The emerging LED technology enables intelligent street lighting that is based on sensing individual vehicles and dimming street lights accordingly. The potential energy savings are considerable, exceeding 50% on roads with low traffic. A possible reason why such applications are not yet emerging are financial uncertainties about the size of the savings, which are needed to motivate the investment. Another barrier to adoption are uncertainties about whether proposed approaches meet standards and regulations for traffic safety. In this paper, an energy efficient street lighting design that meets regulations for rural roads is implemented with the IEC 61499 distributed function block architecture. The intelligent lighting is co-simulated against a traffic simulation using cellular automata. Virtual metering in the IEC 61499 application is used to quantify energy savings in simulation scenarios with different traffic volumes. Across a range of traffic volumes representative of rural roads, our simulations indicate that smart dimming can deliver energy savings of 14% to 70%, with savings increasing as traffic density decreases.