7 separate rrs through the borough of Dunbar? More like 3; PRR and B&O were parallel through town, the West Penn interurban ran on the main streets (but did have private right of way on either side of town).
WM ended at Bowest yard, a mile north of the town. Nearby Connellsville had the P&LE and the P&WV.
The bridge originally referenced by the OP is a remnant of B&O's last attempt to build a direct line from the Pittsburgh main line to Wheeling starting in 1881, following an original survey from 1833. The bridge was constructed in the early 1880s as part of the proposed B&O subdivision, Ohio and Baltimore Short Line (O&BSL). At present day Greene Jct. at South Connellsville, the line had its own bridge across the Youghiogheny River, ran inland about 1/2 mile and crossed the previously mentioned bridge.
It then crossed present day US 119 and went west through Leisenring. About 5 miles of this line was completed before B&O management canceled the project.
It should be mentioned that 4 miles of this line was completed east of Washington,PA., before the work was halted.
By 1890, the east end of the O&BSL was extended about 2 miles to serve coke ovens at an place called Bittner.
The branch died by 1941, the bridge across the "Yock" was closed during WWI years after the present x-B&O "Sheepskin" line bridge was built next to it, although the FM&P line had a western connection to the Pittsburgh line.
The O&BSL bridge abutments are still there in the river, pointing eastward.
The above is from pgs. 142-144 of the book "Sand Patch" by Charles S. Roberts.
The Western MD. Railway Hist. Society has done much research on this area.