Historically, the power to set speed limits belonged to the states. In late 1973, speed limits were as high as 75 mph.
Kansas had even lowered its turnpike speed limit from 80 mph before 1974. Montana and Nevada generally posted no speed limit on rural roads.
States commonly set the speed limit at or below the 85th percentile operating speed (being the speed which no more than 15% of traffic is exceeding) and in the United States was typically set 8 to 12 mph below that speed.
Thus, if the 85th percentile operating speed as measured by a Traffic and Engineering Survey exceeds the design speed, compulsory legal protection is given to that speed—even if it is unsafe.
This speed creep tends to continue until the 85th percentile operating speed is comparable to speed psychologically perceived as uncomfortably hazardous.
The theory behind the 85th percentile rules is, that as a policy, most of the electorate should be seen as lawful, and limits must be practical to enforce.
However, there are some circumstances where motorists do not tend to process all the risks involved, and as a mass choose a poor 85th percentile speed.
This rule in substance is a process for voting the speed limit by driving; and in contrast to delegating the speed limit to an engineering expert.
1973 Oil Crisis
However, as an emergency response to oil price spikes and supply disruptions during the 1973 oil crisis, on November 26, 1973, President Richard Nixon proposed a national 50 mph speed limit for passenger vehicles and a 55 mph speed limit for trucks and buses.
That proposed new speed limit, combined with a ban on ornamental lighting, no gasoline sales on Sunday, and a 15% cut in gasoline production, were proposed to reduce total gas consumption by 200,000 barrels a day, representing a 2.2% drop from annualized 1973 gasoline consumption levels.
President Nixon partly based this on a belief that cars achieve maximum efficiency between 40 and 50 mph and that trucks and buses were most efficient at 55 mph.
Congress then drafted the National Maximum Speed Law (NMSL) as a provision of the 1974 Emergency Highway Energy Conservation Act that prohibited speed limits higher than 55 miles per hour.
The uniform speed limit was signed into law by President Nixon on January 2, 1974, and became effective 60 days later, by requiring the speed limit as a condition for each state receiving federal highway funds, a use of the Commerce Clause of the United States Constitution.
The legislation required 55 mph speed limits on all four-lane divided highways unless the road had a lower limit before November 1, 1973.
In some cases, like the New York Thruway, the 50 mph speed limit had to be raised to comply with the law. The law capped speed limits at 55 mph on all other roads.
A survey by the Associated Press found that, as of the Wednesday, January 2, 1974:
- 12 states already had maximum speed limits of 55 mph.
- Nine states had maximum speed limits of 50 mph.
- 29 states had to lower limits.
This included some states that voluntarily lowered their limits in advance of the federal requirement.
The law was widely disregarded by motorists, and most states subversively opposed the law. Actions ranged from proposing deals for exemption to de-emphasizing speed limit enforcement.
On May 12, 1974, the United States Senate defeated a proposal by Senator Robert Dole to raise the speed limit to 60 mph.
While officials hoped gasoline consumption would fall by 2.2%, actual savings are estimated at between 0.5% and 1%.
The NMSL was modified in 1987 and 1988 to allow up to 65 mph limits on certain limited access, rural roads. Congress repealed the NMSL in 1995, fully returning speed limit setting authority to the states.
The law’s safety benefit is also disputed as research found conflicting results.
According to the National Research Council, there was a decrease in fatalities of about 4000 lives in the first year after the law took effect.
Later, the National Academies wrote that that is, “a strong link between vehicle speed and crash severity [which] supports the need for setting maximum limits on high-speed roads,” but that, “the available data do not provide an adequate basis for precisely quantifying the effects that changes in speed limits have on driving speeds, safety, and travel time on different kinds of roads.”
They also note that on rural interstates, the free flowing traffic speed should be the major determinant of the speed limit because, “Drivers typically can anticipate appropriate driving speeds.” This is due, in part, to the strong access control in these areas but also is an acknowledgment of the difficulty of enforcing speed laws in these areas.
A Cato Institute report showed that the safety record worsened in the first few months of the new speed limits, suggesting that the fatality drop found by the NRC was a statistical anomaly that regressed to the mean by 1978.
After the oil crisis abated, the NMSL was retained mainly due to the ‘possible’ safety aspect.
In 1984, Rock musician Sammy Hagar released “I Can’t Drive 55”, a hit single protesting the National Maximum Speed Limit.
Now WE know em