There are few things more frustrating than driving on Interstate 25 and coming up behind a person who's driving 50 mph. In the passing lane.

Turns out the Colorado Department of Transportation doesn't like it, either. It has been using its electronic signs above I-25 to display safety messages to drivers, including one that reminds people to use the right lane unless they're passing.

"If it's not used as a passing lane, it just frustrates people who are trying to do the right thing, and in the end, it creates disgruntled drivers," CDOT Traffic Safety Communications Manager Sam Cole said. "And that's the last thing we want on our roadways with the amount of roadways we see."

When people only use the left lane for passing, it helps keep traffic moving and can prevent some backups on the interstate, he said.

"It's not only best practice, but it's also the law," Cole said. "It's a law I know (Colorado State Patrol) is enforcing rigidly."

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