Another MD site is the Coordinated Highways Action Response Team:
CHART On The Web
I've used this to find out why I'm sitting in traffic before (usually when there's something major and I haven't moved in a while). Occasionally, I'll have the foresight to check it before hitting the road and make a route decision based on it.
Finally, if you're in the Washington, DC region- WTOP at FM 103.5 runs traffic every 10 minutes on the 8s. It helps to know the roads in the area, but you can usually guess if the problem is going to be yours by hearing inner vs. outer loops on the DC beltway.