33.4.1. Greenberg’s Logarithmic Model

Try these first

1. 1.

   What does the logarithmic model express about the relationship between speed and density?

   Hint

   Think about how logarithms work.

2. 2.

   Define free flow speed.

   Hint

   What does it mean when there are no delays in traffic?

3. 3.

   What does Greenberg’s model predict about speed as density approaches zero?

   • Speed tends to zero
   • Speed tends to infinity
   • Speed remains constant

   Hint

   Think about the extremes of the model.

4. 4.

   Is it true that Greenberg's logarithmic model can accurately predict speeds at all densities?

   • True
   • False

   Hint

   Consider the limitations discussed.

5. 5.

   Calculate the speed when the free flow speed is 50 km/h, jam density is 150 vehicles/km, and density is 75 vehicles/km using Greenberg’s model.

   Hint

   Use the logarithm rules to compute.

6. 6.

   Discuss the implications of the model predicting infinite speed at zero density. How can this affect traffic planning?

   Hint

   Consider how planners use models for predictions in real contexts.