Every car on the road was built for a crash in the thirties. The federal frontal test runs a car into a barrier at 35 mph. The toughest side test strikes it at 37. The crumple zones, the belts and the airbags are sized to those numbers, and the numbers are not arbitrary: they are the speeds the structure is designed and tested to handle. A car at 100 mph brings more than seven times the energy of that side test and eight times the frontal one, and nothing in the car was designed for it.
The square. Speed does not add to a crash. It multiplies it. The energy a moving car carries rises with the square of its speed, so a car going twice as fast carries four times the energy, and the Insurance Institute puts it in one line: when impact speed rises from 40 to 60 mph, a 50 percent increase, “the energy that needs to be managed increases by 125%” (IIHS). That energy has to go somewhere in the fraction of a second the crash lasts: into folding steel first, and when the steel runs out, into the people. Closing Speed shows what the square does when two cars meet head-on and the speeds add. Delta-V is the number the body actually feels, how much speed it gave up and how fast.
The tests. The tests are where the arithmetic becomes design. The federal rating program crashes a car into a fixed barrier at 35 mph and runs a 3,015-pound barrier into its side at 38.5 (NHTSA). The Insurance Institute’s frontal tests run at 40 mph, and by 2021 every new vehicle had earned a good rating in its moderate overlap test, a run that went back to 2013 (IIHS); its side barrier, made heavier and faster in 2021 to match today’s SUVs, weighs 4,200 pounds and strikes at 37 (IIHS). Those are the speeds the cage was built for, and the Institute says so plainly: there are limits to the crash energy a vehicle’s structure, its belts and airbags, and the barriers and crash cushions along the road can manage, and “the higher the speed, the higher the likelihood that these limits will be exceeded in crashes, limiting the protection available for vehicle occupants and increasing the chances of severe injury” (IIHS).
Forty, fifty, fifty-six. In 2021 the Institute, the AAA Foundation for Traffic Safety and the crash-dummy maker Humanetics ran the same crash three times: three identical 2010 Honda CR-Vs into the same barrier, at 40, 50 and 56 mph. At 40 there was “minimal intrusion into the driver’s space.” At 50 there was “noticeable deformation of the driver side door opening, dashboard and foot area.” At 56, “the vehicle interior was significantly compromised, with the dummy’s sensors registering severe neck injuries and a likelihood of fractures to the long bones in the lower leg.” At both of the higher speeds, “the steering wheel’s upward movement caused the dummy’s head to go through the deployed airbag” (IIHS). Sixteen miles an hour separated a driver’s space that held from severe neck injuries and likely leg fractures, and the square says why: 56 mph carries nearly twice the energy of 40. The Institute’s president drew the conclusion: “Higher speed limits cancel out the benefits of vehicle safety improvements like airbags and improved structural designs.”
The room it takes. The second thing speed takes is distance. A driver who sees a hazard needs about a second and a half to perceive it, decide and move a foot to the brake, and in that time the car does not slow at all: at 35 mph it covers about 77 feet, at 70 about 154, at 100 about 220. Then the braking distance grows with the square of the speed. With hard braking on dry pavement, about seven-tenths of the force of gravity, a car needs about 58 feet to stop from 35, about 234 from 70 and about 478 from 100. Put together, a car at 35 stops in about 136 feet; at 70, about 390; at 100, about 700, more than an eighth of a mile. That arithmetic is what The Reaction walks through, and Looking, Not Seeing explains why the second and a half is often longer.
The count. In 2024, 11,288 people died in crashes the police tied to speeding, 29 percent of everyone killed on American roads, and 87 percent of those deaths were on roads other than interstates, the streets and highways with intersections, driveways and cross traffic (NHTSA). The Institute estimates that the rise in speed limits since 1993 cost about 37,000 lives through 2017 (IIHS).
Where the law comes in. Texas law meets speed twice, and Squared walks through both: a speed over the posted limit is prima facie evidence that it was not reasonable and prudent (Transportation Code Section 545.352), and no speed is lawful that is faster than reasonable and prudent under the conditions (Section 545.351). The square adds a third step. At some point a speed stops being carelessness and becomes something a jury can punish. Texas calls it gross negligence: an act that, “when viewed objectively from the standpoint of the actor at the time of its occurrence involves an extreme degree of risk, considering the probability and magnitude of the potential harm to others,” by someone with “actual, subjective awareness of the risk involved” who “nevertheless proceeds with conscious indifference to the rights, safety, or welfare of others” (Civil Practice and Remedies Code Section 41.001). The magnitude of the potential harm is the square. A driver at 100 on a street posted at 45 is not taking a little more risk than the driver beside him; he is carrying nearly five times the energy, into a structure built for 35, with a braking distance nearly five times as long, and if a jury finds, by clear and convincing evidence, that he knew that and did it anyway, the law has a word for it (Section 41.003). Gross Negligence explains what that word opens.
A car is built for a crash in the thirties. Every mile an hour past that is energy the structure has nowhere to put, and the square says exactly how much.
The science and the tests: Insurance Institute for Highway Safety, Speed (the 125 percent line; the limits of structure, restraints and roadside hardware; the 37,000 estimate, 1993 to 2017); IIHS, New crash tests show modest speed increases can have deadly consequences, Jan. 28, 2021 (with the AAA Foundation for Traffic Safety and Humanetics; three 2010 Honda CR-V EX at 40, 50 and 56 mph); NHTSA, Ratings (frontal barrier at 35 mph; side barrier, 3,015 pounds at 38.5 mph); IIHS, Small SUVs struggle in new, tougher side test, Oct. 27, 2021 (4,200 pounds at 37 mph). The count: NHTSA, Traffic Safety Facts: Speeding, 2024 Data, DOT HS 813 823. The law: Tex. Transp. Code § 545.351 and § 545.352; Tex. Civ. Prac. & Rem. Code § 41.001(11) and § 41.003(a). The energy ratios and the stopping distances on this page are arithmetic: energy rises with the square of speed, and the distances assume a second and a half to react and braking at seven-tenths of gravity on dry pavement. General information, not legal advice.
