Why do roads have speed limits?
Short answer
At higher speeds, road users have less time to avoid danger, and crashes can cause more severe injuries. Speed limits help manage those risks.
How it works
When a vehicle is moving faster, it travels farther while the driver notices a danger and begins to brake. It also generally takes longer to stop, making it harder to avoid pedestrians, other vehicles, or obstacles.
Speed limits can take road shape, intersections, pedestrians and cyclists, nearby buildings, traffic, and other conditions into account. The exact rules and numbers differ between countries and local areas.
Key point
A posted speed is a maximum, not a promise that the same speed is safe in every situation. Rain, snow, fog, road work, and congestion may require a lower speed.