This paper presents the results of a controlled-field experiment designed to evaluate the efficiency of a speed recommendation algorithm developed to reduce vehicle fuel consumption at signalized intersections. The evaluated algorithm received instantaneous speed data from the vehicle and computed real-time fuel-efficient speeds that were promptly communicated by an audio signal to the driver to follow. The controlled-field experiment included two other scenarios for comparison. In the first scenario, participants drove freely through the intersection (no communication between the vehicle and the infrastructure). In the second scenario, the time remaining for the current signal indication was communicated to the driver by an audio signal. The experiment was designed as a split-split-plot design in which the scenarios served as the plots, the grade (downhill or uphill) as the split plot, and the time-to-red indication offset (10, 15, 20, and 25 s) as the split-split plot. In total, 1,536 trips were conduct...