Autopilot Slows Rapidly After Exit Ramp

Autopilot Slows Rapidly After Exit Ramp

This has happened several time as I've passed an off ramp, in the right lane and the cruise control reduces speed rapidly from 120KM to as low as 70km.
This happens without someone being ahead of me or not.
Not sure if the car is putting on the brake lights or not but a dangerous situation with this rapid deceleration.
It hesitates for a few seconds and then accelerates back up to the set speed.
Anyone else see this behavior?
And before someone says this, I know, I know I should be driving faster and staying out of the right lane.

walnotr | 7 juillet 2019

I have experienced something similar but not exactly as you describe. On a previous update (12.2 maybe) driving on an interstate, sudden slowdown would occasionally occur as I approached an exit ramp on a left hand curved section of the interstate. The lines would separate dramatically while the road curved to the left. The car would slow until the cameras picked up the “V” lines indicating the left edge of the exit lane.

So, not exactly the same as you describe, but maybe something to watch for. And yes, the brake lights do come on.

BTW, it seems to have improved with later releases, but I haven’t driven the same road post updates.

jjgunn | 7 juillet 2019

Normal behavior. Nav on AP is ending as you exit just as it's programmed. Nav on AP is not available after you exit the freeway.

You can override the slow down by carefully accelerating.

walnotr | 7 juillet 2019

@jjgunn, this is not an NoA issue, the exit is not scheduled but rather a random off ramp while following a planned NoA route. My theory (for what it’s worth) is; the car sees the lines diverge at a rapid pace and it may fall outside the limits of what is expected. As opposed to the car thinking it is on the off ramp and dropping out of NoA.

As they used to teach, when in doubt, both feet out. That may be the default at this stage of development until the edge cases can be worked out.

CharleyBC | 8 juillet 2019

Yes, I've had this happen a few times. It's unnerving. In the right lane, with NoA on. Other cars are not a factor. The one thing I think I noticed is this (but not enough data points to feel this is solid): It happened when the freeway is curving gently left and the off ramp is actually a straighter path, heading off on a tangent. My guess was this confuses the car. Inside the car brain: "Do I go straight? Do I bear left? My route doesn't have me making any turns at this point, so straight sounds good. Oh, but the map shows the highway curving left. Hmm. I think I'll slow down and think about this."

Maybe the higher processing power of HW3 will help it decide faster.

Bighorn | 8 juillet 2019

I figured it was a geofencing issue with the adjacent slower ramp speed.

Devilstower | 8 juillet 2019

I think @Bighorn has this right. I’ve seen the same thing happen in the right lane right before an off ramp. It’s not consistent, but I think it’s grabbing the suggested speed from the ramp.

yudansha™ | 8 juillet 2019

Same thing happens when I am passing rest areas on the left.

FISHEV | 9 juillet 2019

“It hesitates for a few seconds and then accelerates back up to the set speed.”

It does this in a lot of situations with the Beta AP Cruise Control. Passing with cruise on it will brake, drops about 2-3 mph before catching itself and then go back to cruise speed. Never seen that behavior in any other cruise. It will just do it randomly driving along.

Not sure it’s “phantom braking” as much as cruise taking its foot off the accelerator and regen kicking in, car is not intentionally braking it’s just not co-ordinated between slowing and regen braking. It shouldn’t be slowing either but the uncoordinated regen has that effect.

vmulla | 9 juillet 2019

This is a common occurrence. It seems to me that the car was following the exit ramps' speed limits. That's fine as far as rules go, but I'm cases where the exit ramps' speed drops by 30mph the effect can be unnerving.
I'm thinking it's something that will be solved over time as Tesla learns from user behavior in those situations. As long as car is following the rules to keep you safe it's okay - not ideal, but not wrong either.

twistedskipper | 9 juillet 2019

I would be more likely to accept that the car is temporarily adopting the exit ramp speed limit if anyone could confirm that the DISPLAYED cruise control set speed changes, rather than the car just slowing briefly without changing that cruise control set speed. I have not personally seen that set speed change down and then back up in those scenarios. My suspicion has been that it is the recurring confusion when the right side lane marker suddenly goes away and then reappears.