Truckers in semis have the benefit of a CB radio to communicate with other big rig drives, but not you. Instead, these professional drivers use the lights on their semi-trucks as a communication tool. What should you do if you see a trucker flashing their lights at you? Here are five reasons you see flashing semi-truck lights in your mirror.

1. Truckers might warn you of a speed trap ahead by flashing their lights

You’re not privy to the communication between semi-truck drivers on the CB radios, but if you see a truck flash lights at you, it’s time to check your speed. According to Drivin’ & Vibin’, that driver is trying to inform you that a speed trap is ahead. This doesn’t happen in every state. While most states agree this warning falls under the First Amendment right to free speech, not all states allow this warning.

2. Semi-truck drivers use their lights to say “thank you”

If you’ve been courteous to a trucker, they’re likely to thank you by flashing their lights. This can be as simple as flashing them on and off after you’ve allowed the semi to pass you and move into your lane. This is an easy way to show appreciation without direct communication. If you’ve ever flashed your lights at an 18-wheeler to let the driver know they have room to move into your lane, you’ve likely gotten the visual “thank you” of flashing lights.

3. Truckers let you know there’s room for you to change lanes

Whether you’ve passed the semi or simply want to move from one lane to the next, if you use your turn signal, as you should, to indicate you want to change lanes, you might see the semi-truck flash its lights at you. This is the trucker’s way of informing you that you have enough room to change lanes and get in front of them.

4. Lights on semis are used as a warning of unforeseen obstacles on the road

Traveling down two-lane highways can mean obstacles in one lane move to the other, or accidents might impede traffic in both directions. If a trucker passes an accident, broken down vehicle, or obstacle that’s in the opposite their lane, they could flash their lights at you. Similar to the speed trap warning, this is a good time to slow down and be extra vigilant.

5. ##&$(%%#^#^@ Yes, truckers might be cursing at you

If you’ve done something on the road that a semi-truck driver deems unacceptable, they might get behind you and start flashing their lights at you repeatedly. Typically, you’ll know the difference between angry flashing lights and other situations. In most cases, you probably know what you did to anger that professional driver at the wheel of one of these big rigs.

Next time you’re driving, pay attention to when truckers use their lights to communicate with you. This communication could keep you out of trouble or make your time on the road more pleasant.

Next, learn how most owners plan to use the new Chevy Silverado EV, or watch the semi-truck saying thank you in the video below: