London traffic is a collection of maps visualizing traffic density in and around London. Data from 2001 and 2011 has been used, separated by transportation type.
They were built using d3js with data from open street maps and the Department for Transport traffic counts. Traffic density was visualised using svg masking. An example of the source code can be found at this gist. Shapefiles were generated to geojson and then topojson using GDAL and topojson respectively. They use AADF (average annual daily flow) figures for major roads around greater London. It is a demonstration of how d3 can be used to make detailed maps for comparisons.