This is based on the concept of centrifugal force.
If a car on the "inside" lane of a curve tries to navigate with too much speed, centrifugal force will pull it away from the center and, potentially, into the path of oncoming traffic.
Or, if a car is traveling with too much speed from the other direction—in the "outside" lane of a curve—centrifugal force will pull it out to the right and off the roadway.
Hope it helps.