Fuel Crisis.

The fuel crisis of the mid-1970s was also an impetus to clean-air technologies and helped initiate long-lasting changes in the auto industry. Rising gasoline prices led to an increased demand for small cars, and U.S. manufacturers turned out their own models to compete with foreign ones. The future lay in “downsizing” even standard models to reduce weight and increase economy. High-strength plastics and aluminum replaced steel in many components, and smaller, more efficient engines were designed. Chief among these were dual displacement engines, stratified charge engines, and engines whose power is boosted by four valves per cylinder or by turbochargers and superchargers. By the early 1990s nearly all engines boasted electronic controls, such as fuel-injection systems, to manage all vital functions and to provide the most efficient fuel economy and emission control.

As the crisis abated, a national speed limit, set at 55 mph in 1974 in an attempt to conserve fuel, was raised to 65 mph on rural interstate highways in 1987 and entirely repealed in 1995, returning to the states the power to set their own speed limits.