P. T. Barnum would have loved the Triplex. It was an engine of superlatives: more drivers than anything before or since, too big for the shops of its owner, the Erie Railroad, powerful enough to pull a train nearly five miles long. Ninety years ago, in the days before multiple-unit control allowed one throttle to control several locomotives, the Triplex was the ultimate attempt to put as much power as possible in the hands of a single engineer. In the end, it proved a noble, flamboyant, but less-than-successful experiment. Baldwin Locomotive Works built three triplexes between 1914 and 1916 for pusher service on the Erie Railroad's daunting Susquehanna Hill (also known as Gulf Summit) near Deposit, N.Y. The cylinders of the Triplex's middle engine were powered by high pressure steam direct from the boiler, while the front and rear engines used low pressure steam exhausted from the middle cylinders.
Each triplex replaced three ordinary helper engines, and the new locomotives worked well enough to stay on the Erie roster for more than a decade. But the design proved a bit over the top and only one more Triplex was ever built, for the Virginian Railway. Even with their huge boilers, the locomotives could only make enough steam to go 10 mph. One reason was poor draft in the firebox, because only the front cylinders exhausted through the smokebox and created draft; the rear cylinders exhausted through a separate smokestack on the tender. Another inherent problem with the design was that traction from the rear engine decreased as the boiler used coal and water and the tender got lighter.