SR 12 begins in downtown Nashville at an intersection with US 31/US 41/US 431/US 41A/SR 6/SR 11, concurrent with US 41A as its unsigned companion route.

In Cheatham County, SR 12 starts paralleling the Cumberland River before entering Ashland City.

In Montgomery County, SR 12 passes through Fredonia before entering Clarksville at an intersection with US 41A Bypass.

They then continue into downtown, again following the Cumberland River, and coming to an intersection were SR 48 separates.

[2] State Route 455, the Tennessee Waltz Parkway, is a short bypass around Ashland City in Cheatham County.