How smart is the ETA calculation?

[jdcrowley]

If I am on the highway driving towards New York at 65 mph and my destination is the Plaza Hotel in midtown, is the estimated time of arrival calculation (ETA) made by simply dividing the remaining miles by my average speed - assuming, in effect, that I will drive at 65 mph through Manhattan and hit only green lights - or is the Garmin smart enough to realize that I will have to slow down when I get to Manhattan? Does it know the speed limits of the roads on its maps, or where stoplights are? I would doubt that it takes expected traffic into account - your ETA driving through Manhattan won't depend on the time of day, will it?

[OWG]

It adjusts the ETA as you go. For example, yesterday when I left work, I hit a traffic jam on the highway, and it adusted the ETA accordingly as i slowed down. Once back up to highway speed it was adjusted again.

[easyrider]

Is it smart enough to use the distance from the route path (roads) or does it do what the simple Garmin GPS's do and just use a direct line to the destination as the crow flies.

There can be a huge difference in accuracy depending on the route.

[Last Mrk]

If you create a route in a Garmin Monochrome Street Pilot, it doesn't use "as the crow flies" to estimate time of arrival.

[OWG]

Based upon how exact it was with my drive, I'd have to say it uses the routes. I will verify on my way home tonight by comparing the mileage it says with the odometer.

[demiller9]

The ETA is based upon the route that you will be directed to follow, and the average speed predicted for the types of roads involved, ie, freeways are faster than state routes in the city, which are faster than feeder roads, which are faster than residential streets, etc. The (original) Street Pilot has a 'hidden' screen that allows you to see the street categories and what their average speeds are. Mapsource also has a preference screen to set the average speed for various road categories, which is used to do routing on the PC.

I've suspected, but haven't confirmed, that they also take into account the stops you must make when you turn. I think this is why it often takes straight ahead routes in preference to turns.

Don

[demiller9]

(accidently duplicated because the board was running so slowly)
Don

[Hairy Potter]

My experience with ETA has been that the ETAs change as you continue your trip. If, for instance you are stuck in traffic, the ETAs are later. As you again get up to speed and even exceed the speed limit :), the ETAs go back down again. It seems as if, it considers the types of streets as well as your average speed.

[CougerofEQ]

can you change the average raod speeds in the ique like in mapsource????

[thatlonghairguy]

I've found that she's pretty accurate in estimating the ETA according to what demiller9 said about city streets and freeways, etc. If your route is mostly freeway and you drive over the speed limit, you'll see her adjust the ETA, gradually, to reflect an ealier time.

Sometimes I have her recalculate a route based on shortest route, which usually means lots of small streets, speed limits, and stops. Last week I experimented with a 90-minute trip via freeway and a 95-minute trip via backroads. We took the backroads and her ETA was right on the money. (If I had taken the freeway, it would have been a 70-minute trip because I tend to drive a little faster than I should. :-) )