The various meanings of flashing your high beams

[Alps]

Oncoming traffic:
~ Several fast flickers on and off: danger ahead, slow down now and be alert (could be accident, animal in road, rockslide, bridge out, flooding...)
~ One or two moderately fast flickers: speed trap ahead
~ One long flash: you left your high beams on, or your headlights are off (or maybe one is out)
~ Turn on and stay on: all of the "one long flash" meanings, or you are drifting over the line (or cutting a pass too close)

Behind you/same direction:
~ Several fast flickers on and off: I am an asshole who wants to tailgate you. You should slow down to 1/8 mph faster than the car to your right to annoy this type of person to the fullest extent possible.
~ One or two moderately fast flickers: You just cut me off and are going slower than me. Speed up and get back over, or just get back over, and look next time.
~ One long flash: I've been watching you drive erratically for some time now, and now I'm fairly close behind you. Sober up and let me get away from you.
~ Turn on and stay on: You're using up the passing lane and not passing anyone.

[Alps]

"oops, I thought that was the windshield washer fluid"

Actually, that's fun to do to someone tailgating you.  Send the washer fluid up and over the car at 70 mph and onto their windshield.  The tailgater usually takes the hint.

I always appreciate the free windshield wash, myself.

[1995hoo]

you're passing a line of slow-moving trucks and the guy just wants to pass faster.

this I disagree with.  I think it is more courteous to pass one vehicle at a time, allowing faster traffic behind you to go before you pass the next one.

It's often impossible to do so when passing a group of vehicles spaced closely, and it's not practical to suggest drivers wait until it's obvious that there's room to pull back in one car ahead in case a faster driver should happen to come up on the left.

Not to mention that if you cram yourself back into a line of trucks, it can sometimes get downright difficult to pull back out to pass the rest of them if the traffic is heavy. Another consideration is terrain. I WILL NOT, under any circumstances, pull in front of a truck on a downhill grade that's anything more than a minor downhill. I cited I-81 in Virginia earlier and it's a prime example of a road where some of the slopes are bad places to be in front of a truck. Anyone who's driven in the mountains knows what I mean. I don't care if it means another driver behind me gets inconvenienced–I just don't consider it safe to pull in front of a truck going down a hill.

Anyway, the examples people have cited are all reasons why I don't like to state absolute rules most of the time (the foregoing paragraph being a notable exception). I won't say "I'll never pull into a line of trucks just because someone going faster wants to pass." Sometimes it can be fine to do so. But I won't say "I'll always let the faster person by," either. There are just too many variables.

In regard to agentsteel53's comment about passing one vehicle at a time, that's a situation that depends heavily on the traffic. Say you get stuck in the "Grandpa cruise control pass" situation where the trucks are in the right lane going about 65, the speed limit is 70, and you join a line of cars in the left lane all going about 68 because Grandpa up at the front of the line had his cruise control set at that speed and pulled out to pass the line of trucks and now everyone's stuck. Why the heck should I pull back over between the trucks just because some guy behind me wants to go 75? Where's he going to go if I move for him? Nowhere.

[agentsteel53]

I think we both know that you specifically contrived an example out of a situation in which it's clear that grandpa needs to speed up, finish passing, and get over.

I would make that kind of obstruction illegal.  I believe it is the case in Germany.

[agentsteel53]

Oncoming traffic:
~ Several fast flickers on and off: danger ahead, slow down now and be alert (could be accident, animal in road, rockslide, bridge out, flooding...)
~ One or two moderately fast flickers: speed trap ahead
~ One long flash: you left your high beams on, or your headlights are off (or maybe one is out)
~ Turn on and stay on: all of the "one long flash" meanings, or you are drifting over the line (or cutting a pass too close)

Behind you/same direction:
~ Several fast flickers on and off: I am an asshole who wants to tailgate you. You should slow down to 1/8 mph faster than the car to your right to annoy this type of person to the fullest extent possible.
~ One or two moderately fast flickers: You just cut me off and are going slower than me. Speed up and get back over, or just get back over, and look next time.
~ One long flash: I've been watching you drive erratically for some time now, and now I'm fairly close behind you. Sober up and let me get away from you.
~ Turn on and stay on: You're using up the passing lane and not passing anyone.

~ anything in Morse code: I expect you to know Morse code.

[colinstu]

I can't really think of anything new to add to this thread (besides taking it off topic).

Oncoming... I use the same random/"good feeling" amount of flashes regardless of what I mean by it, but when I do it can mean:
* Cop ahead, slow your shit down
* Stopped vehicle in a lane, consider a way to pass a jam (good for roads with intersections and someone breaks down and there's a huge line of cars blocked up and confused why they're not moving)
* It's night out and your brights are on. Turn them off until I pass.

Same direction:
* You pulled a cock move. Horn works better most of the time, but some opportunities only need a more passive warning.

I also flash my hazards for a number of things:
1) I know truckers will flash them as a "thank you" for letting them merge into your lane
2) Someone who's had their turn signal on for no reason.... pull up in front of them and flash your hazards until you think they've gone "huh? wha? *looks at own turn signal* oh." ...it's worked
3) Same as above but if they're tailgaiting you and/or have their brights on. Some get the hint, some are dicks/clueless.
4) I've used it as a "thanks" and "I don't know where the hell I'm going so I might drive slower"

[1995hoo]

I think we both know that you specifically contrived an example out of a situation in which it's clear that grandpa needs to speed up, finish passing, and get over.

I would make that kind of obstruction illegal.  I believe it is the case in Germany.

I didn't contrive anything. It happens all the time on I-81. I-95 through the Carolinas, too (but that road is a lot flatter, at least).

....

I also flash my hazards for a number of things:
1) I know truckers will flash them as a "thank you" for letting them merge into your lane
....

I've also observed that truck drivers will flash their headlights on and off to say it's clear to move back over. I've adopted that habit as well. Most people seem to understand it, although in the DC area I think sometimes people are taken aback when you do something nice!

[agentsteel53]

I think we both know that you specifically contrived an example out of a situation in which it's clear that grandpa needs to speed up, finish passing, and get over.

I would make that kind of obstruction illegal.  I believe it is the case in Germany.

I didn't contrive anything. It happens all the time on I-81. I-95 through the Carolinas, too (but that road is a lot flatter, at least).

it happens everywhere.  what I meant is, you described in great detail your situation and how you expect drivers to react to you, and completely ignored the fact that grandpa is 100% at fault for causing congestion.

it's a deck-chairs-on-Titanic situation.

[empirestate]

Usually the best way to get LLB's out of your way is to approach the exit they were planning to take anyway.

I could not parse this.  do you mean "pass them on the right"?

No; meaning that some people will just get in the left lane for the duration of their travel on the freeway, and often when one of those people does appear to finally get the hint and move to the right, it turns out that they only did so because their exit is coming up and they needed to move over to take a right-hand ramp.

[1995hoo]

I think we both know that you specifically contrived an example out of a situation in which it's clear that grandpa needs to speed up, finish passing, and get over.

I would make that kind of obstruction illegal.  I believe it is the case in Germany.

I didn't contrive anything. It happens all the time on I-81. I-95 through the Carolinas, too (but that road is a lot flatter, at least).

it happens everywhere.  what I meant is, you described in great detail your situation and how you expect drivers to react to you, and completely ignored the fact that grandpa is 100% at fault for causing congestion.

it's a deck-chairs-on-Titanic situation.

Of course he's at fault. But why does that mean I should slow down and move right into a line of trucks just so a prick who's tailgating me can move past and tailgate the guy in front of me? That's what I interpret you to be saying I should do in that scenario.

[Alps]

I think we both know that you specifically contrived an example out of a situation in which it's clear that grandpa needs to speed up, finish passing, and get over.

I would make that kind of obstruction illegal.  I believe it is the case in Germany.

I didn't contrive anything. It happens all the time on I-81. I-95 through the Carolinas, too (but that road is a lot flatter, at least).

it happens everywhere.  what I meant is, you described in great detail your situation and how you expect drivers to react to you, and completely ignored the fact that grandpa is 100% at fault for causing congestion.

it's a deck-chairs-on-Titanic situation.

Of course he's at fault. But why does that mean I should slow down and move right into a line of trucks just so a prick who's tailgating me can move past and tailgate the guy in front of me? That's what I interpret you to be saying I should do in that scenario.

No, he's saying that if you're in that scenario, the flashing is really directed toward the front of the line, not you, and you damn well know it has nothing to do with you because you're one in a line.

[agentsteel53]

No, he's saying that if you're in that scenario, the flashing is really directed toward the front of the line, not you, and you damn well know it has nothing to do with you because you're one in a line.

if someone behind me flashes and I can't do anything because I am obstructed by someone in front, I "pay forward" the flash. 

[Duke87]

If I am letting someone turn in front of me I will physically wave them on with my hand/arm to convey that message (this being what I was taught to do in driver's ed).

I... don't remember the last time I flashed my headlights at someone. It isn't something I typically do, for any reason. Headlights from oncoming traffic on a dark road at night are all blindingly bright to me so I really can't tell whether someone has their highbeams on unless I see them dim them. I don't flash to warn of cops because I am not comfortable with the idea of assisting people in evading the police (paranoid fear: I'm going to get pulled over for warning people that there's a cop). And if I am dissatisfied with someone's speed in the left lane I just pass them on the right - it solves my problem faster and is less confrontational.

[corco]

I typically flash hazards for wildlife/appliances/things like that in the road- that way people behind me can see it too.

I'll throw my left blinker on to tell somebody to either expedite their pass of me or get over so I can pass them.

I only flash for three reasons:
1) Oncoming driver left his brights on
2) I just passed a cop
3) Somebody cuts me off in a dangerous way or passes me and slows down on a wide open road.

[1995hoo]

No, he's saying that if you're in that scenario, the flashing is really directed toward the front of the line, not you, and you damn well know it has nothing to do with you because you're one in a line.

if someone behind me flashes and I can't do anything because I am obstructed by someone in front, I "pay forward" the flash. 

I think what we might be disagreeing about is simply our view of whether that's practical. If I'm immediately behind the guy who's obstructing the traffic, then yeah, absolutely I'd flash my lights at him. If it went on for an extended period I might blow the horn as well. But if I'm fourth or fifth in a line of traffic stuck behind a slowpoke, I'm unlikely to bother flashing my lights regardless of what the guy behind me does, simply because I see little point in it. The odds are slim to none that the guy in front of me will interpret it as directed at the lead driver.

But if the guy behind me comes up and tailgates me as a way of telling me he wants to go faster, he can go fuck himself.

[agentsteel53]

I think what we might be disagreeing about is simply our view of whether that's practical. If I'm immediately behind the guy who's obstructing the traffic, then yeah, absolutely I'd flash my lights at him. If it went on for an extended period I might blow the horn as well. But if I'm fourth or fifth in a line of traffic stuck behind a slowpoke, I'm unlikely to bother flashing my lights regardless of what the guy behind me does, simply because I see little point in it. The odds are slim to none that the guy in front of me will interpret it as directed at the lead driver.

But if the guy behind me comes up and tailgates me as a way of telling me he wants to go faster, he can go fuck himself.

you're contradicting yourself.

"if someone is in front of me, he is obstructing traffic"
"if someone is behind me, I am not obstructing traffic"

[1995hoo]

I think what we might be disagreeing about is simply our view of whether that's practical. If I'm immediately behind the guy who's obstructing the traffic, then yeah, absolutely I'd flash my lights at him. If it went on for an extended period I might blow the horn as well. But if I'm fourth or fifth in a line of traffic stuck behind a slowpoke, I'm unlikely to bother flashing my lights regardless of what the guy behind me does, simply because I see little point in it. The odds are slim to none that the guy in front of me will interpret it as directed at the lead driver.

But if the guy behind me comes up and tailgates me as a way of telling me he wants to go faster, he can go fuck himself.

you're contradicting yourself.

"if someone is in front of me, he is obstructing traffic"
"if someone is behind me, I am not obstructing traffic"

You're putting words in my mouth. I never said that a line of four or five cars might not be viewed by certain people as an "obstruction."

My point is simply that, as with so many other things in life, it's a case of what is REASONABLE. (Reasonableness is a significant guideline in many areas of law, especially tort law.) I consider your position here to be unreasonable, especially if you are suggesting that it is either permissible or acceptable for you to tailgate someone who's stuck in a line of traffic because of a slowpoke at the front. Under no circumstances is tailgating acceptable.

Flashing your lights, whatever. Go ahead and do it if it makes you happy, but my point is simply that if you're trying to get every driver in a line of cars to move out of your way when they're all trying to get around a chain of slow-moving trucks or whatever, then you're wasting your time. If you flash your lights in that situation and the people in front of you don't move over, then you have to live with it. Is it annoying? Of course it is. But it's life. We've all encountered the situation where you have to work your way around someone.

This brings me back around to another issue on flashing your lights to say "let me past." I have no problem with that signal as a general matter. However, regardless of whether I'm the flasher or the flashee (is that even a word?), I construe it as meaning the person in front should move over when it is safe and reasonable to do so, not "you're in my way and you need to move RIGHT NOW." I previously mentioned the example of a truck going down a mountain. I don't think it's reasonable to expect someone to move over to the right in front of a truck in that circumstance. Similarly, if there's an on-ramp on the right and someone's trying to enter the highway, I'd say you don't move right until you're past the acceleration lane (unless he's so far back on the ramp you can't come into conflict). I suppose you could say "that means the person in front being flashed should speed up." Yes and no. We've all seen the hyper-aggressive drivers who want to do 90 to 100 mph regardless of the traffic and who'll weave in and out and tailgate everyone. I don't think it's reasonable to demand that someone else speed up to 100 mph, especially if you're in a state like North Carolina or Virginia that has a statute defining reckless driving in terms of speed. That sort of thing is also why in my view the person flashing his lights to ask ("ask," BTW, not "order") a person to move should consider whether it's useful or appropriate under the circumstances. I don't believe that the mere fact that someone in front of you may be "obstructing" you from going faster than you want is necessarily sufficient reason to justify flicking the high-beams. On the other hand, going back to the "Grandpa cruise control" example, if Grandpa could solve the problem by speeding up 5 mph, getting over to the right, and then resuming his preferred speed, then that's absolutely what he should do.

I guess what I'm saying is this: I think in practical terms we probably agree for the most part that the left lane is for passing and people should, when possible, avoid cruising in the left lane and should normally try to complete pass in a timely fashion and move back to the right. I think we also agree that flashing the high beams to say "please move over" CAN be appropriate. It's the part beyond "can" where we seem to disagree. Your comments come across to me as an attempt to prescribe an absolute set of rules, i.e., "You should always ____." I shouldn't be surprised to find that sort of attitude on a road-related site where some people advocate slavish adherence to the MUTCD even if it's impractical or if the MUTCD is wrong. But I've simply found in years of driving that it's not realistic to view the roads in that way. We all know that it doesn't matter what the law might say or how the driver's manual says you "should" do something or how the MUTCD drafters think people "should" interpret a sign–in the real world, conditions are usually far from ideal.

My rule of thumb is that if I find that I'm constantly having to flash my lights at other drivers to demand they move over, and if the majority of the other drivers would have to slow down in order to move over to let me past, it's a sign that I'm probably going unreasonably fast for conditions (because "conditions" includes other traffic). I don't encounter that situation much anymore. When I was in my 20s I tended to drive at very high speeds and to get annoyed at people I considered "slowpokes." I generally don't bother anymore, mainly because my insurance rates are pretty low and I'd like to keep them there! (I've never been in a situation where I'm the one at whom a lot of drivers are flashing their lights!)



One final thought: All my comments above apply to situations where there are two lanes in one direction. I do not believe it's EVER appropriate to demand that someone in any lane other than the left lane (or the right lane in a right-hand drive country, of course) should speed up or move over for you. Pass on the left when you can.

[Truvelo]

Over here flashing your lights can have opposite meanings to elsewhere. Instead of letting other traffic know you're coming through it's often used to let vehicles out of side roads or to let oncoming vehicles proceed if there's an obstruction in the road narrowing it down to a single lane.

On freeways truckers will flash their lights to let a truck passing them know it's safe to pull back in.

Of course, flashing lights (usually several times in quick succession) is used to inform oncoming traffic of a speedtrap or if animals are in the road.

[agentsteel53]

while 100mph and weaving is certainly reckless, I do believe it is reasonable that drivers, when getting into the left lane to pass, proceed at speeds closely approaching the threshold below which they will be safe from police interference.  in California, this is widely recognized as "80mph on the freeway"*.  95% of drivers will either constantly go at this speed, or speed up as necessary when getting into the left lane to pass. 

* gee, this well-known numerical limit on driving speed, beyond which one can reasonably expect a citation, and below which one can reasonably proceed without such expectation...

wouldn't it be nice if this information - those two words, and the number - were somehow combined on a single highway sign, posted at regular intervals? 

nah, I must be dreaming.

[kphoger]

Flashing your brights at me, I will translate as the following:

(1) It's dark and I don't have my lights on.
(2) I left my brights on, and they're blinding you.
(3) There's an obstacle ahead.
(4) There's a cop ahead.
(5) You're letting me go first at an intersection or one-lane pass (USA only).
(6) You're going to go first (and I should wait) at a one-lane pass (México only).

The message I most commonly want to communicate but cannot:  You left your signal on.  Alternating between brake lights and turn signals cues some drivers to it, but only a few.

[agentsteel53]

here's one that is tough to communicate.  "we've established that a resident of the left lane is driving erratically and needs to be passed.  you have started to pass him on the right.  good idea.  however, you are slowing down.  I as well would like to pass him on the right; please continue going at an advanced rate of speed."

[J N Winkler]

One of the trickier aspects of driving, in my opinion, is our inability to specifically and concisely communicate our intentions or grievances to fellow motorists with anything more precise than a signal light, horn honk or hand gesture (rude or otherwise). In particular, I've noticed the the flickering of high beams seems to carry more intended meanings than other types of signal, so I'm curious to what people have used this technique to convey.

My personal philosophy is that the highway isn't the place to use automotive appliances such as the horn or high beams to communicate grievances; I do that from time to time, but I never fool myself that I have been anything but childish in doing so.

In the US I hardly ever flash my high beams because I believe it is nearly impossible for that to be seen uniformly as a facultative gesture.  Warning of enforcement action downstream, wild animals in the road, etc. are all examples of facultative use, but the problem is that a flash is visible to everyone on the road (not just the intended recipient) and can be misinterpreted by someone for whom it is not intended.  Drivers likely to be confused by a flash are not necessarily visible to the driver doing the flashing.

In the UK I have occasionally flashed my high beams in the contexts Truvelo describes (letting the other driver know you will keep open a gap in traffic for them, etc.), but even there I have reservations because it is still the other driver's responsibility to check that his way is clear, and I don't want inadvertently to encourage him to maneuver into an obstacle I cannot see but which should be visible to him.

[agentsteel53]

also bear in mind that flashing headlights might mean something as simple as "vehicle has hit a bump in the road". 

[empirestate]

Over here flashing your lights can have opposite meanings to elsewhere. Instead of letting other traffic know you're coming through it's often used to let vehicles out of side roads or to let oncoming vehicles proceed if there's an obstruction in the road narrowing it down to a single lane.

On freeways truckers will flash their lights to let a truck passing them know it's safe to pull back in.

Of course, flashing lights (usually several times in quick succession) is used to inform oncoming traffic of a speedtrap or if animals are in the road.

If by "over here" you mean the U.K., it's certainly not opposite from U.S. usage, at least in my experience. But more broadly, that's an important point; evidently in my example I ran across a driver who comes from a place where flashing lights is used prohibitively rather than permissively, and it's that unspecificity of meaning in this kind of signal that got me interested in the question. It's increasingly my belief that perceived poor driving habits in NYC and other major cities is mostly due to a high percentage of motorists who learned to drive in countries where the rules are different, are less emphasized by society, or simply don't exist. (That's not to excuse them, just to distinguish them from people who are just terrible at driving overall. Many of the "terrible drivers" in American cities would become highly skilled motorists if suddenly transported to their native areas, just as I can speak well when I'm in an English-speaking country, but I speak extremely poorly in, say, Uzbekistan.)

[bugo]

If a vehicle is coming the other way and the driver flashes the high-beams, I check to see if I forgot to dim mine. (When I first got my current Acura, sometimes jerks flashed their brights at me because they didn't like the HID headlights that come standard on the car. That hasn't happened in several years, so I guess people are accustomed to improved headlights.)

If it's daytime and I see a driver coming the other way flashing his high-beams, I interpret it as warning of a speedtrap. (Some people flash the low-beams on and off instead.)

I've heard some people say you should flash your high-beams to tell someone he forgot to turn on his headlights, but I've always understood that flashing your lights on and off is the correct way to send that message.

I do not understand the current fad of shining your high-beams at someone when you don't like his driving.

But it's OK to blind other motorists with your Acura.