Adequate and appropriate illumination across the highway isessential for safety. High-pressure sodium luminaires (HPS) are usually standard throughout Pakistan. However, with the advancements in illumination technologies and growing trend of energy efficiency, retrofitting of conventional HPS luminaires with light-emitting diode luminaires (LEDs) is becoming popular. Low energy consumption, high color rendering index (CRI), longer life span, and variety in correlated color temperature (CCT) make LED luminaires ideal for replacing inefficient HPS lights. The retrofitting of HPS with LED illumination system comes with a capital cost, and its feasibility depends on the energy conservation potential. This study presents a case of 4,014 HPS luminaires installed across an 85 km long highway in second highly populated city of Pakistan. A targeted energy audit of HPS illumination system was conducted and compared with the proposed LED system of equivalent illumination quality. The results indicate that by retrofitting the HPS luminaires, the energy consumption can be reduced by 60% and with 83.3% reduction in the apparent power. Furthermore, the proposed LED illumination system will significantly improve the power quality, light noise, energy losses, carbon footprint, and operational cost.