Google Maps Directions Adds Real-Time Traffic Estimates
First time accepted submitter constpointertoconst writes "If you use Google Maps to calculate directions, you may now notice (if your route is covered by their traffic data) an 'in current traffic' travel estimate for current route. Some may recall that Google Maps had a similar estimate in the past, but it was removed last year due to poor accuracy."
Another great way to avoid getting speeding tickets is to not break the speed limit.
As the link of TFA says; the congestion data is derived from the opt-in data they crowdsource from 'My Location'.
The only way your 'traffic data' could be shared 'unknowingly' is through ignorance.