The actual designation is DD40AX. The Centennial was an interesting locomotive, but limited in its application to runs like UP’s Sherman Hill. It was essentially two GP40s back to back on a single frame.
Only 47 were built and were soon replaced by more flexible single engines in MU lash-up.
A better loco, today, is the EMD SD70MAC, which develops 137 kilopounds continuous tractive effort with 33% adhesion versus 133.7 Kp for the DD40AX.
