# AP max speed limit



## shareef777 (Mar 10, 2019)

I'm trying to understand what the logic is behind the max speed allowed when AP is engaged. For example, I can be driving down a local highway with a speed limit of 55mph. AP won't allow any speed above 60mph from being set. Similarly, I've driving down local highways with speed limits of 45mph and it'd let me set it up as high as I want. What's the logic in where/what is allowed with auto pilot?


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## GDN (Oct 30, 2017)

You are likely experiencing this on 2 lane or limited roads. City streets and 2 lane or "Non-interstate" is the best way I can likely describe it is that you'll only get speed limit or 5 MPH over speed limits EAP. On the Interstate/4 lane divided highways you can go over all you want up to 90 MPH and the 90 MPH had some information last week that started to debunk that limit.


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## shareef777 (Mar 10, 2019)

GDN said:


> You are likely experiencing this on 2 lane or limited roads. City streets and 2 lane or "Non-interstate" is the best way I can likely describe it is that you'll only get speed limit or 5 MPH over speed limits EAP. On the Interstate/4 lane divided highways you can go over all you want up to 90 MPH and the 90 MPH had some information last week that started to debunk that limit.


That's a great description. I know I've been able to go 10 over the limit on interstate highways, but I meant that I've also been able to do that on non-interstate highways as well. Curious if these (what I assume to be local) non-interstate highways actually go on and extend into other states so AP allows higher speeds.


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## Bokonon (Apr 13, 2017)

shareef777 said:


> I'm trying to understand what the logic is behind the max speed allowed when AP is engaged. For example, I can be driving down a local highway with a speed limit of 55mph. AP won't allow any speed above 60mph from being set. Similarly, I've driving down local highways with speed limits of 45mph and it'd let me set it up as high as I want. What's the logic in where/what is allowed with auto pilot?


Is the second local highway you mentioned (where you don't have the +5 mph Autosteer speed limit) physically divided by a median or barrier of some sort? In my experience, that has been the determining factor for whether the Autosteer speed limit applies to a given highway.

My sense is that each road in the map data is flagged in some fashion (whether "divided" or something more specific like "Autosteer speed-limited"), and that flag determines whether or not the limit is imposed. Changes to the map data could theoretically remove (or add) this behavior on any given road.


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## NOGA$4ME (Sep 30, 2016)

I would say the term you are looking for is "limited access" roads, not just whether there is a median or barrier. A limited access road is one with on- and off-ramps, whereas some roads have at-grade intersections which would disqualify them from the higher speed limit.

Having said that, here are two counter-examples in my area:










This road (circled in blue) is a limited access highway, but it just has a regular street name. AP will only allow speeds 5mph over the posted limit on this road.

Meanwhile, this road:










is an at-grade intersection road with a 55mph, but AP seems to gladly let me set it to 62mph (although I may have to double check this--I don't normally use AP on this road).

I think one difference is that in the former case, the highway as a regular "street name", whereas in the latter, this is a US highway (US-70).

We should also talk about interchanges and off-ramps as well. Zooming in a little more on that first picture:










I've drawn lines on a particular ramp, which I will call an interchange (because it's from one limited access highway (I-540) to another limited access highway (Aviation Parkway). A computerized nav system, however, might see it as an off-ramp because it's going from a numbered highway to a non-numbered road. The speed limit on I-540 is 70mph, while the limit on Aviation Parkway is 60mph. There is a yellow 45mph speed warning sign about halfway through the curve, but no actual speed limit sign until you are well onto Aviation Parkway. The car can actually take that ramp at 70mph no problem, but most cars take it from 60-65mph.

The behavior of autpilot's speed is as follows:

On I-540, you can have the speed set up to whatever the highway AP limit is. The limit on this highway is 70mph. For the beginning of the blue section, it slows down to 70mph, and then to 65mph. At the red section is slows down to 45mph. I don't think this is because it thinks it needs to slow down because of the curve or visibility--when it does this it usually just slows down and the set speed remains the same. So either the 45mph speed recommendation is annotated in the map, or it somehow considers this an actual off-ramp and a 45mph limit for off-ramps is programmed in. Then in the black section you can set the speed to 65mph (5 over the 60mph limit on Aviation Parkway). This must be the point that it considers itself "on" Aviation Parkway, even though it technically isn't yet.

It is an interesting subject for discussion and theories!


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## turnem (Apr 26, 2019)

I really wish they'd open up the Autosteer speed limit on surface streets to +8 or something in that range. Sometimes +5 is just ridiculous. I get it though... I understand why they are doing what they are doing but another 3mph would make a big difference.


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## Long Ranger (Jun 1, 2018)

I think @Bokonon pretty much covered it, but the manual specifically says that 1) the highway needs to be divided, and 2) it needs to have limited access (on/off ramps) or else the +5 mph limit applies. I drive a divided highway with side street access and the +5 mph limit applies there. The divider alone doesn't seem to be sufficient. And of course there may also be places where the map data isn't accurate.

The manual text:
Restricted Speed
Autosteer is intended for use only by a fully attentive driver on freeways and highways where access is limited by entry and exit ramps. If you choose to use Autosteer on residential roads, a road without a center divider, or a road where access is not limited, Autosteer may limit the maximum allowed cruising speed. The maximum allowed cruising speed on such roads is calculated based on the detected speed limit including a Speed Assist offset of up to +5 mph (10 km/h).


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## Bokonon (Apr 13, 2017)

Long Ranger said:


> I think @Bokonon pretty much covered it, but the manual specifically says that 1) the highway needs to be divided, and 2) it needs to have limited access (on/off ramps) or else the +5 mph limit applies. I drive a divided highway with side street access and the +5 mph limit applies there. The divider alone doesn't seem to be sufficient. And of course there may also be places where the map data isn't accurate.


Thanks for looking up the proper manual citation. 

I was about to use the term "limited access" or "controlled access" highway in my post above, but immediately thought of a few counter-examples around here that are similar to @NOGA$4ME's stretch of US-70 described above. This includes a divided state highway that I follow for the bulk of my regular commute (MA Route 9) where Autosteer speed is not limited, yet there are numerous at-grade intersections, including several unsignaled, perpendicular intersections with narrow, residential streets.  (Yeah, it's always fun when someone abruptly slows down from 60 mph to make one of those turns... without signaling, of course...)

And this reality speaks to your other point: the map data isn't always accurate, whether by accident or by design. Perhaps sometimes a human makes a judgment call and manually flags a non-limited-access road as limited-access, because it's "limited-access enough" to allow Autosteer to operate without speed limits. So, net-net: the only way to know for sure whether Autosteer speed is limited on a given road is to actually drive it.


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## Frully (Aug 30, 2018)

I really really wish that they would change +5 (or +10km in my case) would apply as a percentage. I routinely want to go 10% over, to prevent people constantly overtaking and subsequently ruining my windshield. I pass practically no-one at that speed... It's just the going average.


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## Kizzy (Jul 25, 2016)

For roads with no speed limit data, I’ve seen a max of 45mph available with Autopilot. This is inconvenient when the actual speed limit is 50mph.


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## MarkB (Mar 19, 2017)

turnem said:


> I really wish they'd open up the Autosteer speed limit on surface streets to +8 or something in that range. Sometimes +5 is just ridiculous. I get it though... I understand why they are doing what they are doing but another 3mph would make a big difference.


When FSD occurs, I'd expect to to not allow anything over the speed limit.

I'd expect it to follow all the rules of the road, not just certain ones.


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## Klaus-rf (Mar 6, 2019)

MarkB said:


> When FSD occurs, I'd expect to to not allow anything over the speed limit.
> 
> I'd expect it to follow all the rules of the road, not just certain ones.


 In most places I have driven during my 45+ years of driving, this would make FSD the most dangerous vehicle on the roadways.

Driving at or under the speed limit around here (especially on freeways) gets you passed and cut off by inches and brake-checked constantly. Definitely NOT safe.


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## NOGA$4ME (Sep 30, 2016)

MarkB said:


> When FSD occurs, I'd expect to to not allow anything over the speed limit.
> 
> I'd expect it to follow all the rules of the road, not just certain ones.


I agree. In an FSD world, I would expect Tesla to become liable for driving the car. It will likely follow the law to the letter. Which could be quite annoying!


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## Klaus-rf (Mar 6, 2019)

All the current laws say the vehicle *owner* is financially responsible for all driving incidents / accidents / collisions / etc. while the driver is responsible for any / all moving violations.

How are police going to cite Tesla?? Especially if the car is occupied? Those laws don't exist yet and will take many years to get sorted.


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## MarkB (Mar 19, 2017)

Klaus-rf said:


> All the current laws say the vehicle *owner* is financially responsible for all driving incidents / accidents / collisions / etc. while the driver is responsible for any / all moving violations.
> 
> How are police going to cite Tesla?? Especially if the car is occupied? Those laws don't exist yet and will take many years to get sorted.


I'm talking FSD. -- the robotaxi fleet, where there is no "driver". The only choice is to follow the laws, including speed limits.


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## MarkB (Mar 19, 2017)

Klaus-rf said:


> In most places I have driven during my 45+ years of driving, this would make FSD the most dangerous vehicle on the roadways.
> 
> Driving at or under the speed limit around here (especially on freeways) gets you passed and cut off by inches and brake-checked constantly. Definitely NOT safe.


I tend to drive speed limit plus 8 kph. Sometimes that's not as fast as traffic and I might adjust upward a bit to keep up with traffic, but it depends on how much over the limit that might be. I don't tend to keep up with traffic "just because".

Some parts of the world the limit is an actual limit.

L5 autonomy might require actual limits.


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## undergrove (Jan 17, 2018)

Klaus-rf said:


> In most places I have driven during my 45+ years of driving, this would make FSD the most dangerous vehicle on the roadways.
> 
> Driving at or under the speed limit around here (especially on freeways) gets you passed and cut off by inches and brake-checked constantly. Definitely NOT safe.


I have spent virtually my whole life driving in SoCal (60+ yrs). I usually drive at or under the speed limit when I can do so without unnecessarily disrupting traffic flow--which is most of the time. i avoid leftmost lanes and HOV lanes except in heaviest traffic. Following these principles, I rarely get aggressively passed or cut off.

I do this for overall safety, but mostly to conserve energy (The national 55 mph speed limit in the late 70's was intended to conserve energy, but it also drastically reduced highway fatalities). This has always been a concern in my selection of cars and driving style, but in the 21st century I think energy conservation is a duty of citizenship. It is the easiest and most readily available way to reduce carbon pollution, which I think is one of the main reasons most of us choose to drive EVs.

It does take me a little longer to get where I am going, and I have to plan accordingly, but in reality it is a very small percentage of the total travel time, and I enjoy the reduction in trip anxiety. I realize that many people may not feel that they have the luxury of even that little bit of time, but as the climate crisis intensifies, as it inevitably will, we are all going to have to make major adjustments in our way of living. Driving speed will be minor by comparison. Kudos to all you EV drivers for being in the vanguard.

I will now get off my soap box to make room for anyone who might like to flame me. Please don't use carbon based fuels to do so (Contradiction? - Perhaps you could use an arc welder ; )


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## MarkB (Mar 19, 2017)

undergrove said:


> I have spent virtually my whole life driving in SoCal (60+ yrs). I usually drive at or under the speed limit when I can do so without unnecessarily disrupting traffic flow--which is most of the time.





undergrove said:


> I do this for overall safety, but mostly to conserve energy (The national 55 mph speed limit in the late 70's was intended to conserve energy, but it also drastically reduced highway fatalities).


Agreed.

Going with "the flow" isn't always safer, if that flow is going to fast.

In BC, we had some highway speed limits increase by 10 k/h in 2014.

Some of those increase resulted in significant increase in crashes and fatalities.

Many info those speed limits have been rolled back.

https://www.cbc.ca/amp/1.4893914


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## turnem (Apr 26, 2019)

undergrove said:


> I have spent virtually my whole life driving in SoCal (60+ yrs). I usually drive at or under the speed limit when I can do so without unnecessarily disrupting traffic flow--which is most of the time. i avoid leftmost lanes and HOV lanes except in heaviest traffic. Following these principles, I rarely get aggressively passed or cut off.
> 
> I do this for overall safety, but mostly to conserve energy (The national 55 mph speed limit in the late 70's was intended to conserve energy, but it also drastically reduced highway fatalities). This has always been a concern in my selection of cars and driving style, but in the 21st century I think energy conservation is a duty of citizenship. It is the easiest and most readily available way to reduce carbon pollution, which I think is one of the main reasons most of us choose to drive EVs.
> 
> ...


Good post. I must say that the more I've driven with AP the more I'm coming comfortable with going the speed limit regardless of what the traffic flow is doing.


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## Kizzy (Jul 25, 2016)

turnem said:


> Good post. I must say that the more I've driven with AP the more I'm coming comfortable with going the speed limit regardless of what the traffic flow is doing.


I'm content to be "trapped" behind slightly slower traffic when using AP. It also saves energy so it's a win.


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## MarkB (Mar 19, 2017)

Kizzy said:


> I'm content to be "trapped" behind slightly slower traffic when using AP. It also saves energy so it's a win.


I backed off from Mad Max -- that extra 1 or 2 km/h just wasn't worth the lane changing required.


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