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> And then another driver t-boned her because he didn’t have enough distance to stop, also cleary partially at fault IMO.

Not partially at fault; completely and totally at fault (except if we're talking about someone deliberately trying to cause a crash in which case I'll settle for partially). The reality is there could be a hundred reasons the car stopped, the driver being an idiot is only one of them. Mechanical failure, something unseen from the following car, a door flying open, someone stepping out in front of them, a queue in front of them which is not obvious from behind etc.

If you are not leaving enough room to come to a stop when the car in front does then you are riding your luck, there are no two ways about it.

It sounds like the example was not of a car they were following, but one that pulled out infront of them and stopped in their lane. Just as you are referencing possible excuses for that driver, we could come up with possible excuses for the driver that pulled out (like pulling out suddenly without enough distance to react even if the other car was going under the speed limit).

We also need to understand that being at fault isn't 1-to-1 with who was being safe. Typically, if you pull out and get t-boned by someone who has the right of way and is generally following the law, the person being t-boned is at fault for failing to yield. Where a vehicle is impacted plays a huge role in investigators determining who is at fault. Now if you run into the back of the person in front of you, it's almost always your fault, unless the person in front was driving carelessly or recklessly (brake check, for example) but would still involve partial fault in many cases.

So really, we can't say either way without knowing a lot more.

One car length is way more than 15 feet to my mind, probably 40 feet or more depending on speed. See my other comments about how nuanced this entire dialog will inevitably be. Don't you think it's more reasonable to assume we have different definitions of a car length? Perhaps I've used the term in a grossly incorrect manner. "One car length" to me equals "one unit of minimum safe distance taking into account road conditions, traffic conditions, and speed"

Not just 15 feet, that'd be insane!

I think you are confused (either that or I am!). I’m pretty sure a car length is literally the length of a car, which for a Crosstrek is around 15 feet.

Given this confusion, it does seem like it explains the root of the disagreement here, but that said, I don’t think it’s unreasonable for people reading your comment to assume that when you said “car length” you meant the length of a car.

> One car length is way more than 15 feet to my mind, probably 40 feet or more depending on speed.

A car length is, literally, the length of a car. It does not vary with speed.

Exception: https://en.wikipedia.org/wiki/Length_contraction (coming soon in a software update to a Tesla near you)

Sure, but saying this is meaningless when we're actually talking about follow distance. Cars are different lengths.

To me, a car length should simply mean the minimum safe _length_ at which to follow the car in front of you.

Exactly; car lengths vary by model, not by velocity.

I get it. You'd prefer to use the phrase "car length" to not literally mean "length of a car" in this context. Apologies if I seemed pedantic but, as evidenced by this thread, your use of car length is going against the grain.

Safe following distance is often expressed in multiples of car length. What car? Sure, good point. Pick one; it's close enough! (If you're actually thinking about following distance in any terms at all, even roughly estimated, you're ahead of the safety curve and you clearly are!)

Ideally, following distance could be accurately estimated in metres and adjusted continuously by velocity and driving conditions. AI can do that. People just kind of eye it and say, "it was raining and I followed about four car lengths behind him" or "we were inching along and I was half a car length behind him". Good enough for meat brains!

Safe driving!

This would lose all communicative benefits. Teaching a young inexperienced driver “just always keep one car length” where one = safe, is meaningless.

I don’t know you, but I believe a majority of people underestimate safe stopping distance. That’s why the webpage I posted, which is one of many similar ones, exist. That’s also in part why there are so many accidents.

People are also bad at estimating feet, so telling someone keep 80 feet is also not helpful.

But people are pretty good at estimating how many cars can fit between them and the next car.

So telling someone, hey, you are tailgating that guy and only one car could fit in front of you, but you need 10 car lengths to be safe, has a lot more communicative power.

> Teaching a young inexperienced driver “just always keep one car length” where one = safe, is meaningless.

Not if taught correctly, which I think it's important to note that we can't really do via textual communication.

In the driver's seat, during a driver's education course, you might learn that a car length is the length of an average car, but you also learn how to count the seconds of stopping distance you have in front of you. In addition, you learn that weather, traffic, and other factors can affect stopping power/distance, the point being that the whole system is incredibly dynamic and variable.

One can't reduce a dynamic traffic situation down to "X car lengths = safe." Similarly, saying "1 car length = a safe distance" doesn't really help either.

The idea is to teach people what "safety" actually looks like. How it's referred to is secondary. The proof is in how badly I was misunderstood when I said 1-2 car lengths. I _know_ I'm keeping enough distance, because I know how to judge a safe traffic situation.

I don't really care what a car length is or isn't, it's fairly irrelevant because safety is a much bigger picture than units of measurement.

You could just admit that you used the wrong term? One car length = the length of a car.

Sure, I'm fine with admitting that. It was an inevitable misunderstanding anyway because cars are different lengths so "car length" is largely meaningless.

The Subaru's adaptive cruise control system treats car lengths as variable units based on speed. It's much more liberal than I made it sound in the original comment. It sounded reasonable when I wrote it, but infinite nuance strikes again I suppose.

Have an upvote for the adaptive cruise control comment. It's this way on the Tesla, too - follow distance is described as car lengths, but it's actually speed-parameterized follow distances in reality.

Personally, I find it somewhat confusing, but people should probably be more aware that it's a thing and not necessarily someone mixing up terminology.

> One car length is way more than 15 feet to my mind, probably 40 feet or more

Cars in your area are on average 40 feet long?

A car length is about the length of an average car.

Either way, with a 40 foot "car length", 1-2 car lengths is then ~80 feet. The above stopping distance chart puts a 40mph stopping distance with reaction time at almost 140 feet. <80 feet away is driving way too close at 40mph! Especially for a car you know is doing a maneuver which could result in them braking suddenly such as turning into another field of traffic.

With the amount of semi-trucks in my area, actually yes, average length of vehicles you encounter on the road is probably close to that.

I just used the term "car length" with entirely too much room for interpretation and am now getting torn apart for it, my mistake. I swear I'm not tailgating people LOL

> I swear I'm not tailgating people LOL

If you're going 40mph and approaching nearly stopped cars at <80 feet, you're absolutely tailgating people and creating extremely risky situations.

Don't get me wrong, I've had my emergency braking trigger for similar circumstances of someone turning into a parking lot off a feeder of a highway. But I don't blame my equipment, I acknowledge I'm not a perfect driver. The car knew it could have been quite a challenge to stop in time and so it took action. The better action would have been for me to be going slower and approach that situation with less speed, not to just blame the car for being cautious and forcing realistic safety margins.

Nobody's approaching nearly stopped cars, I think you have misunderstood some other facet of my post. I sometimes approach _decelerating_ vehicles, _while I am also decelerating_

> Nobody's approaching nearly stopped cars

Yes they are, further up this comment chain is:

> for example, if they're turning and will be gone in a second anyway

That car turning is a nearly stopped car, doing a maneuver which could result in them stopping suddenly and unexpectedly. Going 40mph less than 80 feet away from that car turning is absolutely an extremely risky manuver. You don't know they're going to be gone in a second, you're assuming it, and if your assumption is wrong its a collision because you cannot possibly stop in time. Emergency braking triggering in this scenario is 100% justified.

You can turn the wheel of a vehicle without being stopped. People change lanes at speed on the highway every day. Please try to assume good faith. "Turn" does not always imply a 90 degree turn with a full stop prior. I am not approaching cars at speed while they are stopping to make a 90 degree turn...

Changing lanes is called changing lanes, not turning. They're inherently different maneuvers.

Either way, if you are rapidly closing the distance to a car which is changing lanes, you don't know for certain they won't cancel the maneuver and go back to being in the lane. You're still assuming that, and assuming you'll be able to slow or stop fast enough to handle it.

If your AEB is constantly getting "false" alarms, maybe it is not the AEB that needs adjustment. Maybe driving in a fashion where the car's AEB doesn't constantly give "false" alarms would be a lot safer.

It is by no means a constant occurrence. I've edited my original comment to disclaim this as you seem unable to assume good faith about any of this. It has happened only twice, both times with a fairly wide margin where human intervention could have occurred should it have been needed (it wasn't).

Changing lanes is a type of turn because you _turn_ the wheel to change lanes. You also might turn 45 degrees in a roundabout, or 90 degrees at a stoplight. They are all turns.

I'd agree that it's an assumption. Though your assumption that the distance is closed _rapidly_ is also just that - an assumption, and one made in bad faith despite my efforts to correct it.

The mere act of being in a car on the road involves dozens of assumptions made every single minute about the traffic conditions. Very little is known for certain, ALL maneuvers are to some extent based on assumptions.

This conversation is no longer productive, thanks for your participation anyway though.

I don't understand this - are you implying that the only way to safely drive on highways is to always maintain a follow distance equal or greater to your stopping distance?

I don't think it's reasonable to prepare for the car in front of you to stop in place as though it had hit a brick wall. Instead, the safe follow distance is derived from the current speed and breaking power of the vehicle I'm operating and the vehichle that's behind me, and the distance to the vehichle behind me.

It's effectively impossible to maintain safe stopping distances in many places. Speaking from experience in Chicago, it's just a concept that doesn't exist for many people. And if you are driving slower in order to maintain a safe stopping distance, you're creating an extra hazard on the road by maintaining a larger speed differential from the rest of traffic. Not to mention, you increase your own risk of accidents because of all the people that will aggressively cut you off.

I personally always try to maintain a safe-ish stopping distance, but I'll also ensure that I'm never in a position where I'm missing a swerve ready escape route.

Little known fact: You can travel the exact speed of the car in front of you while also being any distance N behind them. If I'm traveling greater than 50MPH, I leave at least 3 car lengths between me and them, this is to allow for reaction time to stop at the same rate they are stopping.

In California that just means that in the span of 15 seconds 3 other cars are going to move in front of you and the car that was ahead of you.

Why does that matter at all? Just slow down to get more space whenever that happens.

In my experience they will aggressively cut you off anyway, so you might as well give yourself some breathing room.