The first plot is of a study particular to specific roads and their current configuration in Bangkok. The second arrives at an equality that I don't fully unde

The first plot is of a study particular to specific roads and their current configuration in Bangkok. The second arrives at an equality that I don't fully understand, but applying it's formula shows about a 2.6x greater spacing requirement when moving from 30mph (8.5 ft) to 80mph (22.8 ft). Which is close to what the two second rule would tell you when going from 30mph (88 ft) to 80mph (234 ft). Interestingly, if you look at actual braking distances, then for 30mph (45 ft) to 80mph (320 ft) shows a 7x change in distances. So, the above advice relies on the fact there will be no fixed obstructions in the road and that anything in front of you will have to brake as hard as you do. Perhaps this is why pedestrians still do so poorly on the roads, but it also makes me suspicious that you can just apply this formula equally to 30mph traffic and 80mph traffic. The hazards are different, the road duty cycle is different, traffic controls exist on one and barely on the other. Even so.. using the basic 2.6x capacity reduction factor going from 30mph to 80mph, you're getting a 2.6x capacity increase from the change in speed. As soon as you add _one_ additional lane, the 80mph road makes a bunch of sense.