Chelsea tractors

Recalling a conversation from dinner earlier during the week, it would be interesting to see a graph showing the growth of "Chelsea Tractors" in London plotted against the installation of road humps. We would assert (mischievously) that Ken Livingstone (and his ilk) are directly responsible for the increase in the use of big vehicles (with high ground clearance) such as 4x4s, because they are better equipped to cope with the speed bumps.