How Google Tracks Traffic


We all love their traffic alerts, but how exactly does GoogleMaps know how clogged the highway is on your way out of town this weekend?

As the Fourth of July weekend approaches, many of us will be hopping into our cars en masse in search of a long awaited break. Along with an overcooked burger and some mosquito bites, traffic will inevitably factor into each of our weekends. Luckily, we now have smartphones—which, thanks to Google, might actually give drivers some clues as to what to expect on the road ahead. But how exactly do they know? Is it creepy? Are we taking it for granted? Here’s how Google is mining travel data to help perfect their maps application, and what else you might stand to gain from Google mapping traffic.

If the eerily targeted ads that appear on the sides of a Gmail inbox are any indication, Google knows a lot about its customers. The information they catalogue about us helps them do their job–they can better target ads to us, and thus they make more money. But the company is gaining still more data as it  expanded from the browsers on our computers to launch Android phones, the most popular smartphone in the country. Luckily, we stand to gain from one of the manifestations of the information Google now collects, through mapping traffic.

The earliest iterations of Google Maps had no traffic feature–it was simply focused on getting people from Point A to Point B. Eventually, it added the capability to show how intense traffic would slow a driver down, so users could see how long the same route would take “in heavy traffic.” This was based off of “historic data they could gather,” about what traffic was like on that particular route when it existed, says Mike Dobson, president of Telemapics, a company that tries to solve geographical problems.

But in March of last year, Google Maps became much more useful to drivers, because in addition to offering directions, they also started to offer real-time views of how congested the roads were. If a road is colored green, it means it’s moving along, but a yellow road suggests some traffic and a red road means even more congestion. It’s like Google has its own traffic helicopters traversing the roads at all times–except that they don’t. If you’re like us, you assumed that Google Maps was using some iteration of the cameras it uses for Google Earth to map traffic. But that theory kind of flew out the window when you watched Season 4 of Arrested Development and realized it’s actually the Michael Bluths of the world who are doing that job, with car-mounted cameras.

So how does Google know what traffic is like on the roads, nearly all the time? From our smartphones, of course. Whether you like it or not, “telephone companies have always known where your phone is,” Dobson says, because cell phone companies need to use location to appropriately charge customers for calls. That means the companies are constantly monitoring location based on the strength of signal to a cell tower, which allows the phone to switch towers as it travels. Since 2011, the Federal Communications Commission has also required that phones come with GPS, so between the triangulation with cell towers and the GPS requirement, your phone is a marked man.

Google realized that as more and more people continued to switch to smartphones, they had a miniature army of traffic monitors that they could make use of. Thus, the traffic flow that you see on your map is a highly accurate real-time display of the number of Android phones that are currently trying to make that same trek. Basically, they’ve crowd-sourced traffic information (a spokesperson for Google directed us to this explanation of the process). Of course, Google uses its own algorithms to exclude anomalies, like a postman who chooses to stop much more frequently than the average driver. Dobson also notes that there must be a threshold for how much data they have before they’re willing to label a road green, yellow, or red, rather than gray (which means there isn’t enough data), but they’re not releasing that number.

Now, this has stirred up some controversy about whether the process is an invasion of privacy. But both Dobson and Zhan Guo, a transportation policy professor at New York University, nearly laughed when asked about privacy concerns. That ship has already sailed. Google explains that people can opt in or out of sharing their travel data with Google under their phones’ settings. But the company does note that they do try to protect the information–Google itself doesn’t even know what data is coming from which car, and they cut off the first few minutes and last few minutes of each trip in order to further disguise them.

If you choose to opt in, you’re helping to provide what’s already a very helpful service–users get more realistic estimates on how long their drive will be, and they’re more prepared to hit traffic. Guo suggests that what Google offers is even more helpful than what a traditional traffic reporter can give, say over the radio or through road-side alerts. Not only is it more likely that Google’s information is more up-to-date, but you get to see Google’s maps as a visualization. For traffic information, Guo says this type of visualization directly over a map will always be more influential than your average radio update.

And eventually, the information could be much more useful. Dobson proposes a future scenario where Google could suggest to 5 percent of users that they actually reroute a trip, either lessening traffic or reducing the chance that there’s a delay in the first place. “That ability probably makes travel better for all of us,” he says. Guo says that giving advice to reroute traffic will be tricky, as drivers who travel a route every day have the best sense of what takes the longest time. If there are limited other options for getting from point A to point B, suggesting alternatives is fruitless, because everyone will rush to clog another road. An algorithm that reroutes precisely the right amount of traffic is still likely years away, he suggests.

But if Google knows when to subtly advertise therapy when I’m being a little too melodramatic on Gmail, I bet they’ll be able to figure this one out.


  • Mr Bongo

    You could have summed that up in three or four sentences – finally got there in the fourth para. Thanks.

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    • soiboy

      he went to journalism school, so….

    • macarrech

      I came to the comments to write the exact same thing.

      • blare pierce

        same…. really didn’t need a whole novel first

  • DogLoverinKailua

    Really appreciate the in-depth explanation and the humor. I just discovered the traffic data tonight and it was spot on for the trip into my little town (which ironically has been “discovered” itself and is quite congested at rush hour.) Once home I was curious about how/where “” got the data and found your article. Thanks!

  • Eddie

    Agree. Poorly written article just the facts next time without all the “entertaining” writing

  • Phil Fought

    They also didn’t mention the Waze app data integration. Google incorporates that data with their own to provide super real-time details. Google even annotates when the incident information is coming from Waze.

    • Driver A

      Google bought Waze a while back. Waze is also a user imputed source.

  • Tech Kitsune

    I worked on road construction. You want to know how Google gets that kind of information? It’s called a wire-loop sensor. They’re built into just about every major freeway and at pretty much any automated traffic signal – INCLUDING the metered ramps leading onto highways/interstates – all across the country. They’ve been present for about 50-ish years and they’re built into every new street intersection and highway now.

    And it’s publicly available information.

    • rarnedsoum

      That is just for traffic light signaling. No data is transmitted to a central location.

      • GDT

        Actually, “depends”.
        Some (not all) of them are transmitted. Garmin used this data for live traffic, long before Google activated live traffic from crowdsourced info.

    • Jayson Earleywine

      That does not explain the roads that don’t have loop wires. Check out the local streets or county roads near you and you will see that Google maps can tell (with a high degree of accuracy where slow downs are. It has to be the way it is explained in the article.

  • teraBAP

    Plenty of crap in the article.

    • Still_Mantis

      Really. Author doesn’t even know the difference between google earth and street view.

  • Patrick94GSR .

    Ah, so that’s how it works. I was using Google Maps navigation recently and it alerted me of an unexpected traffic jam up ahead, and showed me a route to get around it. Of course it added a few miles but it said it would be 11 minutes faster. As I came to the exit, sure enough I saw all the traffic stopped ahead. Thanks Google Maps/traffic!

  • Law_dog1

    Still no answers about how they know about the accidents? How do they get info for that? I see accidents showing up as red dots, who is given that info to google? How is that done?

    • Hello…Jerry

      They obtain that info from their Waze integration. So, if someone on Waze reports a crash, it’ll show up on both Waze and GoogleMaps.

    • Justin

      Google Maps source traffic information from Waze. A simple Google search on “waze” you would know that Waze is acquired by Google back in 2013.

  • Max

    It’ll be Melodramatics Anonymous !

  • Sam

    Unexpectedly long, and too many dramatics, but the only usefull information is also available on Wikipedia, infact most of the actual useful facts are strait copy from there.

  • VanVedan

    This was painful to read.

  • MaJo

    We all know that google tries to get as many information as possible and they make money with it, but also apple with IOS love information, so it is not only the big G…

  • Phil

    You thought they used the cameras used to create Streetview images..?! You thought there was a Google Maps car in every location all the time? Or are you one of those people who thinks the satellite imagery on Google Earth is real-time?

    I want to know how Google distinguish between people in cars and people on foot.

    On the point of directing different drivers along different routes, that would mean a big change in driver behaviour. We’d have to really learn to trust the software’s traffic information (which is often not very accurate, in my experience). Currently, when my car’s navigation system suggests redirecting me because of traffic I always ignore it because it’s rare that the time added to my journey due to the congestion will be greater than the time added by taking a longer route.

    • scdog

      “I want to know how Google distinguish between people in cars and people on foot.”

      From what I’ve seen, it can’t when it’s only pedestrians. There’s a 2-block stretch of busy street near me that periodically closes to pedestrians only. During those periods, Google Maps shows that stretch as having very heavy traffic since the only moving phones are all going about 3mph.

      But when a single stretch of road is showing a mix of phones moving at 3mph and phones moving at 30mph, Google’s algorithms probably assumes that the 3mph phones are people walking on sidewalks and weeds them out of the calculations.

  • Ron Villanueva

    Great… spent the whole weekend reading this.

  • Ashwani Kumar Jaiswal

    Lets take a situation here: Let say if there is a congested road (“Red” in terms of google Map) and on that road 80% of drivers do not have their phone with them. so will it show “green” for the person hitting that road in next 5 minutes?
    As per the logic given in this article, Yes it should show green because the google map will have the data of only 20% people having phone on that road and not 100 because 80% doesnot have their phones? am i correct?

    • Justin

      Since year 2000 it’s impossible that 80% of people will forget to bring their phone out let alone smartphone. You should say “what if 80% of the smartphone users turned off GPS location.”

      Nope, remember Google Maps also tracks the velocity of the vehicles? Like you said even there’s only 20% smartphone users who turned on GPS location on that particular road, Google Maps still able to track how fast the cars are moving at that road to determine the traffic condition.

      • Ashwani Kumar Jaiswal

        Make Sense.. Thank you

      • Thanks a lot

    • Prameet Kamat

      Also, well, they would statistical sampling -like exit polls data- you need 5% data to get nearly 95% accurate results.

  • where’s a copy writer or editor when you need one?


    A very irritating article.same thing again and again.

  • Dalhat Ahmed

    Thanks for sharing this, is really helpful. My concern is I am using Google map here in Nigeria but I never see the color changes. The color from my cell screen is always green whether the road is congested or not. Thus, I cannot be able to know whether the road is CONGESTED or NOT. So I am wondering, why the traffic feature is not working in Nigeria?

    • Cesar Orellana

      Because in Nigeria don’t read and speak english… Nigeria should have their own traffic system with all the money they have stolen from Credit Card and bogus check fraud…

      • John Alex

        Like seriously?

        You must be sick in the head. @Dalhat Ahmed. It works in lagos and most major cities. I have used it. You need to turn on your mobile data though

  • Rusty Jennings

    I should of just ask “OK Google”.