Traffic density refers to the number of vehicles present on a specific stretch of road at a given time. It is usually measured in vehicles per mile or vehicles per kilometer. High traffic density can lead to congestion, making it difficult for vehicles to move efficiently. Factors affecting traffic density include the time of day, road conditions, and the presence of events or construction. Urban areas often experience higher traffic density compared to rural areas due to more vehicles and limited road space. Understanding traffic density helps in planning and managing transportation systems effectively.