Trip Optimizer is a locomotive control system enhancement applicable to diesel-electric hauled freight that can achieve double-digit fuel savings. Energy savings derive from managing train momentum, with anticipation of its effects, to reduce the net energy outlay by the train as it completes a trip. GE’s system has two major components: the first is a planning system that derives an optimal way to drive the train (throttle together with a corresponding speed trajectory versus distance) subject to speed restrictions along the route and locomotive operating constraints; the second is a dynamic control system that executes the plan closed-loop, correcting for modeling errors from various sources and assuring proper train handling consistent with railroad requirements. To compute a plan, information about the track to be traversed (grade and curvature versus milepost), the power consist makeup (number and type of operational locomotives) and load (tonnage, train length etc) is required together with updated speed restrictions, work crew locations, and other constraints that may vary from day-to-day. This paper first gives an overview of the Trip Optimizer system in operation as implemented on GE Evolution locomotives. Next, key components in the architecture are briefly described, including how the system is operated with the aid of graphic interfaces. Results of pilot testing of the production system on various revenue service trains on Class 1 railroad’s territories are then summarized to demonstrate actual fuel savings in the 4-13% range while achieving acceptable train handling.