Module 1 : Traffic Stream Characteristics

Lecture 03 : Traffic Stream Models

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	Pipes' generalized model Further developments were made with the introduction of a new parameter (n) to provide for a more generalized modeling approach. Pipes proposed a model shown by the following equation. $$v = v_f{\left[1-{{\left(\frac{k}{k_j}\right)}^n}\right]}$$ (1) When $n$ is set to one, Pipe's model resembles Greenshield's model. Thus by varying the values of $n$, a family of models can be developed. Multi-regime models All the above models are based on the assumption that the same speed-density relation is valid for the entire range of densities seen in traffic streams. Therefore, these models are called single-regime models. However, human behaviour will be different at different densities. This is corroborated with field observations which shows different relations at different range of densities. Therefore, the speed-density relation will also be different in different zones of densities. Based on this concept, many models were proposed generally called multi-regime models. The most simple one is called a two-regime model, where separate equations are used to represent the speed-density relation at congested and uncongested traffic.