The Fortieth Anniversary of the NMSL: Reverberations from a Failed Federal Act

By Gary Biller, NMA President

If I could travel back in time to change just one event to benefit motorists and highway safety, it would be 1974 to prevent the enactment of the 55 mph National Maximum Speed Limit (NMSL). While the United States still may not have attained the driving freedoms and safety of the German Autobahn today with that reversal of history, it would be years if not decades closer to that goal1.

In late 1973 President Richard Nixon proposed the 55 mph NMSL as part of the Emergency Highway Energy Conservation Act. The Conservation Act went into effect in 1974 as a countermeasure to the oil embargo instituted by the Arab members of OPEC in cooperation with a handful of other Middle Eastern countries.

The Conservation Act, and the NMSL in particular, was designed to reduce U.S. gasoline consumption by 2.2 percent. It failed, with actual savings estimated between 0.5 to 1.0 percent2. The efficiency of traffic flow suffered under the 55 mph regime. Traffic is at its smoothest level when vehicles are streaming at near-identical speeds. Congestion, lane changes, and sudden braking/accelerating are kept to a minimum. The optimum safe travel speed has been determined to be a few miles per hour above the average speed of free-flowing traffic (see adjacent Crash Involvement vs. Speed graph). Because of fewer vehicle interactions at that speed, it is also the most fuel-efficient speed for most vehicles.


With many drivers ignoring the restrictive 55 mph limit, the NMSL created two classes of drivers: those who kept up with surrounding traffic and those who abided by the posted speed limit. The former became technical violators of the law while driving at safe speeds while the latter created the speed differential that researchers found increases the risk of crashes.

The 1974 federal requirement forced 29 states to lower their posted limits, many previously set at 70 or 75 mph. (Two states, Montana and Nevada, didn’t post highway limits in the years prior to the NMSL.) Meanwhile thousands of new speed traps sprung up around the country because the enforced speed limits were set well below the average speed of traffic, sacrificing safety for revenue.

One need look no further than the National Highway Traffic Safety Administration’s FARS (Fatality Analysis Reporting System) database to see the benefit of raising limits back to prevailing traffic speed levels. The 55 mph NMSL was fully repealed in 1995 and states have been raising their maximum speed limits ever since. As of January 2014, when Illinois and New Hampshire post higher 70 mph limits, 37 states will have speed limits of 70 mph or higher.

And yet the most recent years on our nation’s highways have been the safest. In 1995, the last full year of the 55 NMSL restriction, the highway fatality rate per FARS was 1.73 per 100 million vehicle miles traveled (VMT). The 2011 rate—the most recent year of finalized data from the same source—was 1.10 per 100 million VMT, a reduction of 36.4 percent since 1995.

The key to safer highways is the establishment of speed ceilings based on rounding up the 85th percentile speed of free-flowing traffic. Many states are moving in that direction and are realizing safety improvement. Ohio, for instance, saw the number of turnpike deaths drop to its second lowest annual total in 2012 (according to the Plain Dealer), the first full year with a posted 70 mph limit.

One of the most effective and certainly most entertaining treatments of why setting proper speed limits is essential to highway safety is provided by Canadian Chris Thompson in his video “Speed Kills Your Pocketbook.” If you are at all interested in the relationship between speed and safety, watch as Thompson drives the point home.


1 2011 data from the German Federal Highway Research Institute show the fatality rate on the Autobahn was 0.32 per 100 million vehicle miles traveled (VMT). The U.S. 2011 highway fatality rate per NHTSA’s FARS data was 1.10 per 100 million VMT. The state with the lowest fatality rate that year was Massachusetts at 0.62, still almost twice the German rate. The highest? Montana at 1.79 fatalities per 100 million VMT followed closely by West Virginia at 1.78.

2 The Office of Driver Research in the U.S. Dept. of Transportation found the fuel savings to be 1 percent, and some independent studies determined the savings to be a much lower 0.5 percent. (Ref Copulos, Milton R., “The High Cost of the 55 MPH Speed Limit,” Sept. 1986).

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