40' PRR X31A Box Car

Prototype Information

The Pennsylvania Railroad introduced the 40-foot X31 boxcar in 1933 to fight off growing trucking competition. PRR designed these all-steel cars with a unique rounded “round-roof” or “wagon-top” profile. This shape maximized interior loading space while fitting tight tunnel clearances. Shops at PRR’s Altoona Works built the initial X31 and X31A variants with double doors and distinctive horizontal steel ends. Auto plants used the extra overhead clearance and wider door openings to pack finished cars using internal racks.

The PRR expanded the X31 fleet to over 10,000 cars, making it a cornerstone of 1930s and World War II rail traffic. The railroad also built single-door versions for general freight and grain service. As automakers shifted to bi-level and tri-level auto racks in the late 1950s, PRR rebuilt many double-door cars for standard merchandise. Their tough steel construction gave them exceptional lifespan. Thousands of X31 boxcars survived through the Penn Central merger, with some remaining in freight and maintenance service into the late 1970s.