the s1 was the largest passenger locomotive ever constructed, the cast steel locomotive bed plate made by general steel castings was the largest single-piece casting ever made for a locomotive. in order to negotiate sharper radius curves, s1 was equipped with lateral motion devices made by alco on its first and third set of drivers, allowing 57.2 mm (2.25 inches) of lateral play on the axles, but these proved to be inadequate. unlike other experimental duplex engines like prr's class q1 #6130 4-6-4-4, there were no flangeless wheels or blind drivers adopted on s1.