In developing countries like India, the road traffic is heterogeneous in nature, consisting of vehicles of wide ranging physical dimensions, weight and power sharing the same lane. Passenger Car Unit (PCU) is the metric used to convert heterogeneous traffic-flow rate or volume into equivalent homogeneous traffic. The PCU factors have direct impact on capacity values and design service volumes of different categories of roads and other facilities. For the design of signalized intersections, PCU values recommended for various categories of vehicles are given in the Indian Roads Congress code IRC-SP41 (1994). There has been substantial development in vehicle technology during the last couple of decades. Therefore, it is necessary to re-assess the PCU values based on field studies. In this study, an attempt has been made to learn the characteristics of mixed traffic flow at signalized intersections. This work provides the details of an empirical study carried out to determine the PCU values for various types of vehicles, so that a comparison of results with PCU factors recommended by IRC code is possible. Moreover an attempt has been made to find the effect of length of passenger cars on PCU. Data were collected from two signalized intersections and the headway ratio method and regression method were used to estimate the PCU of different types of vehicle. The PCU values obtained in this study are compared with the values established earlier. It is found that the estimated PCU values are different from those being used in India, and they are inversely related to the length of passenger car. Studies reveal that PCU values have a great impact on signal design, emphasizing the need for further studies in this direction.
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