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sleepydoc

Well-Known Member
Aug 2, 2020
5,498
9,611
Minneapolis
The speed limit on a road I take to work drops from 50 MPH down to 35 as it enters a residential area. When the car passes the 35 MPH sign, the speed limit on the screen drops, but the car takes about a quarter mile to actually slow down. It almost feels like the computer puts the car in neutral and lets it coast until the speed drops and it's definitely not using regenerative braking at all and If I disengage AP/FSD the car readily slows down.

Has anyone else experienced this? FSD already does a poor job anticipating speed limit changes, not responding until you actually pass the sign but this actually worse. My concern is it's not uncommon for cops to lurk in the area so I could justifiably get a ticket if I let FSD do it's thing.
 
I've experienced it. Sometimes it's good in that it's not a problem to slow down gracefully - especially if someone is riding the car's a__ too closely, I'd rather not be driven into. Sometimes the beta picks a good speed limit to change to. Sometimes, not so much. It's beta, you have to watch it like a hawk.

My experience w/ speed changes is unless it's in some tiny town, or an active school zone, folks are generally ok to let things glide.But maybe I'm just lucky.

I mean after all, when someone is in front of you and they slam on their brakes hard because they realized they had drifted 5 MPH over the speed limit - most people don't care for this happening in front of them so abruptly.
 
I prefer this from a comfort perspective. Aside from anticipating the speed change, this is how most people drive. In my experience, it doesn't take a quarter mile. more like 1/8 mile, and that's acceptable to me.
I strongly agree with this. I hate how forceful AP is with speeding up/slowing down on the highway and much prefer the gradual FSD behavior here. It does sometimes take a little longer than I'd prefer but I never felt it was too unreasonably long.
 
The main problem is it doesn't read the signs far enough ahead and start slowing before the sign as we humans do. This does leave you speeding since the sign is a hard marker for the limit.

My biggest slowdown complaint is the thumb wheel. You can spin it down and it continues and takes "forever" too slow. All the while I'm coaching it politely by saying: SLOW the F$$$ down you dumb a$$.
 
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The main problem is it doesn't read the signs far enough ahead and start slowing before the sign as we humans do. This does leave you speeding since the sign is a hard marker for the limit.

My biggest slowdown complaint is the thumb wheel. You can spin it down and it continues and takes "forever" too slow. All the while I'm coaching it politely by saying: SLOW the F$$$ down you dumb a$$.
I strongly agree with this. I hate how forceful AP is with speeding up/slowing down on the highway and much prefer the gradual FSD behavior here. It does sometimes take a little longer than I'd prefer but I never felt it was too unreasonably long.

I think this started a few releases back.

May be a change to reduce "phantom braking" ? Sudden slowdowns because of speed limit issues can result in "phantom braking".
 
I think this started a few releases back.

May be a change to reduce "phantom braking" ? Sudden slowdowns because of speed limit issues can result in "phantom braking".
Let me add to what I stated. It starts slowing too late. We humans see the speed limit sign and modulate the accelerator so we smoothly slow before or as we enter the new speed zone. I hate to say but I think the main problem is the cameras don't have enough resolution to identify/read the speed on the signs until it is too close to slow down like a human would before entering the new speed zone.
 
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Let me add to what I stated. It starts slowing too late. We humans see the speed limit sign and modulate the accelerator so we smoothly slow before or as we enter the new speed zone. I hate to say but I think the main problem is the cameras don't have enough resolution to identify/read the speed on the signs until it is too close to slow down like a human would before entering the new speed zone.
They can also use the map. I don't think they use the map to anticipate what is coming up in terms of speed changes ...
 
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Let me add to what I stated. It starts slowing too late. We humans see the speed limit sign and modulate the accelerator so we smoothly slow before or as we enter the new speed zone. I hate to say but I think the main problem is the cameras don't have enough resolution to identify/read the speed on the signs until it is too close to slow down like a human would before entering the new speed zone.

From what I can tell, the speed limit shown on the visualization only changes after you pass the sign, usually the instant the sign goes by. To me, this is a programmed threshold; I think vision identifies the new speed well before passing the sign. I'll email them and suggest the speed change (gently) before passing the sign.
 
I've said it before, and I'll say it again.

The car needs to use maps for the speed limit setting.

Humans know what the new speed limit is before we even reach the sign so we've already adjusted our speed down to it before we reach it. Unless we're total morons, and in that case a cop is hidden somewhere just past the speed limit sign to nab us.
 
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From what I can tell, the speed limit shown on the visualization only changes after you pass the sign, usually the instant the sign goes by. To me, this is a programmed threshold; I think vision identifies the new speed well before passing the sign. I'll email them and suggest the speed change (gently) before passing the sign.

I agree with the need for this, but emailing them is an exercise in futility.

Still worth doing.

But, futile.
 
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I've said it before, and I'll say it again.

The car needs to use maps for the speed limit setting.

Humans know what the new speed limit is before we even reach the sign so we've already adjusted our speed down to it before we reach it. Unless we're total morons, and in that case a cop is hidden somewhere just past the speed limit sign to nab us.

Actually for me, due to FSD beta changing set speeds, it's made me way more aware of speed limit changes on the streets I drive every day. I guess no one really follows them. It's very common here to be going 50+ on a 35 road. Unfortunately, when the car tries to slow from 50+ to 35, I have to intervene or incur the wrath of the impending tailgater. I test FSD beta with speed offset at +5mph to try not to annoy people too much.
 
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I've said it before, and I'll say it again.

The car needs to use maps for the speed limit setting.

Humans know what the new speed limit is before we even reach the sign so we've already adjusted our speed down to it before we reach it. Unless we're total morons, and in that case a cop is hidden somewhere just past the speed limit sign to nab us.

They can also use the map. I don't think they use the map to anticipate what is coming up in terms of speed changes ...
I can virtually guarantee that they do use map data. There's a road on the way to our cabin that slows down to 35 as you drive through town, then goes up to 55 again. My car dutifully recognizes and slows down, then speeds up. Except about 2-300 feet after the 55 MPH sign it suddenly drops down to 35 again (the speed limit on the display also drops to 35. The same thing occurs when approaching from the other direction, despite there being no signs (there are actually no signs at all after the 55 MPH, so it's not a case of it reading incorrectly.)

I'd also point out how the car knows the speed limit as soon as you turn on to a road, long before it sees a sign. The only way to do this would be via a map database.
From what I can tell, the speed limit shown on the visualization only changes after you pass the sign, usually the instant the sign goes by. To me, this is a programmed threshold; I think vision identifies the new speed well before passing the sign. I'll email them and suggest the speed change (gently) before passing the sign.
I've had the car adjust the speed limit even when it's obscured at the moment I pass it so it's either via GPS or by recognizing the sign at a distance.

I've also had the car incorrectly interpret other signs as speed limit signs (e.g. the county and state road signs in some areas are of a similar design so the car thinks County Rd 35 is actually a 35 MPH sign)
 
I prefer this from a comfort perspective. Aside from anticipating the speed change, this is how most people drive. In my experience, it doesn't take a quarter mile. more like 1/8 mile, and that's acceptable to me.
I'm ok with it slowing down gracefully and not just slamming on the brakes, but a quarter mile is excessive, IMO. Typically in an ICE car you'll let your foot off the accelerator and the car will gently slow down due to engine compression but this is significantly slower than that, to the point that it feels like the car is actually intentionally slowing the deceleration. (it's odd that it has no problem aggressively dropping the speed on the interstate when using TACC but when it actually needs to drop the speed it takes its own sweet time!)
 
I can virtually guarantee that they do use map data. There's a road on the way to our cabin that slows down to 35 as you drive through town, then goes up to 55 again. My car dutifully recognizes and slows down, then speeds up.
I get the impression that the car has some default speeds for various types of roads that it uses in the absence of detecting a speed limit sign. I've had FSD slow way down after turning off a highway onto a residential or county road when there was no speed limit sign in sight, often at speeds much lower than the eventual posted speed limit.
 
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I can virtually guarantee that they do use map data. There's a road on the way to our cabin that slows down to 35 as you drive through town, then goes up to 55 again. My car dutifully recognizes and slows down, then speeds up. Except about 2-300 feet after the 55 MPH sign it suddenly drops down to 35 again (the speed limit on the display also drops to 35. The same thing occurs when approaching from the other direction, despite there being no signs (there are actually no signs at all after the 55 MPH, so it's not a case of it reading incorrectly.)

I'd also point out how the car knows the speed limit as soon as you turn on to a road, long before it sees a sign. The only way to do this would be via a map database.

I've had the car adjust the speed limit even when it's obscured at the moment I pass it so it's either via GPS or by recognizing the sign at a distance.

I've also had the car incorrectly interpret other signs as speed limit signs (e.g. the county and state road signs in some areas are of a similar design so the car thinks County Rd 35 is actually a 35 MPH sign)

I agree that they do use map data in addition to vision, but they don't do it all that well. It's not consistent.

For example on my way to work there is a section that goes from a 25mph limit to a 30mph limit, but the car is unaware of this. Yet, when I travel on that exact road the other direction on my way home it reads the 30mph limit and adjust the speed accordingly. The speed limit sign is only on one direction.

What I'd like is a consistent maps based speed setting that either occurs before or after its in the new speed limit area depending on whether the speed limit increases or decreases.

Speed signs should only be used to flag the section for review or as a temporary speed limit (construction for example).
 
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Ofcourse they do. But, they don’t anticipate and prepare by slowing down.
no. FSD isn't good at anticipating. It doesn't anticipate speed limit changes and it also doesn't anticipate stops/red lights. Even if the light is red (or there's a line of cars) it will keep accelerating up to the set speed until the time that it needs to start braking rather than maintaining a more moderate speed so it needs to brake less.
 
Just to test I used TACC rather than FSD this morning and the car slowed down over about 400 feet, roughly ¼ the distance it used during FSD. The deceleration was what I would consider appropriate - just enough that you could feel it but not aggressive and certainly less than what full regenerative braking gives.

This appears to be a quirk with FSD. I'll try to find some other areas to test it; most places the limit only changes by 5 MPH or so so it's not a common situation.
 
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