18. Routing Engine Performance

All the bells and whistles aside, what really matters on any GPS is the quality of the maps, and how well the GPS figures out how to get from point A to B..

The single most common complaint I hear is "the GPS took me on a crazy route that I would never have chosen", and "that definitely was not the best/shortest way."

Arguably the most critical components of any turn-by-turn GPS navigation system are the routing engine and map accuracy. The routing engine is the software on a GPS that decides which route the unit should choose to get from point A to point B. Many people falsely 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. In fact, routing engine quality should be at the top of any GPS buyer's checklist.

The two largest mapping data providers are NAVTEQ and Tele Atlas . NAVTEQ used to have the advantage in mapping quality in North America, however in recent years Tele Atlas has improved its US database and both companies are now roughly equal in quality.

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.

All Magellan and Garmin GPS units use NAVTEQ mapping data, while TomTom uses Tele Atlas.

To test the Garmin nüvi 885T's routing engine, I entered three different trips of varying distance in three different regions of the United States and compared the nüvi's results to a Magellan Maestro 4250 and a TomTom GO 720.

Our first test took us along the Northeast, starting in Southbury, CT and ending in New York City:

Magellan's Maestro 4250, Garmin's nüvi 885T, and TomTom's GO 720 all get us to our destination address, but Garmin's nüvi 885T 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 GO 720 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 4250. TomTom also uses yards instead of feet, which is less commonly used here in the Units States.

Yahoo! Maps (not shown in the table 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. Google Maps also chooses the same route as the Garmin nüvi

So far Garmin's nüvi is in the lead in our routing battle. However, sometimes a GPS that routes perfectly well in one area can perform terribly in another region. Our first test used a trip that was approximately 80 miles in length and took us 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's GO 720 chooses the worst route. While Magellan and Garmin both route us along the 101 highway from San Jose to San Francisco, TomTom's GO 720 instead chooses highway 885T 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 4250 and the Garmin nüvi 885T 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. Occasionally the Magellan unit would verbally announce what side of the street the destination was on, but that was the exception and not the rule.

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's actual angle, a feature not found on either the Maestro or the TomTom GO 720. Garmin wins routing test #2.

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

The results of test #3 are consistent with the previous two tests: TomTom's GO 720 chooses a route that's about 30% longer than Magellan's Maestro or Garmin's nüvi Garmin chooses a route that's slightly longer in distance than Magellan's Maestro, but is actually a shorter drive time, and Magellan's Maestro plots an acceptable route that's only slightly worse than Garmin's. It's interesting to see such varied routing results even on a short trip of less than 3 miles -- just goes to show you how different every GPS unit actually is.

The routing engine on the Maestro 4250 produced consistently solid results, soundly beating TomTom's new GO 720 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 GO 720 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.

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

All three tests show Garmin currently has the strongest routing engine. Magellan's Maestro unit performed admirably, coming in second place. TomTom's GO 720 (with TomTom's newest maps installed) came in 3rd place in all three tests.