Radar cruise control in the fog

If you are using DRCC to go faster than the visibility conditions allow, you are no different than those Tesla drivers that turn on Autopilot and go to sleep, play games, eat, etc. The system saves them the majority of the time, but not always. Accidents in fog are likely happening now because people are putting too much trust in DRCC.

There are many different types of radar.

Commercial planes use weather radar. That isn't trying to look through fog and rain, but to see it. It is used to fly around the worse parts of a storm. It does not see other planes. That is done by air traffic control radar; an S-band system that uses microwaves.

DRCC uses millimeter waves. The effective range is far, far, far shorter, and have high atmospheric attenuation.
If measurements could be made, you would likely find the car is following closer in the fog than on a clear day.

S band - Wikipedia
Extremely high frequency - Wikipedia

 

This is why I linked a scientific paper specific to radar cruise control that says automotive radar penetrates fog.

As to your statement that "if you find yourself 'covering the brake' with your foot at the ready, you've probably already made a dangerous mistake in terms of speed choice or following distance," that's not logical and based on assumption. The way I was taught to use cruise control in drivers ed is that you are always supposed to keep your foot hovering (not pressing) when using any kind of cruise control. That doesn't mean you're driving dangerously, that's just safer.

Everything else held constant, it's safer to have DRCC on in the fog. It's an extra layer of safety. It can help avoid accidents.

From the article you posted:

So in their terms, a kilometer is considered short. But when I drive an hour a day, 4 months a year, through heavy fog, I welcome any increase in margin of safety, even if it's "just" a kilometer or even less.

 

Certainly your foot needs to remain available to operate the brake. We may be arguing semantics on this point; I'm happy to let it drop.

Now this point I will dispute. The radar system is always on for the autobrake safety system as @john1701a pointed out in post #17. The car is using the same radar system with the same range limitations subject to the same atmospheric phenomena to warn the driver about the same potential obstruction ahead. The extra layer of safety enabled by radar technology is already present regardless of the status of the cruise control. Given that the purpose of cruise control is to partially automate the act of driving, adding the use of cruise control to this situation can only reduce the driver's positive authority over the car while cruise is in use.

The act of letting up on the accelerator to reduce speed is incredibly instinctual and very effective in a low visibility situation. Abandoning the layer of safety provided by that reflex to rely solely upon the radar system simply isn't good enough for me and my passengers.

If my own reduction in speed leads me to fear that I might be hit from behind, the only reasonable conclusion is to get off the road and wait for conditions to improve. Over the years this strategy has allowed me to (eventually) drive past several pile-ups without deeper involvement and I am satisfied by that result.

 

If you read the TSS-P brochure, you'll see that automatic emergency braking is designed to provide a potential speed reduction of 25mph. It's not designed to safely stop the car, but it might sometimes. It reacts late so as not to be too intrusive. I've never had it activate, but I've had the red BRAKE warning and beeping activate a few times (about 50/50 useful vs false alarm).

If automatic emergency braking activates, presumably it applies maximum ABS braking. My point above was, if the road is slippery, then by the time it activates it might be too late for any significant braking. Stopping distance could be significantly longer than on dry pavement.

The DRCC will safely and (somewhat) gently bring the car to a complete stop assuming it detects the car in front of you. Assuming there's a disabled car in the fog ahead, gentle braking gives the driver more time to react; it doesn't require as much traction; and it gives cars behind you more time to react.

TSS 2.0 (which we don't have) is a little better and offers a potential speed reduction of 32mph.

Cruise control on slippery roads does have some issues. In one case I was driving a different car, overloaded with three bikes on the back and all my stuff driving across the country. The tires were a little worn (still above the legal limit but probably 4-6 32nds), and it was raining, and there was less weight on the front suspension then usual. I had the cruise control on, and at one point the car decided to kick down to second gear unexpectedly, maybe because it started hydroplaning. I felt the front wheels slip, and I cancelled the cruise control really fast. Luckily nothing bad happened, but if it had taken longer to cancel the cruise control it might have been worse.

I can't say that cruise control is a good idea in bad conditions, but it would be nice to have an extra safety net besides just the last second automatic emergency braking.

 

I hear what you're saying, but there's two points that I disagree on. First, I appreciate what you're saying about using it with common sense, not exceeding your own capabilities, not becoming over-confident, not relying solely on the DRCC. I'm not talking about solely relying on the radar system, I'm not even talking about automating driving - it's just a driver's aid that's available to help you drive your own car and if used correctly it can save you from an accident, because no matter how careful you are, an unexpected situation can always come up. Also, though you're right reduce speed is instinctual, there's still a response lag of moving your foot from one pedal to the other, whether it be a tiny difference measured in milliseconds, it exists.

Second - automatic emergency braking (AEB) vs DRCC. Have you experimented with AEB? It's pretty tough to get it to actually activate. I've had people cut me off really close in traffic and the AEB wouldn't go off, not even the visual alert. While with DRCC, set to the longest following distance, you get a picture on your display when it encounters a car up ahead (I have my HUD set to display DRCC, so don't even have to take my eyes off the road). Even before it brakes, it usually lets you see if it detects something up ahead. The amount of lead time on that cannot be compared to the AEB.

 

I understand that the milliseconds saved by the DRCC are valuable and serve to enhance safety- my argument is that you should be going so much slower (or stopping) such that milliseconds wouldn't matter.

Our Prius has the auto brakes but not the DRCC. I rent a lot of cars for work. A few have had radar cruise and I've driven one Toyota with the feature, an Avalon.

I did enjoy using the feature, although I felt that it followed uncomfortably close behind leading traffic in most situations. This experience has colored many of my preceding comments. I've tried to find a reference to the actual following distances allowed by the DRCC system but I haven't found anything.

Follow me (ha!) on this:

If that Avalon set to maximum following distance makes me think it is following a bit closely;

And:

Then I am led to believe that the car ahead of you was quite close. Certainly closer than the 264' that the 3-second rule would resolve to at 60mph. Okay, you didn't cite your speed for that incident and I would have guessed it was lower anyway.

Let's say you were going 30, where the 3-second rule resolves to 132 feet of separation. I'm still not sure I ever got that Avalon to trail that far behind a leading car, and you can't actually lock in a cruise setpoint much lower than that- perhaps 25mph / 110 feet?

Zero visibility is valid criteria for temporary road closure in many jurisdictions. A threshold used by meteorologists for "zero visibility" is <100 meters or 330'. That is 1/10th of the internationally accepted visibility distance used to define "fog."

In sum, I suggest that if DRCC is reacting to a car you can't see, it is past time to pull over and wait it out.

Just to acknowledge it, the 3-second rule is intended for daytime / good weather / dry roads. It's also fairly impractical to achieve in modern American suburban arterial highway traffic. But for the sake of this argument let's lower our safety standards and call it a minimum for poor conditions like night and fog.

 

Maybe he's desperately trying to accelerate away from you to get the glare of your headlights out of his field of vision.

 

"Solely" is not far enough. I must go further and say that DRCC also must not be the primary method. It must be secondary, with the driver's visuals remaining primary.

That guy quoted within post #10, traveling 50 mph in impenetrable fog, is clearly using DRCC as his primary. That is dangerous and inexcusable.

Cars are not the only obstacles that must be avoided. There are many other sorts of items that must be avoided, things that today's AEB and DRCC systems seem to still be having more difficulty identifying. So when someone is using these systems to drive beyond their fog vision ...

 

The kilometer quote was for when millimeter waves are used communication systems, not radar ones. 5G uses MMW, and is the reason why so many more cell points need to be installed in order to provide the same coverage as past systems. The distance is also for a clear day. From the link, "Absorption by humidity in the atmosphere is significant except in desert environments."

The max range of DRCC is probably at the max following distance. The only published value I found is 150 meters. Adaptive Cruise Control | HowStuffWorks

Toyota specifically warns that the DRCC might not 'see' a stopped car. The software is designed for following moving ones.

If you are driving at speeds that the DRCC sees cars ahead before you do, then you are solely relying on it.

A poster here hit a wild boar because none of the driver aid systems recognized it.

 

Not sure if it's been mentioned, but getting somewhere by car should never be do-or-die (could be the latter...). If conditions are near white-out, just take the day off.

 

With so many people defending DRCC in fog and apparently driving beyond their own human vision, I think it is important to post the DRCC warnings section of that Toyota document Trollbait linked.

This flat-out says that DRCC will not detect stopped and dramatically slower-moving vehicles, both of which will be common in dense fog. It has difficulties detecting high clearance vehicles, motorcycles, and empty trailers with small rear surface areas (think particularly of that high empty overhanging flatbed, at just the right height for clean decapitations).

It has difficulties managing fog, curves, narrow roads, on- and off-ramps and merges, overhanging structures, bridges, tunnels, lane departures (both you and the vehicle ahead), or a vehicle ahead driving at the edge of the lane (e.g. hugging or straddling the fog line).

Note also the disclaimer that this list is incomplete, see your Owner's Manual for a more comprehensive description.

 

The DRCC can (at least usually) see stopped cars, but if reacts pretty late. Presumably they design it not to be slamming on the brakes all the time for things next to the road.

Speaking of fog, I wonder what functionality relies on the camera? For example if the camera is blocked, the forward collision warning system becomes disabled. Does DRCC use the camera, and to what extent?

 

According to the Toyota brochure images I posted in Post#33, yes it does. It uses both the camera and the millimeter-wave radar.

The "at least usually" part is the killer that makes it unsuitable as a primary driving means. "Usually" is no-where near good enough. Not anywhere close.

With human drivers, U.S. traffic deaths are now slightly over 1 death per 100 Million vehicle miles traveled, and even that seemingly rare rate produces 40,000 fatalities per year. The various driver aids must not be used as a primary driving means until they are demonstrated or certified as being significantly better than that.

 

For the driver aids in general, it means handing over primary crash avoidance to the aids, with the human retreating to a secondary role of overseer.

In fog, a prime example is that writer quoted in post #10 traveling at 80 km/hr in impenetrable fog, and depending on DRCC to slow him down before he can see the taillights himself. He isn't the only one appearing to justify using it to over-drive their human vision.

If you have DRCC, by all means leave it turned on. If it cuts crash risk by 10-20%, it is worth it. But if it cuts crash risk by 50% or more, then the driver is doing something hazardous and taking too much risk.

 

(1) If I can stay far enough behind to come to a full stop without hitting him (should he suffer a full-stop crash or depart the road), yet still see him as a decent visual reference, then I keep up and follow.

Having a visual reference point (taillights) out at a useful distance is a significant help in gauging actual visibility. Gauging visibility distance into a white-out fog without reference points is much more difficult and uncertain. Plus, his headlines lighting up the roadside (and center stripe and fog line) can show objects out to a somewhat greater distance than can my own headlights, which cause greater interference by needing to brightly light up more fog in the round-trip sensing path (headlights to object to retina).

(2) If the fog-speed-traction combination is such that I cannot fully stop within the distance where his taillights are sufficiently clearly visible, then I disengage and slow down, driving solo.

 

I think the concern with cruise control, standard and auto, and why owner's manuals recommend not to use it, is that you might get lax and go faster than you should with it on. You set the speed under conditions with better visibility, and don't think to adjust it as conditions worsen. In the case of DRCC, it will likely adjust speed to the car ahead, but situations like that car leaving the road can result in the cruise control suddenly flooring it, which can be bad on a clear day. Or a car could be stopped part way off the road.

There are numerous situations in which the DRCC may not work. The odds could be low for those occurances, but the driver needs to be able to see what is ahead in order to take action if they do happen. I want DRCC for my highway car, and I think it can help in the fog. I said not to have faith in it preventing an accident earlier, because when you do, you are more likely to take extra risks. It can help, but drive like you don't have it.