In September 2009, Norfolk Southern unveiled the latest in alternative energy locomotive technology at its Juniata Locomotive Shop in Altoona, Pa. NS 999 is a prototype 1,500-horsepower switching locomotive that relies solely on rechargeable batteries for power.

NS 999 is an entirely electric locomotive that uses a lead-acid energy storage system comprised of 1,080 12-volt batteries to operate in railroad switching applications without the use of a diesel engine and with zero exhaust emissions. The plug-in locomotive also can regenerate dynamic braking energy through a system provided by Brookville Equipment Company. The recovered dynamic braking energy continually replenishes the energy storage system, and uses this recovered energy for tractive effort in rail operations. The batteries are carefully monitored and controlled through an elaborate battery management system to assure safety and maximum battery life, and when fully charged NS 999 is able to operate three shifts before recharging is required.