Advanced Driver Assistance Systems (ADAS) have proliferated across the new vehicle market, and many of these systems have seen mixed success. Some, like automatic emergency braking and blind spot monitoring, are great ideas, but most of these systems are fallible. That includes high beams that automatically dim when the headlights of an oncoming car are detected. While this headlight-switching technology can make driving easier, it can also make driving more dangerous if the lights dim when there’s no oncoming traffic to be concerned with – a malfunction that can be triggered by the sudden appearance of reflective road signs.
First, let’s learn a little bit about how modern automatic high-beam systems work. You know those cameras you see at the tops of modern car windshields? Among many functions, at least one of those cameras is used to detect light from oncoming vehicles and vehicles ahead, then beam that information through the car’s computer network and cycle the high beams. In theory, this should allow for more precise detection of vehicles within the camera’s framing and depth of field. In practice, a camera system has limitations, namely that light detection isn’t the same thing as headlight detection.
To understand what’s going on here, we must first know a little bit about image sensors. Over the past few decades, two types of image censors CCD and CMOS have seen a degree of popularity, and Tokyo Electron’s Nanotec Museum has done a great job summarizing the differences and similarities.
A charge-coupled device (CCD) image sensor has an array of capacitors, each carrying an electric charge corresponding to the light intensity of a pixel. A control circuit causes each capacitor to transfer its contents to its neighbor, and the last capacitor in the array dumps its charge into a charge amplifier. The bucket-brigade style of data transfer is characteristic of CCD sensors.
In contrast, a complementary metal oxide semiconductor (CMOS) image sensor has a photodiode and a CMOS transistor switch for each pixel, allowing the pixel signals to be amplified individually. By operating the matrix of switches, the pixel signals can be accessed directly and sequentially, and at a much higher speed than a CCD sensor. Having an amplifier for each pixel also gives another advantage: it reduces the noise that occurs when reading the electrical signals converted from captured light.
The key here is that an image sensor captures light, and light is light no matter if it’s a direct source or reflected. While modern automatic high-beam systems are usually fairly good at detecting direct light sources like headlights within their cameras’ framing, reflected light can be confused for headlights, which is annoying when our roadsides are full of reflective surfaces.
Some 52 years ago, 3M engineer Tim Hoopman started to have a crack at prismatic retroreflective sheeting that could be laminated to road signs for increased reflectiveness at night. According to 3M, it almost worked, except this initial prototype wasn’t effective from every angle. However, after 12 years of research and development, the chemical firm was finally granted a patent on a film that worked from every angle. Today, laminated sheeting like this is used on a majority of traffic signs in North America, and this is where the problem with automatic high beams starts.
Remember how I said that light is light? It turns out that the high-beam light put out by a car’s headlights, then reflected by road signs to that car’s automatic high-beam cameras may cause the automatic high beams to turn off. At night on low-traffic, well-lit sections of interstate highways, this is more of an annoyance than anything. However, on rural roads without much lighting and with no barriers to gate off crossing wildlife, high beams cutting out mid-drive can be dangerous.
These drop-outs due to road signs have been noted by owners of multiple makes and models of vehicles, like the 5thgenrams forum poster in the screenshot above who wrote that “any road signs plays havoc with the high beams” and posted a video of the situation to YouTube. Watch the clip for yourself, and you’ll be able to see high beams cutting off shortly after approaching road signs on multiple occasions within a 98-second period.
Mind you, Ram owners aren’t the only drivers to be irritated by the performance of their automatic high beams. Polestar owners on Polestar Forum, Honda Ridgeline owners, and I’ve noticed this issue myself in multiple press cars across various makes and models. To a camera, incoming light is incoming light regardless of whether it’s reflected or not, and it’s up to the embedded systems in cars to decipher road signs from headlights. Many do a poor job.
Speaking of inconsistency, many Tesla owners have complained about repeated cycling of automatic high beams, and it’s a larger problem in some Tesla vehicles than others due to variances in override controls. In most cars, you turn on the high beams by pushing the left steering column stalk toward the dashboard, where it then holds in place. However, Tesla’s been on a minimalism streak, and with that has come the elimination of steering column stalks. In the new Model 3, along with the current Model S, Model X, and the Cybertruck, getting the high beams to stay on requires holding a button for a few seconds. As per Tesla:
Press and hold to turn on high beam headlights – touchscreen displays a brief timer and you must hold for the duration of the timer to latch the high beam headlights to the on position. When headlights are on, press the button a second time to turn them off.
When you’re in motion, every second counts, and the quicker you can activate a function, the quicker you can get back to focusing entirely on the road. Keep in mind that at 60 mph, a vehicle travels 88 feet per second, so by even shifting your attention away from driving for four seconds, you’ll have traveled more the length of a football field from goal line to goal line.
It’s worth noting that automatic high beams can be useful safety aids. Humans often aren’t great at judging appropriate times to use their high beams, and the visibility difference between low-beam headlights and high beams can be staggering. In the words of the Insurance Institute for Highway Safety:
Researchers from IIHS and the University of Michigan Transportation Research Institute found that drivers in and around Ann Arbor, Mich., didn’t use their high beams enough (Reagan et al., 2017). Only 18% of drivers who were isolated enough to make use of their high beams did so.
Using high beams when conditions allow makes it easier to spot obstacles in time to avoid them. For example, a driver of a 2023 Subaru Solterra should be able to spot an obstacle in the left lane 202 feet ahead while using low beams and 533 feet ahead while using high beams.
High-beam assist could improve the high-beam use rate if drivers are simply forgetting to turn on their high beams, are unsure whether oncoming vehicles are far enough away to do so safely, or underestimate the effect of high beams on visibility.
Automatic high beams have improved vastly over the past few years, but they’re still sometimes no match for the human eye. While this feature does offer real safety benefits, technology isn’t infallible, and if something is operating in an obviously incorrect way, it’s often best to use your own judgment and override the system.
(Photo credits: Acura, openclipart, 5thgenrams, Tesla Motors Club, Honda)
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Question: are all the modern ADAS features defeatable? Like are you stuck with auto high beam, or can you manage low/high beams manually? What about lane assist?
The more car tech evolves, the more worried I get that my 2013 vehicle with no ADAS or internet will be totaled and I’ll end up in a surveillance mobile I don’t control the function of.
At what point do we just stop and admit we need better driver training? You know who doesn’t complain about their highbeams and visibility? People who are taught *exactly* what the function is and when to use it. It also stops people driving around with them on in residential streets blinding every poor soul coming towards them.
Cars aren’t toys, they aren’t household appliances, they are *tonnes* of steel, being propelled across the earth at speeds that if abruptly interrupted can be life altering.
People need to get over their inconveniences and learn to control these things with the wrinkled lump inside their skulls, or just hand their licence over and get on a bus.
Yet another reason Tesla (since it has the damn hold button/look at screen BS) is fucking stupid coming up w/ shit “solutions” which are actually problems and didn’t need to be “fixed” for the sake of “disrupting” This is called going backwards
It it ain’t fucking broke, don’t fucking fix it
I can’t prove it, but I think that those systems turn the lights on too soon after passing a car. On the opposing end, I see a car coming, that turns their high-beams off, and then 20 feet in front of me, they snap back on, for fun sudden blindness.
I don’t have them on my ’14 BRZ, and have no way to tell if I’m right, or if people are just turning them on manually too soon.
There is a simple solution: Don’t use the auto function on the lights – problem solved. I’ve never used auto lights in my Ridgeline and I’m always using my high beams at every opportunity.
Vehicles with auto high beams drive me nuts anymore. As a dog walker during darker hours, I get blinded all the time by vehicles with them on. High beams should never be on when in a neighborhood; low beams should be just fine for the posted speed limit.
Given that headlights are LEDs now, you could randomly turn them off for an imperceptible moment, and the camera could look for that flicker, and know it was a reflection of your own lights. Because it’s random, it wouldn’t sync enough to be fooled by other vehicles headlights. The better flashlights dim by cycling on and off, you don’t notice if it’s fast enough.
I hope a lot of automotive engineers see your comment, smack their foreheads, and grumble “why didn’t I think of that”!
I think part of it is reflective signs have gotten real bright. Lots of times I find myself dimming my headlights to reduce the reflected glare from a large white sign on a dark road. If you have a line of yellow arrows in a curve, it can really keep you from seeing what’s on the side of the road.
You make a good point but I wonder if it’s the different color temperature of today’s headlights (LED) that make the reflection brighter. I remember feeling that the signs glowed back less brightly with my yellow LED fog lamps on, and – of course – with my halogens too.
In the 80s a gf had a fancy Buick(?) with a cool ray gun on the dash. It was the light sensor—complete with knurled knob on the back to adjust sensitivity. Actually worked pretty well.
I am the light sensor in my old cars 🙂
Teh Auto HB on my Bolt works fairly well, but doesn’t turn off when I think it should. As I approach an intersection, a car on the cross road doesn’t emit enough light to turn them off so I end up blinding someone who is waiting for me to go past so they can come into traffic. Side marker lights aren’t bright enough for the system to recognize.
The system in my ’22 Hyundai Kona never was fooled by reflected signs. Worked great under all situations.
I’m really starting to wonder if all of the driver assistance features and automated systems are just enabling drivers to pay less attention.
We’re only just now beginning to realize what the unintended consequences are from the decades of adding bulk to all the vehicles through passive safety advances through the years requiring every new model to grow.
So in ten years are the drivers going to be completely incapable of paying attention to anything happening through all these automation and self-driving efforts? Not to mention the constant fight of actively pulling attention off the road by adding all the screens and features buried therein while hurdling down the road at high speed.
I know things are already bad and we’ve been distracting ourselves with phones, food, music, passengers, etc forever. But things are getting out of hand and we’re not really paying full attention to what goes on inside the car for average drivers when designing these systems.
TL;DR: I fear for the future.
Remember what all the humans looked like in “Wall-E?” That’s what’s happening with all these systems.
Or you just put a button under your left foot!
I miss the floor mounted high-beam switch!
I used to like it but then I got my Austin Healey. Left foot switch is less convenient with a clutch!
I don’t miss it. Anywhere that got snow and used salt on the roads would find the switch rusted and unusable when you needed it. Taking the switch off, freeing it up with some sort of lube and reinstalling it was a regular occurrence.
I don’t miss the darn things at all.
Or the corrosion would affect the circuit: hit a bump and the headlights flicker off for a second. Went down a washboard road in a 70 F100 one time looking like we had a strobe light going
Learning to drive in Texas, this was not a problem I ever encountered.
My first experience with auto high beams was my wife’s ’20 Kia Soul. It was a neat little toy, but it gets confused way too easily by exactly the subject of the article. Driving around a neighborhood can be enough to make you think you’re in “da clurb.”
I finally got it on my personal vehicle with my ’22 Mazda CX-30. While I’m sure there’s another step in this technology line, it was close to night and day. The CX still gets stumped by signs, mostly when the sign is on a curve in the road and looks to be head on, and there is the odd times that coach lights on houses will read like headlights. However, the system as a whole is much better.
Bonus for the CX: the implementation of the high beam system. If the headlight switch is set to “on,” there is no choice for the auto high beam, and the stalk is like any other car to activate the high beams. If the switch is in the “Auto” mode, auto high beams are on by default; if there is a need to turn that system off (for instance, a runner on the side of the road like noted below), the button on the end of the stalk is the on/off switch for the auto high beams, there is no monkeying around* to get back to the normal headlights.
*: The system in The Wife’s Kia is dumb to turn off. First, you press the stalk forward to activate auto high beams. Then, if you want the system off, you press the stalk forward again, to activate normal, on-all-the-time high beams. THEN, you pull the stalk backward to turn off the high beams. This is why I rarely use the auto high beams in that car!
The system in my ’15 Ram sucks. In no particular order, it does the following annoying things:
These systems seem like such a good idea and I tried hard to leave it on, but eventually its refusal to turn high beams on was the last straw and I turned it off.
Of course, this problem could be alleviated if the NHTSA would get around to finalizing the rule allowing adaptive high beams like what’s been available in Europe for years.
But thanks to the bureaucratic mentality, we Americans can’t have nice things (unless, of course, you were lucky enough to buy a car with the correct hardware and software that could be properly, erm, told what to do, but that’s a different story for a different day).
This is really the solution. The concept of low/high beams is made irrelevant by modern matrix headlights. Who cares if it dims around a reflective street sign if the everywhere else around it is still lit up.
I thought I’d like auto high beams but after the first few times it didn’t work I just turned it off and left it off. Operating high beams manually is simply not that hard.
The only modern safety system I’ve really liked (and it was a surprise to me) is the rear cross-traffic alert. It sees around corners where I can’t, and regularly spots cars and pedestrians hidden by my giant c-pillars or behind the brodozer parked next to me.
I turned auto high beams off in my truck also. Too often they shut off for no reason or stayed on long enough that I had to turn them off manually to avoid blinding someone. Pointless system IMO.
I love that cross traffic alert. I agree that it’s about the only one I’ve used that really seems to be worth it.
Most pointless is the little light that comes on when the car detects a pedestrian. There are situations where the person is on the sidewalk in a curve but the car hasn’t figured out that I’ll be turning and not hitting the person. The flashy light goes off and the car screams at me for nothing.
First time this happened in my Vauxhall Insignia (UK equivalent of Buick Regal) I was so surprised I almost drove into the pedestrian… Hadn’t read the manual, of course, do I had no idea it did that.
The auto high beams in my 2017 Mazda get fooled by lamps at the end of driveways and sometimes by flood lights. My wife’s 2018 Honda doesn’t have as much trouble with things like that.
Same here with my Mini Cooper. My work commute includes a road through a swanky neighborhood that has a lot of the masonry pillars topped with lights at driveway entrances. They tend to keep the high beams off. In this case at least, it’s on a 30 mph road so high beams aren’t really necessary anyway.
My biggest beef with auto high beam systems is different. As a frequent nighttime runner/pedestrian I am often blinded by vehicles that never dip their high beams for pedestrians. The problem has grown worse over the past couple of decades. Drivers can override the auto system, but increasingly, they don’t. They’re too used to the system dipping the headlights for other cars and they drive everywhere with high beams enabled, even when they don’t need them. I wear a high reflective vest and leg and wrist cuffs, which (I confirmed with my local police by testing in all weather) make me visible from over a half mile away, especially in high beams and I can actually see most drivers adjust their lane positions a safe way off to widen passing distance, but they don’t usually drop their high beams, which makes it extremely difficult to see any side of the road irregularities or puddles that may cause me to lose footing. The problem isn’t with the system, except that it doesn’t account for pedestrians, it’s with drivers’ over reliance on automated systems. All this auto everything stuff can be dazzling, but not necessarily in a good way.
Similarly, if I am waiting at the end of my track to join the road in the dark, cars with auto high beams only see me side on and will not dip, blinding me as I look left and right. Drivers without auto high beams see me waiting and dip.
The system in our VAG products works well, but the system in our previous Cadillacs was excellent. I always wondered how it distinguished different types of light because they do a pretty good job of knowing when to turn the high beams on and off. The main annoyance we have now is the system has to be manually activated every time you drive, you can’t even code it to come on automatically with VCDS.
What I find pretty interesting on my Pacifica is that if the car in front of you has a busted taillight, the high beams goes on automatically. Neither my Chevrolet or Polestar have this behavior. The Polestar has on consideration street lights, if there is no traffic but there are street lights, the high beams will not come on.
The auto high beam systems on my 2016 Miata and my 2020 Ford Fusion respond very differently. The Miata seems to operate very precisely and accurately, responding nearly instantly and correctly. The Fusion tends to dim the headlights too slowly or not at all in response to oncoming traffic. Pulling the turn signal stalk to the low beam position on the Miata keeps it locked in that mode and pushing it toward the dash locks it in automatic mode, cycling between high and low as needed. The Fusion seems to operate (sloppily) in automatic mode regardless of the position of the stalk. However they both seem to be able to differentiate road signs from oncoming traffic.
My personal experience with this in a rental Civic was that it… really isn’t a problem. The high beams automatically come on, which is nice. And yes, they flick off for some road signs. But dark rural roads that you really need high beams on just don’t have that many signs. And it’s not like the turn off for very long or that the lights completely go out. 1-2 seconds of low-beams and then back to high-beams. Unless you are going way too fast, you haven’t even made it halfway to the point where your low-beams ended at the start before the high-beams are back on.
Just give me an old fashioned low-hi switch and no automation.
…and on the floor. How old fashioned can you get?
I want a hand crank for my windshield wipers.
The photocell system in my 76 Lincoln MK lV worked fine……well it did after I cleaned the eye.