The Soap Box Derby is a youth soapbox car racing program which has been run in the United States since 1934. World Championship finals are held each July at Derby Downs in Akron, Ohio. Cars competing in this and related events are unpowered, relying completely upon gravity to move.
Here are a couple of postcards from the 1950's showing large crowds and the Race at Akron's Greatest National Sport Event.
"All American Soap Box Derby." Air view showing Derby Downs Hill with Grandstands and Finish Line. Famous Goodyear Zeppelin Dock in the Background.
Akron's Greatest National Sport Event. "All American Soap Box Derby." Scene showing Derby Downs with Race being run.
LINK: Here is more info on the Soap Box Derby @ Wikipedia