<P> The National Maximum Speed Law (NMSL) in the United States was a provision of the Federal 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than 55 miles per hour (90 km / h). It was drafted in response to oil price spikes and supply disruptions during the 1973 oil crisis . </P> <P> While Federal officials hoped gasoline consumption would fall by 2.2%, actual savings were estimated at between 0.5% and 1% . </P>

When did the speed limit change to 55 mph