Here are some maps highlighting a wide variation in the speed limits in force in urban areas in different towns and cities based on OpenStreetMap viewed using the Speed limit mapping view of ITO Map. Oxford and Berlin both make considerable use of 20 mph limits or the km/h equivalent (shown in green on these maps) with most of the other roads at 30 mph (shown in orange on the map). Norwich and my home town of Ipswich make some use of 20 mph but use 30 mph for most residential roads and have some core roads operating at 40 mph limits (shown in red). Stevenage has much higher roads with a core network operating at 40 mph and nearly all of the rest operating at 30 mph. This may be due to Stevenage being a ‘new town’ and having been built with separation of pedestrians and motorists in mind from the start. In Milton Keynes the core network operates at 60/70 mph and pedestrians only use these roads to access bus services. There is limited information in OpenStreetMap about the speed limits for most of the rest of the residential roads in the city.
Speed limits in Oxford, mainly 20 mph (green) with some 30 mph (orange)
Speed limits in Berlin, mainly under 40 km/h (green)
Speed limits in Norwich, some 20 mph, lots of 30 mph and some 40 mph (red)
Speed limits in Ipswich, mainly 30 mph with pockets of 20 mph and some 40 mph
Speed limits in Stevenage, core route at 40 mph with nearly all other roads at 30 mph
Speed limits in Milton Keynes, core routes at 60/70 mph (light blue and bark blue)
It is worth remembering that a child hit at 40 mph has a 90% chance of being killed, at 30 mph it is 50% and at 20 mph it is 10%. I will publish some maps in due course showing both speed limits and road casualties. In the mean time why not help improve the coverage of speed limits in OpenStreetMap?
Pedestrian Liberation 
I wonder if the speed limit maps can be merged with something like this?
http://www.citybeast.com/cyclingsafetypage.html
I seem to remember there was something similar for for pedestrians.
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O.T. Note re my Gravatar: It’s a work in progress. It hasn’t come out right and the text needs clarification. I’m neither an apologist for the NAZIs nor their monstrous deeds. It’s a tribute to the Munchausenesque Lord Monckton and his latest slur on anyone who disagrees with him. That would include anyone who’s actually read the references he cites and realises he’s not being honest about his claims.
Nice website. May well be possible. I will send you an email off-line.
Peter
These are very good maps.
My question would be: Do you have any data on actual travel speeds on the various road types? The numbers on the signs often bear little relationship to the actual travel speeds, and no city has the resources to enforce speed limits on all their small residential streets. James C. Walker, National Motorists Association, http://www.motorists.org, Ann Arbor, Michigan USA (Frequent visitor to Britain to see family in West Yorkshire)
I don’t yet have access to any actual speed check data from the police which would only be available at spot locations anyway. I will however soon be in a position to show both speed limits and traffic casualties on the same map.
I am very well aware of the limitations to this approach and request that we don’t get into a big discussion on these limitations here. The point of the post was purely to show the wide range of local policies with regard to speed limits in various UK towns and be able to compare them to other places.
It would be great if you could add speed data for the Ann Arbor area to OSM so we can start to see a bigger picture emerge. I notice that the predominant speed limit in Sterling Heights to the north of Detroit is under 30mph which is nice to see.
http://www.itoworld.com/product/data/ito_map/main?view=124&lat=42.532127357459565&lon=-83.1611730415621&zoom=12