I’ve just spotted that the “traffic” button on Google Maps has gone live. I’m not sure exactly when this happened.
This feature overlays up to the minute traffic data provided by the Highways Agency at all levels of zoom of Google Maps, which makes it useful to see exactly where queues are forming. As I type at 5pm on a Friday, the usual congestion is visible on the M25!
The Highways Agency provide the same real-time information on http://www.trafficengland.co.uk as well as sites for Scotland and Wales, but the colour-coded overlay showing average speed on Google Maps makes it easier to see precisely where the problems are.
Another feature is the ability to select historical data for any day of the week and time, to see where queues are likely if you are planning a trip.
The Highways Agency provides its traffic information to Google in a Datex II format, which is a European standard developed specifically for road data information exchange.