm also sure it ain't rocket science either.

Daggers · Posted: Tue Apr 18, 2017 9:03 am Post subject:

I think the routing algorithm is much more complex than looking at the speed limits of the roads. I seem to recall reading somewhere that each road is divided into segments which have an average driving time associated with them. It's then a case of looking at all the options and calculating the cumulative driving time.

The problem comes where some of these driving times are inaccurate. On a dual carriageway, the driving time should equate to something near 60mph, while on an A road, it will be less, and on a B road, significantly lower, although each road will have its own timings.
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marksfish · Posted: Tue Apr 18, 2017 9:48 am Post subject:

Kremmen · Posted: Tue Apr 18, 2017 9:54 am Post subject:

One of the pitfalls is asking for the shortest route. It does just that in a silly way.

I've still got the last, now obsolete, Microsoft MapPoint and that does a superb job. It never uses daft side roads when faster roads are available even if longer. Shame the data can't be transferred.
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Satnav:
Garmin 2599 LMT-D (Indoor test rig)
DashCam:
Viofo A119 V3
Car Average MPG :

cottonsocks · Regular Visitor Joined: Apr 29, 2010 Posts: 189

cottonsocks · Regular Visitor Joined: Apr 29, 2010 Posts: 189

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