Routing calculation on GO 2505 TM IQ Routes

[Diversify]

I have been using my GO 2505 TM for some time now. I try to better understand how it's comes to it's route that it is choosing and even more challenging: try to explain it to my lovely wife .
Our device is setup with always fasted route, IQ routes ON and a FM traffic receiver with the setting to ask if we want to avoid the traffic.

Now it is my understanding and correct me if I am wrong please. That IQ routes takes in account the historical data and can suggest a different route depending on which day and what time of the day.
I also understand that if I go off the suggested route it will start recalculating the route from the point I am at that moment.

Now sometimes when I leave my home and and take one different turn then the route suggestion, it starts recalculating, I understand that. But it then suggest a complete different route. I live in a big city and to get back on the original route is very close. I only took a different turn. I didn't move a 10th of a mile of the position the and the last calculation was 2 minutes ago. How can it now come to a complete different route? I hardly moved position and I don't believe in those 2 minutes there was new historical data to suggest a different route.
It is almost if the device thinks you want a alternative route.
It confuses the heck out of my wife because she thinks it could be because of traffic. I don't believe because the device is set to ask you if you want to avoid it.

It doesn't always do this because sometimes if a a road is jammed for some reason and you try to avoid it keeps sending you back to that road, no matter how many recalculations. But I know how to avoid that with the "avoid part of the route" and that works great.
But I can't understand the above situation. My wife just want one thing: Give me the fastest route. But how can it change that much without hardly getting of the original route in such little time?

Thanks in advance.

 

[dhn]

The routing algorith, especially with IQ routing AND the added information of traffic is a weird thing at times.......

Suffice to say this:
If, with all its data, the routing detects an alternate even one minute faster than your current route, then it will suggest it.

But, its not perfect 100% of the time and local knowlege always trumps any gps' routing at times.

 

[Diversify]

DHN. Thanks for your quick reply . I agree on the local knowledge. And also think that it is the IQ routes that makes the device so unpredictable. Is there independent research on how well this actually works or even better what kind of local historical data there is? If your local knowledge is better then the historical, you might as well turn the feature off.

 

[dhn]

Remember, IQ data is compiled from **other** drivers driving the same roads as you. If you are in an area with relatively little traffic, or a newer area, there may not be sufficient IQ data at times to make a decent suggestion.

Also, I assume you're using the 880 map as each new release contains more IQ data than a previous one.

 

[canderson]

If, with all its data, the routing detects an alternate even one minute faster than your current route, then it will suggest it.

I have been noting that even that isn't quite 100% completely really actually true. What's even sillier - you have only the choice to accept the alternate or live with the message until you make some sort of turn. Check out the attached screen shot. Guess I need to remember to report this sometime as a "whatsupwiththis" sort of bug.

 

[dhn]

You know.... it has been reported repeatedly 'over there' about this issue and the alternate route message never disappearing.

But I HAVE seen it disappear with no intervention on my part. I wonder whether it happens if and when the alternate route is no longer a viable choice, time wise.

 

[canderson]

In my recent (today included, as it happens) experience, it disappeared the first time I made a turn onto another road and while still following on the same route that would have been used in either the original or modified route. Still - just clutters up the screen until then.

 

[Diversify]

Remember, IQ data is compiled from **other** drivers driving the same roads as you. If you are in an area with relatively little traffic, or a newer area, there may not be sufficient IQ data at times to make a decent suggestion.

Also, I assume you're using the 880 map as each new release contains more IQ data than a previous one.

I understand that and I think that is the frustrating part of IQ routes. Because you don't know if or when IQ historical data becomes a factor on your route. The only thing you notice it that sometimes it will suggest a different route for something you drove 100 times without any traffic warning given. You can only guess that is because IQ data kicking in.
So now you have to choose to trust or your local knowledge or the new route.
I really like to know how well iq routes work in my area and there is no way to find that out. To give an example: if there are two possible routes to my destination, route A we have historical data, but route B we don't. How is that compared? And from how many people? Maybe is just based on 2 people that can't drive for sh*t. You just don't know.

Another example and this is from my wifes daily commute from DC to Virgina. There is a major road that during peek hours changes from a two way onto a 1 way. Till this day the device keeps sending her to that road on hours that it is not possible. Should there not be a moment by now that IQ routes should come to the conclusion that it is not the fastest route? If it was only from your own data alone? Or should we wait till a 100 other people with IQ routes on the same road for this to take effect.

IQ routes is a great idea, but there is so little info known about it to fully trust it.

 

[canderson]

Actually, you will often know whether IQ is kicking in or not. When you dial up a destination and the route is planned, you will see how much delay (and there often is some) is attributed to IQ and how much to your traffic receiver. If ANY shows up for IQ, you know it's being used. So at least for those runs, you know it's a factor of some sort.

As for what happens when IQ data exists for one possible route but not another... roads with no IQ data are broken up into three categories with one speed associated with each. It's been a while, so don't hold me to the specific speeds, but I recall something on this order: Secondary surface roads were assigned averages of 20mph. Non-limited access highways were assigned 40mph. Limited access highways were assigned 60mph. That was how all calculations were done before IQRoutes was put into production.

Last, you will find that no GPS device available (yet) knows about time sensitive directional HOV lanes. That said, the road your wife drives probably should be identified as HOV or similar, and if your unit is programmed correctly, should always ask if she wants to use that piece of road. That's how it works coming in and out of the north end of Denver.

 

[Diversify]

canderson, that is some great info, thank you very much. I never notice that it will mention something about IQ when planning the route and delay is mentioned. I will try that out.