tracks which run under NASCAR sanction require certain emissions control devices. Many short tracks run mufflers in compliance with noise ordinances at some tracks; in the early years of the Camping World Truck Series, some races were held at venues which required mufflers, a requirement still used in NASCAR's K&N Pro Series (East and West) and Whelen (North and South) Modified Tours. NASCAR continued to use lead additives in its race gasoline until the 2007 Auto Club 500 at California Speedway on February 25, which led to concerns about the health of those exposed to the fumes of the cars (fans and residents living near the race tracks). Lead is a well-known environmental risk, but the performance needs of race engines (in particular, the high compression ratios and sustained/repeated operation at high rpm and load) once made it difficult to switch to unleaded fuel. In the United States, the commercial use of leaded fuel has been phased out since the early 1970s, when catalytic converters were required to be installed on new cars, making unleaded fuel a requirement (leaded fuel will destroy a catalytic converter). The sale of leaded fuel has been mostly banned in the US since 1996, but exemptions exist for auto racing, aircraft, farm and marine equipment. NASCAR eventually took steps to eliminate the need for leaded fuels. In 1998, NASCAR and then-fuel supplier Tosco (Now ConocoPhillips, the company that produces the Union 76 brand of fuel) conducted an unsuccessful test of unleaded fuel in selected Busch Series races. In July 2006, in the first in a four-week test run of unleaded fuel, the first race since 1998 to run unleaded gasoline, known as Sunoco 260 GT Plus, a commercially available racing fuel, was held during a Busch race at the Gateway International Raceway in Madison, Illinois. The testing in July 2006 was successful with no suspected engine failures or malfunctions from the new fuel. In October 2006, NASCAR stated its intention to transition to unleaded fuel in all three top series (Craftsman, Busch and Cup) in 2007, starting with the Auto Club 500. During the first race in which unleaded fuel was used, there were a number of engine failures during the race, leading many to believe that the unleaded fuel is to be blamed. The drivers who encountered failures include Dale Earnhardt Jr. and Martin Truex Jr. of Dale Earnhardt, Inc. and Kasey Kahne of