Pittsburgh's light rail system is descended from PCC-based streetcar lines running south of the city that had the good fortune to have both their own rights of way and the use of a dedicated tunnel through Mount Washington. These advantages earned the system a light rail style conversion in the 1980's complete with a downtown subway and dedicated bridge across the Monongahela River. While the rebranded Mount Washington Transit Tunnel continued to underpin the network, the Allegheny Port Authority and its predecessors had recognized the Mount Washington Tunnel as a single point of failure and therefore maintained an alternate surface route up and over the hill. Christened the 52 Allentown in 1984, this alternate route, terminating at South Hill Jct, would see declining levels of service until it was discontinued entirely in 2010. However tunnel diversions kept the old 52 Allentown in service as a ghost line, light rail trains running doors closed through the eponymous neighborhood on an as-needed basis. For out of town railfans catching a ride over the 52 was particularly difficult as the diversions were not often scheduled in advance, however in 2025 the tunnel was to undergo a long term renovation with Route 47 and 42 trains diverted over the 52 for the better part of a year. This allowed me to schedule a trip to Pittsburgh to get photos and videos of this rare occurrence.
My arrival in Pittsburgh was too late in the day to properly ride the 52 Allentown, but I was able to catch the arrival of westbound Amtrak Pennsylvanian Train 43 with P42DC leading the usual consist.
It was at this point I had my first ever encounter with a Rule 280a "Clear to Next Interlocking" signal indication displayed eastbound on Track #1 at the former CP-EAST PITT. Displayed as a flashing white marker light next to a standard Medium Clear, the signal us used in cab signal territory without wayside intermediate signals for train movements that are not cab signal equipped. In this case said movement would be Train 43 shoving back to CP-HOME where the turning wye is located.
By displaying Rule 280a instead of a Restricting, the shove move would be able to operate at speeds up to 45mph, saving considerable time across the 8 mile round trip.
The following morning I caught a light rail train at Steel Plaza and was in place to get photos as it crossed over at Panhandle Interlocking and onto the short single track that would lead to the street running up and over Mt. Washington via Allentown.
The whole trip takes about 8-10 minutes, about 5 minutes longer than the trip through the tunnel. The ride was downright exciting as my LRV's operator was really flooring it up the twisty grade. A temporary infill station was also added along the route in the Allentown neighborhood.
My outbound SD400 LRV, running on a 47S service, at South Hills Jct
South Hills Jct is built around a large double track scissors crossover. Although from the point of view of the platforms the crossing routes over the diamonds are in a geometrically straight path, from a railroad interlocking point of view those would be the diverging routes. Normally the light rail trains get a solid yellow lamp for a Restricting indication into street running track. However for the "diverging" route, they get a flashing yellow.
In its original configuration trains from the Overbrook and Beechview lines would merge into the transit tunnel with the option to use the 52 Allentown Route.. With Overbrook Line trains making use of a new flying junction since 2004 and the 52 being discontinued in 2010, the scissors crossover sees rather limited use in its role as a crossover. Here SD400 LRV #4221 crosses northbound over from the Beechview Line to the 52 Allentown line.
Pride month pay have been over, but SD400 pride unit #4239 was still roaming across the light rail system in early July, along with 4202.
Here we see SD400s #4227 and #4201 along with CAF LRV #4317 running out of the junction and up the incline towards Allentown.
CAF LRV #4315 descending southward from the Allentown route. The CAF LRVs were a supplemental order of vehicles to support the re-opening of the Overbrook line, which was closed between 1993 and 2004.
Like the northbound trains, southbounds would roll towards the junction and get a Restricted Diverge flashing yellow signal on the dwarf.
View along the axis of the scissors crossover route from the Beechview/Overbrook lines to the Allentown Line with CAF LRV #4317 and SD400 #4253.. While this routing is physically straight, as far as the interlocking is concerned this a diverging route.
In this video we see an inbound 42S South Hills Village (via Beechview) train with SD400 LRV's #4231 and #4235 passing an outbound 42S with CAF LRV's #4310 and #4313 with #4310 sporting the new "Pittsburgh Regional Transit" paint scheme.
In my previous visit to South Hills Junction in 2023, both PCC loops were still present for short turns both from the north and south. Since that time the southward loop for PCC's coming off the 52 Allentown has been removed along with its boarding platform. PCC's were used through 1993 as the old Overbrook line had wooden trestles that could not support the weight of LRVs.
On the other hand, the old Route 47/52 platform had been re-paved. Before the Overbrook Line rebuild this platform had served the PCC's using the 47 route as well as all 52 Allentown cars which terminated at South Hills Jct.
Another view of LRV's crossing over to the Route 52 with SD400 #4250 and CAF LRV #4308.
The tunnel closing also affected local bus traffic which also had to detour up and over Mt Washington. Here bus #6236 passes inbound SD400 #4227.
All of the construction miscellany made getting a view into the tunnel a bit difficult, but I was able to manage a photo.
Back to the South Hills Jct platforms where I caught SD400 #4224 passing #4201 and #4206 arriving southbound.
The return trip was not quite as exciting, I'm guessing the operators know they have a bit more leeway for speed on the steep ascent since the grade will quickly bring the car to a stop without use of brakes.
Heading north across the Panhandle Bridge I encountered CAF LRV #4314 painted in the new "Pittsburgh Rapid Transit" branding.
Final photo of this set if SD400 #4224 after dropping me off at the Honorable United States Steel Plaza.
All in all Pittsburgh Light Rail is a great little system that still presents a lot of heritage due to the early date of its light rail conversion. If the MWTT ever shuts down again I urge you all to schedule a visit.
