Pennsylvania State Route 108 runs east-west in Northwestern Butler County. This runs from Pennsylvania State Route 8, near Branchton, to the Lawrence/Butler County Line, near Elliott Mills. PA St Rt 108 passes through the following town in Butler County. Slippery Rock PA St Rt 108 is multi-plexed in Butler County. Pennsylvania State Route 173, near Slippery Rock. PA St Rt 108 intersects the following highways in Butler County. Pennsylvania State Route 8, near Branchton. Pennsylvania State Route 173, near Slippery Rock. Pennsylvania State Route 173, at Slippery Rock. Pennsyvlania State Route 258, at Slippery Rock. Interstate 79, near Elliott Mills.
