Google maps should have historical driving times

I thought of this idea while I was looking up some directions with Google maps: Wouldn't it be great to display driving times depending on departure time?

For example, if you leave at 6PM on a Friday in Atlanta traffic, it usually takes x amount of time to drive this route. You could then adjust the departure time and you can see how that affects total drive time.

It's an interesting idea and would be great in cities with heavy traffic. Google, care to implement?