I decided to treat myself to a new GPS... my trusty little Garmin i2 worked fine, but entering the destination information via a scroll wheel was tedious. So, after playing around with the various models at Best Buy, I ended up choosing a TomTom One XL-S, which in addition to the option of a QWERTY on-screen keyboard (which none of the other brands appeared to have), gives me a nice big color screen, and it says the street names too. I also like how it presents navigation information (being able to select what information you want displayed, and specifying that it be displayed along the side of the screen, leaving more vertical room for the map).
Anyway, I used it on our Thanksgiving trip to Texas, and when navigating to a restaurant in an unfamiliar town, I noticed something peculiar. Turns out the restaurant we were looking for was just a few blocks off the Interstate on a major road. It had us exit on that road, but instead of sending us straight to the restaurant, it directed us on a circuitous route that undoubtedly added several minutes to the trip. As a result of this routing, we ended up arriving on the same side of the street that the destination was on... going straight there right off the Interstate would have involved a U-turn. To a certain extent, I agree with this logic... I like to avoid U-turns when possible. But I just thought the big circle it sent us on was a little excessive.
Later in the trip, a similar thing happened. This restaurant was right on the highway, so I didn't need help finding it... I was just using the GPS to get an ETA. As we approached, instead of directing us to make a U-turn, it wanted to send us along a series of back streets, even though the restaurant was right there in front of us. In this case, of course, I was able to just ignore the GPS.
So far I'm a little surprised at how aggressively the TomTom tries to avoid U-turns. At a minimum, "avoid U-turns when possible" should be a user-selectable option.
But this is a relatively minor problem. A more significant issue involves the TomTom's choices in routing, and in its ETA calculations... and after experimenting with the unit yesterday, I believe the two issues are both at least partially linked to bad (or inadequate) map data.
I put in a route that I drive regularly... from my suburban home to my office in New Orleans. Getting there involves exiting the Interstate onto a 4 lane major street that the office is on, and driving about a mile. Very direct and simple.
The route that the TomTom created would send me PAST this exit to the next exit, down that adjacent major street, then on a stair-step route through some smaller streets to arrive at the office. Examining the map of the route, I think I know why it made this decision... because of the path the Interstate follows, that second exit is actually a bit closer to the office (on the north/south axis) than the exit of the street the office is actually on...
(the red line indicates the route I normally take)
So, it's thinking is probably "stay on the Interstate as long as possible". But, there's no way that this route, through back streets with stop signs every block or two, is faster (and yes, I've confirmed that the TomTom is indeed set to "fastest" not "shortest" for routing preference). And, FWIW, Google Maps gives the correct route.
This has me a bit concerned... in this case, I don't need the GPS to tell me how to get to the office, so this particular routing issue is inconsequential. But what if this was not a familiar location? Instead of going straight there in the most efficient route, I'd instead be on a nice scenic tour of the French Quarter.
From the reading I've done on the issue, I know TomTom's routing engine is often blamed for this kind of stuff. However, I think it goes beyond that.
I ran through this route in the demo mode (where it "drives" the route for you) and observed the speeds it used. Surprisingly, when it was driving through these small streets, it showed a speed of 31mph. The speed limit on these streets is 20mph. I then forced it to go my route (again, marked by the red line)... the speed limit is 35, and it showed a speed of 33mph.
So, in other words, it's overestimating speed on the small back streets, and underestimating speed on the big street, which has the effect of making it think my route is slower and that its route is faster.
Moving on, I then set up a route over the stretch of highway where the TomTom had calculated an abnormally high ETA during our Texas trip. This is a 4-lane divided highway with speed limit of 70 for most of the way (sometimes slows to 55 through towns, maybe even 45), and very few traffic lights. The TomTom shows a speed of 62mph during the open stretches, and 37mph through towns, which is far lower than reality.
In contrast, when I set it to travel on the Interstate, it shows a speed of 75mph (speed limit is 70mph)... I assume the 75mph takes into account that most people drive a little over the speed limit. However, even through the New Orleans metro area (maybe a 15 - 20 mile stretch), where the speed limit drops to 60mph, the TomTom still shows 75mph.
As another test, I tried the small residential streets around my house... 20mph speed limit, TomTom shows 31mph.
So, it appears that the TeleAtlas folks are simply applying blanket rules to various classes of roads... "Interstates are 75mph, major highways are 62mph, major highways through towns are 37mph, small residential streets are 31mph, etc.", instead of using the actual speed limits, and I think this is causing much of the strange routing and ETA behavior I'm experiencing.
I'm very tempted to return it and go with a Nuvi. But I REALLY like the TomTom's UI and feature set. Plus, the performance of the GPS receiver really seems superb... it locks on almost instantly upon powering up (even inside).
--Michael
Anyway, I used it on our Thanksgiving trip to Texas, and when navigating to a restaurant in an unfamiliar town, I noticed something peculiar. Turns out the restaurant we were looking for was just a few blocks off the Interstate on a major road. It had us exit on that road, but instead of sending us straight to the restaurant, it directed us on a circuitous route that undoubtedly added several minutes to the trip. As a result of this routing, we ended up arriving on the same side of the street that the destination was on... going straight there right off the Interstate would have involved a U-turn. To a certain extent, I agree with this logic... I like to avoid U-turns when possible. But I just thought the big circle it sent us on was a little excessive.
Later in the trip, a similar thing happened. This restaurant was right on the highway, so I didn't need help finding it... I was just using the GPS to get an ETA. As we approached, instead of directing us to make a U-turn, it wanted to send us along a series of back streets, even though the restaurant was right there in front of us. In this case, of course, I was able to just ignore the GPS.
So far I'm a little surprised at how aggressively the TomTom tries to avoid U-turns. At a minimum, "avoid U-turns when possible" should be a user-selectable option.
But this is a relatively minor problem. A more significant issue involves the TomTom's choices in routing, and in its ETA calculations... and after experimenting with the unit yesterday, I believe the two issues are both at least partially linked to bad (or inadequate) map data.
I put in a route that I drive regularly... from my suburban home to my office in New Orleans. Getting there involves exiting the Interstate onto a 4 lane major street that the office is on, and driving about a mile. Very direct and simple.
The route that the TomTom created would send me PAST this exit to the next exit, down that adjacent major street, then on a stair-step route through some smaller streets to arrive at the office. Examining the map of the route, I think I know why it made this decision... because of the path the Interstate follows, that second exit is actually a bit closer to the office (on the north/south axis) than the exit of the street the office is actually on...
(the red line indicates the route I normally take)
So, it's thinking is probably "stay on the Interstate as long as possible". But, there's no way that this route, through back streets with stop signs every block or two, is faster (and yes, I've confirmed that the TomTom is indeed set to "fastest" not "shortest" for routing preference). And, FWIW, Google Maps gives the correct route.
This has me a bit concerned... in this case, I don't need the GPS to tell me how to get to the office, so this particular routing issue is inconsequential. But what if this was not a familiar location? Instead of going straight there in the most efficient route, I'd instead be on a nice scenic tour of the French Quarter.
From the reading I've done on the issue, I know TomTom's routing engine is often blamed for this kind of stuff. However, I think it goes beyond that.
I ran through this route in the demo mode (where it "drives" the route for you) and observed the speeds it used. Surprisingly, when it was driving through these small streets, it showed a speed of 31mph. The speed limit on these streets is 20mph. I then forced it to go my route (again, marked by the red line)... the speed limit is 35, and it showed a speed of 33mph.
So, in other words, it's overestimating speed on the small back streets, and underestimating speed on the big street, which has the effect of making it think my route is slower and that its route is faster.
Moving on, I then set up a route over the stretch of highway where the TomTom had calculated an abnormally high ETA during our Texas trip. This is a 4-lane divided highway with speed limit of 70 for most of the way (sometimes slows to 55 through towns, maybe even 45), and very few traffic lights. The TomTom shows a speed of 62mph during the open stretches, and 37mph through towns, which is far lower than reality.
In contrast, when I set it to travel on the Interstate, it shows a speed of 75mph (speed limit is 70mph)... I assume the 75mph takes into account that most people drive a little over the speed limit. However, even through the New Orleans metro area (maybe a 15 - 20 mile stretch), where the speed limit drops to 60mph, the TomTom still shows 75mph.
As another test, I tried the small residential streets around my house... 20mph speed limit, TomTom shows 31mph.
So, it appears that the TeleAtlas folks are simply applying blanket rules to various classes of roads... "Interstates are 75mph, major highways are 62mph, major highways through towns are 37mph, small residential streets are 31mph, etc.", instead of using the actual speed limits, and I think this is causing much of the strange routing and ETA behavior I'm experiencing.
I'm very tempted to return it and go with a Nuvi. But I REALLY like the TomTom's UI and feature set. Plus, the performance of the GPS receiver really seems superb... it locks on almost instantly upon powering up (even inside).
--Michael
