The time zone shift on I-40 in Tennessee? It's at mile marker 328.2. That's where Central Time gives way to Eastern Time as you cruise across the state.

The line between zones zigzags along some county borders. It's not entirely clear why they chose this particular path. About a quarter of Tennessee's counties end up in Eastern Time. The rest? Central Time.

Driving east from Nashville to Knoxville, you'll hit that time change. It's kind of surprising how abrupt it is. One minute you're in Central, the next - Eastern. Going west? Same deal, just reversed.

This split's been around since '47. Seems East Tennessee wanted to join the Eastern club back then. So now Knoxville and Chattanooga are an hour ahead of Nashville and Memphis.

It's important to keep this in mind when you're on I-40. Don't want to mess up your schedule, right? Remember to fiddle with your clock when you cross that invisible line. It's just a small adjustment, but it can make a big difference.