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NoA brakes on highway for merging vehicles

Poweroftwo

Member
Oct 29, 2018
9
6
Massachusetts
My wife and I are big fans of Tesla. We have a model 3 and a Y and both have NoA. I love to use NoA on the highway, but have found this issue to be a safety concern that should be resolved as anytime the car brakes suddenly and unexpectedly it could cause an accident.
When driving in the right lane of the highway, if there is a car on the on-ramp that is merging onto the highway, our Tesla will brake sharply. As we are on the highway and have the right-of-way and are often going faster than the merging car, I worry that the braking will cause someone behind me to rear end us. This happened even before the update where the Tesla will slow down if the cars in an adjacent lane are going slower.
 

Puddles

Member
Jun 2, 2017
730
930
Fresno, CA
Tesla's dilemma is this: When on a converging course with merging traffic, should it accelerate or brake in order to complete the zipper merge? To date, we have seen no evidence that the car will autonomously accelerate to avoid a collision. And it's not hard to see why they would be reluctant to incorporate this response. Which leaves only the other option.

In most cases, I find the zipper merging to complete very smoothly. The only cases of hard braking are when it is necessary due to the merging vehicle coming in very slowly. While this is definitely annoying, I'm not sure this is something we can blame Tesla for.

I learned early on that I had to unlearn 40 years of driving habits to use autopilot, one being, it was more important to cover the accelerator than the brake. If traffic is merging slowly, it is pretty easy to tap the accelerator, which a) undoes the braking and b) gets me by the slow traffic handily.
 
Mar 25, 2019
31
36
Colorado
In general, our job as the non-merger is to maintain our constant speed so the merger can more easily adjust their speed to effect the merge.

We shouldn’t regularly as a matter of course move out of the lane to make room for the merger, as now we are just moving the risk over one lane. I try to only do this for vehicles with extra challenges getting up to speed, e.g. semi-trucks.

Of course, we also have the responsibility to take evasive action at some point if we decide the merger might hit us. And many mergers do seem to expect us to get out of their way these days.

Sometimes my Model 3 has done a gentle job of it, but other times it has slowed more dramatically and sooner than I would have, before there seemed to be a clear risk of collision. I don’t remember it ever maintaining speed, as I would normally try to do.

I hope it gets better some day, or that we all are in FSD vehicles and we don’t care anymore because we’re sleeping or watching a movie.
 
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kwest2

Member
Apr 28, 2017
254
262
Boston, MA
I think this is why often on NOA it will move from the right lane to left lane right near an exit and on ramp and say "following route". Sometimes it just tries to avoid these situations. But agree, I had a few of those hard stops in a recent road trip I took.
 

McFlurri

Active Member
Apr 27, 2016
1,501
1,728
Kitchener, Ontario
I think this is why often on NOA it will move from the right lane to left lane right near an exit and on ramp and say "following route". Sometimes it just tries to avoid these situations. But agree, I had a few of those hard stops in a recent road trip I took.
My car has NEVER done this
 

strider

Active Member
Oct 20, 2010
3,630
1,005
NE Oklahoma
Yep. At its best, Autopilot drives like a 15 year old on Day 1 of their driver's permit. It "drives off the end of its hood ornament" as my Dad would say. In all cases its answer is to brake abruptly, which is absolutely dangerous. It does nothing smoothly and makes passengers nauseous. It also can't handle anything extraordinary like construction, pot hole, etc.

Buying FSD now is simply lighting money on fire, unless you plan to keep the car for >10 years.
 

Avid

Member
Oct 1, 2018
335
208
Houston, Tx.
One way to alleviate this situation is to manually reduce/increase speed by using the thumb wheel speed adjustment when confronted with a merging vehicle. As such, it's not an idea solution as you essentially have to intervene, but it's better than the alternative of sudden braking.

Having said the above, I don't remember the last time this has happened to me. I think in my case the merge has been smooth.
 

Puddles

Member
Jun 2, 2017
730
930
Fresno, CA
It is a common perception that merging traffic must yield. This is in the California Driver's Handbook, but that is not the law, it is DMV opinion. Generally, the law (in CA anyway) considers neither party to have the absolute right-of-way. We are expected to work together to get the job done. And as a practical matter, the through traffic usually has more opportunity to give way (move over, better visibility to adjust speed, etc.)

Here's my source, although it's behind a paywall so you have to be clever with your browser to actually read the article.
 
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Puddles

Member
Jun 2, 2017
730
930
Fresno, CA
In all cases its answer is to brake abruptly, which is absolutely dangerous. It does nothing smoothly and makes passengers nauseous.

This was my experience 2 years ago, but for the last year+, the abrupt braking occurs in a small minority of cases. In my conditions, AP has gotten much smoother and smarter.
 

novox77

1.21 Gigawatts
Nov 25, 2017
1,928
4,110
NH, MA
I think this is why often on NOA it will move from the right lane to left lane right near an exit and on ramp and say "following route". Sometimes it just tries to avoid these situations. But agree, I had a few of those hard stops in a recent road trip I took.

My car has NEVER done this

My NoA regularly moves me away from an off/on ramp area if I don't need to exit.


It is a common perception that merging traffic must yield.
In most places in the country, there is a yield sign on the ramp. Highway drivers have the right of way in this situation, and it's up to the merging car to modulate speed to merge in safely.
 

CharleyBC

Active Member
Jun 28, 2019
1,465
1,673
Talent, OR
What bugs me with the merge problem is situations like this. I'm cruising in the right lane. A car is merging from the right. The merging car is a little ahead, but moving more slowly. Extrapolation shows that at my greater speed, I will comfortably and safely be in front of the other car well before the two lanes actually become one. That is, no action needed at all to avoid a collision. And the car brakes.

My impression in these situations is it is not considering time very well. It "gets" space, but not so much time.
 
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SammichLover

Banned
Dec 8, 2018
2,618
1,649
Yup
My NoA regularly moves me away from an off/on ramp area if I don't need to exit.
This is likely road database driven. If so, how often it happens depends on how good the database is populated for where you drive.

There are actually some AP/FSD features that at first seem to be driven by perception but around the edges you can see it is actually melding a road feature database with sensor input. A good example of this is the new stoplight feature. That notification of a streetlight coming up you see might actually be database driven, sometimes. Someone else in this forum mentioned they saw evidence of that with a notification coming up for lights there were around a bend with trees at the side of the road seeming to block line of sight. I see a related piece of evidence for this on a local recently built raised, no-intersection toll road. It follows the path of a prior highway, and service roads had been built along side.

On the toll road, raised 16+ feet in the air and with barriers on the side that afford no vision of the service road whatsoever, and no signal lights or anything approximating them for miles ahead, I get "Streetlight ahead" notification where there are underpass cross-road intersections below me.

However after I'm off that toll road and onto the service road further down I get a "Streetlight ahead" notification, and a streetlight graphic on the console screen with no lights illuminated, when the service road is passing a minor railroad crossing of a railroad running parallel to the service road. The reason, pretty sure it is identifying the crossing lights as signal lights.

It'll do the later as well occasionally for "caution, stoplight ahead" signs, too. At least momentarily it misidentifies the sign as it gets up really close on it. And then as it is passing it it figures out it isn't actually a set of lights.

So some of the stopsign feature behavior is triggered via road database and it seems some is purely visually triggered.
 
Last edited:

jkdman123

Member
Jul 15, 2019
350
272
San Diego
I haven’t seen ‘abrupt’ braking when next to a merge lane, but I have seen it brake faster than necessary which can at the least be annoying to cars behind you. They need to smooth it out.

With regards to driving in the far right lane, I tend to avoid it on autopilot. For some strange reason, the system seems to put too much weight on centering the car in the perceived lane. This means that the position of the lane line on the right side is weighted too much. When coming up to a part of the highway where the right line starts to diverge or converge (on ramps, off ramps, merge lanes, etc.) the car will quickly move right to ‘center’ itself in what it thinks is a wider lane. It’s disconcerting and I’m sure it looks to other drivers like you’re not fully in control. The car should put most of the weighting on the lane line to the left of the car.
 

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