I Think The Speed Limit Is…

It’s Friday, April seventeenth, and welcome to HigherIQ. Yesterday we talked about why half the world drives on one side of the road and half on the other. Today we’re staying on the road, but the question is different: how fast are you allowed to go, and who decided? The number on the speed limit sign feels like an engineering specification, something calculated by experts based on road design and stopping distances. In reality, it’s the product of oil embargoes, wartime rubber rationing, a Victorian-era law that required a man to walk in front of your car waving a red flag, and a political argument between safety and freedom that has never been resolved. The speed limit is one of the most debated numbers in American life, and the story of how it got to sixty five is stranger than you’d expect. The first speed limit in history was set in the United Kingdom in 1861, when Parliament capped mechanically powered vehicles at ten miles per hour. Four years later, the Locomotive Act of 1865, commonly known as the Red Flag Act, reduced that to four miles per hour on rural roads and two miles per hour in cities. The law also required that a person walk sixty yards ahead of any self-propelled vehicle carrying a red flag to warn pedestrians and horse riders of its approach. The law was designed less for safety than to protect the horse-drawn carriage industry, which viewed the automobile as a competitive threat. It stayed on the books for thirty years until Parliament repealed it in 1896, raising the limit to fourteen miles per hour. The first London to Brighton car run was held that year in celebration, and it’s still held annually. The first speed limit in the United States appeared in Connecticut in 1901: twelve miles per hour in cities, fifteen on rural roads. Other states followed, but as late as 1930, twelve states still had no speed limits at all, and twenty eight didn’t even require a driver’s license. The early automobile era in America was remarkably unregulated. Montana and Nevada, in particular, never set numeric speed limits on highways. Their standard was the “basic rule”: drive at a speed that’s reasonable and prudent for conditions. No number. Just judgment. World War II brought the first national speed limit. The Office of Defense Transportation established a “Victory Speed Limit” of thirty five miles per hour in May 1942, alongside gasoline and tire rationing, to conserve fuel and rubber for the war effort. It was widely ignored and lasted until the war ended in August 1945. After the war, states went back to setting their own limits, with highways typically posted between sixty and seventy five miles per hour. Then came the oil crisis. In October 1973, OPEC imposed an oil embargo on the United States in retaliation for American support of Israel during the Yom Kippur War. Oil prices spiked a hundred and thirty percent. Gas lines stretched around blocks. On November 26, 1973, President Nixon proposed a national speed limit of fifty miles per hour. Congress settled on fifty five and passed the Emergency Highway Energy Conservation Act in January 1974, which withheld federal highway funding from any state that didn’t comply. The law was pitched as a fuel conservation measure. The government hoped it would reduce gasoline consumption by 2.2 percent. The actual savings were estimated at somewhere between 0.5 and 1 percent, a figure so small it was almost within the margin of measurement error. But something unexpected happened. Traffic deaths dropped sixteen percent in a single year, from over fifty five thousand in 1973 to about forty five thousand in 1974. A 1984 National Research Council study estimated the lower speed limit was saving between two thousand and four thousand lives per year. The law that was passed to save fuel turned out to save lives. The rationale shifted underneath the policy without the policy itself changing. The fifty five mile per hour limit was, to put it mildly, unpopular. Western states with long, straight, empty highways considered it absurd. Drivers in Montana, Nevada, and Texas viewed it as an overreach by a federal government that didn’t understand the realities of driving five hundred miles through open desert. Compliance was spotty. Some states barely enforced the law and used speeding tickets primarily as a revenue source. The tension between the federal mandate and state resistance echoed yesterday’s driving-side episode: the central government imposed a universal rule, and the places where it fit least pushed back hardest. In 1987, Congress compromised, allowing states to raise the limit to sixty five miles per hour on rural interstate highways. Forty one states did so immediately. The number sixty five didn’t come from engineering analysis. It came from political negotiation between the fifty five that safety advocates wanted and the seventy five that western states had posted before the oil crisis. It split the difference. That’s why your highway speed limit is sixty five: not because a traffic engineer determined it was optimal, but because Congress cut a deal. In 1995, President Clinton signed the National Highway System Designation Act, which eliminated federal speed limits entirely and returned all authority to the states. The reaction was immediate. Texas jumped to eighty five on a forty mile toll road between Austin and San Antonio, the highest posted limit in the country. Montana reverted to its old basic rule: no numeric speed limit at all during daylight hours, just “reasonable and prudent.” That lasted until 1999, when the Montana Supreme Court ruled the standard was too vague to enforce without violating due process. Montana then set a numeric limit of seventy five. The public health data on the 1995 repeal is sobering. Researchers found a 3.2 percent increase in road fatalities between 1995 and 2005 attributable to the higher speed limits, accounting for an estimated twelve thousand five hundred deaths that might not have occurred otherwise. Fatalities rose nine percent on rural interstates and four percent on urban ones. The Insurance Institute for Highway Safety found that each five mile per hour increase in the speed limit was associated with an eight percent increase in fatality rates on interstates and four percent on other roads. The physics are simple: kinetic energy increases with the square of velocity, so a car traveling at eighty miles per hour carries sixty percent more energy in a crash than one traveling at sixty five. The debate has never been resolved because it’s not really a debate about speed. It’s a debate about what kind of risk a society is willing to accept for the sake of convenience and personal freedom. Americans drive roughly three trillion miles per year. At any speed limit, some number of those miles will end in a fatal crash. A lower limit saves lives but costs time. A higher limit saves time but costs lives. Neither side of that trade-off is wrong in any absolute sense. It depends on what you value, and Americans have consistently valued mobility and personal autonomy more than marginal safety gains, which is why the trend since 1995 has been toward higher limits, not lower ones. Germany’s Autobahn, the most famous road without a speed limit, tells the other side of the story. About thirty percent of the Autobahn network has no posted limit. Germany’s traffic fatality rate is lower than the United States’ rate, despite the higher speeds. The difference comes from driver training requirements (which are far more rigorous and expensive in Germany), vehicle inspection standards, road design, and enforcement of other traffic laws. Speed alone doesn’t determine safety. The infrastructure around speed does. So if this comes up in conversation, here’s how to think about it. The first speed limit required a man to walk in front of your car with a red flag. The fifty five mile per hour national limit was a fuel conservation measure from the 1973 oil crisis that accidentally turned out to save thousands of lives. Sixty five was a political compromise, not an engineering recommendation. When the federal limit was repealed in 1995, states raised their limits and roughly twelve thousand additional people died over the next decade. Germany runs portions of its highway system with no speed limit and a lower fatality rate than the US, because the speed itself matters less than the system built around it. The number on the sign isn’t science. It’s a negotiation between how fast you want to go and how many people a society is willing to lose. Have a good weekend. Stay informed, stay curious, and we’ll see you tomorrow.