# Online mapping, who is more accurate?

I’m planning a little roadtrip for Labor Day weekend to get out of Saint Paul. I’ve been looking at a couple places and finding that the distances from point A to point B are the same, but the driving times are much, much different.

Saint Paul, MN to Rapid City, SD
Mapquest: 610.94 mi (about 8 hours, 37 minutes)
Yahoo maps: 614.4 mi (about 8 hours 25 mins)

Saint Paul, MN to Mackinaw City, MI
Mapquest: 514.51 mi (about 8 hours, 59 minutes)
Yahoo maps: 513.6 mi (about 10 hours 12 mins)

I can understand the mileage differences since they may choose different centers of the town to start and stop in, but the time disparities seem rather huge. So, which, if any, is more accurate?

Less than 8 and a half hours to drive 614 miles?

Wouldn’t that be kind of, uh, illegal? Even if you drove nonstop you’d have to average over 70.

Seems something weird is afoot.

Not with a speed limit of 70-75, and in that area you can get away with doing 80 no problem. That’s also driving time, it doesn’t include stop time.

I would say that each program has different speed limits for each type of road. I know the mapping program I use only allows you to make one speed limit for each type of road, so a highway is only 65, or 55, or 75, back roads are 45. That’s probably what the longer ones have done, given all highways a limit of 65. While the lower ones have different limits.

Wow, your idea of a little weekend road trip is different than mine. . .

All of those mappers give turn-by-turn distances and times, IIRC. Why don’t you check out a couple of individual segments and compare assumptions? Look at an interestate segment and see what the speed assumptions are (by doing a little arithmetic).

I use a GPS, which makes certain assumptions about your speed based on the speed limits of the roads. It assumes that in a 55 MPH zone you’ll do 62, for example. This is hard-coded, I can’t change it. Also, it does not factor in any time spent sitting at red lights (maybe it figures the two will cancel each other out).

The differance in milage is only 2-4 miles. Right now, travelling west to Rapid City, you will spend more miles than that in detours. This is, after all, summer (road construction season) in the Midwest.

But I certainly agree that this is a good idea, any time, for any reason:

WAG - google maps times every interstate-class seg at 65 mph.

The other two time them according to state speed limits - recognizing, for instance, that in Michigan the speed limit is (70?).

The other differences may be explainable by things like mileage is measured by Pythagorean distance for one site, whereas another uses great-circle distance, whereas another may go with the distance provided by NavTeq data. For measuring a road segment length the differences are negligible.

Regarding times, most (especially the free) navigation tools paint a REAL rosy picture - you can go the speed limit on each arc, and node time is instantaneous.

These differences are going to be the least of your problems.