 At Amphoe Tha Sala, the route runs very near the coast (10–50 m) for about 2 km.This is the only section of Route 401 that runs adjacent to the sea.The section of Route 401 between the intersection with Route 4008 near Amphoe Phun Phin and the intersection with Route 4103 near Ban Tha Pae was once heavily used as a main access route to Bangkok for the lower southern provinces.