Cool video and explanation of why traffic jams occur on otherwise un-obstructed roads, courtesy of New Journal of Physics and the The Lede blog at the New York Times. Apparently the key factor is traffic density. As a multi-modal commuter I see (and participate) in these all the time. The funny thing is that this justifies the smug feeling you’re getting as you blow by the car-muters stuck in traffic – you’re not just going faster, you’re doing your part to reduce vehicle density and pointless traffic jams. Try not to lord it over the trapped-in-traffic though, they’re already frustrated enough.