I-840 is a new Interstate highway in the Nashville area. The highway that was state route 840 will be re-signed as I-840 over the next few months, and TDOT expects the work to be done by the end of the year. They’ve already received federal approval to do so.
I-840 branches off from I-40 near Lebanon and rejoins I-40 near Dickson. It makes a wide arc through communities to the south of Nashville. It also crosses I-24 and I-65.
The highway was completed three years ago, but by re-signing the route as an Interstate highway, TDOT is hoping to encourage through traffic to avoid the congested highways in and near downtown Nashville.
Fun fact: Since this Interstate is a bypass (off of I-40), it receives an even-numbered prefix. Spurs, on the other hand, get an odd-numbered prefix.