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Comment by mxwsn | Hacker News Reader

Whoa hold on, table 1 of stopping distances is calculated for 2.5 second reaction time which is 10x longer than conventional human reaction time. Then the stopping distances are compared to radar/lidar/camera to argue that AVs can struggle to stop within detection range. It's possible a computer might need 2.5s to make a decision to stop. But the current analysis isn't based on that.

This analysis seems really suspect to me. Any clarification would be appreciated.

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Author here. the shorter reaction times you mentioned are collected under ideal conditions, like the person knows they are being tested and only needs to push a button or whatever. In driving, the reaction time is end to end, including perception, decision-making, and actuation (moving your foot, pressing pedal all the way, shifting, etc.)

Also recommend checking out the citation. It is an accepted value used in American highway design.

A human decision to stop is not binary 1/0. If I am approaching a hazard, first thing to do is raise alertness. Also, lift foot off accelerator pedal. Then, put foot on brake. Then, apply some pressure to brake. All this stuff happens on a gradient depending how quickly I need to react and stop.

So between which endpoints shall you measure "reaction time"? I'm already priming my reaction by actions which lead up to it. Obviously, an automated driving system doesn't need some of these steps, but it's still running through the same scenario and "thought processes" to reach a decision and course of action.

Once at lunchtime, I had two coworkers in my car. I was driving a manual-transmission Acura Integra in light rain, heavy traffic in downtown Palo Alto. I had a left turn signal and I proceeded through the intersection, when an oncoming car was coming straight at us and couldn't stop. I punched the accelerator and sped through the turn without incident. My coworkers both congratulated me on making the correct decision: to hesitate, or to hit the brakes, would've surely crashed us. But what was my reaction time? My foot already on the gas, I simply made a snap decision in the moment to follow through.

I had a guy do the exact opposite: he slammed on the brakes doing a left turn in front of me. I t-boned him. If he had had a passenger they would have been severely injured: he was driving a Kia, I was driving an Isuzu Trooper. My entire family was in the Trooper, and we were fine. The Trooper's radiator (and air conditioning) were broken, but we put in a new radiator and drove it another 150 thousand miles. That Trooper Would Not Die.

That's a good argument for taxing cars (partially) by weight.

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