| State: | PA |
| Type: | PA |
| Route: | 318 |
| Map Custom: | yes |
| Length Mi: | 15.916 |
| Length Round: | 3 |
| Length Ref: | [1] |
| Direction A: | West |
| Terminus A: | at the Ohio state line near West Middlesex |
| Junction: | in West Middlesex |
| Direction B: | East |
| Terminus B: | in Mercer |
| Counties: | Mercer |
| Previous Type: | PA |
| Previous Route: | 317 |
| Next Type: | PA 1926 |
| Next Route: | 319 |
Pennsylvania Route 318 (PA 318) is a 15.9adj=midNaNadj=mid state highway located in Mercer County, Pennsylvania. The western terminus is at the Ohio state line in Shenango Township near West Middlesex where the road continues as Ohio State Route 304. The eastern terminus is at PA 158 in Mercer.
PA 318 begins at the Ohio border in Shenango Township, where the road continues west into that state as SR 304. From the state line, the route heads east on two-lane undivided Hubbard-Middlesex Road, passing through areas of farms and woods with some homes. PA 318 reaches an intersection with PA 718 and continues through more forested areas with residences. The route heads into the borough of West Middlesex and becomes Main Street, crossing the Shenango River into residential and commercial areas. In the center of town, the road crosses PA 18. PA 318 continues past more homes prior to heading back into Shenango Township, where it becomes Mercer West Middlesex Road. The route heads east-northeast through rural areas of residences, reaching an interchange with I-376.[2]
Past this interchange, PA 318 continues through areas of farmland and woodland with homes, passing under I-80. The road continues into Lackawannock Township and runs through the communities of Bethel and Greenfield. Upon heading into East Lackawannock Township, the route curves south then east, passing through agricultural areas. PA 318 passes through a mix of fields and forests as it turns northeast onto Pulaski Mercer Road. The road makes a curve east and enters the borough of Mercer, where the name becomes West Butler Street. In Mercer, PA 318 passes homes before reaching its eastern terminus at PA 158.[2]
| State: | PA |
| Type: | PA-Alt-Truck |
| Route: | 318 |
| Location: | Mercer County, Pennsylvania |
| Formed: | 2013 |
| Decommissioned: | 2018 |
Pennsylvania Route 318 Alternate Truck is a truck route around a weight-restricted bridge over the Little Neshannock Creek on which trucks over 33 tons and combination loads over 39 tons are prohibited. The route follows PA 18, US 62, and PA 158. The route was signed in 2013, but it was decommissioned in 2018 following a bridge repair.[3]