22.Routing Engine Performance

One of the most critical components of any turn-by-turn GPS navigation system is the routing engine. The routing engine is the software on a GPS that decides which route the unit should select to get from point A to point B. Many people falsly assume that simply having the same maps on two GPS devices will result in the same routing choices. Not so, as there is a great deal of math and decision-making involved when calculating the "best" route.

Not surprisingly, this also one of the most difficult and complex aspects for GPS manufacturers to get right, and is the aspect of GPS navigation that is least well understood by consumers. Let's take a closer look at the Maestro 3140's routing engine:

Maestro 3140 ships with NAVTEQ mapping data from 2007, so that is already a major plus. Mapping data is typically several years old on any given GPS, so having current mapping data is a major benefit to the Maestro 3140.

The two largest mapping data providers are NAVTEQ and Tele Atlas . NAVTEQ is more accurate and complete in North America, so it's preferable to buy a GPS that uses NAVTEQ rather than Tele Atlas (as of this writing). (for more detailed information on both NAVTEQ and Tele Atlas, check out "NAVTEQ vs. Tele Atlas, Which one is Better?")

However, there is a lot more to a routing engine than just the mapping data provider. How a given GPS will determine the "best" route is the result of not only the mapping data, but also how many additional data points, or attributes, are factored into the equation. For example, are certain roads closed after hours or on the weekend? What is the average rate of speed for a given road? Statistically speaking, more accidents happen when making left turns as opposed to right turns -- is the GPS unit factoring that into the route? Each company takes all this data and compiles it in different ways, making unique decisions about what data is more important than others. The number of attributes used varies depending on how much money the manufacturer is willing to spend on their mapping data. For example, a full NAVTEQ map database that includes all available attributes can cost the manufacturer twice as much as a basic set of attributes.

To test the routing engine on the Maestro 3150, I input 3 different start and end destination addresses of varying distance in different geographic regions and compared the results to the TomTom ONE XL, Garmin's nuvi 660 (note that although the nuvi 660 is more expensive than the Maestro 3140, all Garmin nuvi units (and StreetPilot c5xx units) share the same routing engine and mapping data, so this is a fair test of Garmin's routing logic), and Yahoo Maps. Take a look at the table below to see how Maestro's routing engine stacked up against the competition.

Magellan, Garmin, and TomTom all get us to our destination address, but the Garmin nuvi chooses a slightly faster route, provides more detailed navigation instructions, and is also the only GPS to announce what side of the street our destination address is on.

TomTom's ONE XL faired the worst in this test, routing us in such a way that the destination address is actually on the left side of the street. We would then either have to make an illegal U-turn or go around the block to arrive at 135 Central Park West on our right. TomTom also has less detailed navigation prompts than the Magellan Maestro 3140, despite having a larger screen. TomTom also uses yards instead of feet, which is impractical here in the Units States.

Yahoo! Maps (not shown above) chooses a route identical to Garmin's route, but estimates the trip will take 3 minutes longer (1 hour 22 minutes) than Garmin estimates.

So far Garmin's engine appears to be the best. However, sometimes a GPS that routes perfectly well in one area can perform terribly in another region. Our first test was approximately 80 miles in length and took us along the Northeast from Connecticut to New York City. For our second test, I started out at Fry's Electronics in San Jose, California and entered a destination address at 300 Grove Street in San Francisco (about 46 miles in distance).

Again Garmin chooses the best route, Magellan chooses the second best route, and TomTom chooses the worst route. While Magellan and Garmin both route us along the 101 highway from San Jose to San Francisco, TomTom instead chooses highway 880 North to 80 West -- an odd choice that adds around 4 miles ( 6 minutes) to the journey. Even worse, TomTom again has us arriving on the wrong side of the street, with our destination address on the left.

Both the Magellan Maestro 3140 and Garmin nuvi arrive with our destination address on the right side of the street, but only the Garmin actually tells us what side of the street our destination will be on. Garmin's maneuvering instructions are also by far the most detailed. It's not shown in the table above, but the angle of Garmin's turn icons actually vary to indicate the upcoming turn angle, a feature not found on either the Maestro or the TomTom ONE XL. Garmin wins routing test #2.

For the third test, I chose a short, 3-mile trip from Boston to Cambridge, Massachusetts:

Again the results are consistent with the previous two tests: TomTom's ONE XL chooses a route that's about 30% longer than Magellan's Maestro or Garmin's nuvi. Garmin chose a route that's slightly longer in distance than Magellan's Maestro, but is actually a shorter drive time. It's interesting to see that routing results for all three units were very different even on such a short trip of less than 3 miles.

The routing engine on the Maestro 3140 produced solid results, soundly beating TomTom's new ONE XL unit, and closely matching Garmin's routing engine. Garmin edged out Magellan in all three tests, choosing slightly more efficient routes with more detailed turn instructions and shorter drive times.

TomTom's ONE XL unit performed poorly in all three routing engine tests, producing the longest routes in all three tests, and putting us on the wrong side of the street at our destination address.

Only Garmin's GPS unit announced what side of the street our destination address was on.

Throughout my testing I noticed that if I strayed off course, although the Maestro would almost instantaneously "re-calculate" the route, it would keep trying to route me back to the original path instead of accepting the change and re-routing on the new road. In some cases this added 10 miles to the trip and had be doubling-back in circles instead of just re-calculating the route going forward on the new road. In a side-by-side comparison along the same route, Magellan's routing engine had me doubling back (adding 15 minutes to the trip) while Garmin's nuvi GPS simply re-routed me along the road I was currently driving on (although the Garmin did make me wait a nail-biting 30 seconds before it finally figured out I had missed the turn).

In summary, Magellan's routing engine isn't quite as good as Garmin's, although it does come in close 2nd place, and TomTom's routing engine is a distant 3rd place.