I've been driving trucks for about 13 years now, so I have to chime in here. When you''re talking about "flashing your lights to let a passing truck know that he's clear to move over", I ask you,
PLEASE do not flash your high beams at night!!! I can't count how many times I've happened to look in the mirror to see if I'm clear, only to get blasted by high beams

. If you do that, you will have temporarily blinded driver behind the wheel of an 80,000lb truck right in front of you! Please, at night, turn off your headlights for a few seconds (leaving the parking lights on at all times) and then turn them back on. Remember, the truck driver, whose eyes are used to the darkness, is looking into his mirror after he/she gets in front you. Flashing the high beams at night is dangerous for everyone on the road, as well as just plain rude. Daytime, yes; night time, no! Most truck drivers use this "momentary headlights off" method, however there are some who aren't so courteous.
Now, as a way of saying "thank you" to someone who has flashed you to let you in (many truckers will do that to pickups towing trailers), since our trucks aren't wired with a "blink" switch (a simple momentary-off toggle switch for the parking lights, I've always wanted to add that to my truck), simply turn on your emergency flashers and let them flash two or three times. That's better than turning your lights on and off, because you won't confuse someone in front of you by letting them see your headlights going on and off. Some driver in front of you might think you're telling him it's okay to come over into your lane. The emergency flashers are easily visible in daylight hours, too.
My other pet peeve: poorly aimed driving lights/fog lights, and headlights, too. What I do in my Dodge, if I have my fog lights on, I always turn them off when I come up behind a truck, even though I know they're not pointing up in the air. I figure if there's anything I can do to make a truck driver's job more pleasant, I'll gladly do it, because I know what it's like.
Don't get me started on the topic of people who drive in traffic with their high beams on!!

That's when a rocket launcher under the hood would be a nice little accessory.
Andy