Hacker News Reader

Comment by nearbuy | Hacker News Reader

This is well studied by researchers, and 1-2s is the typical reaction time for real drivers with real muscle memory when reacting to an unexpected hazard on the road.

There are a lot of reasons people could sometimes react faster (for example, if they anticipate the hazard, or if they're just above average in reaction speed), but one to two seconds is the reaction speed we find most of the time.

The fastest human reactions aren't to unexpected road hazards. We have a much faster reaction speed in tests where you just have to click the mouse each time the screen flashes. Our reactions are fastest when you know in advance the event is about to happen. But this isn't relevant for road safety.

View on HN

Your wording is kind of misleading. While the human reaction time to the unexpected is not great it's the human's ability to predict within reason what the likely next things to expect are expansive.

Like just running a first pass sanity analysis on the 1-2sec timeline fails because if it were true in practice all those idiots who screech about how normal traffic doesn't keep following distances worthy of semi trucks to the traffic ahead would be proven right as every braking event would cause a pile up. So either humans react much faster to the unexpected (not likely, we've measured) or humans have a huge "context window" for what to expect that makes the 1-2sec number not relevant in the base case.

No it's not. 1-2 seconds is what we find in practice for real drivers responding to unexpected hazards.

Your close following distance example doesn't show anything. A normal braking event on the highway doesn't require a fast reaction. If you're driving 100 km/h and you're following 1.5 seconds behind the car in front of you (about half the recommended following distance) and they brake to 80 km/h, you have about 9 seconds to slow down or switch lanes. That's plenty of time.

The risky scenario is if the car in front of you has to do a full, hard emergency stop and you're following too closely. That's rare, and collisions are common when it happens.

If you know the car in front of you is going to brake because you can see the traffic ahead slowing down, that's not fast reaction time. That's just you seeing cars slow down and reacting at a normal speed. An AI has just as much time to react to that as you do.

What research studies are you citing?

Reply on news.ycombinator.com