Speed increases your chances of a crash because it shrinks the time you have to react, dramatically extends the distance your vehicle needs to stop, and overwhelms your tires’ ability to grip the road. These effects don’t scale in a straight line. They compound, which is why even modest increases in speed produce outsized increases in risk. In 2023, speeding was a contributing factor in 29% of all traffic fatalities in the United States.
Stopping Distance Grows Exponentially
The single most important concept here is that braking distance is proportional to the square of your speed. That means if you double your speed, your braking distance doesn’t double. It quadruples. A 10% increase in speed causes roughly a 21% increase in braking distance. This relationship comes from basic physics: your brakes have to remove all the kinetic energy your vehicle has built up, and kinetic energy equals half your mass times your speed squared.
Total stopping distance has two parts: the distance you travel during your reaction time (before your foot even touches the brake) and the distance you travel while braking. At 50 km/h (about 31 mph), your reaction distance is roughly 15 meters and your braking distance is about 10 meters, giving you a total stopping distance of 25 meters. At 90 km/h (about 56 mph), those numbers jump to 27 meters of reaction distance and 32 meters of braking distance, for a total of nearly 60 meters. At 110 km/h (68 mph), you need over 81 meters to come to a full stop.
Notice what’s happening: the braking portion of that distance grows much faster than the reaction portion. At 30 km/h, braking accounts for less than a third of your total stopping distance. At 110 km/h, it accounts for more than half. The faster you go, the more your stopping distance is dominated by the part you can’t control.
You Have Less Time to React
Your brain needs roughly one second to perceive a hazard and begin responding. That reaction time stays constant regardless of speed, but the distance you cover during that second does not. At 50 km/h, you travel about 15 meters before you even start braking. At 110 km/h, you cover 33 meters in that same second. A child stepping off a curb, a car pulling out of a driveway, debris in the road: whatever the hazard, higher speed means you’re significantly closer to it before your brain can even begin to act.
This shrinking time window also degrades the quality of your decisions. Research on driver behavior under time pressure shows that when the gap between you and a hazard is small, you’re forced to sacrifice accuracy for speed of response. In less extreme situations, you might steer smoothly around an obstacle. Under time pressure at high speed, you’re more likely to overcorrect, brake too late, or choose the wrong evasive maneuver entirely.
Crashes Hit Harder at Higher Speeds
Speed doesn’t just make crashes more likely. It makes them more severe. The energy your body absorbs in a collision follows that same squared relationship with speed. A motorcycle weighing 150 kg and traveling at 60 km/h carries about 270,000 joules of kinetic energy. The same motorcycle at 120 km/h carries 1,080,000 joules, four times as much. That energy has to go somewhere during impact, and it goes into crushing metal, shattering glass, and injuring people.
This is why the statistical relationship between speed and fatal crashes is so steep. A widely used model in traffic safety research, developed by Swedish researcher Göran Nilsson, found that fatal crashes increase with the fourth power of the change in average speed. That means a 10% increase in average speed on a road leads to roughly a 46% increase in fatal crashes. Serious injury crashes follow the third power, and all injury crashes follow the second power. Small speed changes produce large changes in outcomes.
Tires Lose Grip on Curves
Your tires can only generate a limited amount of sideways grip. When you drive through a curve, your vehicle needs centripetal force (provided by tire friction) to follow the curved path instead of sliding straight ahead. The force required increases with the square of your speed, so taking a curve at 60 km/h demands four times as much sideways grip as taking it at 30 km/h.
Once the required force exceeds what your tires can deliver, the vehicle skids, overturns, or drifts into the opposing lane, a guardrail, or a ditch. Road engineers design curves with a maximum safe speed based on the friction limits of typical tires in typical conditions. Exceeding that speed, especially on wet or icy surfaces where friction drops significantly, pushes you past the point where physics allows the car to stay on the road. No amount of steering input will help once you’ve exceeded the available grip.
Why Small Speed Increases Matter
People tend to think of speeding risk in terms of dramatic excess, going 100 in a 60 zone. But because all the key physics relationships are squared (or worse), the risk curve is steepest in the range of speeds most people actually drive. Going 70 km/h instead of 60 doesn’t feel meaningfully faster, but it increases your stopping distance from about 32 meters to nearly 41 meters. That’s an extra 9 meters, roughly two car lengths, of road you need to avoid a collision.
At highway speeds, the margins get even thinner. At 110 km/h, you need over 81 meters to stop. At 90 km/h, you need about 59 meters. That 20 km/h difference creates a gap of more than 22 meters, enough space that one driver stops safely while the other is still traveling at significant speed when they reach the hazard. In real-world terms, that gap is the difference between a near-miss and a collision, or between a fender bender and a fatality.