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When it calculates distance between two points on a road, does it take into account any changes in elevation? Say, for example, the road goes up a hill and then down a hill. Will the distance calculated by Google Maps (while going over the hill) roughly match the distance shown on my odometer?
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Let’s say I’m driving my car and Google Maps says I will reach my destination in 58 minutes. Does it calculate this based on the posted speed limit, or my current (and actual) speed?
- I have read the Google does use elevation in its distance calculations but but the dataset it pulls from is not very accurate (but, apparently it is the only one there is suitable for their purpose).
The digital elevation model used for most of the earth is from the SRTM recorded in February 2020. It’s a general survey and not specifically accurate by any standard. It simply happens to be the only digital elevation data that covers most of the earth. In the US, elevation data points are 30 meters apart and everything in between is interpolated. In other areas, the points may be 90 meters apart. The Jet Propulsion Lab will only guarantee accuracy of the data points as +/- 16 meters 95 % of the time.
There’s no documentation of how the elevation profile works. Over the years, it has had various glaring errors. You can’t use it for the level of accuracy you’re looking for. - SOURCE
- I believe Google uses near realtime data to calculate the time a trip will take. Map a trip at 2a and map the same trip at 2p and you will get very different travel times. Google is watching all the Android phones and can get data on how long someone who made a similar trip (or a few people) take to get from A → B. In fact, I have occasionally had Google Maps chime in while driving that an accident has occurred ahead and then suggest a new route to make the trip faster.
Thanks! But let’s suppose I map the trip beforehand using Google Maps, and it’s on a 55 MPH road with zero traffic. It says the distance is 53.2 miles and the estimated time is 58 minutes. I then drive at 300 MPH. Will Google Maps suddenly change the estimated time to 10.6 minutes?
If you are using the real-time directions then yes. Google will assess where you are and distance left to go and recalculate. BUT…I think it will recalculate based on where you are now and assume local travel conditions for the rest of the trip and not assume you will maintain a 300 MPH speed when everyone else is going 55.
Almost no roads are steep enough for the difference in length to be significant.
And it can’t base time estimates on just your current speed, because even without extreme speeding, you’ll still have very different speeds on different kinds of roads. Just because you’re doing 70 now on the interstate doesn’t mean you’ll still be doing 70 after you get off at your exit. But I think it uses typical average speeds for each road (possibly modified on the fly, if everyone’s currently slowing down for an accident or something), not the official speed limits.
When biking, it shows elevation changes over the route, but it’s not always accurate. I’ve seen it showing the elevation on my route literally fall off a cliff (and then back up it), because it was just using the elevation of the ground, and didn’t know there was a basically-level bridge over the valley. Though the particular case I saw was fixed years ago.
Not a substantive answer, but I know that where I am earlier iterations of Google Maps had issues because it calculated travel times based on the posted speed limit, which is not at all realistic round here due to winding dual carriageways and traffic.
Minor nitpick, Google is watching all the phones using Google Maps which includes iOS.
That’s because early versions of map routing data only had information about speed limits. Incorporating crowd sourced real time speeds was comparatively late in the development of those systems.
Source: I worked on those routing algorithms for most of my career as a computer programmer.
I’ve often wondered, as a thought exercise -
What would happen if people started some form of a challenge about “beating” the maps timings by the biggest amount.
When I’m on a deadline, it does amuse me to see the ETA dropping/getting closer to my deadline.
There was a time the colour would change depending on whether you were ahead of or behind schedule.
Google maps estimates how much longer it will take you based on how fast other vehicles are traveling on the road ahead of you. If it doesn’t see other vehicles ahead of you, it assumes the road is open and that you’ll go about as fast as traffic goes when there’s is no congestion.
If no accidents develop or clear up while you are traveling, and you drive at about the ambient speed limit, its estimates are shockingly accurate. If you strictly observe the speed limits, it will underestimate how much time you need in most places, as ambient traffic is generally faster than the posted limits, at least around here.
I think it can be significant.
I agree if it were a straight line it’d not be a big deal but it is rarely a straight line. Most roads up a mountain switch back and fort a lot. That adds a great deal of distance to the drive.
I think Google knows the road distance from data collected rather than calculating a straight-line distance between two points as if the earth were flat.
Round here the vast majority of traffic sticks to the speed limit. But yes, if you dont speed, its very accurate.
Google definitely knows how much length the switchbacks add. That’s separate from how much additional length there is due to the rise or fall of the road.
Google definitely is not using the speed limit unless there is no traffic.
Where I live traffic congestion means average speeds are much lower than posted limits and Google still gets the estimated time really close.
There are a few roads where I live and the posted limit is low and everyone drives faster. Google gets those times right too.
I think Google is mostly tracking phones and uses them to estimate times. Google knows where everyone is.
Oh that’s for sure. We were using the real distance along the road, not the straight line distance, back when I first started working on those systems in the early 90s.
I can verify that it generally is insignificant.
I once had a landowner that wanted us to re-survey all of the existing oil and gas lease roads on his property for a term renewal on those leases, so he could use the 3D measurements rather than the standard horizontal-only values the original leases were written with; it cost a hell of a lot more for the survey than he got in extra payments over the life of the leases!
The change overall was very, very minor (and I don’t live in remotely flat country).
I use Google Maps every day when I drive to/from my office. And it’s rarely the same time from one day to the next because traffic conditions vary so widely. It can be 25 minutes if there is zero traffic (which I’ll only see very late at night unless you’re talking about during the pandemic, that was the one good thing about Covid) or it could be over 40 minutes if there is a bad accident.
And the ETA can and will change mid route based on traffic condition changes or my driving. For example, there are a couple of choke points on my trip that I know how to navigate well based on driving the same route for many years, and I can shave off minutes not by speeding but by knowing when to get into which lane to navigate those slowdowns more efficiently. So if it estimates that I’ll arrive at 8:15 AM because a particular highway exit is backed up, by the time I’m past that exit it might say my ETA is now 8:12 because I knew not to get into the exit lane too early.
A 10% grade is considered a very steep road. That’s a slope of 0.1, or a rise of a tenth of a mile over a horizontal distance of 1 mile. Now, you might think that that would mean a 10% error in distance if you just used the two-dimensional map, but the Pythagorean Theorem comes in here. If a right triangle has two legs of 1 mile and 0.1 mile, then the hypotenuse will be 1.005 miles. In other words, using the horizontal map distance instead of the true three-dimensional distance, for a very steep 10% grade, results in an error of half of a percent.
I use Apple maps on the road, and it adjusts for traffic. Like, my last trip the phone gave an eta of, say 1 hour 35 minutes. Then it jumped to 2 hours. then 2 hours 15, and finally 2 hr 30. And I’m still cooking along at the speed limit but I knew up ahead traffic was stopped. And yes it took an hour to get through once I hit it.
It also assumes you are taking the regular lanes. In town, the eta was listed as say 20 minutes but I was in the diamond lane and made it in 10.
I’m surprised that it didn’t reroute you to an alternate route that was better, before it got to that point.