Hacker News Reader

Comment by chrismealy | Hacker News Reader

I want to know how it handles rain.

I think a self driving car will do a much better job operating in the rain than a human being. Rain makes it difficult to see and wipers are sometimes worn out and make visibility even worse.

Slick driving conditions are also dangerous for human drivers but these days there are electronic stability systems in place to make it less dangerous to drive in the rain. If you have a car that can turn all traction controls off you can easily see the difference of assisted and non assisted driving in the rain.

I think the bigger problem will be heavy snow. What happens when you park your car at the mall and come back to find the sensors covered in 4 inches of snow? Very curious to see how they deal with that issue.

Not yet. That's why Google's been testing in Nevada.

Wait, did you actually want to know how it handles rain, or were you asking a rhetorical question implying that it can not handle rain? If the latter, it would've been friendlier to say "it doesn't handle rain well, here's why: [...]"

I think he probably started searching for answers after he posed his original question, and found some. Not that he was asking a question he knew the answer to.

> What happens when you park your car at the mall and come back to find the sensors covered in 4 inches of snow? Very curious to see how they deal with that issue.

You turn off the self driving and manually drive home? The car doesn't have to be perfect to have value. It's perfectly ok if the first version doesn't handle rain, or snow, or fog.

Since the article didn't touch on environmental factors I suspect "it doesn't" is the answer to handling rain/snow. However, since one of the cameras is a laser that builds a 3d model of the world, I suspect that once the algorithms are developed it will have the potential to surpass human performance when visibility is poor (heavy rain/fog).

The LIDAR sensors should be able to handle most rain conditions, but it breaks down when you get into heavy rain. I'm not precisely sure where the line is drawn.

Snow however is a different problem. I think even light snow is impossible for LIDAR to penetrate. Not to mention the issues that arise when tires slip on ice, snow is covering signage, etc, etc.

Do you have any sources for any of this information?

Because they seem entirely made up and the "issues when tires slip on ice" have been mitigated with computerized ABS systems for the past 20 years

I've done a lot of work with perception systems and sensors. GP is right on the money with the problems. Rain is even difficult.

Snow is the worst though - it is both wet and super reflective. Super reflective dazzles your laser/obscures cameras. Wet screws up your radar.

Funny thing about ABS systems is that the pump actually forces the brake pads open. The designer's thinking is that a turning wheel is able to steer, while a vehicle with sliding wheels is directed pretty much by momentum alone. This results in longer stopping distances.

So far as ice -- it's coefficient of friction in the real world is not a constant -- it varies based on local conditions. So you can't predict your ability to stop & steer on it - you can only react. Your best defense is to install ice-rated tires in early winter to increase your traction. Google will likely have to do some testing in Wisconsin to see how the software reacts to icy conditions, and is able to somehow automatically recognize ice/slush and adjust stopping/acceleration rates appropriately.

Well, in principle ABS shouldn't necessarily result in longer stopping distance: sliding friction is lower than static friction, so if you can control the braking precisely enough, not locking the wheels should result in shorter stopping distance along with not losing control. I'm not saying current systems are that good, though.

"ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces for many drivers; however, on loose surfaces like gravel or snow-covered pavement, ABS can significantly increase braking distance, although still improving vehicle control." (with citations) http://en.wikipedia.org/wiki/Anti-lock_braking_system

On dry surfaces, a professional driver is able to do Threshold Braking, which in non-ABS cars maximizes stopping power by taking braking just up to the limit before the tires start sliding. On cars with ABS, the intent is to minimize the rate at which the ABS pump activates in order to maximize stopping power (pulse ... pulse ... pulse vs. pulse.pulse.pulse)

ABS has an advantage over regular systems in that the computer is able to control braking effort on a per-wheel basis. Something a human with only one pedal to push can't do. IIRC, the best ABS systems are able to cycle at about 10Hz.

Something I vaguely recall reading about is that in a panic stop on ice, the heat from the sliding friction will melt a very small bit of ice under the contact patch, turning it into a hydroplaning situation. I need to see if I can find that reference again...

ABS allows you to take maximum advantage of the traction you do have, but it doesn't magically improve your traction. The problem the GP is referencing is that the driver (be it human or computer) operates the vehicle using some sort of model for the maximum available traction. (Some) Humans are able to notice when it is snowing, re-tune their model and drive at an appropriate speed. It doesn't seem impossible that some heuristic could be invented to do the same for a computer driver, but I don't think anyone has demonstrated that heuristic yet.

Well, I have some sources for that information:

http://www.newyorker.com/reporting/2013/11/25/131125fa_fact_...

It's a long article, but search for "rain." Here's the most important quote for our purposes:

    Left to its own devices, Thrun says, it could go only
    about fifty thousand miles on freeways without a major
    mistake. Google calls this the dog-food stage: not quite 
    fit for human consumption. “The risk is too high,” Thrun 
    says. “You would never accept it.” The car has trouble in 
    the rain, for instance, when its lasers bounce off shiny 
    surfaces. (The first drops call forth a small icon of a 
    cloud onscreen and a voice warning that auto-drive will 
    soon disengage.) It can’t tell wet concrete from dry or 
    fresh asphalt from firm. It can’t hear a traffic cop’s 
    whistle or follow hand signals.

Reply on news.ycombinator.com