Dude if you are going 85-90 miles an hour and you aren't leaving AT LEAST 2 cars in between you, please stay off the road. You should be keeping 3 seconds of distance between you and the car in front of you. At 90 miles per hour that's a hell of a lot more than 2 car lengths.

It's possible they didn't mean at the same time. Minimum 1 in all situations, including going 5mph in traffic, where 2 might be a bit conservative.

Yeah: driving with a 2-car gap in stop-and-go traffic is NOT normal.

op is posting about the people who cut him off. If I use adaptive cruise control at 2 or 3 (stopping distance) car lengths, then I'm just cut off every time, even though there is nowhere to go.

The end to this unsafe and traffic causing behavior is something I look forward to in more self driving cars. (Fewer drivers racing dangerously for "pride" points to end up at the same traffic light in 500')

> op is posting about the people who cut him off. If I use adaptive cruise control at 2 or 3 (stopping distance) car lengths, then I'm just cut off every time, even though there is nowhere to go.

Then your entire state, or at least, the residents of it that drive on the freeway need be in prison. Or, at least, to have their licenses revoked.

Agreed. "Parity" doesn't mean in all cases, it means in the majority of cases and this seems like a edge case (where 2 car lengths isn't good enough).

Just to clarify, when it says "1 car length", the car adjusts the amount of space depending on speed. So its not literally just one car length.

> because the gap is so large

I drive with a six car gap and even that was a close-call when someone had a contact about 3 cars ahead.

The good part is that if the car in front of you flashes the brake lights, that seems to trigger the braking. And some of the newer cars blink hazards automatically when braking hard.

My Subaru is also vision only (Eyesight), which also has the cameras too close together (in my opinion) to detect a car ahead braking, but it did not slow down quickly when facing a stationary car facing the wrong way around (my feet went down before the car did anything).

All of these need more parallax, at least better than a human to do this well. But they do react to visual cues like brake lights and hazards. Though sometimes, it sees a motorcycle nearby as a car in the distance simply due to the lack of parallax.

"more sensors good" is not always a good thing, when the sensors disagree with each other. Sometimes more sensors just mean more corner cases and braking at bridges throwing shadows on the road.

So just removing something feels wrong, when I don't see them improving the thing they're putting more eggs into.

I think this is where Tesla is not credible right now, when they say they're improving something in the car, but it is a thing I cannot see, check, confirm or test.

> "more sensors good" is not always a good thing, when the sensors disagree with each other.

When they disagree, one of them is wrong. Would you rather have just the wrong sensor or both the wrong one and the good one as inputs to decide what to do?

What's the point of using car lengths as a metric of follow distance.

Because humans are not good at eye-balling distance, especially while moving. The only other point of reference is going to be the only other thing travelling on the roads at a similar speed... cars. Hence, the rough comparison of "car-lengths".

I use the 3 second rule...

It isn't really car-length, is it speed-adjusted to scale larger at high speeds and closer at low speeds.

But the display on the screen shows a car with a line and the numbers 1-7 as you adjust it so people shorthand refer to it as "car-lengths"

> Vision-only vehicles are still limited to a max of 85mph and 2 car minimum following distance for autosteer while radar is 90mph and 1 car following distance.

Is that common knowledge, what's the source of that I'm curious.

I can confirm first hand, owning a legacy 2018 Model S with front facing radar and a Vision 2021 Model Y.

Aha so we’re talking about a Tesla design spec constraint not some fundamental safety thing or computational limit or some other physical barrier or whatever. Interesting.

Just from a physics stand-point, you can't bring your car to a safe stop (or any kind really) in two car-lengths at 85mph. If you take the most generous scenario possible, that the car in-front of you will continue for another two car-lengths (but at a slower speed than you), it's still pretty much impossible to bring your car to a complete stop in four car-lengths.

I thought I remembered being taught in driver's ed that you should leave a 1 car gap for every 10mph of speed. 1-2 cars at 85mph is clearly not enough distance to stop.

That is similar to what car length adaptive cruise control does. In heavy, fast traffic, you won’t get your 7-9 car length though, due to frequent cutting in and weaving around you.

> The two car following distance constantly leads to cars cutting in-between you and the car in front of you because the gap is so large.

stop caring about this.

its like a neon sign saying that you're an unsafe driver.