4 in Harrison Township, Allegheny County, Pennsylvania, is a lock that was built 1920-1927, and opened in 1927, 24.2 miles upstream from the mouth of the river in Pittsburgh.

It is located about 24.2 Miles up the Allegheny River from the Point in Downtown Pittsburgh.

4 has an average water elevation of 745.4 feet above sea level and extends about 6.2 miles upriver to Allegheny River Lock and Dam No.

3 has an average water elevation of 734.5 feet above sea level and extends about 9.7 miles downriver to Allegheny River Lock and Dam No.

[4] Traffic through the lock was about 1.8 million tons in 1998, including shipments of coal, petroleum, sand and gravel, ore, steel, chemicals, fertilizer, salt, flour, lime, and slag.