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Route Efficiency

Hello, first post. At this point I'm not requesting any recommendations, but I would like to improve my knowledge of what would be reasonable expectations for an auto-mounted GPS.

Not counting hand-helds, I bought my first GPS - a TomTom XL340 - in 2009. Aside from a few obvious map errors it's been a solid unit that still works well, given its dated map. With the high cost of replacing that map, and assuming one would work as well as another, I bought the Garmin 2597LMT six months ago.

The Garmin 2597LMT does not work as well as the previous, older TomTom. On a trip to an unfamiliar city last month its shortcomings became evident. With "Quickest" chosen, and no restrictions other than dirt roads, it routed us oddly away from main freeways, sometimes doubling back, sometimes in the opposite direction, and always slower than my manual map reading. I understand from lurking here and reading years of posts that this is not odd - it happens to many/most people.

I have a limited sample - one TT works and one Garmin doesn't, adequately. So at this point, as a part of my basic education, is this aberrant routing behavior is limited to Garmin? Is it mostly Garmin?

If htis is too simple a question, please expand and explain what I should be asking. Thanks.

Comments

  • sussamb 792 Points
    edited September 2014
    I suspect you've got some settings incorrect, I rarely have issues with my Garmin (and I have 3 auto GPS).

    You may want to disable TrafficTrends and myTrends. I've seen posts here that say those can create rather strange routes so I turned them off in my latest unit (the only one that has them) the minute I got it :)
  • Boyd 1966 Points
    If you've got a couple days to spare, you could have a look at this 16 page thread. :)

    http://forums.gpsreview.net/discussion/13967/x/p1/
  • Boyd, thank you - I read that one earlier and it was an eye-opener. It seems odd that you'd have to use a "via" in order to get reasonable routes, but that would be a workaround, of course. (My wife won't use the 2597 anymore and won't let me sell it back to Amazon where some unsuspecting soul could get lost or killed with it...)

    sussamb, except for quibbling about the meaning of "incorrect" settings, when those are factory feature defaults, I suspect you're right; I will disconnect them and see if that improves anything. I say "I" will do it, because my wife ants not part of Garmin.

    Still, is this a Garmin issue not present (or not frequently noted) in TomTom?
  • Spelling correction: "...my wife wants no part of Garmin."
  • sussamb 792 Points
    edited September 2014
    I think all GPS have the occasional routing that doesn't quite match what the user might expect, TomTom has issues too:

    http://discussions.tomtom.com/t5/Map-quality/Strange-routing-instructions/td-p/364498

    Just have to bear in mind any GPS is just another navigation tool ... which occasionally may not match what the user expects.
  • Tim 1474 Points
    Any GPS can of course produce strange routes from time time. The two major factors are (1) the accuracy of the underlying map data and (2) the strength of the routing algorithm.

    As for map accuracy, this will vary from location to location so it is difficult to say which might be better for you without people having local knowledge of both maps. (Difficult to find.)

    As to routing quality beyond the extent of the underlying map data, manufacturers need to balance the expense of faster processor speeds and the patience of people waiting for the GPS to calculate a route in addition to just having route smarts. A GPS won't consider all route possibilities and the more shortcuts it looks for the longer route calculation will take... so at some point the GPS just spits out the best route it has found, which isn't always the best.

    In my years of experience with multiple brands across different parts of the country I'd give a slight edge in map accuracy to the maps Garmin licenses from 'Here' while at the same time giving an edge to TomTom when it comes to smart routing algorithms.
  • It still seems odd to me that in order to obtain the best basic service one must disable features that might have been the reason for the purchase in the first place. Still, I'll do that and see what improves. I'll even turn off the traffic to get a basic functionality.

    My basic question is answered; TomTom has route aberrations, also.

    Tim, thanks. My sense also is that the routing algorithm is the problem with my 2597. Possibly, as Boyd's link suggested in one post, Garmin simply underestimates the delays of off-freeway traffic and traffic lights.

    I have decided not to update the maps and software of my XL 340 (still 2009) - it works, and I don't want to screw that up with bad maps of useless algorithmic "improvements." Also, many of the places we travel in the American West simply don't change that much, so we'll use it for that travel. For areas that are more dynamic I'll have to get this Garmin working acceptably or I'll change to TomTom.

    Thanks.



  • Oh, and i should have mentioned that while I'm not a knowledgeable GPS-guy, and am/was a professional navigator and am well-versed in equipment failures and the accompanying need to follow the route with a map. Perhaps I was spoiled by the reliability of the XL 340, but I have now relearned my lesson. Still, had this 2597 unit been in my aircraft, I would have accidentally dropped it on the tarmac and driven over it to prevent it ever showing up again...
  • Tim 1474 Points
    When TomTom started collecting historical speed/flow data they quickly went from having questionable routing to the best routing. Garmin soon after started collecting historical/flow data and they still haven't been able to catch up to what TomTom has done. I simply don't understand why with the amount of data they should have been able to collect, especially here in North America.

    I know it is TomTom's speed/flow data that is part of the magic because there are companies out there who license the TomTom map data but (to my calculation) are not licensing the TomTom speed/flow data. In those examples the routing is often worse than Garmin's routing.

    Given that Garmin should have been able to collect a sufficient amount of flow data I can only conclude that the underlying data structure and algorithms the engineers at TomTom have built is superior to what the Garmin engineers have developed.
  • dhn 330 Points
    If you were to speak to mvl about it, he feels that there is a fatal flaw in TomTom's IQ routing algorithm that results in Garmin now having better routing.

    Mvl has, therefore, abandoned any TomTom PND for personal daily driving. Somewhat akin to Gates going over to Apple (well, not quite but you get the idea...).

  • Tim 1474 Points
    Yup, like I mentioned above so much of this is very regional.
  • Hmm. I didn't see the "regional" issue until now. Thanks. The horrific routing wasn't at home at home (the American Southwest), but rather occurred during a visit to Baltimore two weeks ago, where we received some interesting routing through neighborhoods where HBO's "The Wire" was filmed. To be fair, it mis-routed me through some pleasant tree-lined suburban neighborhoods, also, as well as pointing me west on the beltway when I needed to go east.

    To my mind, that's even worse. How can one perform due-diligence on a GPS unit at one location when that test is not representative in other places?
  • Tim 1474 Points
    Jaywalker said:

    How can one perform due-diligence on a GPS unit at one location when that test is not representative in other places?

    Been trying to answer that question for the past eight years or so running this site! :)
  • Boyd 1966 Points
    Jaywalker said:

    The horrific routing wasn't at home at home (the American Southwest), but rather occurred during a visit to Baltimore two weeks ago, where we received some interesting routing through neighborhoods where HBO's "The Wire" was filmed.

    That is exactly the behavior I have observed from "trafficTrends" on my Nuvis. Disable trafficTrends and see what happens. In an apparently misguided attempt to avoid stoplights, trafficTrends would route me through tiny neighborhood streets in Philadelphia. The main roads were almost always faster, especially due to the fact that the neighborhood streets were only a single lane one-way, and everytime someone pulled in or out of a parking space you had to stop. :)
  • I just tried with trafficTrends turned off. It's hard to determine whether it actually cleared any issues, but I know it continued to tell me to turn onto the street I was already on, so trafficTrends off didn't fix everything.

    I spoke to Garmin Customer Service about it just now. He noted the unit had just been updated to 4.50, so he led me through a hard reset. We'll continue to look for aberrations, and if present, we'll send it back to them. He agreed the erroneous routing should not happen; neither of us mentioned that it's been happening for five years, at least...
  • Possibly related issue - sorry if not appropriate.

    I have a garmin nuvi 3760, my previous two satnavs (a tomtom and a garmin, sorry I cannot remember models), didn't exhibit the same behaviour, so I am not sure if it is just my 3760.


    1) I notice that the satnav will direct me off a motorway, to only route me more or less straight back on it. For those in the UK, this happens on the M1 going south around St. Albans, around the A414. I also notice it around the M6 Toll and the M42 junctions. As I know these routes well myself I ignore the device.

    My only thought, is that for some reason, the actual distance using the "off then on" is slightly less than staying on the motorway and the satnav software doesn't have much of a buffer to say "stay on the same road, although the distance is marginally less, the act of exit, and enter will actually slow you down".

    I just looked at a google map of the M1/A414 junction and it does look like on the slight curve where the roads are side by side, the M1 is on the outside, and the A414 on the inside, so it is conceivable that the A414 may be a few yards less than staying on the M1. As you drive this route, it really does seem like exit, drive for a few seconds or a minute, then re-enter.

    2) My device seems to have trouble knowing where one road starts and another ends in cases where the physical road is renamed. Again this seems to happen on the M6 toll, where it is often shown as the M42, but the actual motorway signs indicate that it is in fact the M6 Toll.

    It is not a great problem, again because I know the route, but it can be confusing. If it tells you to take the M42, when actually all you want to do is stay on the M6 Toll. My thought here is that perhaps the mapping files themselves, do not indicate exactly where one road starts, and another ends; although it does seem to work on the M6/M74 split at the border of Scotland and England.

    Having read this thread, I have disabled Trends, and I'll update the point if it behaves differently

    cheers

    alex
  • sussamb 792 Points
    2) sounds like a map error, you can report map errors here to HERE who supply Garmin with their maps:

    http://mapcreator.here.com/mapcreator/54.72612211016687,-12.257260843749748,6,0,0

    1) Does occasionally happen. It could simply be a result of a GPS error with your 3760 not knowing quite where you are given that the roads are very close together. You can confirm this by running the route in simulation mode. What does your nuvi do then? If it stays on the expected route then it's due to a GPS error.
  • sussamb said:

    2) sounds like a map error, you can report map errors here to HERE who supply Garmin with their maps:

    http://mapcreator.here.com/mapcreator/54.72612211016687,-12.257260843749748,6,0,0

    1) Does occasionally happen. It could simply be a result of a GPS error with your 3760 not knowing quite where you are given that the roads are very close together. You can confirm this by running the route in simulation mode. What does your nuvi do then? If it stays on the expected route then it's due to a GPS error.

    Thanks for that. I'll check it out
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