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out of curiosity

Dear Lazyweb,

What are mapping sites' estimates of the drive time between two points based on? I'm talking about when you go to Google Maps or Mapquest to get directions, and it gives you an estimate of how long the drive will take. I'm curious as to where those estimates come from. Speed limit data? Actual measurements of vehicle speeds at particular parts along the roadways? (In which case, how do wait times at traffic signals get factored in?) Actual measurements of vehicle travel times between sets of points?

Comments

( 4 comments — Leave a comment )
(Deleted comment)
thewronghands
Dec. 4th, 2008 05:25 am (UTC)
My best guess, totally not based on anything, was speed limit plus knowing how many lights are there, stop signs, etc., such that they could calculate an average time spent waiting for traffic regulators. City driving definitely seems to assume some stopping and waiting, or the time estimates would be much faster. So, I'd guess that it's an average wait time based on "percentage of time green, percentage of time red" and time cycle of light. That way, you could average out how many lights they'd hit and how long they'd spend there.
brian_252
Dec. 15th, 2008 05:27 pm (UTC)
using empirical traffic data
(Anonymous)
Dec. 16th, 2008 05:51 am (UTC)
it's a mix...
Pretty much everything one could know about GIS travel time data is in here:

"Travel Time Data Collection Handbook"

http://www.fhwa.dot.gov/ohim/tvtw/natmec/00020.pdf

"The test vehicle technique has been used for travel time data collection since the late 1920s.
Traditionally, this technique has involved the use of a data collection vehicle within which an
observer records cumulative travel time at predefined checkpoints along a travel route. This
information is then converted to travel time, speed, and delay for each segment along the survey
route....

...License plate matching techniques...A signpost-based system, typically used by transit agencies for
tracking bus locations, relies on transponders attached to roadside signposts. AVI transponders are located
inside a vehicle and are used in electronic toll collection applications. Ground-based radio
navigation systems use triangulation techniques to locate radio transponders on vehicles, and are
used in route guidance and personal communication systems. The monitoring of cellular telephone
activity is also being tested for potential travel time collection applications. GPS receivers...inductance loops,
weigh-in-motion stations, or aerial video to estimate or calculate travel times..."
( 4 comments — Leave a comment )