From AutoBlogGreen (Jan. 28, 2008):
"We've all encountered speed bumps and odds are most of us hate them, especially the really enormous unpainted ones that tear holes in your oil pan in poorly lit parking lots. Well now we have another reason to despise speed bumps. They increase fuel consumption and emissions. A lot! In a study conducted the Millbrook Proving Ground in England, researchers found that their test car achieved 48 mpg (U.S.) when running at a steady 30mph. When the same car was forced to negotiate speed bumps with the constant braking and acceleration, the mileage dropped to under 26mpg with a corresponding increase in CO2 emissions. The results corroborate a previous study by the Transport Research Laboratory which found an 82 percent increase in CO emissions and 37 percent jump in NOx emissions on roads with speed bumps."