A Highway Capacity Software developer designs and develops software applications that analyze and simulate traffic flow on highways, roads, and intersections. They utilize principles from the Highway Capacity Manual (HCM) to create models for predicting traffic congestion, calculating road capacity, and optimizing traffic signal timings. They work with civil engineers and urban planners to implement solutions for traffic management and infrastructure planning. They also ensure the accuracy of the data, troubleshoot software issues, and update the software as per changes in HCM guidelines or technological advancements. Their goal is to improve traffic conditions and promote efficient transportation systems.