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Discussion Starter · #1 ·
On a recent trip I was using a Garmin alongside the vehicle's Nav setup. I had it loaded with some waypoints I wanted to check, but I questioned the arrival time of a 300 mile trip from the Prius Nav screen. The Garmin unit reported a 5 hour arrival time whereas the Prius was reporting 6 hrs. 22 min. :?:

Seems like a big discrepancy for a Nav set.

Oh, the Garmin was right.

The Prius was way off in it's estimation of time to destination. It got better as I got closer, but the error is still too large. I wonder if the unit really uses the speed in calculating or some sort of approximation of the speed vs. distance.
 

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I believe that the factory nav system uses a very simple algorithm and static values of 55 MPH for freeway and something like 25 MPH for surface streets. I believe I have read that somewhere and my mental calculations that I have done when I have been driving seem to bear that out. This seems consistent with the nav systems I have had on other cars as well. I think there are only a few manufacturers for the factory installed systems so that isn't surprising.

On the positive side, it does give you a pretty good worst case scenario if you stop a few times or hit unexpected traffic on a long trip.
 

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You can adjust the speeds used for the time calculations.

Assuming that the photo on page 80 of the US 2004 Prius Navigation Owner's Manual is correct, defaults are probably:
Residential: 25MPH
Main Street: 35MPH
Freeway: 55MPH
you can adjust these speeds up/down as you feel best suits your area's drive times and average speeds.
Menu>Setup>Estimated Travel Time>Set Speed
 

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Discussion Starter · #4 ·
mrv said:
You can adjust the speeds used for the time calculations.

Assuming that the photo on page 80 of the US 2004 Prius Navigation Owner's Manual is correct, defaults are probably:
Residential: 25MPH
Main Street: 35MPH
Freeway: 55MPH
you can adjust these speeds up/down as you feel best suits your area's drive times and average speeds.
Menu>Setup>Estimated Travel Time>Set Speed
Thanks. I had forgotten about that.

I will go out and re-program the default speeds. The battery (12 volt) had died a few weeks earlier and the Nav had reset to locations back east from west coast or Zone 2.

Seems odd though that the Prius Nav setup doesn't do the calculations based on speed from satellite acquisition as does Garmin.
 

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"Seems odd though that the Prius Nav setup doesn't do the calculations based on speed from satellite acquisition as does Garmin."

It is not clear that the arrival time estimate is improved by using on-the-road history. In your data base of one, it would have. But in many other cases involving intermittent urban traffic and variable rest stops, you would be adding "garbage" to the calculation. It's an estimate based on speed assumptions, which you can modify if you wish. It's not a mindreader.
 

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I noticed on my trip to NY that the trip wasn't taking nearly as long as the Nav system estimated.

So, if I travel an average of 65 mph on X-ways but stopped every two or three hours and I wanted a more realistic ETA, changing the setting to 60 mph would probably give me a more realistic result. Of course heavy construction in the summertime has to be taken into account, too.

Thanks. That's good to know. :)
 

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The Garmin unit may have a learning feature (some do.) It will base estimates on your history of driving on each type of road. I suspect it has more road types as well. I am frequently surprised at how well my Garmin unit does at ETA.
 

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Discussion Starter · #8 ·
Stairman said:
The Garmin unit may have a learning feature (some do.) It will base estimates on your history of driving on each type of road. I suspect it has more road types as well. I am frequently surprised at how well my Garmin unit does at ETA.
None of my three Garmins have a history mode (excluding tacks) or learning mode. I have the eMap, 60cs, and Quest. They learn from the Garmin City Select map set somehow, even in strange environments. I've been surprised as well on how well the Garmin units do with respect to ETA or Time-to-Next-Waypoint time (depending on how I set the screen up). You stop and the time slows down; speed up and the time becomes shorter. The displayed MPH on their screen is pretty darn accurate from my exprience (actually, I think my Prius speedometer may be indicating 1 mph over what the Garmins are showing on their screens at higher speeds).

The Garmin ETA's are pretty close to the minute and not several hours off as my recent trip was in the Prius verses Garmin comparison. I will also note that I should have used the Garmin route suggesions as the Prius really took some "slow" roads in comparison to what the Garmin was suggesting. It was interesting to note the differences betwen the two.

I don't understand why the Prius is stuck in the dark ages with antiquated Residential, Main Street, and Highway modes when other hand-held and stand-alone units do far better at moving calculations and no need to input estimated speeds as in the Prius. The speed restrictions that Toyota put in place don't seem to help either: i.e cannot go higher than 25 mph Res. or 75 mph on Highway - like I-5 mid CA valley traffic ever moves slower than 75 mph nor people drive 25 mph in my neighborhood. :shock:

Anyway, I've max out the speed dial settings on the Prius and will wait and see what the next trip does.
 
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