How Speed Affects Your Chance of Surviving a Crash (30, 50, 70 km/h)

Quick answer: Speed does not add risk, it multiplies it. The energy a car carries into a crash rises with the square of its speed, so a collision at 100 km/h is not twice as violent as one at 50 km/h, it is four times as violent. The WHO's rule of thumb, confirmed across dozens of studies, is that every 1% increase in average speed raises the risk of a fatal crash by about 4%. For a pedestrian the curve is brutal: struck at 23 mph (37 km/h) the average adult has a 10% chance of dying, at 32 mph (51 km/h) it is 25%, at 42 mph (68 km/h) it is 50%, at 50 mph (80 km/h) it is 75% and at 58 mph (93 km/h) it is 90%. Those figures come from the AAA Foundation's analysis of US pedestrian crashes and are the reason so many cities are moving to 30 km/h streets.

Why doubling your speed quadruples the damage

Kinetic energy is half the mass times the speed squared. Mass does not change during a trip, so the only thing a driver controls is the square term. Going from 50 to 70 km/h feels like a 40% increase; in energy terms it is 96%, almost double. Going from 50 to 100 km/h is a four-fold increase in the energy that seat belts, airbags, crumple zones and human bodies have to absorb.

That is why the difference between a survivable and a fatal crash is often only 15 or 20 km/h, and why the same bend that is a scare at 60 becomes a fatality at 80.

Stopping distance grows even faster than you think

Stopping distance has two parts: the distance covered while the driver reacts (about one second for an alert driver, longer when tired or distracted) and the braking distance, which also rises with the square of speed. On a dry road with good tyres:

• 30 km/h: about 8 m thinking + 5 m braking = 13 m
• 50 km/h: about 14 m thinking + 14 m braking = 28 m
• 80 km/h: about 22 m thinking + 36 m braking = 58 m
• 100 km/h: about 28 m thinking + 56 m braking = 84 m
• 130 km/h: about 36 m thinking + 95 m braking = 131 m

On a wet road the braking part roughly doubles. A car that would just stop in time at 50 km/h is still travelling at around 35 km/h when it reaches the same point from 60 km/h. Our stopping distance calculator does this arithmetic for any speed, surface and reaction time.

The pedestrian survival curve

The AAA Foundation for Traffic Safety analysed real US pedestrian crashes and produced the most-cited survival figures in road safety:

• 23 mph (37 km/h): 10% risk of death
• 32 mph (51 km/h): 25%
• 42 mph (68 km/h): 50%
• 50 mph (80 km/h): 75%
• 58 mph (93 km/h): 90%

Age matters: a 70-year-old pedestrian faces roughly the risk at 35 mph that a 30-year-old faces at 45 mph. This curve is the evidence behind 30 km/h (20 mph) limits in residential streets across Europe, and behind the WHO recommendation that streets shared by cars and pedestrians should not allow more than 30 km/h.

The 1% rule

Across countries, when average traffic speed rises 1%, fatal crashes rise about 4%, serious-injury crashes about 3% and all injury crashes about 2%. The reverse is also true: a 5% drop in average speed cuts road deaths by roughly a fifth. This is why a 10 km/h reduction in a speed limit typically produces a measurable fall in deaths within a year, even though most drivers slow down by only 3 or 4 km/h.

The countries with the lowest death rates on our safest countries to drive list, such as Norway, Sweden and the United Kingdom, combine low urban limits with consistent enforcement. The countries at the top of the most dangerous countries to drive table almost all pair high speeds with mixed traffic of pedestrians, motorcycles and trucks on the same road.

What the limits are, and where they are highest

Germany's derestricted Autobahn sections and 130 to 140 km/h motorway limits in Poland, Bulgaria and parts of Italy are the top of the scale; most of the world sits at 100 to 120 km/h on motorways and 50 km/h in towns. The full comparison is in our highest speed limits in the world article and the driving laws by country table, which lists urban, rural and motorway limits for 195 countries.

In the United States, speeding was a factor in 29% of crash deaths nationally in 2024, and in more than 40% in Vermont, Alaska, Montana and North Carolina. Every state's figure is on the car accidents by state pages.

Speed and the crash types that kill

• Head-on collisions on two-lane rural roads: closing speeds add together, so two cars at 90 km/h meet at 180 km/h. No production car is designed to protect occupants at that energy.
• Run-off-road crashes into trees and poles: a tree does not crumple. Side impacts into narrow objects are survivable at 30 km/h and rarely above 50.
• Rear-end crashes at motorway speed: the following car's stopping distance, not the collision itself, decides the outcome.
• Pedestrian and cyclist impacts: the curve above. The car's speed at the moment of impact, after braking, is what matters, which is why a lower approach speed helps twice, through shorter stopping distance and lower impact energy.

What to do with this

• Treat the posted limit as a maximum for perfect conditions, not a target.
• In rain, at night or with pedestrians around, take 10 km/h off. That single decision moves you a long way down the survival curve.
• Keep at least a two-second gap at any speed and four seconds when it is wet.
• Check your tyres: worn tread can add 20 metres to a stop from 100 km/h in the wet. The tire age checker explains why age matters as much as tread.

For context on how many people this costs, see how many people die in road accidents every day and the live accidents today feed.