We know how Google Maps plots much of the real time traffic. In short, they watch people via their mobile phones and see how fast they are driving in real time. But how do they go about the predictive traffic?

If you click on the “Traffic” button and then select “change” from the real time and select the “traffic at time and day” you will be able to have Google predict traffic conditions on a certain day and time.

So how does this work?

Dave from Google explained a bit on how that works in a Google Maps Help thread. He said:

So what I understand, Google pulls out outlier data caused by accidents or other issues and does some basic statistics to formulate a good prediction based on the live traffic data they collect on a daily basis.

Forum discussion at Google Maps Help.

Update: Dave from Google commented:

Thanks for the clarification.