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Joined: Jun 20, 2005 Posts: 1096 Location: Solihull, UK
Posted: Thu Jan 29, 2009 10:26 am Post subject:
Perhaps it would help if we knew what route TT was suggesting for you. From Oxfordshire to Leeds, I would have expected to be directed M40-M42-A42-M1 (although I've already mentioned earlier that I have had some strange instructions on the M40 recently). What does TT suggest, and what are your alternatives?
I can see the sense in cecilrhode's suggestion - if a portion of the M40 immediately after the junction is set too slow, then TT will look for am alternative, and send you on a different route. Immediately after you have ignored its advice, it has to recalculate its route, and now incorporates this (apparently) very slow section of road. Then, once you have covered the slow section - faster than TT was expecting - it recalculates your arrival time and discovers that it was similar to the original route that it was suggesting.
Are you sure when it first recalculates it is not first taking a new 4th route which could be very similar but just that bit different then after a while it recalculates to one of your other two routes?
Not really, since the 3 routes are so clear cut being motorway or dual carriageway, and there just are no other routes which make any sense. The reason I started this thread in the first place is because what I think is happening is that for the first few minutes TT wants to take me back to the exit I just missed regardless of whether it's faster to do that. I can imagine some programmer somewhere has thought "well it might be more inconvenient to the driver to go a way he wasn't expecting than be delayed 10 minutes", but then after 5 minutes when apparently the driver is still persevering with the new route (although in practice he has no choice because he is on a motorway) to think "oh well I'll replan if he is happy not going back". Now what I've conjectured there doesn't make total sense either, but there's definitely a fault in TT's logic somewhere. I know I'm being pedantic but having been in IT for 43 years these sort of things niggle me _________________ Tony
(TT940)
Joined: Feb 27, 2006 Posts: 14893 Location: Keynsham
Posted: Thu Jan 29, 2009 11:36 am Post subject:
TT GO920 and MS Autoroute Express both say M40 J10 - A43 - M1
Alternatives to consider might be M40 J15 - A46 - M69 - M1
or M40 - M42 - A42 - M1.
The magical mystery is no mystery. The TT is supposed to get you from A to B by whatever route choice you select, in accordance with its innermost workings - algorithm if you like.
If you drive a route which you do not know, I would suggest you pay attention to the TT if you happen to stray off the route - it will try to get you back on route to your destination, by Turn around when possible, turn around at the next side road or lamppost or whatever it sees as a suitable turning point. It may see a shortcut back to the original route. It may see another route altogether. Either way, ignore it at your own risk of ending up in a farmyard.
If you know where you're going and you are better at it than the TT, use your own directions. From the replies here, it doesn't seem as if we have any members who write algorithms to explain how the TT's algorithm works. _________________ Dennis
TT GO920 and MS Autoroute Express both say M40 J10 - A43 - M1
Alternatives to consider might be M40 J15 - A46 - M69 - M1
or M40 - M42 - A42 - M1.
If you know where you're going and you are better at it than the TT, use your own directions. From the replies here, it doesn't seem as if we have any members who write algorithms to explain how the TT's algorithm works.
Dennis you are stating the obvious there. Yes, those 3 routes you have described are exactly the 3 routes I am talking about.
I am not saying I know better than the TT, however all things being equal when there is no traffic to worry about, then it is a toss up between the routes, and one thing TT can't tell me is which service area I fancy getting my coffee at today (that being a personal whim on the day).
One thing I do know is that there is a fault somewhere in its replanning logic because it patently and indisputably is not giving me the fastest route for the first 5 minutes after changing my mind. As I keep saying, going back is not the fastest route which is a fact that TT itself confirms 5 minutes later (before I have passed any other exits and therefore nothing has changed since it last planned).
And the reason why this is not totally academic is because if I know there is a fault then I'm unlikely to trust it when it replans me on a route I don't know and have inadvertently overshot a junction.
I could put this to bed by looking at the route it initially replans but I drive solo and I don't like fiddling with it on the motorway.
Incidentally, my 910 used to have this same bahaviour going back at least 18 months so it's not a recent phenomenon. _________________ Tony
(TT940)
I can see the sense in cecilrhode's suggestion - if a portion of the M40 immediately after the junction is set too slow, then TT will look for am alternative, and send you on a different route. Immediately after you have ignored its advice, it has to recalculate its route, and now incorporates this (apparently) very slow section of road. Then, once you have covered the slow section - faster than TT was expecting - it recalculates your arrival time and discovers that it was similar to the original route that it was suggesting.
But the fault in that logic is that even if that were the case, that bit of road is common to both routes so it would cancel out (I already pointed this out earlier) i.e. the delay would apply equally to going back or carrying on - since TT changes its mind before the next exit is reached. _________________ Tony
(TT940)
Joined: Nov 14, 2003 Posts: 2143 Location: Surrounded by A1, M1 & M25
Posted: Thu Jan 29, 2009 12:11 pm Post subject:
Although this is probably not your issue, the Traffic can have an effect on replanning along a journey.
An example I use is I drive from London to the North East and I can go M1 or A1, the problem is that the device does not report the traffic 200 miles up the route, so a valid route when leaving London may have a blocked road out of range of the current traffic information.
The other issue is one of the alternate routes may have an incident on it which TT will take into consideration when choosing an alternative but unless it selects that alterntative with the incident on it, you will never know about the incident unless you browse the traffic map.
However if I was on a two hour journey and TT added 10 minutes which dissapeared later, I would not really be concerned. _________________ Drivelux
Although this is probably not your issue, the Traffic can have an effect on replanning along a journey.
.
However if I was on a two hour journey and TT added 10 minutes which dissapeared later, I would not really be concerned.
I know this is not a traffic issue, it is too reproducible and it happens when I know there is no traffic anywhere on my route
As for not being concerned, my point is that if I can't implicitly trust TT on replanning it will create a huge driver distraction when I am on an unfamiliar route and have to make a decision about whether to believe it or not. I am just the sort of person who cares about 10 minutes, and yes I know I shouldn't, but that's how I'm made. _________________ Tony
(TT940)
Joined: Mar 01, 2005 Posts: 1513 Location: West Mids
Posted: Thu Jan 29, 2009 1:04 pm Post subject:
TonyD wrote:
I am just the sort of person who cares about 10 minutes, and yes I know I shouldn't, but that's how I'm made.
I think you've hit the nail there. There's "something" fishy going on but TomTom would never release how they plan routes as that's their main point of existance.
You say you feel that you may not be able to trust it replanning a route but (unless I'm reading this wrong) it's when you decide not to follow it's chosen route that the 10 mins extra occurs. Even then, after a while it corrects itself and personally I can't see how this would be a distraction. I think you may be the only one bothered about this. _________________ Gerry
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that you may not be able to trust it replanning a route but (unless I'm reading this wrong) it's when you decide not to follow it's chosen route that the 10 mins extra occurs. Even then, after a while it corrects itself and personally I can't see how this would be a distraction. I think you may be the only one bothered about this.
Yes, you are reading this wrong The problem is if I accidentally overshoot a junction, can I then trust the replanning it does. If I am not on a motorway and have choice (i.e. there are road junctions appearing before it has had time to settle down) about whether to accept the new plan it will give me a problem. I console myself with the fact that this is somehow linked to the fact that there are indeed no other exits and it probably will always sort itself out. I will be happy to drop the subject now, but it will nevertheless niggle me for evermore until TT fix it.
(Actually when I first posted the message I expected someone to pipe up and say "oh yes that's the well known planning bug")
Edit to correct quotes - GPS_fan _________________ Tony
(TT940)
Joined: Nov 14, 2003 Posts: 2143 Location: Surrounded by A1, M1 & M25
Posted: Thu Jan 29, 2009 1:50 pm Post subject:
If you have the time why not plan some routes as you normally would and note the times and directions. Then plan a route starting immediately after the junction where you have the problem and again note the times and directions. Then finally plan a route from where approx 5 minutes from the junction would be and again note the times and directions. You could even demo the routes and see if there is a point where it suddenly changes.
This could either point out any issues on the map or allay your fears over the replanning. _________________ Drivelux
Joined: Jan 04, 2007 Posts: 2789 Location: Hampshire, UK
Posted: Thu Jan 29, 2009 2:16 pm Post subject:
TonyD wrote:
The problem is if I accidentally overshoot a junction, can I then trust the replanning it does.
It usually does a pretty good job of re-routing but, if it's of such great concern, you'll just have to pay attention and not overshoot a junction _________________ Andy
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I encountered a similar problem. A friend and myself, once a month make a 1.5 hour trip north. He has a 730, I have the 720 with the 730 software, so both the same units, same maps etc. A few months back, three quarters of the way in to this trip my tomtom sent me in a different direction, than my mates, (we had the 2 units going to see if there was any differences) And for miles it kept telling me to turn around, then it kept telling me to turn right. Eventually it realised that the road we were on was better and it settled for the same route as my mates again.
However the last time we did this trip, mine took the route that my mates used last time and his took the deviation that mine was making previously!
Both units identical, both were using the same IQ routes, no traffic tmc rds.
Why would they do this!
Joined: Oct 08, 2007 Posts: 2544 Location: Toronto CANADA
Posted: Thu Jan 29, 2009 2:28 pm Post subject:
One thing nobody has brought into the discussion is the strength of the gps signal in the car at the time? What does that have to do with anything? Well, as I understand it, the 'maps' we use really are a bunch of lat/long points overlayed by a drawing that resembles a map (for our comfort).
One would thing, well same map, same routing algorithms, (between the 720 and 730) why not exact same roads?
Musing then .... maybe the satellites 'see' one car in slightly different location than the other because the satellite strengths/locations don't match between the two vehicles and therefore 'think's one car is closer to road B than it really is so routes the car that way.
Or putting it another way, if you are capturing, say, 4 satellites, chances are the routing you go will not be as precise as if you are capturing 10 satellites.
Just my thoughts................ _________________ David
If you have the time why not plan some routes as you normally would and note the times and directions. Then plan a route starting immediately after the junction where you have the problem and again note the times and directions. Then finally plan a route from where approx 5 minutes from the junction would be and again note the times and directions. You could even demo the routes and see if there is a point where it suddenly changes.
This could either point out any issues on the map or allay your fears over the replanning.
That's an idea. How do I actually designate an arbitrary point on a road as the starting point ? _________________ Tony
(TT940)
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