TomTom's rerouting algorithm

tdenson · Occasional Visitor Joined: Dec 28, 2012 Posts: 14

I have used TomTom PND's and the iPhone version for years, and more recently the Android version as well, but I have always been irritated by the algorithm used to get you back on the best route when you take a wrong turning. Every week I do the same journey from Oxfordshire to Leeds and for personal preference I take a non-optimal route (but only by about 30 seconds, hence the personal preference for other reasons). What I find is that TomTom tenaciously tries to get me back on to the original route, even if that will take me up to half an hour longer. Why does it do this instead of just doing a fresh reroute - I have just got into the habit of redoing it manually as soon as I pass the relevant junction. It doesn't matter on a route I know, but it means I can never trust it to reroute me when I take a real wrong turning, and I then have the added distraction as well as being lost of manually having to load a route while driving. It just seems crazy.

Andy_P · Posted: Tue Sep 17, 2013 1:03 am Post subject:

Have to say.. I don't think I've seen that.
I've never used the Android app. but I've used many different TomTom models, and I used to take an alternative route to work, much like you do - my preferred route is just a little bit longer.
Once I've deviated from Tom Tom's calculated route, it will repeatedly ask me to "turn around when possible" for a couple of minutes, but ONLY until it realisesthat renaining onthe new routes is now quicker than backtracking.

Can you give an example of where it is doing something different? Give us enough detail forums to be able to recreate the routes.
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jeff-d · Posted: Tue Sep 17, 2013 12:22 pm Post subject:

Yes, I've had this happen several times, Tomtom is desperate to reroute back onto the original route rather than the destination.
Several years ago I was travelling along the A47 East towards Peterborough. The Tomtom route kept me on the A47 past the A1, then down the A1260 Nene Parkway, then left onto the A1139 Fletton parkway.
I took the A1 southbound and joined the A1139 directly from the A1.
However Tomtom was so desperate to get me back to the original route that it wanted me to leave the A1139 at the roundabout where the A1260 joins, go across said roundabout and then immediately rejoin the A1139 using the slip road that I should've used originally.

Anita · Posted: Tue Sep 17, 2013 1:13 pm Post subject:

Andy_P · Posted: Tue Sep 17, 2013 5:25 pm Post subject:

I can understand there being some routing decisions that seem very strange....

But the TT's poor little brain has no opinion or free will, it can only make the simplest of decisions, i.e. is the original route still the fastest one or do I need to recalculate?

So we need to try to work out (in every case):
1. Is the route it decides actually faster?
2. Is it making a wrong choice because the map data has an error for the "time to travel" for a certain section of road, so it THINKS the original route is still faster?
3. Is it making allowances for Traffic delays the driver doesn't know about (assuming it's a Traffic-capable model)?
4. Is there a software bug that is stopping the TT making ANY change to the route, or delaying it unduly?

At the moment I can''t think of any more possible reasons, but I'll keep pondering.
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DennisN · Posted: Tue Sep 17, 2013 10:11 pm Post subject:

I have some sympathy with this topic as I am also occasionally disappointed at TT's stubborn wish to stay with a route.

A simple example is returning clockwise along M25, routed to J15 then along M4. But my preference is to drop off M25 at J12, then M3 and up to Bracknell. Last time I did that, my TT actually wanted me to return along M3 to pursue original route. It did eventually agree to go along M3, but only after a comparatively long time.

Another is Southampton back to Keynsham. Fastest route is definitely M3, A34 to Newbury and M4 westward. BUT if I use A36 via Salisbury I save 30 miles, £4.50 of fuel and I don't usually need to get home so urgently as to justify gobbling fuel like that. But it always takes some persuading - even as I travel up the start of A36 it still wants me to head off for M4 for several miles.

Now in my case, I'm always running at least two TTs side by side and they regularly give different instructions, with one going along with me quite quickly whilst another gives me grief far too long. I am no longer running the same maps and Navcores on my different models so I cannot give any progressive reports on this. But I do agree with OP, it happens too often to be satisfactory in my opinion.
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tdenson · Occasional Visitor Joined: Dec 28, 2012 Posts: 14

Sorry about the late posting, I've only just realised I didn't have email notifications and I thought my post had been ignored !

The route I am talking about that it does it repeatedly on is Thame-Leeds.
I have 3 choices

1. M40-A43-M1
2. M40-A46-M69-M1
3. M40-M42-A42-M1

Route 1 is usually TomTom's preferred one but mine is route 2. I do this journey every week and have done for 6 years. Every single time without fail I pass the A43 and for up to half an hour TomTom tries to get me back onto the A43 resulting in anything up to a 40 minute extra journey time. I hit the Navigate to Home and within a few seconds I have the optimal route again. Why can't TomTom do this automatically for me. It's nothing to do with traffic I don't know about (as it happens I have just moved to an iPhone 5S from a 5 and am having problems restoring purchases (see separate post) so I don't even have traffic enabled at the mo, but TomTom still does it.

tdenson · Occasional Visitor Joined: Dec 28, 2012 Posts: 14

[deleted]

Bunty1948 · Posted: Fri Oct 11, 2013 12:00 pm Post subject:

tdenson · Occasional Visitor Joined: Dec 28, 2012 Posts: 14

AliOnHols · Pocket GPS Verifier Joined: Oct 15, 2008 Posts: 1936

There must be something in the settings.
None of my four TT's or my TTapp insist on the old route for more than a few seconds. After about 100m they recalculate a new route.
Isn't there a tick box somewhere to avoid U-Turns? or am I imagining that?
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tdenson · Occasional Visitor Joined: Dec 28, 2012 Posts: 14

Anita · Posted: Thu Oct 17, 2013 10:28 am Post subject:

When set to calculate the fastest route and I divert from it my GO720 tries to get me back onto the original route all the time it's faster to do so. As soon as I reach a point where there is a faster alternative that's the one it directs me onto.

It seems to do this regardless of the length of the route.
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tdenson · Occasional Visitor Joined: Dec 28, 2012 Posts: 14

washman · Regular Visitor Joined: Mar 30, 2006 Posts: 75

Hi

I would have thought that if you have traveled that route for six years, you should not need any device to help you find your way.

Washman
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