Auto Speed Change in Autopilot

[Bodyhauler]

I have noticed that while driving in autopilot, as I come to a change in the speed limit, the car automatically changes the speed to match.
If I'm driving 70mph and the speed limit drops to 55mph, the car automatically drops to 60mph. when the speed limit goes back up to 70mph, the car goes back to original 70mph speed by itself.
The thing is, it doesn't do it all the time. I just recently noticed it doing this and think it's pretty cool. But other times I have to manually change the speed.
Is there a particular thing I need to do to make it automatically change speed limits or is it just a fluke and happens when the car wants to do it?

 

[TicoMcC]

Just a guess, but it probably has to do with the (outdated and sometimes just wrong) speed limit database that Tesla uses. Does the speed limit shown on your IC always match the speed to which Autopilot changes (or doesn't change)?

 

[Bodyhauler]

I'm not talking about the wrong/outdated/invisible speed limits.
I'm talking about actual speed limit changes, like when coming into a town and the speed limit changes.

For example: I drive down a state hwy and come to a little town on the hwy. The speed limit drops to 55, the car drops to 55. Then the speed limit drops to 45, the car drops to 45. then i get to the other side of town and the speed limit goes up to 55, the car goes up to 55. Then the speed limit goes up to 70, the car goes back up to 70.

I think it's great. But it doesn't always do this. That's why I'm wondering if there's a trick to it or what.

 

[Bmac]

But as I think as @TicoMcC said, the car is not reacting to the posted speed limits its reacting to what it is reading from the open source speed limit database. Also, you may not know this yet, but you can program your car to always drive faster than the speed limit by a set miles per hour. Mine is set 5 mph. So if I am doing 70 and the database indicates a 55 mile-per-hour zone, my car will drop down to 60 mph. Since you haven't set this variable yet, your car will drop down to the speed limit retrieved from the open source speed limit database. it's probably a coincidence that so far the open source database speed limits are matching the posted speed limits.

You do have to be careful about this, as there are some roads where the speed limit is posted at 35 miles an hour, but the open source database is indicating 55 miles per hour. The car will attempt to reach 60 mph in my case. I don't think I can blame the car when the officer catches that.

Someday, Elon promises that the Tesla will again be able to read posted speed limit signs.

 

[Bmac]

But as I think as @TicoMcC said, the car is not reacting to the posted speed limits its reacting to what it is reading from the open source speed limit database. Also, you may not know this yet, but you can program your car to always drive faster than the speed limit by a set miles per hour. Mine is set 5 mph. So if I am doing 70 and the database indicates a 55 mile-per-hour zone, my car will drop down to 60 mph. Since you haven't set this variable yet, your car will drop down to the speed limit retrieved from the open source speed limit database. it's probably a coincidence that so far the open source database speed limits are matching the posted speed limits.

You do have to be careful about this, as there are some roads where the speed limit is posted at 35 miles an hour, but the open source database is indicating 55 miles per hour. The car will attempt to reach 60 mph in my case. I don't think I can blame the car when the officer catches that.

Someday, Elon promises that the Tesla will again be able to read posted speed limit signs.

Also, you may not know this yet, but you can program your car to always drive faster than the speed limit by a set miles per hour.
Just to be clear this setting only works when the car is on autopilot. The setting has no influence on your driving speed when not using autopilot -- just the very adaptive cruise control.

 

[Bodyhauler]

I think I wasn't clear about my question. I know about the +5 mph on AP and the other things everyone's posting.
My question should be: On the same stretch of road, (ie: my example) sometimes it automatically changes speed down and then back up, but other times on the same stretch of road, it won't change automatically.
Didn't know if there was a reason for it or not. Or how to make sure it does it.

 

[Jan Fiala]

There are two levels of speed limit in Tesla. Hard and soft. Hard limits are automatically adjusting the maximum speed (+ offset). Soft limits are only displayed but not limiting the current AP speed limit. You'll get used to which is which.

Unfortunately Tesla reacts to a hard speed limit first AFTER passing the speed limit sign, rendering the AP useles on small roads trough villages. Unless you of course are ready to get speeding tickets. Such a retarded behavior...

 

[TIppy]

I have noticed that while driving in autopilot, as I come to a change in the speed limit, the car automatically changes the speed to match.
If I'm driving 70mph and the speed limit drops to 55mph, the car automatically drops to 60mph. when the speed limit goes back up to 70mph, the car goes back to original 70mph speed by itself.
The thing is, it doesn't do it all the time. I just recently noticed it doing this and think it's pretty cool. But other times I have to manually change the speed.
Is there a particular thing I need to do to make it automatically change speed limits or is it just a fluke and happens when the car wants to do it?

90 mph is the upper limit on autopilot for divided highways, but for surface streets, the limit is 5 mph above the local speed limit. This will cause the speed to adjust as the local speed limit changes when not on divided highways. This assumes autopilot is set higher than the local speed limits.

 

[tanderson92]

I have noticed that while driving in autopilot, as I come to a change in the speed limit, the car automatically changes the speed to match.
If I'm driving 70mph and the speed limit drops to 55mph, the car automatically drops to 60mph. when the speed limit goes back up to 70mph, the car goes back to original 70mph speed by itself.
The thing is, it doesn't do it all the time. I just recently noticed it doing this and think it's pretty cool. But other times I have to manually change the speed.
Is there a particular thing I need to do to make it automatically change speed limits or is it just a fluke and happens when the car wants to do it?

I'm not sure everyone's getting what you're saying, but I came here wondering the same thing. I'll reach a speed change that Tesla knows about because it's displayed right there in the car. The autopilot will sometimes slow down in reaction to that speed change; but in my limited experience more often than not it keeps driving 55mph when it knows the speed limit is actually 45mph. I thought it might take a while so I decided to let it stay at 55mph for a bit...right past a cop who luckily got one of the other drivers who decided not to slow down.

As for speeding up, I have yet to see that happen on AP. I'll reach the speed limit change (on the screen, not the outside posted signs), and the autopilot doesn't speed up. I wait as long as I can stand it and then manually dial up the speed. I didn't know about clicking the icon but will try that next time.

 

[TIppy]

I'm not sure everyone's getting what you're saying, but I came here wondering the same thing. I'll reach a speed change that Tesla knows about because it's displayed right there in the car. The autopilot will sometimes slow down in reaction to that speed change; but in my limited experience more often than not it keeps driving 55mph when it knows the speed limit is actually 45mph. I thought it might take a while so I decided to let it stay at 55mph for a bit...right past a cop who luckily got one of the other drivers who decided not to slow down.

As for speeding up, I have yet to see that happen on AP. I'll reach the speed limit change (on the screen, not the outside posted signs), and the autopilot doesn't speed up. I wait as long as I can stand it and then manually dial up the speed. I didn't know about clicking the icon but will try that next time.

On divided highways autopilot won't adjust your speed. If you are not on a divided highway, autopilot limits your speed to 5 mph above the local speed limit. If autopilot is set to 50 mph and the local speed limit drops to 40 mph, your speed will be lowered to 45 mph. If the speed limit then goes back up to 50 mph, your speed will go back up to 50 mph. However, if autopilot is set to 40 mph and the speed limit increases to 50 mph, your speed will not be increased. Any speed offset you have set will be applied but also clipped to 5 mph above the current speed limit.

 

[RGloverii]

I can explain this for AP1. Not sure if AP2 behaves the same.

If you first set a high speed limit using TACC, then immediately start Autopilot, the car will remember that high limit you had originally set. It doesn't display that limit anywhere, but it is remembered. It will then automatically adjust it's max speed up and down based on the speed limit signs during your journey, but will not go any higher than that 'max' speed you had originally set via TACC.

If you do NOT first set a high speed in TACC, then Autopilot just goes by the speed limits and the visible max speed you have set on the dash display.

Example time:

Start driving your car, with no TACC or Autopilot engaged. Start TACC, and give it a max speed of 70MPH. Then engage Autopilot. The 90MPH maximum speed is remembered, but not displayed anywhere. As you continue to drive while Autopilot is engaged, it will automatically raise and lower it's speed based on the speed limit signs, but will not exceed that 70MPH. As soon as you disengage Autopilot, it will forget the 70MPH speed, and you'll have to start over from scratch.

It took me a long time to figure this out. But now, I use this method whenever I'm using Autopilot on roads with lots of changing speed limits.

Good luck. Hope this proves to be helpful. Sure makes driving on non-highways with Autopilot a lot better for me.