Does the GPS calculate and update estimated time of arrival based on actual speed or the pre-entered speeds for highway and smaller roads. I had a Garmin and it seemed to be pretty accurate. This one seems to rely on the pre-entered speeds. Also can this GPS read our speed. Garmin constantly displayed my speed. rex
It's based upon pre-programmed speeds. Those can be adjusted to suit your actual driving style/conditions best to help make them more accurate. Also, the time updates the closer you get....thus, the closer you get the more accurate the time estimate becomes. It's difficult for the system to accurate update based upon your actual speed b/c it can't predict if you'll maintain that speed the entire distance or what speed you'll actually drive on the smaller roads and such. All in all I find the Prius Nav time estimates to be pretty good considering all the potential variables (ie. Traffic, road conditions, weather, construction, stops along the way, etc.)
My Delorme PC-based GPS and my Prius both use pre-entered speeds to calculate time of arrival. It's more accurate to use actual car speed for estimates if your trips are short, but the longer they are, the more the calculation should be based on pre-entered speeds. On long trips you stop to buy drinks, go to the bathroom, and even eat. This lowers your 'average' speed. Simply set your pre-entered speed to what speed you normally drive if all your trips are short, or to a slower speed if your trips are long. You are in control of the accuracy...
