National Maximum Speed Law for the 55 mph speed limit offered, "Speed limit 55. It's not just a good idea. It's the law.". Intelligentsia riffed that with a more absolute statement based on the speed of light: "186,000 miles per second. It's not just a good idea, it's the law." National Maximum Speed Law 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 . It was drafted in response to oil price spikes and supply disruptions during the 1973 oil crisis. While Federal officials hoped
Speed limits in the United States be presented in a court, such a defense is difficult for out-of-town motorists. Metric speed limits are no longer included in the Federal Highway Administration's Manual on Uniform Traffic Control Devices (MUTCD), which provides guidelines for speed limit signage, and therefore, new installations are not legal in the United States. Prior to 2009, a speed limit could be defined in kilometers per hour (km/h) as well as miles per hour (mph). The 2003 version of the MUTCD stated that "speed limits shown shall be in multiples of 10 km/h or 5 mph." If a speed limit sign indicated km/h, the