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Comment by ecshafer | Hacker News Reader

I would be interested to see waymo adapt to the snow and ice, where “hit the breaks” Is the wrong answer, and the correct is to drop the car into neutral. I believe waymo will figure this out in time, nut SF and Phoenix are idealized driving conditions.

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The correct answer is to not drive so fast (or at all) in conditions where braking might lead to a skid. I'd expect an autonomous vehicle to be rather better at this given they can hook directly into the electronic stability control system in a vehicle and constantly monitor temperature (and ideally measure upcoming road temperature).

Also, shifting into neutral is really only a thing for old vehicles without ABS/ESC. In modern vehicles, you let your foot off the gas slowly.

I am in upstate new york, unless the situation is extremely bad, just dont drive isnt a valid answer for 5 months a year.

> snow and ice, where “hit the breaks” Is the wrong answer, and the correct is to drop the car into neutral

This is only true with 2WD and no automatic stability control, and if you’re going down a slope. For every other case, ABs will out perform in snow and gentle braking will evenly distribute traction force with stability control doing microsecond evaluations.

It is also the case that Waymo will be dramatically better than all humans in ice because it is going to take the aviation approach and stay in the depot, rather than fooling itself into believing it is competent at driving on ice.

You still need to be in neutral as the ABS/stability control doesn't control the engine. 2wd makes no real difference other than rear wheel drive tends to be the most susceptible to this issue, but any wheel can lose traction.

> stability control doesn't control the engine

Stability control is tied to power in all modern systems.

I spend about 5 months every year driving in snow and ice - this is the first I'm hearing about dropping it into neutral. Can you elaborate on when that would be appropriate? Obviously you shouldn't be slamming on the brakes, but they do work fine in snow and ice. I don't see how rolling into things while not in gear is an improvement?

I think it's often about when you're on rural single lane roads and perfectly bad ice/snow/slush conditions where you need to keep your speed very low, and sometimes even very moderate braking can cause your vehicle to veer off the road and into a snow bank, not necessarily the need to avoid something in front of you

They mean go into neutral and lightly brake. In a 2WD car, the braking force applies more strongly to the non-powered wheels. Since those were traditionally the back wheels, this meant when going down a hill the front wheels would have more traction. Those are also your steering wheels, which means them locking up is bad. Again, this is the sort of advice that is germane in highly restricted environments which become folk knowledge and later mis applied by humans in ways that reduce safety.

(You also only get into this scenario when your stopping distance is shorter than your reaction time and perception length. Something automated drivers can manage better than humans.)

I remember being taught the neutral trick for emergency braking back in the 90's, and it had nothing to do with traction in poor conditions. It was simply to remove any engine power that might extend your braking distance. It's definitely bad advice in any modern car.

When you let off the throttle your wheels start driving the engine and slowing you down. In snow/ice that engine breaking alone can be more braking force than is safe and so you go into a skid. Shifting to neutral removes engine braking and allows for more controlled slowing down.

When it's those conditions though I just use a light touch on the throttle to make wheel speed match ground speed, a lot of easier than trying to shift in and out of neutral.

I think the OP means in a manual transmission. Auto will decouple at low speeds / engine braking won't be as severe. In a manual car, in 1st gear, I could possibly see it.

As someone who grew up BEFORE ABS, drove in the winter (in Canada), including first winter owning my own car with sport tires because I couldn't afford winter tires, spun / slid a few times even with top-of-the-line winter tires, etc.

ABS is a game changer in the snow. I used to go to an empty parking lot every winter during early snowfalls to play around and skid, start/stop, etc. Even EARLY ABS ('94 VW) means that 98% of the time (IMHO), the answer even in snow/ice is "slam on the brakes". Sure, you might have a few percent longer stopping distance than an expert who can do threshold braking - are you an expert? And the fact that you don't lose control of the steering is a huge advantage.

If you are in a situation where your car is sliding, like down a slick hill. You dont hit breaks, you put the car into neutral and steer into the way your car is sliding to try and keep the car on the road.

If hit the brakes is the wrong answer, you are driving too fast.

Almost all of these tricky situations are avoided by slowing down and giving more space around hazards.

? just brake and rely on the abs

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