If you try to brake a motorcycle as fast as you would a car, it has a tendency to flip over. And in general different vehicles have different stopping distances, so "just have the whole line of cars all panic brake at once" is going to have them smashing into each other.

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ninalanyon 2 days ago | parent [-]

Only if they are all driving too close the the car in front. If you keep to the recommended 3 seconds separation you will most often be fine even in bad weather. I drive my Tesla S on Autopilot with the separation set to the maximum which is about 3 seconds and it makes for a comfortable motorway driving experience.

	▲	AnthonyMouse a day ago \| parent [-]
		How close cars are to each other is generally determined by traffic volume. If there are twice as many cars, they can only be half as far apart because otherwise they can't physically fit on the same length of road. If you try to leave more space than that, other cars will merge into the empty space. The only way to actually do it overall is to reduce the traffic volume (or add more lanes), which is not something an individual driver has any control over. Which is to say, in practice cars will be following too closely whenever there is high traffic volume, and systems that don't work under real life conditions are broken.