Spanntown Road is near SR (state route)-840, not I (Interstate)-840. Actually, there is no I-840 anywhere in TN, though I guess there might be an I-840 (interstate loop off of I-40) in some other state.

As I understand it, SR-840 was designed to be part of the Interstate system, but the feds wouldn't accept the results of the environmental impact study. The local honchos wanted the route so badly, they went ahead and built it without the federal funding, and so it is properly designated as SR-840. It seems I also recall the politicians promising the local landowners that were affected by it that there would be no commercial development along the route . . . we'll see how long that holds. Looks like it's already weakening between Smyrna and Lebanon.