When is quickest not quickest according to Garmin

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

There are two threads running at the moment about strange routing even when the fastest route is chosen. I responded to one and made an error in that I hadn't realised that the Garmin 2598 was trying to route me off the Autoroute completely and not just cutting across the junction.

I have gone into Basecamp and recreated the route. It is from Eurotunnel to Auchan. I have done this many times before and it always took the A16 to junction 31 and then the St Omer road (N42) and off at la Capelle.

This time it wanted to take me off at Junction 33 and cut across country via Rupembert. Basecamp gives the time as 29 minutes.

However, if I enter the cash and carry on the other side of the N42 opposite Auchan, then it continues to Junction 31 and takes 28 minutes. The latter is the fastest in real world driving.

This change to routing has only occurred in the last 12 months.

Hmmmmm!

M8TJT

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

Because one is called '3598 or 2599' and the other is '2598 - unreliable fastest routing'. This also includes Basecamp so the issue must be across the board.

sussamb · Posted: Sun Jul 26, 2015 10:28 am Post subject:

Would love to check that but can't find Auchan ... is your spelling correct?
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sussamb · Posted: Sun Jul 26, 2015 10:41 am Post subject:

Well I've found the location I think you are using and can see that just a small change in Basecamp produces a different route as you say, with Basecamp choosing the cross country route as according to it it is a minute shorter.

There will always be examples like this as any routing algorithm can only process it's set of rules, which is why it's always worth a quick look at the map on your satnav so that you're aware of any funnies like this.
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IanS100 · Posted: Sun Jul 26, 2015 3:39 pm Post subject:

This sort of thing is inevitable, here's an example (from the TomTom website) not too far from me:

The start points about 50 feet apart (but there must be a point at which they only are 1cm apart) and finish are the same:

Route 1: 54.5 mi - 1:15 hrs

Route 2: 35.2 mi - 1:17 hrs

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M8TJT · Posted: Sun Jul 26, 2015 4:07 pm Post subject:

19.2 miles extra to save two mins?? What kind of stupidity is that?
(unless you know differently)

Kremmen · Posted: Sun Jul 26, 2015 5:02 pm Post subject:

That's the thing. I'll bet all the issues are similarly related.
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Allan_whoops · Frequent Visitor Joined: Feb 18, 2006 Posts: 369

The Garmin routing algorithm must have changed about 12 months ago as it always took us via Junction 31 before then. We use the satnav as its the end bit I always forget, either going left into the shopping area or right into the trading estate!

sussamb · Posted: Sun Jul 26, 2015 6:17 pm Post subject:

More likely it's a difference in the current map ...
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IanS100 · Posted: Sun Jul 26, 2015 7:55 pm Post subject:

Kremmen · Posted: Mon Jul 27, 2015 5:26 am Post subject:

I think you've hit the nail with the bit about you only need it for the last bit of the journey.

I'm the same. I know the best way to get roughly where I'm going but it's once you get almost there that finding the street is where these units come into their own.

Quite often I ignore major route advice and get the, go back and try again, but it soon recalculates and sees sense.
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DashCam:
Viofo A119 V3
Car Average MPG :

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

The problem comes if, like me, you use it for the traffic information on the route. As it isn't going down the obvious route, it doesn't take into account traffic issues which are on it. So if you ignore the route it is trying to take you down, you may end up caught in traffic etc.

With regard to the map changing, all those roads have been there for decades. The only change may be more roundabouts on the cross country route but that will slow it down not make it faster.

sussamb · Posted: Mon Jul 27, 2015 8:16 am Post subject:

What may also have changed is speed limit info, plus if you have traffictrends active that may have different 'trends' now.

Whatever the cause the fact is that this can occasionally happen, and on TTs also as pointed out above.
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Allan_whoops · Frequent Visitor Joined: Feb 18, 2006 Posts: 369

No, the Autoroute is still 130km/h and the cross country roads are 90kmh. I don't have Traffictrends enabled and never have done. Maybe this is more of a lesson about not updating the Firmware?

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