BNSF Railway's train U-PITKAI1-05A (Pittsburg CA to Kaiser [Fontana] CA) descend southern California's Cajon Pass with a pair of diesels unique to the BNSF - General Electric ES44C4 locomotives, which feature A-1-A trucks with a non-powered center axle that can be raised off the railhead by a slight amount, depending upon the adhesion required. The lead engine, 6646, is from the second batch, and the second unit, 6602, is from the first group. The differences include much heavier handrails stanchions on the second order.
