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Comment by mfalcao | Hacker News Reader

Just watched this while eating. It's half an hour long, so here's a summary:

- He owns a 2022 Hyundai ioniq 5, USA version

- The brake lights generally work fine, however when in one-pedal mode (i.e. accelerator does regenerative braking for the first X% of travel) they only activate when the vehicle is about to stop so long as the driver has the accelerator ever slightly depressed

- This is a problem because the regenerative braking is quite strong - he goes from 60 mph/96 kph to 0 in 13 seconds and the stop lights never illuminate

- He thinks this should not be allowed and Hyundai should recall the cars to fix this

- However, in the US this is perfectly legal - regenerative braking is not considered as part of the "service brake", so illuminating the stop lights is not required

- The EU on the other hand just fixed this gap in the law in March, by requiring that stop lights be illuminated whenever the deceleration exceeds 1.3 m/s^2

View on HN

I have actually thought about this when driving a Tesla which also has the regenerative braking. Here's what their website says for the record, it sounds like it works exactly how I would want, just depends on the threshold for deceleration they set:

""" During regenerative braking, Tesla will still activate the brake lights when the vehicle is slowing down, even if the brakes aren't being used at all. Tesla determines whether to turn on your brake lights based on your vehicle's rate of deceleration. If you're unsure if your brake lights are on, look at your Tesla screen, the car in the display shows the brake lights lit up when the brake lights are activated. [0] """

[0] https://www.notateslaapp.com/tesla-reference/1051/how-tesla-....

Yea the Tesla brakes work exactly how you would want. As soon as you start decelerating, even w/ regen, the lights kick in. Not sure how Hyundai messed it up after having an example..

Hyundai/Kia will do the minimum necessary to comply with the local laws.

Interesting, would seem more efficient to comply with as many laws as possible that don't clash and have one configuration, only tweaking for local oddities.

I have a complaint about Tesla on this one. In Europe they ship vastly better tail lights with a different color for turn signals. As I understand, the superior signals are acceptable, though not preferred, by US standards. But Tesla makes a separate, different, worse part to use in the US, rather than giving us the good stuff also and reducing their manufacturing variation.

As an European I always wondered about why in the US they have red turn signals. It seems...odd, so to speak?

Suburban and Americans aren't so good at living with the level of aggression that city driving requires, and so prefer having clearly delineated left turn time to something perceived as fighting in traffic.

It’s cheaper (or was) - early cars had one red light on each side and could blink it for a turn signal, but it was also the brake.

Later a second light was added for the taillight but they did it in the same bulb.

Thanks for the explanation! It still seems odd to me that it hasn't been regulated somehow, having 2 different colors for 2 different actions is safer.

It's a pattern for Hyundai/Kia. The whole thing with "no anti-theft immobilizers" is only where it's not mandated.

Their business is shaving pennies, hence why they didn't install immobilizers in states that didn't require them, in order to save a few bucks per car.

My 2020 Bolt does the right thing also. I only wish the lights would stay on while I'm stopped at a light but that's minor.

Do you not hold the brake when you are stopped? I know electric cars don't have to creep like an automatic ICE, but I drive stick and still hold the brake at a stop because not randomly drifting forward or backward is safer and it also is important in the rare case of getting rear ended

I don't know about GM, but in a Tesla, if you have 1-pedal driving enabled, then it automatically holds the brake. And the brake lights stay on.

> I know electric cars don't have to creep like an automatic ICE

They don't have to, but funny enough, it's an option in a Tesla. My wife uses it simply because it's what she's used to.

The Mustang Mach E is somewhat similar, if I remember correctly.

When slowing down with regenerative breaking it triggers the lights based on how fast it’s slowing down.

So if it’s just a tiny bit (slowing from 35 to 30 over a few seconds) it won’t kick on, but from 70 to 35 over a few seconds would.

We had manual transmission cars that could slow down from engine braking for decades and that never lit the brake lights. I'm not convinced this is an issue. It is your responsibility to keep a safe following distance from any car in front of you regardless of circumstances. You should be able to safely not rear end the car in front of you even if it immediately hits a brick wall and stops completely, and even if the brake lights are entirely missing.

Yep.

I drive a Jeep Wrangler and between its manual transmission and the fact that it's less aerodynamic than a cow, I can and often do slow from highway speeds to ~25 MPH without touching the brakes. It's never been an issue.

EU regulators were convinced it was an issue. And do many drivers follow you so distantly?

> You should be able to safely not rear end the car in front of you even if it immediately hits a brick wall and stops completely, […]

I don't think that's the usual expectation. Maintaining absolute braking distance is what railways do, whereas cars commonly operate on relative braking distance plus a safety margin accounting for your reaction time.

Over here, both driving schools and other general road safety education talk about keeping 2 seconds following distance (or half your kph-speed in metres, which corresponds to 1.8 seconds following distance), and traffic engineers commonly give the capacity of a single lane of traffic as 1800 vehicles/hour, which again corresponds to 2 seconds distance (this time as measured vehicle front to vehicle front, instead of tail to front of following vehicle).

And this is where I take a minor quabble with TC. He thought that GM “over engineered” the volt’s brake light system because it used an accelerometer. But honestly I think it is the easiest way. The only “trick” is to make it stay on once stopped (I’m sure there are conditions when you wouldn’t want them on when stopped though).

In fact it looks like the new standards are going to be defined by the rate if deceleration regardless of the means used to do so. Which means basing the lights on an accelerometer is the most reliable way to meet the spec. It shouldn’t matter how you are slowing down, just that you are.

Why do we need an accelerator when we know how fast the wheels are turning directly? The first derivative of wheel speed is almost always car acceleration. Is this to handle some edge cases like not turning the brake lights on when we're actually sliding on ice with the wheels locked? Seems unnecessary.

Could be as simple as "the controller doesn't have wheel speed on its can bus"

Why is it unnecessary? Isn't the primary goal of brake lights to inform people of deceleration and the secondary goal to indicate when a vehicle is locked stationary?

Showing a speeding vehicle behind you that you've lost control and should slow down is well within the conops of brake lights.

I think there's an agreement on the goal.

I believe the poster is asking why do we need another sensor to achieve that goal? We already have a speedometer based on wheel motion. A trivial computation gives acceleration.

What do you save by not having that sensor? Nothing. What do you lose by not having that sensor? The ability for the system to perform its requirements.

I'm assuming you read the context of loss of traction being a requirement.

Relatedly, having a dedicated accelerometer sensor is a baseline dependency of many of other modern features like cross-comparing compass headings and GPS for map heading information (much less any of the Level 2+ "self-driving" mechanics). Most cars likely want one, anyway, even in base models. It's one of the cheapest sensors in a suite of increasingly standard sensors (in almost any form factor of device, not just cars, but phones/watches/toasters/etc).

> What do you save by not having that sensor?

A $9000 repair bill in 6 years when your mechanic tells you “Sorry your car is immobilized and won’t start, the deceleration brake light sensor went and we need to remove the motor and 3/4 of the wiring harness to replace it”. And for anyone who thinks I’m being sarcastic, try owning a BMW or an Audi and you’ll know it’s the truth.

The problem there is owning an Audi or BMW, not the sensor itself.

A MEMS accelerometer is pennies. If it is critical then add redundancy and don't accept single fault tolerance. If it is optional or the signal can be estimated from other sources with acceptable error then fail gracefully. This is honestly simple stuff. Accepting less from manufacturers is a bad deal.

>>A MEMS accelerometer is pennies.

That's an dishonest argument (perhaps not intentionally). NOTHING is "pennies" to a consumer when it comes to repairing a vehicle. More frequently, you pay $1,500 in labour and parts to replace something that costs "pennies" in some bulk manufacturer wholesale catalogue.

Modern cars are getting more and more awesome, in terms of safety and convenience; but the sticker shock when going to dealership for repair is also becoming bigger and bigger, and it absolutely is intertwined with the significant effort to make 3rd party or even self-repair difficult to impossible.

So again, IFF this is an easily replaceable part that is thought-through and cross-checked intelligently with other existing sensors, brilliant. But can you at any level understand my skepticism that any of these are true? :)

I'm not talking about the price of maintenance but the cost of manufacture. Please give generous interpretations rather than ones that fit an argumentative narrative. Assuming the topic is cost of repair rather than manufacture makes no sense when we're talking about system engineering to accomplish functional requirements.

I have owned a troublesome 2010 BMW for 8 years now. No individual repair has been over $2,700.00. Most are closer to $1,500. I was quoted (by a dealer) $15,000.00 for engine repair once but it turned out to be a spark plug. $9,000.00 sounds like a dealer quote. Find a good independent shop.

Because tires can block, not all tire turn at the same speed all the time, because redundancy is a good thing... There a lot of reasons. And if the number of sensors in your car bother you, well, the early 80s, with carbs and without ABS, are last model years you can buy.

Many late 80s/very early 90s fuel injection vehicles have shockingly low numbers of electronic sensors also. MAP, O2, TPS, CPS is all you really need. Some of them are even analog.

No need to get snarky :)

Redundancy is a good thing. Do we feel manufacturers are cross-checking accelerometer with the speedometer? If not, there is no redundancy gained.

On the other hand, if your speedometer is faulty, or not working, you'll know pretty fast. If your dedicated accelerometer is faulty, you might have no idea what your brake lights are doing in the back.

Dunno; it just feels "we need to know acceleration, let's add an accelerometer" is a non-imaginative, add-cost, add-complexity idea. Again, if we think ABS and speedometer and the new accelerometer are being cross-checked and sanity-checked, awesome, but I'm just a bit cynical of that, compared to adding the 3rd thing to do the same thing.

> add-complexity idea

You're on a forum where a lot of people think Kubernetes is a good idea.

;-)

No idea what Kubernetes are, and I am serious here, since I am no software dev. On the hardware side of things, there is redundancy and complexity. Those two might look similar on the surface, they are totally different beasts so.

To simplify it as much as possible, Kubernetes is a system that deploys and manages containers. Containers allow multiple programs to run under the same system while being completely isolated.

However, Kubernetes is actually incredibly complex. It's powerful, but holy hell does it add complexity. And yet it's basically a buzzword and people are using it in very basic scenarios that don't call for the complexity that Kubernetes adds.

So that's where my joke comes from. There are people that behave as if adding unnecessary complexity is a feature.

Thank you a lot for the explanation!

An accelerometer will show braking when going at constant speed down a hill. Change in wheel speed is better.

I’d say you are braking somehow if you are going at a constant speed downhill, are you not?

> Why do we need an accelerator when we know how fast the wheels are turning directly?

Because the car doesn't precisely know the wheel's radius. The radius depends on the rim, tire, and tire pressure - and the car's operator may have accidentally or deliberately chosen something unexpected for any one of those 3 parameters.

ABS relies on the fact that the computer knows how fast the wheels are turning in relation to each other. Wouldn't seem to be much of a leap to leverage that system to determine if the car is slowing down.

You're not wrong but how much does not precisely knowing the wheel's radius change things?

The operator would also experience an incorrect speedometer. For the purposes of a brake light it'd be off (either lighting up too soon or too late) by some amount but I imagine it'd be "close enough" except for the most pathological cases of tire sizes.

You don't need to know the wheel radius, you just need to the rate of change of the wheels RPM. Then the brake light could be set to some conservative value where regardless of any realistic tire size/inflation scenario the brakes will activate at a reasonable deceleration.

In any case, with standard gas/brake pedals on ICEs, I can barely tap the brakes and have my brake lights turn on without any deceleration on my part, or I can do that and still be pressing the gas and so actually be accelerating with my brake lights on.

If the car doesn't know the size and speed of the tires it also can't accurately display the current speed, which seems like at least as pressing a problem.

Edit: Or is detecting deceleration more sensitive? I guess I don't know how precise it needs to be relative to how precise a speedometer needs to be.

This is not a problem. We know this isn't a problem, because ABS almost always uses wheel speed sensors to do it's thing, and ESC usually taps into the same wheel speed sensors. Hell, those sensors are often used to tell you when your tires are low on pressure, and yet that doesn't prevent any of the other functions from working, or even affect your speedometer enough to care.

Changing wheel size enough to affect readings of speed does not change the broad slope of the derivative of wheel speed.

One more possible reason might be when driving down a hill: When descending a sufficiently steep incline, I may be braking just to maintain my speed! That said, I'm still _feeling_ negative acceleration to maintain a constant speed. (That said, if I'm doing this for more than a handful of seconds, I'll generally downshift, and _that_ doesn't trigger brake lights, despite also causing increased negative acceleration. So maybe regenerative braking is analagous, and fine without brake lights?)

I don’t think it’s such an edge case at all. I imagine it would be disconcerting to the driver behind you if you slammed on the brakes on a wet road, locked the wheels into a skid, and the brake lights went out. (Shouldn’t happen with modern braking systems, but still…)

>The first derivative of wheel speed is *almost* always car acceleration.

There you go, you answered your own question. When it comes to safety features, "almost" always working isn't really good enough.

The BMW i3 is the same way.

This sounds like a recallable defect in the OP’s car’s software.

One drawback of this is the person behind may incorrectly assume you’re brake checking them; i have had a number of tailgating drivers retaliate by accelerating in front of me and slamming on their brakes (which is especially stressful with a kid in the car). Stuff like this makes me deeply regret choosing Tesla.

I would love a control panel option to turn automatic brake lights on/off.

It's really annoying to signal something to others that you don't intend.

I think there are a bunch of things tesla does that prevent you from being a good driver.

some examples:

- you can't flash your headlights (unless you traverse menus on the touchscreen)

- you can't set the wiper interval

- quickly turn on the defrost?

- turn on the hazard lights? (you should google it, it's funny)

newer cars go even further - no stalks, touch controls for turn signals, horn and wipers on the steering wheel

What model and year do you have?

My 6 month old Model Y has a dedicated button for hazard lights on the ceiling.

I can flash lights by pulling the left stalk (I forget if forward or backwards).

Wiper interval I do miss but what I usually do is either hit the wiper button once on the stalk and set via screen or use the voice interface to say “wipers speed 1”.

Can’t you turn defroster on with the voice interface too?

> - you can't flash your headlights

You can flash the high beams which is good enough, IMO.

> - you can't set the wiper interval

You absolutely can. In my Model 3, if I press the button on the left stalk, it makes the wipers wipe once and shows the wiper options on the screen. I can set them to Off, Slow, Medium, Fast, and Auto.

The only exception is when the car is on Autopilot. Then, it's forced to be Auto. The quality of Tesla's auto-wiper software is questionable, though.

> - quickly turn on the defrost?

There's a button for that now.

> - turn on the hazard lights? (you should google it, it's funny)

? It's a button above the mirror?

> ? It's a button above the mirror?

Yep. FWIW, Hazard Lights is the one control that is mandated to be a physical button by US law.

> You can flash the high beams which is good enough, IMO.

flashing high beams at night is a good way to set people off and wind up in a road rage incident. some people interpret that signal very aggressively and will retaliate.

I feel like the psychology behind being a driver is a problem.

> he goes from 60 mph/96 kph to 0 in 13 seconds and the stop lights never illuminate

I ride a motorcycle and I give Teslas a lot of cushion when riding behind. They're common enough in the bay area to be treated specially, because of the one pedal driving (my car is set to "creep", but it is still strong at 70mph).

The way the car changes speed and the way the Model S looks from behind, it takes a bit of time before you realize it is getting too big in your PoV without lights coming up, particularly as people lift off through turns or highway onramps.

The cars which are bigger or higher up like an ID4 or Rivian seem to not suffer from this sort of "hidden width" that the Tesla has, the wheel flares melt into the backdrop when looking at it.

I don't think Technology Connections is ever going to drive a Tesla or test it, but the low profile fast cars are much harder to figure out speeds off from parallax without the brake lights.

Engine breaking on a motorcycle can be quite significant as well. I've thought about this being a problem there too.

Diesels with a J-brake can also decelerate quite abruptly, though in that case there's still a remarkably loud audio queue from the engine compressing

In the safety classes I’ve taken, there’s usually been training (albeit brief) of being aware if others are behind you, but building the habit of using the engine to decelerate that you flash your brake lights and or apply enough brake to trigger them without heavily braking.

This was also an issue when I had a larger manual car with a medium size (4.6l) v8.

At lower speeds <45mph, it was entirely possible for me to be significantly decelerating using only the engine, where I would make sure to at least flash my brake lights several times.

I own a Canadian Ioniq 5 and it is indeed quite dangerous. I have been honked a few times in my year of ownership. Now, I usually release the pedal completely to at least flash the brake light to show people behind me that I am decelerating. But my wife hate the sensation so I usually don't use 1-pedal when I am with her. Which is sad because I really enjoy driving in this mode.

I totally agree, when you are decelerating at more than x/(m|k)ph light should come on.

On a different matter, first generation car, and there is a huge flaw with a high percentage of Ioniq5/Ev6/Genesis GV, have a ICCU (Integrated Charging Control Unit) failure at around a year of ownership. My car at the dealer for over a month without an ETA on part delivery :(

Exhaust brakes on truck or engine braking behaves the same way. There can be strong deceleration without brake lights.

Deceleration threshold is great solution because it signal what is happening.

Trucks use exhaust braking because it's quicker than braking using the brakes without overheating. They can get away without brake lights only because the noise makes it obvious when trucks are exhaust or engine braking.

Engine breaking, which any manually car driver uses, does not produce any indication that you're slowing down. Technically, the engine noise is louder, but not enough to notice outside of the car.

You can engine brake in any "manumatic" like Subaru with their flappy paddle CVT. You could drive a manual without engine braking more than a normal automatic; nothing forces you to downshift. You could also only up shift and use neutral when braking with actual brakes, which I think a lot of people do when learning manual.

Indications that the car in front of you is breaking include brake lights, distance between you and them, and weight transfer to the front (nose down, rear up). Only one of those is affected by the thick pedal.

It's illegal to drive in neutral. And of course you can engine break in automatic cars, but you're not likely to.

>It's illegal to drive in neutral

What law says that?

Dunno about other states, but in Oregon, it is explicitly forbidden to coast in neutral downhill

https://oregon.public.law/statutes/ors_811.495

> A person commits the offense of unlawful coasting on a downgrade if the person is the driver of a vehicle on a downgrade and the person coasts with the gears or transmission of the motor vehicle in neutral or with the clutch disengaged.

However, this only refers to going downhill. It says nothing about approaching a red light or any other scenario where you might consider choosing to coast.

You're right of course, but these days engine braking is most commonly used by tow vehicles, whether that's a family car or a big hauler. Either way when towing, these are generally required to have trailer brake controllers that are activated by deceleration so that the trailer brake lights do come on.

When we cross the Cascades or Rockies in our Land Rover Discovery towing an Airstream, we have to shift and engine brake on the downslope for miles (to avoid overheating the breaks) and it's noticeable that the trailer brake lights go red, while the Land Rover doesn't unless I tap the brake pedal.

Thank you for the summary. I understand how creators are incentivized by YouTube to produce longer content, but it is a bit ridiculous that this 30 minute video could have been 6 tweets.

Of all the YouTubers out there, I wouldn't call out Technology Connections for padding their content. Sure, you can get a short summary of the useful information, but the show is about more than "short collection or facts". It's like saying "it's ridiculous that an episode of Mythbusters is half an hour, you can fit the results in a tweet!"

I would. He repeated his points several times.

I give Mythbusters a pass because the padding is intentional entertainment (that I happen to enjoy, obviously).

I don't watch TC because the padding doesn't come across as entertaining to me; it feels like a lot more beating around the bush. There's a _lot_ of repetition.

To go off on a tangent, someone went and edited Mythbusters episodes to remove the fluff and called it Smyths. There's a torrent of it and it's a way better watch.

I've seen those, and while I understand it, I feel it loses a hell of a lot of the pathos of what mythbusters was. A huge amount of the goodness is the interplay and personality of Adam and Jamie, and it gets lost I think in those edits. Add that to Mythbusters not exactly being scientifically sound, and more like "these TV effects artists build a weird contraption that MAYBE answers a question that isn't well formed". Cutting out the recaps is useful though.

I absolutely would say that about Mythbusters.

> Thank you for the summary. I understand how creators are incentivized by YouTube to produce longer content, but it is a bit ridiculous that this 30 minute video could have been 6 tweets.

This isn't even the worst example, because the additional content is at least part of the entertainment (even if not the most efficient).

Padding is par for the course among Youtubers. If you play a lot of video games, you'll notice this, because gaming news and tutorials are often done on Youtube.

There are a couple of different thresholds for algorithmic promotion and monetization - I believe 10 minutes is the biggest one - so a lot of videos are padded with filler content just to make the threshold.

You'll also see it on videos for "how to pronounce ______", because they can't monetize below a certain threshold, so they'll pad it with useless filler in order to make the video over 30s long.

Some of us still have semi-intact attention spans. TC caters to that kind of audience.

Imagine how much you could brag about your attention span if the video was 8 hours long!

If you haven't watched a 4 hour youtube video essay by one of the greats, you are genuinely missing out.

I watch long videos at any time. Usually during coding. For instance this summary and review of utopia: https://www.youtube.com/watch?v=PFx2QM0Z8Qo 7 hours : 41 minutes, watched it one go.

I love AltShiftX book and movie reviews. The Dune ones are long and interesting.

How much money would they have made from those six tweets?

Content follows the money. Even if it’s anemic like YT, it’s still a lot more than zero.

Do you watch sporting events and say, “why did this take so long? They could have put it into one tweet: the Knicks lost again.”

TikTok really is killing online video...

Imagine if Vine had succeeded.

Imagine if Elon brings back Vine....

tbh, I liked Vine. It allowed someone to write a joke and punchline without allowing them to fill it in with bullshit.

> but it is a bit ridiculous that this 30 minute video could have been 6 tweets.

In the video, he researches relevant laws in the EU and US, and explains the details and implications of those laws. He compares to previous solutions from another manufacturer, GM, and also personally verifies that his car's automatic cruise control mode does properly use brake lights, and also shows how that is following the letter of the law.

There is no cruft in the video, just a lot of densely packed content. Yes you can summarize the video in a few sentences, but you miss out on a lot of the details.

I watched the video for like 4 minutes and it was 4 minutes of him saying “the brake light doesn’t come on until your foot is all the way off the pedal.”

Our 2014 BMW i3 lit the brake lights when regenerating...hard to say how firmware changes may have altered this behavior over time, and there were firmware changes for our US based i3, but the Ioniq situation in the post seems like an expensive accident waiting to happen.

> they only activate when the vehicle is about to stop so long as the driver has the accelerator ever slightly depressed

Do the brake lights come on if you don't have the accelerator depressed at all?

Yes they do, but releasing it all the way is jerky. To fix this, EVs should limit the jerk rate rather than introducing the brake at full power when you release the accelerator. This is how it’s done by most metro trains.

Note: one-pedal mode slows the car as the accelerator is released.

> - He thinks this should not be allowed and Hyundai should recall the cars to fix this

Why do a recall? Sounds like it's a simple software fix. Can be deployed over the air.

Software fixed are "recalls"

Yup.

Which is why it's so annoying when Tesla recalls hit the news. So many people treat it like a huge event, when really, it's just a small software update.

AFAIK eGMP (platform for Ioniq, EV6, GV60) OTA updates are limited to infotainment system - you have to go into the dealership for major system updates. (I have an EV6)

My 2021 Hyundai Kona EV illuminates the brake lights immediately when the regen kicks in. Strange that that's not the default behaviour on the other model.

It's quite annoying that Hyundai got this so wrong, while a long list of other makers got it right. Even without regulators demanding they do so.

And there I was naively thinking the new EU rule existed, and was applied by OEMs, since regenerative breaking is a thing...

We should determine what rate of deceleration counts as 'coasting', and anything beyond that counts as braking.

Unless said legislation/determination only applies to electric cars, they'll have to give manual ICE vehicles a look-at as well; my TDI for instance can engine brake so well that it behaves very similarly to regenerative braking, and the service brakes get used only where absolutely necessary. Transport trucks with exhaust or Jake brakes and a light(er) loads can get often get away with similar-to-EV single-pedal driving regardless of whether the transmission is automated or not.

This might be a hot take, but if you're actually paying attention to driving it's not exactly difficult to see a vehicle decelerating in front of you, brake lights or not.

I'm only on my second set of brake pads on my TDI and you're right. However in most real driving situations, engaging the engine braking requires feathering the brake long enough to get it to downshift.

So while my brakes aren't on the whole time, they are on when I first make myself a problem that needs to be managed.

>engaging the engine braking requires feathering the brake long enough to get it to downshift.

What? No, you put in the clutch, pull out of gear into neutral, rev match up to the engine speed for the lower gear, plop the shifter into it, release the clutch. What do you use the friction brakes for? Hell, you can skip the rev matching completely if you don't mind clutch wear and jerkiness.

Even with a DSG-equipped car like the parent likely has, you can use the "manual" mode ("M" on the shifter) and downshift to as low as the car will allow. This also has the benefit of 'preparing' the transmission for further downshifting, as it will pre-select the next gear down instead of up. My car is indeed a 6MT, and downshifting happens exactly as described.

I believe they're talking about a manual transmission TDI. In which you could simply downshift and engine brake, without engaging the brakes.

The EU has defined it as a deceleration of 1.3 m/s^2.

In manual cars, it's always felt wrong how much and how fast the car can decelerate by changing to lower gears without the brake light turning on - even if you are not technically using the brake, you can lower the speed so much as to create a dangerous situation with the guy coming behind, and therefore turning on the brake light would be appropriate.

It’s a feature not a bug. Everyone immediately SLAMS the brake when they see a cop and it’s a dead giveaway if you want to get a speeding ticket. Engine braking has saved me more than once because you can slow down without being an immediate target for the cop.

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