Nav: Time to destination; main roads vs. freeways

On page 51 of the 2006 nav manual, it says that "Travel time and arrival time is calculated based on the set vehicle speed information." This implies that they use the speeds set for residential, main streets, and freeways from the setup screen.

The only reason for using those preset speeds should be for estimates before the car begins moving. After that, the nav system should know your speed and be able to recompute time enroute based on your average speed.

So the questions:

1. Mine seems to be terribly pessimistic. I'm driving at 70mph with 140 miles to go, and it doesn't estimate anything near two hours. It was probably 20-40 minutes "slow." Is it using average speed or is it really using those silly preset speeds? (And you can't adjust them while you're in motion!) *

2. Does anyone know what "main streets" means? Are they using the standard definition of a freeway (formal exits and entrances, and no other intersections)? Thus a "highway" is a main street?


(*) I set 45mph for "main roads" and 70mph for freeways. But much of US101 in California is not true freeway. This leads me to suspect they used 45mph since it wasn't a freeway, which would explain a long enroute estimate.

 

Yes, I know how to set the speeds. I'm going to have to set 55mph for the "main roads" since we have many highway-speed roads that are not freeways.

I'll also check road colors on the map to try to figure out what roads are what. Another thing that the manual doesn't bother to explain!

I realize the nav can never predict the road ahead. But since the set speeds can't be changed while in motion, it becomes even more dumb than it has to be.

 

<div class='quotetop'>QUOTE(mssmith95 @ Apr 1 2006, 04:44 PM) [snapback]233552[/snapback]</div>

Yup!

Meanwhile, I now figured out the story with the roads for the 2006 nav.

- Freeways are red,

- Main roads are blue,

- You soon get the knack:

- Residential Streets are black.

US101 from San Jose to San Luis Obispo is about 200 miles, but more than 50 of those miles are not official freeway. So the "main road" speed is used in the calculation.

I just set my main-road speed to 55 (the max). Unfortunately, in my rural area we all do 60 on the "main road" highways. I can't set it that high...too bad.

 

<div class='quotetop'>QUOTE(KTPhil @ Apr 4 2006, 11:50 AM) [snapback]234811[/snapback]</div>

My understanding is that the override doesn't work on the 2006 models, so I haven't bothered to try.

As for the time estimate, yes, I'm just doing that mentally. Because one cannot change the preprogrammed speed settings while moving, they're virtually useless. If I hit traffic, the preset speed was too high and there's no changing it (hardly time at most traffic lights to play with it.)

I still think an estimate based on average speed is better than using a totally silly preset speed. Average speed over, say, the past ten minutes would correctly predict for long runs of open road (like a 200mi trip down US101 between the Bay Area and L.A.). It would do fairly well for normal surface street traffic.

Sure, it can't predict ahead. As it is, we're certainly taking its predictions with a grain of salt. If it used an average-speed prediction, then the time estimates would be better. Not perfect, but better.

 

<div class='quotetop'>QUOTE(David H. Hawkins @ Jul 4 2006, 10:05 AM) [snapback]281034[/snapback]</div>

That would be cool; they'd need to add some storage for the data, but it'd be neat.

And it would provide something more for the NSA to illegally access.