Yeah, people are bad at guessing and the usual "Plan continuation bias" kicks in.

I was travelling in a group to eat lunch with friends once, after heavy rains. We reached a site where the road needs to fit under a bridge and is known to flood, there's standing water, and the driver figured it's probably not too high, he drives in and nope, water over the air intake, bye bye engine and we walked the rest of the way to lunch

I absolutely should have said "No, don't" but the plan says we have to drive under that bridge, there is no plan B. Of course plan A being "Wreck car" is a stupid plan, but the bias meant I didn't say "No" and I should have.

You wouldn't die there, just trash the car, the flooding is localised - but there are definitely other sites around here where in flood conditions you could die if you drove into water that's deeper than you realised.

This case makes me think of my brother's place in rural Tennessee. To get to his house, you drive through a small creek, year round. For a hundred years in their community, they've managed without a bridge. I'm not sure driverless cars are ready for edge cases like this. Also, no one tell Enterprise I drove their rental through a creek.

Texas has it easy.

I've seen several places in England (and at least one in the western United States) where they have fords.

For those not familiar, water runs over the road full-time, and people are expected to just drive through it like it's no big deal. Except for right after a storm, when it is a big deal. It's essentially the intersection of a road and a stream where a bridge should be, but nobody ever built one.

I've lived here over a decade. Lived through multiple floods. Never once have I driven into water without being unaware of it.

Such detailed database of fine grained road geometry gets stale very quickly, due to road maintenance and road construction. In US highway lanes are shifted sideways frequently.

That seems a very risky assumption for any car (self driving or human driver) during flash floods. "Turn around don't drown":

You think you know how deep it is under because you've taken that road many times before (or in your case you have historical laser measurement)

But you don't know:

- Maybe the road under fully collapsed

- Maybe the flow of water is extremely strong, so you need to accurately estimate that too.

You underestimate how frequently details like this change in the real world and how difficult it is to reliably integrate them into the mapping models with very low error rates.

Aggregating this data in something close to real-time, verifying and corroborating that the change to the road model is real and correct, and then pushing those model updates to every vehicle that may need it almost immediately is not really a solved problem.

That's so much extra complexity

If they have a pre-existing database of every road, sure. And if it's kept up-to-date at all times in all vehicles.

I've never heard that. I tend to buy photo-chromatic sunglasses due to them changing quickly to clear when it's cloudy/dark or in a tunnel or, more accurately in the UK, they go dark for those few minutes of sunshine we get per year.

This is how I got my shoes wet climbing around rock pools last weekend.

Right, but humans are terrible at the happy path. I’d take 20% safer on the happy path over 40% less safe in unforeseen circumstances. The failure mode being “stopped car” is also not that bad.

There must be a term for this fallacy.

“I’d rather survive 100% of the time in situations that happen 0.01% of the time than survive 99.9999@ of the time in situations that arise 99.99% of the time”

It doesn't take much of a rainstorm to see localized flooding. Some debris over the storm drain is enough to flood a street. Hard to anticipate that happening.

All that it can take is a broken fire hydrant in the wrong place.

By the time that triggers it is probably too late.

Going to move up and down with every bump and pothole

It would have to know the height of that car above ground, how high the air intake is, etc. A lifter offroader could make it through a much deeper body of water than eg. a prius.

When you're going 35 mph and suddenly hit a 2 ft deep puddle (I've done this), that sensor isn't going to help at all.

Is ultrasound less expensive than a moisture sensor?

The problem with both is they effectively require the vehicle to be in the water already. They need something that can tell depth before the vehicle has to slow down.

I've used an ultrasonic sensor to detect the water level in a tank before, I don't think it would work as you describe.

Also, the sensor didn't work in that context either as condensation kept forming on it.

[dead]

It’s definitely a thing humans do a lot in certain places. Perhaps where you live, it isn’t as much of an issue, so naturally you and nobody you know has encountered it.

I rode my motorcycle into a hole that almost swallowed the front tyre entirely in rural Australia. That hole had just been a slight depression that collected water the last time I rode through it, and there was no visual indication that it was now deeper.

Any human can't necessarily tell the difference between an inch of water, which is perfectly safe to drive on (if slow enough that you don't hydroplane), and a flooded street. They can tell the difference between an inch of water and wet pavement, though.

This is the naive "if you can't stop you're following too close" circular definition based take. Makes for good rightthink points on reddit and communities of similar quality membership but you're not actually gonna build anything useful thinking like that.

In order to drive reasonably humans need to drive through water that is 6-12in deep on occasion. That's just how it is. Near me it's whenever the storm drain at the bottom of the hill clogs.