Sudden Autopilot Max Speed Reduction

[Originalando]

Over the weekend I drove a fair amount of mainly highway and used autopilot nearly the whole time. During the first trip and on the second leg (after stopping to supercharge) the car had a few instances of sudden reduction in Max Speed as indicated on the display. I know phantom braking is an issue, but I wouldn't consider this to be called that, as the screen clearly indicated the Max Speed being reduced to 40mph while the speed limit sign next to it on the display still shows correctly at 70mph. I was in the middle lane of a 3 lane highway and there were no cars ahead of me in any lane, the roads were very clearly marked.

Is this a pretty common occurrence on highways and do many other people see similar behavior with the speed limit being recognized but the Max Speed being greatly reduced?

 

[Grabthar]

From my experiences, the car uses the navigation database (at least sometimes) to determine road speed. If they are in the database wrong, the car will get it wrong too - despite what the sign says on the edge of the road.

 

[GtiMart]

It's possible that for a brief couple of seconds, the car thought the max speed was 40, and it soon after realized it was 70. It can happen when you pass close enough to a side road, or an exit. With the GPS not being "that" precise, the car might think you've exited the highway. I have one place where this happens systematically for me.

 

[Originalando]

Interesting, so it seems the car may default to using the database information even though the camera has picked up the speed limit signs correctly. It's not a trip I make frequently but I will definitely keep it in mind when I go that way again.

 

[EVRider-FL]

When the car can’t determine the speed limit, Autosteer is limited to 45mph. Is that limit different for vision-only cars like yours?

 

[GtiMart]

Soon it won't matter because we'll all be on vision

 

[Originalando]

When the car can’t determine the speed limit, Autosteer is limited to 45mph. Is that limit different for vision-only cars like yours?

When it happened I made sure to look to the screen immediately and saw it still recognized the speed limit as 70mph, but the Max Speed dropped to 40/45mph (honestly not sure if it was 40 or 45 at this point). Once I hit the gas the max speed would rise again to whatever speed I reacted at (for example, 60mph, meaning i slowed by 15mph from my set speed of 75mph), I could then increase the speed back to 75 and continue.

 

[xtattsbox]

Happened to me… it’s dangerous

 

[Keninblaine]

It happened to me yesterday. Car suddenly started slowing down on the 60mph freeway and the max speed suddenly showed 40 mph for some reason. Funny thing is, the car doesn't slow down for any other posted speed limit changes unless I change the speed setting. BTW, I only use cruise control, not lane keep assist or FSD.

FWIW, another flaw in the system is likely unique to my situation of being in a border town next to Canada. The posted speed limit sign entering town is 25 mph, but there is also another sign below it that says 40 kph so Canadians will know the posted speed in their metric terms. My car often picks up the 40 as the posted speed limit in mph. I guess it can read numbers but not letters.

 

[Dewg]

It happened to me yesterday. Car suddenly started slowing down on the 60mph freeway and the max speed suddenly showed 40 mph for some reason. Funny thing is, the car doesn't slow down for any other posted speed limit changes unless I change the speed setting. BTW, I only use cruise control, not lane keep assist or FSD.

FWIW, another flaw in the system is likely unique to my situation of being in a border town next to Canada. The posted speed limit sign entering town is 25 mph, but there is also another sign below it that says 40 kph so Canadians will know the posted speed in their metric terms. My car often picks up the 40 as the posted speed limit in mph. I guess it can read numbers but not letters.

Check GPS. Try driving that same spot again and watch where the car thinks it is.