Photos of cars on freeway, speeding sign

Freeway Management and Operations Handbook

Description of Figure 1-6: Generalized Relationships Between Speed, Density, and Flow Rate on Freeways

These graphs show generalized relationships. The first graph shows speed on the vertical axis, ranging from 0 to Sf miles per hour. Density is shown on the horizontal axis, ranging from 0 to Dj vehicles per miles per hour. A broken line representing oversaturated flow is shown beginning at Sf speed at 0 density and dropping to 0 vehicles at Dj density. Dashed lines emanating from So speed and Do density intersect the oversaturated flow line.

The second graph shows speed on the vertical axis, ranging from 0 to Sf miles per hour. Flow is shown on the horizontal axis, ranging from 0 to Vm vehicles per hour per lane. A broken line representing oversaturated flow is shown as a continuous curve beginning at Sf speed at 0 flow, curving to Vm flow, and curving back to 0 flow. Dashed lines emanating from So speed and Vm flow intersect the oversaturated flow curve at point Do. A dashed line also progresses from 0 to Dj flow.

The third graph shows flow on the vertical axis, ranging from 0 to Vm vehicles per hour per lane. Density is shown on the horizontal axis, ranging from 0 to Dj. A broken line representing oversaturated flow is shown as a continuous curve beginning at flow and density, curving up to Vm flow, and curving back down to Dj density. Dashed lines emanating from Vm flow and Do density intersect the oversaturated flow curve. Dashed lines also progress from 0 to Sf and Soflow.