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Google Maps. Quite an awesome tool when you think about it, especially the real-time traffic mapping. How exactly do they get this data? I don't know for sure but I would wager that android phones constantly phone home with information. How? Well, phones will constantly gather data about local cell masts and the strength of the signal of each - from which you can triangulate your position. On top of that, most phones now have GPS. So, two highly accurate methods of finding your position. Next, you need a huge and highly accurate map of all roads... well, Google have that. So, position + map of roads = you know when the phone is on a road. It's either been dropped or it's in a vehicle. From that all you need to do is look at how your position changes over time and you have speed. 

What's really amazing is that google can do this for each and every android phone; in a city like London that's got to be about 5.8 million phones (8.5 million people, 80% android market share, 85% of London's population is >14). The sheer amount of data being generated and processed is mind bending.

What's google maps got to do with anything? The traffic was backed up because of an accident when I was planning on leaving the office so I thought I would take a different route home. However, I then got distracted by the winter lights again and spent 10 minutes taking some pictures. And once I'd done that I figured the traffic would have cleared. Which it hadn't, but then that's what filtering is for.

... and now Glenn Frey. Bah.

Oh, and these pictures are great!