What is the definition of traffic flow?

Traffic flow refers to the movement of a group of vehicles on a road, capturing the dynamic interactions among vehicles traveling in a common direction. This encompasses not just how fast the vehicles are moving, but also how they interact with each other, including changes in speed and the patterns of movement as they navigate the road.

Understanding traffic flow is crucial for gauging road capacity, identifying congestion points, and implementing effective traffic management strategies to ensure safety and efficiency on roadways. The other options focus on specific aspects of driving conditions, such as speed limits, vehicle density, or spacing, but they do not encompass the broader concept of how vehicles collectively move together on the roadway.