The long road to autonomous vehicle safety

[mostlylong]

@captainccs

the “Six 9s is a fair ballpark” is a quote by you, not some independent party.

Where did you get it?

Al provided a very nice synopsis:

@albaby1

A human driver in the United States will typically go more than 100,000 miles, but less than 1,000,000 miles, between collisions. So a rough and ready estimate of how safe an AI driver is to be safer than a human is that it has to go 1,000,000 miles between crashes.

I’ll add a little more detail.

First I’ll note that the Tesla CEO’s comment from the Q2 2026 earnings call

1. mentioned a safety target of eight 9s, so even safer than six 9s
2. stated that reaching sufficient safety is the only thing keeping their robotaxi fleet from growing

It’s really just about going through what we call the march of nines of reliability, where you need, how many nines of reliability do you need to scale? Ideally, you want 99.999999% reliable. It’s just the march of nines of reliability is, I think, the only thing really constraining our growth in Robotaxi.

As far as sources for accident rates in the US,

First, the Waymo Safety Report provided upthread has a ton of relevant info and references with many details, including many technical research studies:

@mostlylong

per year.
waymo safety report

Second, Al upthread showed a chart of miles per accident:

@albaby1

below chart takes the number of police-reported crashes each year and the total number of VMT (vehicle miles travelled) each year, and calculates the number of miles between such crashes

Third, NHTSA compiles this kind of data:
NHTSA Motor Vehicle Traffic Crashes

For example, look at Tables 1 (VMT) and 2 (Total Crashes) for year 2024.

1. Total Crashes = 6,180,241
2. Vehicle Miles Traveled (VMT, millions) = 3,294,031
3. Crashes per Million Miles = 6,180,241/3,294,03 1= 1.88 = 1.88 crashes per 10^6 miles

The six 9s comes from the exponent 6 for 1 million in 10^6.

Of course, the 1.88 rate above is an overall average over a very wide variety of driving scenarios.

As already mentioned upthread:

@mostlylong

The accident rate depends on the driving scenario: interstate, city, specific routes, time of day, driver demographics, vehicle type and age, etc.

When Waymo tries to benchmark the safety of their AV, they attempt to statistically control for these variables in their specific markets (Phoenix, Bay Area, Austin, etc).

Everything stated by me and Al above about the 9s of vehicle safety is 100% consistent with what the Tesla CEO stated on the last earnings call.