in four stages from 73% in 1921 to 25% in 1925. Taxes were cut for lower incomes starting in 1923, and the lower rates substantially increased the money flowing to the treasury. They also pushed massive deregulation, and federal spending as a share of GDP fell from 6.5% to 3.5%. By late 1922, the economy began to turn around. Unemployment was pared from its 1921 high of 12% to an average of 3.3% for the remainder of the decade. The misery index, a combined measure of unemployment and inflation, had its sharpest decline in U.S. history under Harding. Wages, profits, and productivity all made substantial gains; annual GDP increases averaged at over 5% during the 1920s. Libertarian historians Larry Schweikart and Michael Allen argue that, "Mellon's tax policies set the stage for the most amazing growth yet seen in America's already impressive economy." Embracing new technologies The 1920s were a time of modernization for America—use of electricity became increasingly common. Mass production of motorized vehicles stimulated other industries as well, such as highway construction, rubber, steel, and building, as hotels were erected to accommodate the tourists venturing upon the roads. This economic boost helped bring the nation out of the recession. To improve and expand the nation's highway system, Harding signed the Federal Highway Act of 1921. From 1921 to 1923, the federal government spent $162 million (equivalent to $ billion in ) on America's highway system, infusing the U.S. economy with a large amount of capital. In 1922, Harding proclaimed that America was in the age of the "motor car", which "reflects our standard of living and gauges the speed of our present-day life". Harding urged regulation of radio broadcasting in his April 1921 speech to Congress. Commerce Secretary Hoover took charge of this project, and convened a conference of radio broadcasters in 1922, which led to a voluntary agreement for licensing of radio frequencies through the Commerce Department. Both Harding and Hoover realized something more than an agreement was needed, but Congress was slow to act, not imposing radio regulation until 1927. Harding also wished to promote aviation, and Hoover again took the lead, convening a national conference on commercial aviation. The discussions focused on safety matters, inspection of airplanes, and licensing of pilots. Harding again promoted legislation but nothing was done until 1926, when the Air Commerce Act created the Bureau of Aeronautics within Hoover's Commerce Department.