Before 4.5 I could refresh the traffic indicators in Google Maps by tapping on another app and then tapping back on the Nav app -- which would cause the entire map, including traffic, to refresh. Now the map and traffic data seem to be cached, which makes them display very quickly, but I can't find any way to cause the traffic indicators to refresh. Since I commute about an hour each way every day it's generally true that the traffic patterns change during my commute, but I can't figure out to get the traffic to update. This unfortunately makes the traffic feature pretty much useless to me. Any suggestions?
I'm in your boat commute-wise.
The *only* real answer for true traffic navigation and optimization (on the fly) is WAZE!
Free GPS Navigation with Turn by Turn - Waze
It's an app for iPhone, iPad, and Android smartphones too. (EDIT: it's free) It's crowd sourced traffic updates, showing real speeds on the road, police, accidents, stalls, etc., and you can have it check your route multiple times for updated best paths home or to work. It often times will find a better route on its own while you're driving. But I find if you ask it right before key forks in route options it will do even better, usually giving you 3 updated (to the second) routes.
Good news too in that Google just bought the company this week, so we can only hope that this kind of traffic aware navigation comes to the Google system... and our internal nav on the car.
I actually use more on my iPad for bigger screen display (there's a tailored version for the iPad)... though now in my Model S, I haven't quite figured out how to get my iPad sit/stand in a good display place, without it sliding around, etc.