[bryanlarsen]

25mph is 36 feet per second, about the length of a school bus. The stopping distance at 25mph is 30 feet, assuming perfect reaction time and dry pavement. Human reaction time is about 750ms, so stopping distance is about 2 school bus lengths. You don't have seconds.

25mph is too fast for any street where kids may jump out behind parked cars. Not just school zones, but all residential streets. There's a knee at about 20mph in the traffic fatality stats where below that speed pedestrian collisions are unlikely to be fatal. Above 20mph fatalities become more common quite quickly.

[Mawr]

> The stopping distance at 25mph is 30 feet,

Stopping is nice, but not the entire point of braking. The lower the collision speed, the better.

> Human reaction time is about 750ms

No. Human reaction time is around 250ms on average. What you point to is the time it takes to react to an unexpected stimuli. The number I've seen quoted is about 1s. But that assumes a completely unexpected event that you're not prepared for at all.

So if you're mindlessly passing a school bus at 25mph, then a 1s delay is expected. But if you're doing so with your foot covering the brake while hyper focused on reacting to any sudden movement in front of you, you can do much, much better than 1s. Of course, at that point you might as well drive correctly by slowing down.

[mckn1ght]

This is why school buses flash yellow warning lights before deploying the stop sign and opening the doors.

It should never be the case that someone is surprised by an instantaneous bus stop. The are plenty of context clues in advance. Including the fact that the bus is around at all, which should already heighten attention.

[int_19h]

Even if you won't prevent the collision, reducing the velocity at which it happens is still very desirable, And, given that kinetic energy of the car is proportional to velocity squared, even a little bit of reduction means a lot less energy dumped into the pedestrian.

[bryanlarsen]

Sure, if you've hit the brakes by then. The reaction time delay means you travel significant distance before hitting the brakes.

[scienceman]

For the knee to be useful you have to go below it -- thus 15 mph is a much better neighborhood and school speed limit.

[hyperman1]

To add a data point. In Belgium, the max speed around schools is enforced to be 30 km/h. That should be a bit less than 20mph.

[BobaFloutist]

I wasn't talking about human reaction time.