Module 1 : Traffic Stream Characteristics

Lecture 03 : Traffic Stream Models

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	Underwood's exponential model Trying to overcome the limitation of Greenberg's model, Underwood put forward an exponential model as shown below. $$v = v_f.e^\frac{-k}{k_0}$$ (1) where $v_f$The model can be graphically expressed as in figure 1. is the free flow speed and $k_o$ is the optimum density, i.e. the density corresponding to the maximum flow. Figure 1: Underwood's exponential model In this model, speed becomes zero only when density reaches infinity which is the drawback of this model. Hence this cannot be used for predicting speeds at high densities.