Core: The reaction second and the reaction distance

The reaction second is a time (1 second on average), not a distance: it is the period between the moment you perceive the hazard and the moment you actually press the brake. The reaction distance is what you cover in that second, and has its own rule of thumb: ((speed:2) + 10%) : 2. At 80 km/h: ((80:2)+10%):2 = (40+4):2 = 22.00 m. At 130 km/h: ((130:2)+10%):2 = (65+6.5):2 = 35.75 m. This formula differs from the braking-distance formula (which squares speed); reaction distance grows roughly in direct proportion to speed, not quadratically. Double the speed, and the reaction distance roughly doubles too — very different from braking distance, which then becomes 4x as long.