An estimated 93.5 percent of motorists in the EU are driving on under-inflated tyres and causing an additional 18 million tons of carbon dioxide to be released into the environment. These 18 million tons are the equivalent of 56 million tyres being wasted. To collect this data, Bridgestone conducted free check-ups at various shopping centers and public car parks throughout Europe. Based on 2006 data, Bridgestone also estimates 40 percent of vehicles absorb an additional 2.8 percent in fuel, due to their under-inflated tyres, wasting 8.1 billion liters of fuel every year. Bridgestone, in conjunction with the FIA Foundation (Fédération Internationale de l’Automobile) and national motoring clubs, is part of the “Think Before You Drive” campaign, established in 2005.

A little drawing will help you understand quickly what is wrong with under inflated tires

I now it is a dirty job but that can save you a couple of bucks t the pump and it improve overall safety. So you can't overlook tire pressure anymore now.