Module 1 : Traffic Stream Characteristics

Lecture 02 : Fundamental Relations of Traffic Flow

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	Speed flow relation The relationship between the speed and flow can be postulated as follows. The flow is zero either because there is no vehicles or there are too many vehicles so that they cannot move. At maximum flow, the speed will be in between zero and free flow speed. This relationship is shown in figure 1. Figure 1: Speed-flow diagram The maximum flow $q_{max}$ occurs at speed $u$. It is possible to have two different speeds for a given flow. Combined diagrams The diagrams shown in the relationship between speed-flow, speed-density, and flow-density are called the fundamental diagrams of traffic flow. These are as shown in figure 2. One could observe the inter-relationship of these diagrams. Figure 2: Fundamental diagram of traffic flow