Usability 
Transport For London's Traffic Map was at trafficalerts.tfl.gov.uk/pda. It was one of the most full featured of all traffic sites, although as implied by the "pda" in the URL, this site was designed for high end devices with large touchscreens. The maps are 240px wide and an image map on the main page enables touchscreen navigation. You can also search for a street or road by name. As you can see by the image, the maps are very detailed and high quality. They are zoomable and scrollable and there are options to show an aerial photo overlay and/or congestion indicators at locations of roadwork or accidents. You can also toggle the display of camera icons on the maps. Clicking a camera shows the camera's traffic view.
6-Mar-2013: The Transport for London mobile site has been redesigned and traffic maps seem to have gotten lost in the redesign although they are still available on the desktop site at: www.tfl.gov.uk/roadusers/ Mobile users can follow @tfltrafficnews on Twitter for traffic alerts and updates