HARRISBURG, Pa. — Contractors working for Norfolk Southern over the weekend removed the last classic Pennsylvania Railroad-style wayside position-light signals on the 131-mile stretch of main line between Harrisburg, Pa., and Altoona, Pa. On the original 1854 Pennsy Harrisburg-Pittsburgh main line, the sole survivors lie between Altoona and Pittsburgh, 117 miles. Over the summer, those, too, will be retired.

The work, which began in the fall, is a lead-up to the installation of positive train control. Automatic block signals, also known as intermediates, are being removed entirely, while interlockings are being converted to Safetran four-color hooded signals. Until PTC goes live on the Pittsburgh Line, train and engine crews between interlockings are relying solely on traditional Pennsy/Penn Central/Conrail/NS cab signals to instantly show indications.

In all, the cutover will have resulted in 27 interlockings with more than 100 signals being replaced, and more than 60 automatics with more than 200 signals being removed. While Conrail and NS had made a few spot replacements, position-lights overwhelmingly guarded the main line until now.

Work is being carried out on Sundays to minimize the impact on traffic. Now designated as NS’s Pittsburgh Line, the 248-mile route handles 50 to 60 freights a day, plus Amtrak’s Pennsylvanian. Once known as the PRR’s four-track Great Broad Way, the line is now mostly double-track, with alternate single-track relief routes available between Johnstown, Pa., and Pittsburgh, and three tracks on the 40 miles over 2,200-foot-high Allegheny Mountain. Signals are spaced mostly at intervals of two or three miles, but on most of the mountain’s East Slope grade, which includes Horseshoe Curve and reaches a steepness of 1.8%, they are located every mile.

This style of signal has protected, moved, and stopped Pennsy, Penn Central, Conrail, and NS trains for more than a century.

Installed at Paoli, Pa., as early as 1914, position-light signals mimic the action of a movable semaphore blade, the type of signal that they replaced. The railroad collaborated with Union Switch & Signal of Swissvale, Pa., an affiliate of the former Westinghouse Air Brake Co., to design position lights. Wholesale adoption on the Pennsy began in 1921.