GATE 2022 CE (CE2) – Question 63

Traffic Engineering and Transportation Planning · Fundamental relationships of traffic flow · 2 marks · Numerical answer

Assuming that traffic on a highway obeys the Greenshields model, the speed of a shockwave between two traffic streams (P) and (Q) as shown in the schematic is _______ kmph. (in integer)

Speed–flow diagram showing traffic states P and Q. See the attached source image.

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Correct answer: 15

Explanation

Convert each state to density using k=q/v. The diagram gives kₚ=1200/60=20 and kq=1800/30=60 vehicles/km.

Shock speed is $(q_Q-q_P)/(k_Q-k_P)=600/40=\mathbf{15}$ km/h. Its positive sign means travel in the traffic direction.