 The highway is a four lane divided highway from I-840/SR 265 to Interstate 40 where it becomes a four lane non-divided highway to US Highway 70.It then becomes a two-lane highway until it intersects with Airport Road and South Water Ave. in Gallatin.At that point, SR 109 becomes a four lane divided highway once again and continues as a four lane divided highway to just south of the intersection of SR 109 and SR 76 in Portland.