the lack of curve compatibility led to the s1 not being used for its intended long-distance express service. although the s1 had less than half (47%) its total weight on the driving wheels, its factor of adhesion was still very close to the much more successful prr q2, santa fe "northern" 4-8-4s the 2900s, and the renowned n&w class j 4-8-4s. more than half of its weight was being carried by the massive six-wheel pilot (leading) and trailing trucks instead of the drivers. this left the two sets of four duplex driving wheels susceptible to wheel slippage. however, during the 5 1/2 years service history of s1, no serious accident occurred due to wheel slippage. the s1 managed to serve between chicago and crestline, ohio for almost 5 1/2 years, made it having the longest-serving record among all experimental steam engine prototypes of the prr, such as the q1 4-6-4-4 and s2 turbine 6-8-6.