Why do truck flash their lights/indicators when overtaking other trucks?

The first flash from the vehicle passing is to let the one in front know you are about to pass. The passed vehicle will in return flash head lights to inform the passing vehicle that they are passed them and it is safe to change over to the lane. It is not considered rude for a car to do this.

The truck being passed flashes their lights when it is safe for the passing truck to change lanes and get back in front of the truck being passed. The driver of the truck being passed is in a better position to judge when the passing truck has put sufficient distance between the trucks to make the lane change safe.

It would not be rude for you to do this, but it would be misguided and unsafe. Do not guide other vehicles. Leave that to the professional drivers who know all of the conventions, and have the skills to judge accurately and know what the other drivers are doing.

Good question. Keep in most kind trucks have extra lights and the indicator lights on most cars are. by law only supposed to be used for their specific purposes. (You dont want to catch the attention of a by-the-book cop!)

From many hours of driving on highways here in Canada, I believe truck drivers are saying "thanks" for letting them in and flash one another to let the other driver know they have enough room to make a move. (Want a truck drivers take on all of this? Why not go to a truck stop or get a citizens band radio and talk with one a truckers channel.)

In my opinion it would not be rude for a car driver to do it. I have done it and been acknowledged by truck drivers. I think it's great when people actually "share the road." I wish everyone did!

Happy New Year "down there."

Any vehicle that flashes lights behind you is telling you to get over and let them pass. The flashing after the pass is a thank you.

its to let the truck know its save to change lanes, and a thank you from the other truck.....no it would not be rude for a car to help out in the same manner.