510 time-left-to-destination calculation

[ronqureshi]

I have a go 510.
It seems obvious that my GO is calculating
time-left-to-destination as too high.
I dont know what method it uses to do this.
Even simple method of dividing distance-left
by speed does not match manual calculation.
Does anyone else notice this.

 

[fanchee]

Yep. Same here, I've noticed this on a 910 and a ONE. The closer you get to your destination, the more accurate it becomes, but at first it seems WAY off.

 

[hamproof]

I dont know what method it uses to do this.
Even simple method of dividing distance-left
by speed does not match manual calculation.

I believe it assumes 60mph on highways and if it is a mix of local and highway, 30mph.

For example, on my recent 760miles trip, it says it'll take 12.5hr (at the start of the journey) which is about right: 60*12+30 = 750miles. Though it took me 10hrs. in all to make that trip with stops for gas and restrooms But TTG doesn't know I plan to drive 90-100mph on stretches of road either

On mix of local and highway, I find it to be fairly accurate (on weekdays). My 32mile commute takes about 50mins which is what it predicts.

Of course the same commute on the weekend will take me 30mins.

This is on TTG 700.

 

[Thornhump]

There's 150 miles of 4 lane divided highway I travel regularly that calculates as having a speed limit of 35mph and thus shows really wrong travel times. Also, it causes routes calculated in that vicinity to sometimes go wildly afield rather than to use this ostensibly slow road. I had reported the problem to Tele Atlas last spring and in June 2006 got an email that they had updated that highway to 55mph minimum. The newest Tomtom map updates however still have it the old way. So apparently, the new updates are using data that's more than 6 months old.

 

[The Spook]

hamproof is correct.

It doesn't take your speed into account at all, it just looks at the 'road speed' that is in the map data along the route you have left to travel, and calculates a time based on you travelling at that speed. It gets more accurate as you get closer to your destination because the aggregate difference between your actual speed and the 'estimated' route speed is minimised.

If the time-to-destination is too high either you are driving too fast for the road, or the TomTom thinks that you are!

 

[kunderboy]

arrival time is inaccurate

Yes,

The problem is in my opinion with the Teleatlas Map data.

All roads are "classified" and get a speed assigned. This speed is used by the TT to calculate your arrival time, but it is also used to calculate the fastest route. So, if the classification is wrong, there are two consequences. First, you will see that you do not drive the logical route and two, your arrival time is off. I have experienced 25 to 50% detour (wrt what I thought) and arrival times of up to 50% wrong.

I have figured this out by running a route in demo mode. TT shows you what speed you will be driving. This speed is used by TT for the calculations. I will be driving on a freeway (65 mph speedlimit) at about 30 mph according to TT. If I would do that, I think I would have to explain that to a cop very fast. Even funnier is that I drive faster on the off ramp than on the freeway! Yes, I should reach about 50mph according TT. And less funny is that TT thinks I need to drive 50 mph through a 25 mph limit housing development. The speed associated with roads in my area is just... messed up completely.

It's very likely not TT's problem, but TeleAtlas (map provider). I don't really care (I also complain to TT). I get the teleatlas data through TT, so that makes them responsible in my opinion.

So, until TT gets a good set of map data, you will have to deal with this.

Kunderboy

 

[birdy176]

I wish my problem were bad time calculations.

Whenever I save a route, even though way points and the destination correspond to the actual map shown, the turn-by-turn review shows a completely different route. In fact, even after doing a "route-delete" and redoing it, the route details don't reflect the planned route but keep the incorrect one.

That includes even routes deleted with TT Home.

How do I wipe all my itineraries and associated files off the TT 910?

My local 50-miles radius "Favorites" are not affected. Hope someone can help.

 

[lordhamster]

Thats one thing that freaks me out about the Nuvi (or any garmin unit I've ever used) the ETAs are scary accurate right when you turn it on.

I've left Cleveland for Chicago before, and my friend asked what time I'll be there... I told him "11:27pm" he laughed at how odd it is for me to give an exact minute.

He wasn't laughing when I pulled up at his building at exactly 11:27.

This happens so often its scary.

Usually while I'm on my way I "make up time" but then I'll lose time again at rest stops... in the end nearly every time the original ETA is correct.

 

[fanchee]

Yep, I agree, the Nuvi was scary accurate.

 

[lordhamster]

Yep, I agree, the Nuvi was scary accurate.

But I gotta say, I'd give up some accuracy on the ETA for the ability to block a certain part of the route... cheaper international maps and the ability to use the expensive phone service I pay for anyway for something useful (traffic)

Thats why I really like the TomTom... despite mapping issues stateside. I think I'll probably sell the Nuvi

 

[fanchee]

I agree with that, too. That's precisely why I sold the Nuvi and bought the ONE. Couldn't be happier.