I have to say that traffic calming measures are very much a two edged sword. Humps & bumps, they do slow traffic, a bit. & expensive as they are to install they have a much larger cost to the driver. As has already been mentioned they cause more noise & air polution as drivers accelerate-brake-accelerate away. But the substantial unseen cost is however very much down to the driver with the additional cost of maintaining your car. Fuel consumption is appaling with the stop go driving & the hidden cost of replacing suspension bushes, anti-roll bars, tyres, exhausts & steering components are only revealed at annual Service time. When the reaction is all about how expensive cars are to maintin in London! Humps & bumps are nowhere near as effective as a luminously coated Police Officer weilding a spped gun, but unless somebody is knocked over that just doesn't seem to be a priority these days.