Development of PCU factors for four lane roads under Sri Lankan context

Abstract

Passenger Car Unit (PCU) or Passenger Car Equivalent (PCE) is a metric used in Transportation Engineering, to assess traffic-flow rate on a road or an intersection. A Passenger Car Equivalent is essentially the impact that a certain mode of transport has on traffic variables compared to a single passenger car. Roads in Sri Lanka carry heterogeneous traffic, where road space is shared among many traffic modes with different physical dimensions and prevailing loose lane discipline. PCU factors used in Sri Lanka at present are somewhat older and do not reflect static and dynamic characteristics of modern vehicles, road conditions or driver behavior. Data collection was done on various four lane road segments. Location for the study is identified based on uniformity of road characteristics in terms of pavement width, shoulder type, etc. There should be no visual obstructions to traffic because of bus stops, road side developments, etc. No intersection or side roads along the road stretch so that there are no changes in the traffic volume over the entire stretch. No signalized intersection for 3km road length. Traffic volume data was collected using video camera to record vehicles in both directions during peak hours. These video footages were observed and the traffic volumes, speeds and 85% value of road width used by traffic volume were calculated. Then using modified density method proposed by Tiwari (Tiwari, Fazio, & Pavitravas), the PCU factors were derived. 𝑃𝐶𝑈𝑋𝑖 = 𝑘𝑐𝑎𝑟 𝑊85𝑐𝑎𝑟 ⁄ ( 𝑞𝑥𝑖 𝑢𝑥𝑖 ⁄ ) 𝑊85𝑥 The results obtained, showed that there is a variation from homogenous conditions to heterogeneous conditions. These results can be used for traffic volume analysis, capacity calculations, road network planning and design purposes, etc. in Sri Lankan four lanes roads. Further research can be carried out to evaluate PCU factor for 6 lane roads, different highways and intersections.