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TTN3 Overestimating Journey Time

 
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Fuego
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PostPosted: Sat Jun 26, 2004 2:54 pm    Post subject: TTN3 Overestimating Journey Time Reply with quote

How are people finding TTN3 (versus 2) when it comes to over-estimating journey time?

I'm in the UK (set to Miles versus Kms), and a half hour trip, over mixed roads, is likely to be overestimated by around 15 minutes. My road speed settings are at the default values.

My recollection of TTN2 was that it nailed journey times to within 5 minutes.

Is this an issue that TomTom have acknowledged? Anyone know?
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Robin2
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PostPosted: Sat Jun 26, 2004 3:31 pm    Post subject: Reply with quote

It depends entirely on the speeds you set for different types of roads. I have set mine to what I think are realistic, and on a recent 260 mile journey arrived within 5 minutes of the original ETA (after allowing for a stop I made half way)
Robin
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Fuego
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PostPosted: Sat Jun 26, 2004 3:56 pm    Post subject: Reply with quote

Care to suggest your current speed settings (or the ones you changed), please? I've been wary of changing these, as I feel that they might affect the routes chosen. Then again, that may be as much for the better as for the worse.
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Robin2
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PostPosted: Sun Jun 27, 2004 11:54 am    Post subject: Reply with quote

I use 65,59,50,47,40,34,31,25 - they seem to be quite realistic for actual traffic conditions
Robin
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Howarduk
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PostPosted: Sun Jun 27, 2004 8:05 pm    Post subject: Journey times Reply with quote

I have left my settings to default and although it might overestimate the journey time as I progress it works it out. Last night I was coming back from Dover, when I set it the journey time to home was one and three quarter hours.
As I progressed averaging 70 miles per hour the journey time gradually decreased and by the time I got home had estimated the time exactly.

Howard
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Fuego
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PostPosted: Sun Jun 27, 2004 10:54 pm    Post subject: Reply with quote

That simply means that as the journey distance becomes shorter, the absolute value that is the percentage margin of error, shortens, until it becomes zero.

Yes, I too can tell you that to get to the spot that you are standing on will take no time at all ;) but if you're happy with your settings, then that's cool too.

Anyway, I'm going to write down the current speed settings and try Robin2's settings (thanks for responding R2). No harm in trying them, so long as I don't have a critical appointment to go to when I test them.
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oddsock
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PostPosted: Sun Jun 27, 2004 11:43 pm    Post subject: Reply with quote

Robin2 wrote:
I use 65,59,50,47,40,34,31,25 - they seem to be quite realistic for actual traffic conditions
Robin


These are the actual figures I get when I reset to default speed settings in ttn 3.03

dave
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Howarduk
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PostPosted: Sun Jun 27, 2004 11:50 pm    Post subject: Reply with quote

Has anyone driven the ACTUAL speeds as recommended by TT3 for the whole journey without deviating?
Because it would appear to my limited knowledge of mathematics that unless you do that it will always either over or underestimate because it doesn't take into account road conditions or other traffic or time of day which you as the driver have occasion to do and drive accordingly.

Howard
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anarchy-inc
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PostPosted: Mon Jun 28, 2004 9:48 am    Post subject: Reply with quote

Howarduk wrote:
Has anyone driven the ACTUAL speeds as recommended by TT3 for the whole journey without deviating?
Because it would appear to my limited knowledge of mathematics that unless you do that it will always either over or underestimate because it doesn't take into account road conditions or other traffic or time of day which you as the driver have occasion to do and drive accordingly.
Howard


That would actually result in you taking even longer and the estimate would continue to be adjusted outward. These are average speeds and as such you cannot have 65 as a average without sometimes going above and below. If your car (as mine does) has a trip computer that calculates fuel consumption and average speeds, that might be a way of getting an idea of how YOU drive as opposed to how TT3 thinks everyone does. I will see what mine says tonight on the way home, particularly for the M40.

I too find the ETA to be around 5 mins out for most journeys, but I have yet to test it on a trip over 1-2 hours. This Thursday I'll do a longer trip (5+ hours) and we will see how it works on default settings.
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Robin2
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PostPosted: Mon Jun 28, 2004 11:33 am    Post subject: Reply with quote

Oops Oddsock! I had tweaked the speeds with TTN2, and hadn't realised that they have reverted to the default values when I upgraded to TTN3! But as I said earlier, they are pretty good overall averages for a long journey, but of course it all goes haywire if, as happened to me last week, you get stuck behind a slow lorry for 3/4 hour with no overtaking opportunities
Robin
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Fuego
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PostPosted: Tue Jun 29, 2004 1:31 am    Post subject: Reply with quote

anarchy-inc wrote:
If your car (as mine does) has a trip computer that calculates fuel consumption and average speeds, that might be a way of getting an idea of how YOU drive as opposed to how TT3 thinks everyone does. I will see what mine says tonight on the way home, particularly for the M40.


Ok, that will tell you what you can expect on motorways, although the M25 is a far more variable proposition (with slow and stop being popular favourites) than the M40 and even on the M40 it can depend on which way you're going and at what time of day.

Still, I think the answer is probably to set speeds assuming conditions are good (medium traffic, flowing relatively freely, say), and then take any estimate given (based on such speeds) as a an incident-free ETA, with any slow-downs causing re-calculation.

However, it's much harder to gauge when you drive a route over a mixture of roads, particularly since it's hard to know which road is classified as what by TTN.
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