speed limits

I can't tell you what the calculation and if it is based only on speed limits, I have had the 660 for about 8 months and two other GPS before this one, and the ETA is pretty close to the right ETA. What ever calculations it makes it handles the road type and expected average speed will. I have the traffic reciever on mine and it does a great job estimating time of arrival.

The ETA is calculated based upon the "average speed" (which is a driving speed) of the road types on which the route is traveling. It doesn't really know the speed limits, per se, of each road.

On my recent trip from FL to AZ and back I checked for changes in ETA quite often. I noted that the ETA did not change when driving 65 mph in a 70-80 mph speed zones (TX) but ETA did decrease when I drove 75 or so ! I think it calculates an "average" speed for the roads driven also!

Yes.... I agree with MM as well.

I see a change in my ETA constantly throughout my travels depending upon my speed.

No matter if it is a long trip or a short one.

So I "guess" the GPS initially calculates the ETA based on the distance and some sort of speed estimates, but it certainly fine tunes the ETA as you travel.

These GPS thingy's are a pretty smart !

Tim

I thought the Nüvi 7xx shows the speed limit of the road you are currently travelling on? (Implying that that info. is in the map?)

Hi Hornbyp.

I have a 2730 and a 7500 and neither of them has any displayed info on the speed limits on the roads.

I don't know if that info is hidden in the files somewhere or not, but I don't see it.

On the other hand.... we bought a Navigon 5100 for the in-laws for Christmas, and it not only shows the speed limits on the roads, but can sound an alert if you exceed that speed limit by a programmable amount.

It seems like, perhaps it is becoming a common feature in the latest generation of GPS units.

Tim

My Garmin and TT show an ETA, again based on MM's comment which is accurate. My LG (just like what Hornbyp said) knows the speed limit (via display and notification) of every road I take. I've noticed a difference between ETA times and the LG is always more accurate than my Garmin and TT.

My 760 shows speed limits of roads on Interstates and major highways. If I remember correctly, you can manually program it to warn if you are going so much over the speed limit. Nice feature.

The ETA has usually been right on. I am sure it takes the estimated speed, such as city roads has an average speed limit of xx, neighborhood streets have an average speed limit of xx. Either way, it has usually been right on. Of course, I don't set the time in stone, but it's fun to watch and try to fool.

It would seem that with Garmin units, at least slightly older ones (I have an SP2720), speed calculations are based not on a data base of speed limits in the memory, but on the classes of roads in a route. As far as I know, for interstates and major limited-access highways, a speed of 68mph is assumed; for divided four-lane roads, such as major US highways, it is 58; for better two-lane roads, 48, etc. In consequence, if you drive on a relatively narrow two-lane road in some rural parts, it assumes 45-48, while the speeed limit might be 55. In such circumstances, every few minutes another minute drops off the ETA. Of course, if a major four-lane road goes through a congested area with a lot of traffic lights, the ETA runs steadily upward.

I'm not sure, but some newer units may actually have a lot of actual speed-limit data built-in.

I also have a 760 and it is true for quite a few major highways it appears the speed limits are in the Navteq database. I have not been able to find any setting on the 760 however that will cause an alert to happen if I drive over the speed limit. If you find it I would love to know where it is.

Os far as ETA I know my old 2610 allows me to set my own average driving speed on different classes of highways and that is used in calculating the ETA. Changing those speeds causes an immediate change in the ETA. Seems obvious the older units use this method.

Since some of the highway data now includes speed limits it would be interesting to know for sure if Garmin is using it to calculate ETA on the new models. While it seems logical to do so, that doesn't always mesh with reality.