SAN FRANCISCO-- -- Ceremonies in San Francisco on Wednesday marked the U.S. Postal Service's pledge to replace lead wheel weights on the tires of some 31,000 vehicles with steel weights.

The weights correct manufacturing defects in tires and rims, allowing the tire to rotate without wobbling.

The USPS says they will remove about 8,000 pounds of lead, doing away with an estimated 500 pounds of lead that fall from wheels on to roadways each year.

Lead weights will be phased out in California by the end of 2009, as part of a court settlement between Oakland-based Center for Environmental Health against Chrysler and the three largest makers of lead wheel weights for the U.S. market: Plombco Inc. of Canada, Perfect Equipment Inc. and Hennessey Industries.

According to USPS figures, an average of 4.5 ounces of lead is clipped to the wheel rims of every automobile in the United States, and it is estimated 800 tons of the weighs are lost in the United States when they fall off during normal driving conditions.