How do GPS units calculate estimated time of arrival?

Question

Based on current speed? Based on speed limits?

Answer 1

The same way you would manually.

     Take the total distance to drive, the speed at which you are  travelling and divide.

If you are driving 200 miles

at 50 miles/hour

divide 200 by 50=4

ETA 4 hours

Answer 2

Based on the distance and speed limits. They have a huge data base built into them.

Answer 3

GPS units can very accurately know your current speed, but it's unclear whether some factor that in when calculating your ETA.

For the most they'll look at your route, they know the distance of each type of road in your route (freeway, highway, city street, dirt road, etc.).  And different "average" speeds for those roads.  That's how map sites like Yahoo Maps calculates your estimated drive time.

For example, they'll estimate higher speeds for a freeway than a city street.  This is like the speed limit, but not exactly.  Because if the speed limit for a city street is 35 mph, you can't always drive at that speed; you have to stop at red lights, right?  So they'll estimate a lower average speed for a city street...

But back to whether they use your current speed to estimate how much slower (due to traffic) or faster you're going than the "average" speed assigned to each street.  I suppose they could do this, but I'm not sure which units do.  I have a Garmin Nuvi, and when I'm stuck in traffic, I notice that the arrival time is not accurate.  Because it's taking the distance to-be-traveled, dividing by the average speeds for those streets, and assuming any second now I can start to drive freely.

Other interesting GPS facts:

http://www.gpsinformation.org/dale/theor...

Answer 4

As far as i am aware it's based on the distance  and the speed limit.

Answer 5

no, they divide your current distance left by your current speed, but if you want you can go to the website of your GPS manufacturer and download a list of traffic light cameras and low speed locations, so it will give you an alert when ever you are going over the speed limit or if there is a red light camera near

Answer 6

current speed

Answer 7

GPS units r not that fast and sensitive about calculating ur speed momentarly from the satellite. It just calculates the speed limits.