One of the fundamental measures of traffic on a road system is the volume of traffic using the road in a given interval of time. This is also called the flow and is expressed in vehicle per hour or vehicles per day. When the traffic is composed of a number of types of vehicles, it is a common practice to convert the flow into equivalent passenger car unit (PCUs), by certain equivalery factors. The flow is then expressed as PCUs per hour or PCU’s per day. This means that the vehicle count needs to be called by considering their class & type. Another aspect of the traffic flow is its variation. Due to various extend reasons, the rate of traffic flow on a stretch is not constant. Understanding its variation is important for various traffic engineering applications. For example, the variation of traffic flow within an hour is important for traffic signal design. Its implication is that the traffic flow needs to be collected at various shot intervals, typically 5, 10, or 15 mts interval. Needless to say that finer the count interval, the more accurate is the modeling of the variation. The variation of traffic with in an hour is called the peak hour factor which is defined as the ratio of the peak hour flow rate to the total flow. Peak hour factor of 1implies the flow rate is constant, and typically occurs at highly congested traffic.