Google has officially brought back the traffic data to Google Maps driving and transit directions.
Back in July 2011, Google quietly removed traffic data from the web based version of Google Maps. Keeping traffic data only in the mobile version. Google told us then they removed it because the traffic predictions "were not as good as they could be."
Now they are, Google said they use "both live and historic traffic data" to show traffic estimates in driving directions. Here is a picture of what I see now:
The original traffic data looked like this:
When they removed it in July, it looked empty like this:
Google told me how they source this data at Search Engine Land:
The previous traffic feature that was removed from Google Maps last summer provided users with the worst case traffic scenario based on historic traffic data — e.g. “up to 50 minutes in traffic.” That feature was removed because we wanted to improve the freshness of the data. The feature that we’re introducing on Google Maps today works differently and serves a different purpose. The new time-in-traffic feature provides users with the ability to check current traffic conditions and estimates the length of travel time based on constantly refreshed data.
The traffic information comes from a combination of data from third party sources and information that Android users have chosen to share by opting in to the My Location feature on Google Maps. While iPhone users don’t currently contribute to crowdsourced traffic data, we do provide the traffic data to both Android and iPhone map application users so they can benefit from the useful traffic information.
Yes, Google does crowdsource traffic data from Android phones plus they use third-party databases.
Forum discussion at Google Maps Help.