> turn signals should _not_ be used as "an indicator of opportunity

Are you certain about that?

When I learned to drive, we were told to indicate a few seconds before turning, changing lanes, etc. This communicates your intentions to other drivers. In other words, the blinker says, “I’d like to get in the left lane” or “I’m getting off the highway”, not “This car is currently moving leftward.” Otherwise, why not just connect the turn signals directly to the steering wheel?

Before turning is the law. e.g. Maryland Code "(d) Where signals to be given.- When required, a signal of intention to turn right or left shall be given continuously during at least the last 100 feet traveled by the vehicle before turning; except that a bicyclist may interrupt the turning signal to maintain control of the bicycle."

There are actually many states where using the turn signals to change lanes isn't even legally required though, so things are more mixed when it comes to changing lanes vs. making turns.

> There are actually many states where using the turn signals to change lanes isn't even legally required though, so things are more mixed when it comes to changing lanes vs. making turns.

Arizona is one state where it is required judging by a warning I got from a friendly highway patrol officer who chased me ~5 miles while I was having fun on the old ninja during morning rush hour.

Yes of course, but it is a _signal_, not a request. You should _not_ put your signals if there is no room, just to "ask" other drivers to clear the other lane.

Suppose you're in the center lane during some stop-and-go traffic. You want to take the next exit. Do you really just drive along in quiet desperation, hoping for a gap?

I—and everyone I know—would leave their blinker as they creep forward, "requesting" that someone leave a gap big enough to take the exit.

Of course, the vast majority of drivers would do so (including me). That would just be incredibly inefficient to do otherwise. Nevertheless, in my home town, it is against the law (Ontario btw, so I confess I cannot speak for the US).

Same thing goes for the left turn on yellow light. If there is a gapless traffic coming from the other direction, you will probably just creep in the intersection and turn at the end of the yellow, when the other cars have stopped. Nevertheless, by doing so, you are doing two illegal things: 1) going further than the stop line and 2) passing on a yellow (or even a red) when you could have stopped (easily, you were already stopped). Is it a bad thing that people (again, including me) do this? Probably not, doing otherwise would be a huge loss of time for everyone and it does not really increase the accident rate. Yet, it is against the law.

Here's the text of Ontario's Highway Traffic Act: https://www.ontario.ca/laws/statute/90h08#BK232

“The driver or operator of a vehicle upon a highway, before turning to the left or right at any intersection or into a private road or driveway or from one lane for traffic to another lane for traffic or to leave the roadway, shall first see that the movement can be made in safety, and, if the operation of any other vehicle may be affected by the movement, SHALL GIVE A SIGNAL PLAINLY VISIBLE TO THE DRIVER OR OPERATOR OF THE OTHER VEHICLE OF THE INTENTION TO MAKE THE MOVEMENT."

I guess one reading of this suggests that you must first check if it would be safe to make a maneuver, and if so, then and only then, must you use a turn signal. I think you could also read this as requiring safety checks and indicating (in either order) before turning, but I'm not a lawyer. I can't imagine that people are actually prosecuted for signaling out-of-order though.

The driving handbook, however, tells you to check your mirrors, then "Signal that you want to move left or right." (here: https://www.ontario.ca/document/official-mto-drivers-handboo...) which seems to suggest some level of intention-indicating is okay.

>If there is a gapless traffic coming from the other direction, you will probably just creep in the intersection and turn at the end of the yellow, when the other cars have stopped.

While this is illegal in some states, it is not in others. Furthermore, the general rule on reds (again, this might vary by state) is not that you should not be in the intersection, but that you cannot enter the intersection. If you are in the intersection, when it turns red, you clear the intersection.

Isn't that exactly the discussion?

It is against the highway code to do that, so can't be programmed in, as this would be ultimate premeditation of breaking the law.

On the other hand, in the real world, this is how people sometimes use turn signals, so autonomous cars are at a practical disadvantage and can't merge when a human driver could.

For large sections of many highways at rush hour, there is essentially never a space to comfortably merge into. You have to essentially make spaces to merge into whether because someone sees you signal and lets you in or someone isn't really paying attention and has let a gap open up.

Really? My understanding was that the signal is a request to the vehicles behind you in that lane to yield and create space to let you in. That's how I always see it working here in Vancouver and it's a good system. People are very good about creating space in front of them when someone needs to be let in.

Edit: This depends a lot on context. The relative speeds of the two lanes, whether there's a merge, and so forth. If there already had to be enough space to safely change lanes without any other cars slowing down or reacting at all, then turn signals would become unnecessary. Often there's an opening, but to really make it safe the car behind you in your target lane does need to yield to make it safe, and the turn signal is a request that they do so (or at least not speed up).

It is a signal that I am going to get over into that lane one way or the other. You can choose to keep me from doing so in which case I'll get in front of one of the following vehicles and merge there. I don't know where you drive but that is absolutely normal and expected behavior where I do.

It seems like just one of the challenges for autonomous operations. Driving that is pretty much necessary in some locations (and to do otherwise would cause other drivers to route around you in unsafe ways) would often be seen as hopelessly aggressive in others.

In the uk I was taught that indicators were to signal intent, not action. Signaling that you intend to merge, even if you can’t merge currently, would be the thing to do.

I guess the rationale being something to do with giving other road users an idea that you car might do something so they can be prepared if you do.

"In the uk I was taught that indicators were to signal intent, not action."

In LA they are used to signal that you just finished crossing 5 lanes on the freeway all at once to get to the exit you almost missed :-)

Every time I go to L.A., I say to my wife, "Yay! I don't have to use my turn signals for a whole week!"

Yes, those are called victory blinks!

It's supposed to be: MIRROR SIGNAL MANEUVER.

By the time you've hit that indicator you've worked out what you want to do and had a bloody good look round to make sure there's no one in the way and now you're going.

Technically you shouldn't need the indicator because you're driving into the available space for the maneuver.

Just to be clear I wasn't saying "don't use your mirrors". I missed out all the stuff that was irellevant to the discussion like using your mirrors or starting the engine.

Also, it's a cute mnemonic device to help people remember to drive better, but as my driving instructor said, you might need to use "mirror, signal, mirror manouvre" because the mirror is to check what's going on, the indicator is to indicate intent, but you might not be able to manouvre immediately so you might need to check what's going on around you again before you actually make your move.

People who indiate as they are making their manouvre are a PITA and almost universally despised. Almost as much as people who don't use their indicators at all.

There's a few issues with the "Technically you shouldn't need the indicator" world you describe. First, you assume that there's flawless information available to you. You know where everyone and everything is and you've not missed anything. Indicators give people around you a chance to see what you're up to even if you don't know they are there, or don't think they are relevant to you.

Second, you're describing a world in which you always have space and time to make a manoeuvre without impacting others around you. My reality of driving round the North West of England is lots of cars in a small space. People who don't use their indicators are a PITA. It's just selfish. That sudden deceleration for a left turn or sitting in the middle of the road, are you turning right, or have you broken down? Using an inicator is just polite and helps other people drive more comfortably.

Third, it helps people plan. This is linked to the other two things, but I think it's important enough to have as a separate point. Have you ever seen pedestrians look at you/your indicators to work out wether they should cross a road? It happens when driving around town. One particular case I remember, I wanted to turn left, I was driving along and turned my indicator on. Guy about to cross the road, looks over his shoulder, sees my indicator and stops. I make my turn, he crosses the road. Smooth, organised, orderly. Sure, if he had just walked out I would have stopped in plenty of time, but on the main road, with people behind me wondering what I was doing.

> turn signals should _not_ be used as "an indicator of opportunity"

This is just flat wrong and makes no sense. If you want to merge, you’re required to use your turn signal ahead of time. If you don’t know when you’ll have an opening to merge, you may have it on for a long time.

Merging is different than changing lane or turning. In some states, you may have to give the right of way even if you do not change lane yourself.

But I agree it was bad wording on my part. My point was about those drivers who just leave their signal on for 2000 ft and expect that it gives them the right of way over the other vehicles in the lane they want to move -- and usually get angry when they do not.

> > it would seem Waymo programmed its autonomous vehicles to treat turn signals as an indicator that the car is about to execute a turn or merge, not an indicator that it is looking for the opportunity to do so.

> Well, here's one, if not the issue... I do not know the precise wording of trafic Laws in each state, but in many if not all, turn signals should _not_ be used as "an indicator of opportunity".

Certainly not true in NJ.

> A signal of intention to turn right or left when required shall be given continuously during not less than the last 100 feet traveled by the vehicle before turning.

https://law.justia.com/codes/new-jersey/2013/title-39/sectio...

My wording was bad, I admit it.

My point was that signals should be given only when you have the _opportunity_ to do such maneuver. If the lane to your right is crowded, putting your right signal on achieves nothing. In other words, your signals do not give you the right of way.

I do not think Waymo cars are unable to use their signals, but they are probably programmed not to put them on when the turn/lane change cannot be achieved anyway.

When someone indicates his intention to change lanes when there is no room, I slow down. I expect the same of others.

And when that doesn’t happen, you just continue on because chances are high that the next one will.

In many cases of heavy traffic, this is the only way to change lanes.

But that perfectly describes “about to execute a turn”. Not what the article is describing, which is to request that other cars open up a new (previously non-existent) space to allow for a lane change.

Human drivers will sometimes do this, but in my experience they’re just as likely to cut you off once they see you want to change lanes in front of them.

Isn’t it perfectly possible to signal intent even when there is no ability to do so?

>...turn signals should _not_ be used as "an indicator of opportunity".

VA Code §46.2-848: Every driver who intends to back, stop, turn, or partly turn from a direct line ... shall give the signals required in this article, plainly visible to the driver of such other vehicle, of his intention to make such movement.

Emphasis mine.

States typically follow MUTCD[1] traffic rules, but they can diverge on interpretation. One source of different interpretation is what to do on a solid red arrow. (in some states that means stop and proceed as a normal solid red light, in others it means absolutely no turn on read). I imagine there are other areas where rules are interpreted differently.

[1]https://mutcd.fhwa.dot.gov/

There's not much point to the signal if you don't provide it before you take the action.

In the case you hypothesize, signaling early may be illegal (and so a Waymo care wouldn't do it), but backing off ato yield space to a signaling car is still not illegal, so a Waymo car could do it.