A driver waiting to turn left does not see how fast the oncoming car is going. He sees how far away it is, and he turns on that. Distance is the one thing the eye measures well across a road, and speed is the thing that decides whether the distance was enough.
The gap. The human-factors guidelines the National Academies publish for road engineers say it in one sentence: in one study of drivers choosing a gap, the distance to the nearest oncoming vehicle was the best predictor of whether they went, which suggests that “drivers are somewhat insensitive to oncoming vehicle speed.” The guideline then gives a number for the turn it studies, a car turning left from a side road onto the main road. For “Passenger cars executing a left turn: 7.5 seconds,” with half a second added for the additional lanes the turning car has to cross, and “Older drivers accept a critical gap that is approximately 1 s longer than younger drivers” (NASEM, Human Factors Guidelines for Road Systems). Seven and a half seconds is, in the guideline’s words, the gap between oncoming vehicles that the average driver will accept half the time. The driver does not count it. He looks at the oncoming car, reads a distance, and decides that the distance is more than seven and a half seconds’ worth.
The arithmetic. Here is why that works at the speed limit and fails above it. Take an oncoming car 500 feet away. At 35 miles an hour, about 51 feet a second, it arrives in about 9.7 seconds, two seconds more than the guideline’s gap. At 70, about 103 feet a second, the same car at the same 500 feet arrives in about 4.9 seconds. The turning driver saw the same picture both times, a car 500 feet off, and the picture told him the truth at 35 and lied to him at 70, because the gap he could not see was cut in half. Texas writes the turning driver’s duty in terms of distance, not speed: to turn left “an operator shall yield the right-of-way to a vehicle that is approaching from the opposite direction and that is in the intersection or in such proximity to the intersection as to be an immediate hazard” (Transportation Code Section 545.152). Proximity is the word, and a car at 70 is in proximity at distances a car at 35 is not. The figures are arithmetic for an illustrative gap, not measurements from any crash.
The stop. The speeding driver loses twice. The energy his car carries climbs with the square of the speed, so doubling 35 to 70 quadruples it, which is the sum Seven Times the Energy and Closing Speed work through. And the road he needs to stop climbs almost as fast. Allow a second and a half to see the turn begin and get a foot on the brake, then hard braking at seven-tenths of gravity. At 35 the car travels about 77 feet before the brakes act and about 58 feet while they do, roughly 135 feet in all. At 70 it travels about 154 feet before the brakes act and about 234 feet while they do, roughly 390 feet. A driver who saw the turn begin from 500 feet out could stop at 35 with room to spare. At 70 he has used nearly four hundred of his five hundred feet before the car is still, and the turning car is in the middle of them. The second and a half is the budget The Reaction describes, and it is spent at the same rate whatever the speed.
The door. Where the hit lands decides what the body takes. A car turning left across a speeder is struck on its side, and the side is the one part of a car with almost no room to crush, which is the whole of Inches of Steel. The national count shows what that costs. “Frontal impacts accounted for 59% of passenger vehicle occupant deaths in 2024,” and “Side impacts accounted for another 22% of passenger vehicle occupant deaths,” 5,047 people; among car occupants alone the side took 26 percent, 3,059 of the dead (IIHS, Fatality Facts 2024). The person on the struck side meets the door, the pillar and the other car at nearly the same instant, and the injuries that follow, to the chest, the pelvis and the head, are the fingerprint of a hit from the side.
What the numbers do in court. The turning driver’s duty and the speeding driver’s duty are both real, and a Texas jury weighs them against each other. The turn is Failure to Yield, and it will be the first thing the other side says. The speed is the duty the Transportation Code puts on everyone, “a speed greater than is reasonable and prudent under the conditions and having regard for actual and potential hazards then existing” is forbidden, and a driver “shall” “drive at an appropriate reduced speed if” he “is approaching and crossing an intersection” (Transportation Code Section 545.351), the rule of Reasonable and Prudent. The defense of every speed case is that the turn, not the speed, was the cause, and that the speed merely furnished a condition, the line the Fifth Circuit drew this week in a Houston case where a patrol car doing up to 70 in a 35 struck the passenger side of a car turning left, and held that whether the speed and inattention “were substantial factors” or “merely furnished a condition that made the injuries possible” was a question for the jury (Payne v. City of Houston). What answers it is the arithmetic above, done by an Expert from the real numbers: the speed from the striking car’s event data recorder, the distance from the point of impact and the skid or its absence, and the time the turn took from the turning car’s own data or the video. The family’s expert in the Houston case said the collision would not have happened at the speed limit; that sentence is the time-to-arrival sum, and it is the difference between a condition and a cause (Furnished a Condition). The shares are then divided in whole numbers (Comparative Fault), and the recorder that holds the speed is the record a letter must ask for first (Spoliation).
The science is settled. The eye reads distance and not speed, the guideline gives a left turn seven and a half seconds, speed takes those seconds away without changing the picture, and the car that arrives too soon arrives at a door. The question a Texas jury asks is whose number made the picture a lie.
The gap: National Academies of Sciences, Engineering, and Medicine, Human Factors Guidelines for Road Systems, Third Edition (2025), Chapter 10, Non-Signalized Intersections (gap acceptance and speed; the 7.5 second left-turn gap and the half second for additional lanes; older drivers). The door: Insurance Institute for Highway Safety, Fatality Facts 2024: Passenger vehicle occupants (posted June 2026) (frontal 59 percent; side 22 percent and 5,047; cars 26 percent and 3,059). The law: Tex. Transp. Code § 545.152; § 545.351 (subsections (b)(1) and (c)(1)). The case: Payne v. City of Houston, No. 25-20492 (5th Cir. Oct. 21, 2026) (per curiam; unpublished). The sums are arithmetic for an illustrative gap, not measurements from any crash: 35 miles an hour is 51.3 feet a second and 70 is 102.7, so 500 feet takes 9.7 and 4.9 seconds; kinetic energy is half the mass times the speed squared; reaction distance is 1.5 seconds times the speed, 77 and 154 feet; braking distance at 0.7 g is the speed squared divided by twice 0.7 times 32.2, about 58 and 234 feet. This is general information, not medical or legal advice. Figures and text as published at publication.
