Last week, Google quietly announced on Google+ a new feature within the driving directions of the Google Maps app. Now, it will give you the option to reroute you based on less traffic.
So if traffic is building up on the route you are taking, Google Maps will keep checking and will notify you if there is a faster route as you are driving. This is like most new GPS devices that have built in traffic, although, I personally don't trust mine, as I feel it is always 30-60 minutes delayed. I do trust Google Maps traffic data to be more real time and thus, I'd probably trust it to reroute me.
Here is a picture:
Do you even have a GPS these days or you rely on Google Maps or Waze or an app?
Forum discussion at Google+.