Why No Automatic Speed Adjust When Enter New Speed Limit Zone?

[PianoAl]

I'm surprised that when I'm on autopilot and my car detects that it's entered a zone with a lower speed limit, it doesn't slow down.

For example, I've set my speed limit offset to 2 MPH (e.g. "drive 57 MPH in a 55 MPH zone). I'd expect that when I go from a 65 MPH zone to a 55 MPH zone, it would slow down to 57 MPH. It doesn't (I have to tap the display). Depending on the road, it will change to 60 MPH (limited to 5 MPH over the limit).

Why is that? It can stop at traffic signals or stop signs, why can't it slow down (or speed up in the reverse situation)?

 

[XLR82XS]

Have you tried with limit function disabled? My cars don't do that. I set it at 75mph freeway and it stays it at 75.
.

 

[israndy]

I have the same issue as the OP, but I have failed to complain about it in a dedicated post. Now that 2020.36 is starting to ship I hope I won't have to think about it again. With HW3 it should recognize the speed limit signs and actually change speed at that point, not a mile earlier or later and not completely ignore the speed change and force me to tap the sign on the display to get it to recognize that the limit has changed.

But if I was to complain I would ask "How can you tell if the car is responding to speed limit signs or is tracking a fixed speed?"

When you first turn on cruise control the manual states that if you are going OVER the speed limit + your offset in settings it will track that fixed speed, but if you are going UNDER that speed the car will accelerate to track that speed (limit+offset) instead, so as you move from zone to zone the car will change speed reflecting the current limit.

But I often will enter a different zone and have to press the on-screen sign (indicating I want it to track my offset) only to have to do that again at the entry into the next zone. But then the very next zone it tracks on its own... There should be an indicator that it is tracking the speed limit, like backlighting the on-screen sign or somesuch.

 

[PianoAl]

Have you tried with limit function disabled? My cars don't do that..

I'm not sure what you mean. Here are my settings:

 

[PianoAl]

With HW3 it should recognize the speed limit signs

I've confirmed that it now does that, the speed limit displayed on the changing the instant I pass the sign. A great improvement. It failed once, but a truck may have been obscuring the sign.

But then the very next zone it tracks on its own...

Interesting.

There should be an indicator that it is tracking the speed limit

Well, if it always tracks, you wouldn't need that.

I'm guessing this is a safety thing, the engineers deciding that it's too dangerous for the car to slow down. But it slows down for other reasons.

 

[PianoAl]

My cars don't do that. I set it at 75mph freeway and it stays it at 75.

But do they slow when you come to a lower speed limit?

 

[XLR82XS]

Sorry, I meant absolute setting. Relative was causing speed decrease issues for me.
They do not slow at a lower speed limit.

 

[PianoAl]

But I often will enter a different zone and have to press the on-screen sign (indicating I want it to track my offset) only to have to do that again at the entry into the next zone. But then the very next zone it tracks on its own...

I tried this yesterday. Completely on autopilot, I drove through five successive changes in speed limit (55, 45, 35, 45, 55, 65). On each, I tapped the speed limit sign on the display and it changed to the new speed limit. It never tracked on its own. It did limit the speed to 5 MPH over the limit, but it never went to my desired 2 MPH over the speed limit.

 

[smatthew]

That's the way it works. It drops the speed because AutoPilot is limited to speed + 5 on non-divided roads.
You'll notice that on the freeway if the speed limit drops the car does not slow at all. Because the only limit on the freeway for AutoPilot is 90mph.

 

[PianoAl]

That's the way it works. It drops the speed because AutoPilot is limited to speed + 5 on non-divided roads.
You'll notice that on the freeway if the speed limit drops the car does not slow at all. Because the only limit on the freeway for AutoPilot is 90mph.

But why do you think it doesn't drop to my desired speed (limit + 2 MPH)?

 

[smatthew]

Because that's not the way the car is programmed. It's programmed to stay within AutoPilot limits. Could it be changed to take into account your setting? Of course. But that's not the way it is currently programmed.

 

[PianoAl]

Because that's not the way the car is programmed. It's programmed to stay within AutoPilot limits. Could it be changed to take into account your setting? Of course. But that's not the way it is currently programmed.

Gotcha. My question: Why would they not program it that way? What's the thinking? Safety?

 

[israndy]

I have seen it track the speed limit the majority of the time. But I have also seen it not. Am I just confused?

If I press the speed sign button when it says 65 the car tracks that speed limit. Is your assertion @smatthew that it only jumps to that set speed and will not track the freeway speed limit? Say if it goes up to 75 or down to 55? I could swear it does, but the speed limit changes pretty rarely so hard to be positive.

 

[smatthew]

On a divided freeway, there is no tracking of freeway speed limit. The only limit is 90mph.

Wait - there's an exception. Interchanges. After going on a ramp the car re-sets to speed limit + offset.

Maybe they need to add that as a setting. "Maintain speed offset when speed limit changes"

What I have seen is roads where in between towns it becomes a divided highway, and you can set any speed. But closer to town it transitions to undivided road, and the car starts obeying the speed limit + 5 rule. Which I like. I don't want to give small town cops any of my time or money.

And of course, this is based on what I've experienced. If you've experienced something different please let us know!

 

[israndy]

Yeah, OK, been tracking the new software and it looks like maybe you are right. Not sure how I never noticed this before. The new software will MOSTLY see a sign as I drive down a highway and show me passing it, and if the sign represents a change in speed limit the Speed Limit sign on the display will update to that new speed and I will have to touch that sign to make that into the new Set Speed.

I could have SWORN that it tracked the speed about half the time or better, but you may be right. I am noticing that every time the car changes speed in reaction to passing a sign it's always accompanied by a message onscreen saying AutoSteer Speed Limited and then it puts the set speed to the +5 you were talking about.

I have tried to take some movies, but there are just not enough locations where the speed changes as I am driving down the highway and I know in advance it's gonna happen. I need one of those GoPros or an Insta360

 

[PianoAl]

I could have SWORN that it tracked the speed about half the time or better, but you may be right.

This may be the answer:

On a route I drive often, the speed limit goes from 55 to 45 to 35 to 45 then back to 55 as I drive through a small town (no stoplights). The car has never changed its speed by itself except to slow down to 5 MPH over the new limit.

Until yesterday:

When the speed changed from 35 to 45, the car sped up by itself! My jaw dropped.

It didn't change speed for the return to 55 MPH.

This could explain why we see different things. Either the behavior isn't consistent, it's changing with new releases, or there's some variable we're not aware of.

 

[israndy]

I would love to work at Tesla and my job is to talk to the engineers and get people the answers to questions like these.

Although, I have worked at Apple with that mission and found that people are the problem, not the tech. People have the stupidest questions, so perhaps I am being like people right now with my "Does the car track the speed limit" curiosity.

 

[PianoAl]

When the speed changed from 35 to 45, the car sped up by itself!

I've cracked the code.

The speed limit goes from 55 to 45 to 35 to 45 to 55, and I'm on autopilot.

If I don't adjust the speed with the wheel or touch the speed limit sign on the display, the car will change speed up and down by itself.

Specifically, let's say I'm driving 57 MPH.

When I hit the 45 MPH sign, the car slows to 50 MPH.
When I hit the 35 MPH sign, the car slows to 40 MPH.
When I hit the 45 MPH sign, the car speeds up to 50 MPH.
When I hit the 55 MPH sign, the car speeds up (I forget if it goes to 60 or 57 MPH).

Bottom line, if you want the car to change speed, don't adjust the speed. I doesn't matter if you press the accelerator.

 

[israndy]

That does not entirely work.

That only works if you are on a speed limited highway that will not let you go faster than 5 miles an hour over the speed limit. If you are on an unlimited highway and the speed limit changes your speed will not change.

I got psyched out the same way you did seeing the speed change as I have passed thru speed zones I was convinced that the Tesla was smart about seeing new speed limits and was reacting to them but it only reacts to limited speeds and only goes back up if you previously were set to a higher speed. Sorry.

I wish Tesla would implement this.

 

[PianoAl]

That only works if you are on a speed limited highway that will not let you go faster than 5 miles an hour over the speed limit. I

Yes, true.