What traffic flow characteristic describes the relationship between speed and volume?

The relationship between speed and volume in traffic flow is characterized by an inverse correlation. This means that as traffic volume increases, the speed of vehicles typically decreases, and vice versa. This relationship is commonly observed in congested traffic situations where a higher number of vehicles leads to slower travel speeds due to limited road capacity and increased interactions between vehicles, such as lane changes and merging.

When traffic is free-flowing, vehicles can travel at higher speeds with lower volumes on the road. However, once the road reaches its capacity, additional vehicles can lead to traffic jams and a significant reduction in speed. This principle is often illustrated by the fundamental diagram of traffic flow, which shows that the maximum flow occurs at an optimal speed, beyond which increasing volume leads to decreased speeds. Understanding this inverse relationship is crucial for traffic engineering and planning, as it helps in managing congested roadways and optimizing traffic signal timings.