Shockingly, the slow car is often the real threat. On a highway posted at 120 km/h, a driver crawling at 60–70 km/h doubles the speed differential that traffic engineers try to keep small, and that gap is what turns routine lane changes into emergency maneuvers. The physics is simple: kinetic energy scales with the square of speed, but conflict probability scales with relative speed, so each mismatch multiplies the number of potential impact partners across lanes.
The harsh truth is that traffic flow behaves like fluid dynamics, not like a polite queue. When one vehicle moves at half the prevailing speed, following drivers face abrupt drops in time headway, slam their brakes, and trigger shockwaves of deceleration that propagate backwards through the stream. Studies of rear‑end collisions and lane‑change crashes repeatedly show that large speed variance is a stronger predictor of risk than the average speed itself, because every overtake adds another chance for perceptual error and delayed reaction time.
Safety, then, comes less from being slow and more from being predictable. A driver parked in the right lane at 65 km/h while others travel near 120 km/h forces heavy trucks to weave, pushes impatient cars leftward, and quietly inflates exposure to side‑swipe and rear‑end impact. What protects people is alignment with the prevailing flow, disciplined lane discipline, and enough speed to reduce dangerous passing, not an isolated cocoon of slowness.
