Today, I was driving on the highway with light snow but enough to slow traffic. During the drive my car hit a patch of packed snow and ice causing my car to veer slightly to the right. As I corrected my car, a tractor-trailer behind me flashed his brights at me.

What does this mean?

He had plenty of space between us, so I am not sure the cause of why he/she did this. Also, in the past I have had truckers flash me with the brights when I change lanes on the highway. I did not cut them off or give them any cause to be upset towards me.

Is there a secret signal for flashing vehicles I do not know about?

  • 1
    i understand the assumption but i was only going about 35 mph (56 KPH) in a speed zone of 60 MPH (96 KPH)
    – IE5Master
    Jan 5, 2017 at 15:03
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    @IE5Master In that case, they may have flashed their lights because you were going too slow.
    – Brian
    Jan 5, 2017 at 17:33
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    I would read it as a generic "hey pay attention". Veering due to hitting ice may look similar to veering from falling asleep or otherwise driving inattentively. Jan 5, 2017 at 20:54
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    @NateEldredge I like this comment. I didn't think of it that way. He might have not seen the patch of snow or ice and thought i was being careless. What are your thoughts about the second part of the post?
    – IE5Master
    Jan 5, 2017 at 21:28
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    I don't know of any secret light-flashing code, if that's what you're asking. But that doesn't mean there isn't one. Jan 6, 2017 at 4:45

2 Answers 2


Flashing lights has several meanings:

  • It is a warning. In many countries if the oncoming traffic does it, it means "Hey, check your car" which is nearly to 99% that you forgot to turn on the lights or forgot to turn off full beam (you are blinding them). If your car is ok, it means most likely that danger is ahead (accident, unofficially speed control). If the car is behind you, it can also mean that something is wrong with your car or it means "Hey, be careful" (it looks like you are drunk or you had microsleep). If the car is faster than you and wants to overtake, flashing warns you of its presence.

  • It is displeasure. If someone is directly behind you on the overtaking lane, flashing means Hey, give way. It is also mixed with warning if the person doing the flashing thinks you are driving bad, e.g. driving too fast/too slow.

  • It indicates help. If e.g. I see that a car/truck wants to overtake before me, I adjust speed and give a short signal to indicate: I have seen you, you can changes lanes. If two cars passes in a constriction, the car who is willing to wait flashes.

This are the most common and nearly universal indicators. If there is reason to thank the person behind you (you are overtaking and the car on the lane gave you way) or acknowledge (you really had microsleep), it is polite to touch gently and shortly the brake two times, so your follower sees two short red flashes indicating "thanks".

  • @pnuts You are always invited to correct grammar....:o) Jan 5, 2017 at 23:06
  • @pnuts With the amount of tag descriptions I must approve from you, I doubt you will have much time left to wreak havoc :-P Jan 6, 2017 at 0:22
  • To add to your answer's last paragraph: "When an 18-wheeler is passing and one gives them a double-flash of high beams when it's safe for him to return to the right lane, the trucker will often strobe his trailer lights as a "thank you". Jan 8, 2017 at 22:45
  • I think "help" might be better indicated as "giving way", or a possible indication of "yielding". E.G. "I see you, I'm giving you room to change lanes.", or "We're both at a stop. You go first."
    – James Haug
    Jul 7, 2017 at 17:22

This Answer requires some presumption based on experience. But...

  • The driver is alerting you to the presence of a large vehicle behind which in low visibility situation, you might not see. That vehicle requires substantially more stopping distance than a car.
  • The driver saw you swerve, thought you are a bad driver and is expressing their displeasure.

While not this case, truckers flashing lights to oncoming traffic has been a signal that law enforcement is stationed ahead.

As for your previous experience, while you might not think you cut them off, professional drivers have a different, less tolerant, view of such things.

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    To add to this, vehicles flashing their lights can also indicate "go ahead", which may have been the case when switching lanes. I recently had a large truck that was next to me slow down a bit and flash its lights after noticing that I had been stuck behind another truck for a while.
    – Brian
    Jan 5, 2017 at 17:29
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    To expand on @Brian's point, trucks will also use it to signal "you are safe to merge into my lane" or "you have enough room to merge in front of me". I think, in general, they do it more for other trucks than they do for cars because of the additional clearance required, but I've had this happen to me on many occasions when I had my turn signal on. Depending on how bad the serve was that the OP did, it is possible the trucker mistook it for an attempt to merge into his lane Jan 5, 2017 at 18:07
  • Very informative answer and comments. I think he was flashing me now to be more careful and mindful of my surroundings. As for the second part, the Trucker was most likely telling me I had enough room or it was OK to merge. Makes sense
    – IE5Master
    Jan 5, 2017 at 21:33

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