There are EMD GP and SD locomotives that were built in the 1960s and 1970s and are still hauling freight today. So maybe 50 or so years for EMD power while GE locomotives tend to be scrapped after about 20 years or less.

A modern freight locomotive is built for extreme longevity, typically remaining in active service for 25 to 35 years, though many last much longer through "rebuilding" programs. In terms of mileage, a hard-working Class I locomotive can easily cover 1.5 to 3 million miles in its primary lifetime. Because these machines represent a massive capital investment (often $3–$5 million each), railroads rarely scrap them when the engine wears out. Instead, they undergo "mid-life overhauls" where the prime mover, traction motors, and electronics are replaced. In 2026, many older diesel units from the early 2000s are being "re-manufactured" into hybrid or low-emission units, extending their usable life to 50 years. After they are retired from high-speed "mainline" service, these engines often spend another decade as "yard slugs" or switching engines for small short-line railroads, where the mechanical demands are lower but the robust steel frames continue to provide value.