Under uninterrupted flow conditions, which model states that speed and density are linearly related?

Under uninterrupted flow conditions, which model states that speed and density are linearly related?

• A. Actuated Signal
• B. Greenshield's Model
• C. Weaving Sections
• D. Occupancy

Answer: (B)

Greenshields' model describes a straight-line relationship between speed and density in a steady, uninterrupted flow. It expresses speed as v = v_f (1 − ρ/ρ_j), where v_f is the free-flow speed and ρ_j is the jam density. As density increases from zero toward jam density, speed declines linearly, reaching zero at the jam density. This linear link between speed and density under homogeneous flow is the essence of the model, and it also underpins the common speed–density–flow relationships used to build the fundamental diagram. Other concepts listed aren’t about a speed-density relationship. An actuated signal concerns adaptive traffic signal timing, weaving sections deal with highway geometry where lanes merge and cross paths, and occupancy is a detector performance metric, not a speed-density model.

Greenshields' model describes a straight-line relationship between speed and density in a steady, uninterrupted flow. It expresses speed as v = v_f (1 − ρ/ρ_j), where v_f is the free-flow speed and ρ_j is the jam density. As density increases from zero toward jam density, speed declines linearly, reaching zero at the jam density. This linear link between speed and density under homogeneous flow is the essence of the model, and it also underpins the common speed–density–flow relationships used to build the fundamental diagram.

Other concepts listed aren’t about a speed-density relationship. An actuated signal concerns adaptive traffic signal timing, weaving sections deal with highway geometry where lanes merge and cross paths, and occupancy is a detector performance metric, not a speed-density model.