We clearly have different experience on the road. > Since the speed delta is the same it's far worse with 30 to 45, and regulations reflect that. If E(v) = mv

We clearly have different experience on the road. > Since the speed delta is the same it's far worse with 30 to 45, and regulations reflect that. If E(v) = mv²/2, then E(v+dv) = m(v+dv)²/2 = mv² + m v dv/2 + m dv²/2. As you can see, the middle term is proportional to v, the initial speed. Kinetic energy does increase more going 90->105 than 30->45. Maybe this is too abstract, so he're a concrete example. Let's assume a vehicle weighing 1 ton (1000 kg). * Going 30 km/h => kinetic energy is 34 kJ * Going 45 km/h => kinetic energy is 78 kJ, so about 43 kJ more * Going 90 km/h => kinetic energy is 312 kJ * Going 105 km/h => kinetic energy is 425 kJ, so about 113 kJ more It's really basic physics.