21 DOI: 10.7251/JTTTP1901021S UDC: 629.113.011.07 REVIEW Methodology of CalculaƟng Heavy Vehicle Equivalents Marko SuboƟć Faculty of Transport and Traffic Engineering, University of East Sarajevo, marko.subotic@sf.ues.rs.ba Dunja Radović Faculty of Transport and Traffic Engineering, University of East Sarajevo, dunja.radovic@sf.ues.rs.ba Edis SoŌić Faculty of Technical Sciences, University of Bihać, edis.softic@bih.net.ba Abstract: Passenger car equivalents (PCE) present a very important parameter for capacity calculaƟon and road service level as well as a planning segment of road capacity. There are many ways of calculat- ing PCE and most of them are based on Greenshield’s basic method. This paper studies the PCE calcula- Ɵon methodology and condiƟons under which it is applied. The first part of the paper is about role of PCE in analyzing traffic flow, and the rest of the paper is presenƟng methodologies for computaƟon of PCE. Example of the latest method for determining PCE according to HCM-2010 is given in this paper. The goal of the research is presented by structural, parameter and funcƟonal analysis of methods. Fur- ther research direcƟons of PCE are shown as well. Key words: passenger car equivalents (PCE), analysis, heavy vehicle, flow. INTRODUCTION Many studies have been made in order to under- stand the effect of different categories of vehicles on traf- fic flow. PCE is used to evaluate the effect of different categories of vehicles on traffic flow. As traffic flow is made of more than one type of vehicle, PCE values are used to translate a real traffic flow through an equivalent of homogenous traffic. PCE is first mentioned in 1965, and since then many researchers have tried to determine a quantity effect of heavy vehicles in traffic flow during the development of HCM (Highway Capacity Manual) using different methodologies and equality criteria. Ac- cording to the HCM-2000 [1] PCE is a number of pas- senger cars distributed according to a single category of units of vehicles depending on traffic conditions, i.e. an average number of passenger cars that would use the same percentage of capacity of the road as any other ve- hicle (HV, BUS, RV) in given road and traffic conditions. This also creates a unit of measurement of capacity as passenger car/hour (PC/h). Presence of heavy vehicles in traffic flow results in decreased capacity of traffic lanes in intersections, which is shown in [2]. Influence of heavy vehicles on traffic flow is also seen in the fact that heavy vehicles are larger than passenger cars and therefore oc- cupy more space in traffic flow. Also, heavy vehicles are inferior comparing to passenger cars in terms of techni- cal and usage abilities (acceleration and deceleration) and therefore require larger distances between vehicles. In [3] it is presumed that drivers of other types of ve- hicles are maintaining larger safe following distances comparing to heavy vehicles during driving. HISTORICAL DEVELOPMENT OF EQUIVALENTS Papers that have examined PCE were mostly try- ing to estimate PCE regarding different categories of ve- hicles under different conditions of traffic flow and roads ([4], [5], [6], [7]). There are different chronological meth- ods in establishing PCE. For example, HCM-1965 uses speed reduction method to determine PCE for highways, also known as Walker’s method. According to Huber [8] there are three performance measures of PCE: speed, density and passenger car’s speed in both lanes. In 1980, Ra- manayya [9] used the title „equivalent of a car’s design“ in- stead of unit of a passenger car for traffic model observed in urban roads in India. This kind of study is the first that measures flow in metric values instead of PCE values. The study shows that PCE values are not constant due to heterogenous road conditions. This Indian model is trying to translate all vehicles to a unit of „equivalent of a car’s design“. Raghava Chari and Badarinath [10] consid- ered heavy vehicle equivalents through density, which they were calling „areal density“ (density observed in an area). This is the first study that was observing vehicle’s area (the area that vehicle occupies) to measure density. This density is defined as a vehicle on the road per unit of the road section. Determining area density is done with a camera in time interval of one second. Cunagin and Messer [11] are using delay relations as a performance measure to evaluate PCE of heavy vehicles at highways with several lanes. Sumner and Shapiro [12] are using a number of vehicles per hour to present density equivalent because veh/h is in a function of vehicle’s speed and its Received: May 28, 2018 Accepted: April 14, 2019