Module 1 : Traffic Stream Characteristics

Lecture 02 : Fundamental Relations of Traffic Flow

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	Time mean speed ($v_t$) As noted earlier, time mean speed is the average of all vehicles passing a point over a duration of time. It is the simple average of spot speed. Time mean speed $v_t$ is given by, $$v_t = \frac{1}{n}\sum_{i=1}^{n}{v_i},$$ (1) where $v_i$ is the spot speed of $i^{th}$ vehicle, and $n$ is the number of observations. In many speed studies, speeds are represented in the form of frequency table. Then the time mean speed is given by, $$v_t = \frac{\sum_{i=1}^{n}{q_i v_i}}{\sum_{i=1}^{n}{q_i}},$$ (2) where $q_i$ is the number of vehicles having speed $v_i$, and $n$ is the number of such speed categories.