Usability 
BeatTheTraffic is one of the better traffic US sites I've seen yet on the mobile web at least in terms of number of covered cities and depth of information. It covers about 60 metropolotan areas with traffic maps. a list of estimated travel times and delays for popular trips in each region and a list of current incidents. BeatTheTraffic offers a subscription service ($20/year, one week free trial) that adds SMS or email traffic alerts and the ability to add custom routes and a number of other features. The main downside of this site is that the maps are much larger than they need to be (500px wide and around 85 KB each) which means that they won't load in many mobile browsers.