The 4000 series was intended as an interim solution for the Authority's unrebuilt lines, which could not accommodate the newer, heavier railcars.
 As such, they were assigned to the 47D Drake via Overbrook,  47L Library via Overbrook, and 47S South Hills Village via Overbrook lines, as well as the 47 Shannon line, all trans-versing the Overbrook corridor.
 In 1988, Port Authority retired all of its remaining unrebuilt PCC's due to safety concerns, leaving only the twelve 4000 PCC's and four "Super 17's" available to serve the Overbrook, Library, and Drake lines, thus necessitating the use of LRV's on at least one of these lines to maintain service.
 Of the three, the Library line was found to be the best suited to accommodate the larger LRV's with only minor modifications, and the route was modified and redesignated as the "42L Library via Beechview" (as the Overbrook line could not accommodate the LRV's) in December, 1988, and the PCC's were relegated to just the 47D,S, and 47 lines.

Unlike the LRV's which had both high and low level doors, the PCC's had only low level doors and were limited to street level boarding.
 As a result, all major stations on portions of the system that were shared by PCC's and LRV's (these being South Hills Village, Washington Junction, Castle Shannon, South Hills Junction, and all stops north of the Mount Washington Transit Tunnel) had both high and low platforms to accommodate both types of cars.

In 1993, the Overbrook Line was shut down between Castle Shannon and South Hills Junction due to the deteriorated conditions of the track, bridges, walls, and other infrastructure.
 With that, routes 47 and 47S were suspended, and the 47D was reduced to a short shuttle between Drake and Castle Shannon, where riders would be required to transfer to route 42S, 42L, or a bus to continue to downtown.

In 1999, the Drake shuttle was shut down, and the remaining PCC's were retired.
The 4000 series was intended as an interim solution for the Authority's unrebuilt lines, which could not accommodate the newer, heavier railcars.  As such, they were assigned to the 47D Drake via Overbrook,  47L Library via Overbrook, and 47S South Hills Village via Overbrook lines, as well as the 47 Shannon line, all trans-versing the Overbrook corridor.  In 1988, Port Authority retired all of its remaining unrebuilt PCC's due to safety concerns, leaving only the twelve 4000 PCC's and four "Super 17's" available to serve the Overbrook, Library, and Drake lines, thus necessitating the use of LRV's on at least one of these lines to maintain service.  Of the three, the Library line was found to be the best suited to accommodate the larger LRV's with only minor modifications, and the route was modified and redesignated as the "42L Library via Beechview" (as the Overbrook line could not accommodate the LRV's) in December, 1988, and the PCC's were relegated to just the 47D,S, and 47 lines.
Unlike the LRV's which had both high and low level doors, the PCC's had only low level doors and were limited to street level boarding.  As a result, all major stations on portions of the system that were shared by PCC's and LRV's (these being South Hills Village, Washington Junction, Castle Shannon, South Hills Junction, and all stops north of the Mount Washington Transit Tunnel) had both high and low platforms to accommodate both types of cars.
In 1993, the Overbrook Line was shut down between Castle Shannon and South Hills Junction due to the deteriorated conditions of the track, bridges, walls, and other infrastructure.  With that, routes 47 and 47S were suspended, and the 47D was reduced to a short shuttle between Drake and Castle Shannon, where riders would be required to transfer to route 42S, 42L, or a bus to continue to downtown.
In 1999, the Drake shuttle was shut down, and the remaining PCC's were retired.
Port Authority 4000-series PCC