GECX 2041 and GECX 2042, Tier 4, GE demo units. Distributed Power Units (DPU); GECX 2040 and GECX 2043, BNSF C NAMMLT, North Antelope Mine WY to Mill Texas, Tier 4-compliant GEVO's feature much larger radiators with split cooling. Pre-production demonstrator GEVO's also feature a "hump" in the middle of the long hood, which houses a urea-injection exhaust aftertreatment system. No railroad has ordered the urea aftertreatment system, making the "hump" irrelevant on Tier 4 production models. The Tier 4 units have been unofficially named "ET" rather than "ES", the "T" stands for "Tier 4". This designation is currently only used by BNSF. Train on Colorado's Joint Line approaching BNSF's Big Lift Terminal, Colorado.