Nuvi 660 ETA eratic

I use the eta to plan my start and arrival times on most trips. My 660 provides very accurate information on all trips assuming I make no extended stops along the way. Each time I do stop for a few minutes for coffee or gas the unit recalculates the eta to within a few minutes of my actual arrival.

gusb

On my 670... similar model, I have not seen this issue. I just completed two long drives and was watching ETA closely, as a matter of fact. The Nuvi did a good job of adjusting ETA. For example, when I got stopped in traffic on the interstate due to a lane-blocking accident, it added a minute to ETA for each near-stand-still minute. It didn't assume that since my speed was now 3mph on average, that I would need another 100 hours to complete the remaining 300 miles of the trip. It assumed I would be able to resume close to the normal speed limit at any moment. As I later averaged above speed limit, it adjusted ETA slowly downwards.

Is your issue only particular to one location, which might suggest a programmed-in data error, or is it general to many different locations?

I have a 660 and use it for everytrip and so far the est has been right on. I had to wait 20 minutes for road construction on the last trip and it adjusted for the extra time. No problem yet.

Mine seems to do the opposite. It stays pretty constant even when I'm expecting it to change i.e. I hit traffic or speed up etc...

Yes. Definitely. Mine "bounces" quite a bit on certain stretches of road. Its a pretty consistent location where the erratic behavior kicks in.

it seems when there is a changing traffic pattern in certain areas. Normally it is very consistent. I have been using this for a couple of years so i am used to the normal operation.