A good lesson to start the weekend with... had too much to drink? Don't drive. Period.

TMZ is reporting that Katy Perry's GOLD Promotional Vehicle has been struck by a drunk driver this afternoon.

"The collision occurred 15 minutes ago near a truck stop in Pennsylvania.  We're told the driver of a semi-truck slammed into Katy's whip, causing substantial damage to the cab.  We're told the semi driver is in the process of being arrested for drunk driving.

Now the good news.  The precious cargo is fine ... because Katy wasn't in the truck at the time of the crash.  As for the others who were inside, we're told they're ok."

TMZ has obtained pictures of the crash.