I’ve started trying to add speed limits data to roads in my patch of Southwark. Two things made me start looking at them… First, I go everywhere by bicycle, which means speed limits and London congestion are of very little relevance to my journey times. But I noticed that journey planners like CloudMade’s offer wildly optimistic journey times for cars. Even ignoring congestion, I thought, they can’t be taking account of speed limits, which across London are lower than the national assumptions. For example, most main roads have a 30 mph speed limit and a growing number of roads, residential and main, have a safer 20 mph limit. The second reason is that speed limits have been a big issue for cyclists recently, featuring in campaigns around issues like Blackfriars Bridge and Southwark’s Transport Strategy. So here’s a snapshot of our data around Peckham and East Dulwich after a few…