Investigation of passenger car equivalent (PCE) for through - traffic at signalized intersection in istanbul

Heavy vehicles have considerably different size and performance characteristics from passenger cars. Therefore the heavy vehicles can have a significant impact on traffic operations. It is therefore essential to properly account for this impact in the traffic operations analysis in order to reflect the operational quality of the roadway as accurately as possible. This study focuses on trucks, pick-up trucks, large trucks, minibuses, midibuses and buses. Signalized intersections are the one roadway facility that can be particularly sensitive to the presence of commercial heavy vehicle traffic. Like other facilities, the length of has a negative impact on the capacity of the signalized intersection; however, the reduced performance characteristics of these heavy vehicles has an even greater impact on signalized intersection than uninterrupted flow facilities due to the more frequent need of decelerating, stopping and re-accelerate to cruise speed. The reacceleration duration to cruise speed is much more greater for heavy vehicles, when compared to passenger cars, the presence of heavy vehicles can have implications on signal coordination. This effect may be greater when heavy vehicles are present at the front of a discharging queue. When the traffic stream stops at the intersection, the inter-vehicle spacing decreases, resulting in increased vehicle density. At this higher density, it is clear that heavy vehicles occupy more space than passenger cars due to their physical characteristics. Once the signal turns green, and after a short period of start-up lost time, vehicles start departing at the saturation flow rate and it is here where the heavy vehicles have the greater impact due to their operational capabilities. Large trucks have poorer acceleration than passenger cars; therefore it will take them more time to reach their desired speed. With poorer acceleration characteristics, heavy vehicles slow down the traffic stream and increase their time headway. Furthermore, with their longer length, heavy vehicles increase the time headway of the vehicle following them. In arterial roads where the Free Flow Speed is low, the cruising speed of all vehicles may be similar. Once the vehicles reach their desired speed and have a constant cruising speed, the impact of heavy vehicles to the traffic will be again mostly due to their length. The most common method used for the analysis of signalized intersections is contained in the Highway Capacity Manual (HCM). In this method, the base saturation flow rate of the signalized intersection is defined in units of passenger cars per hour green per lane (pc/hg/ln). To account for the presence of heavy vehicle in the traffic stream, the HCM includes a passenger car equivalency (PCE) value. In the current edition of the HCM, a PCE value of 2.0 is applied for all heavy vehicles, with no distinction between different sizes of heavy vehicles. Some transportation professionals have questioned the validity of this PCE value recommended by the HCM. They are concerned that the impact of heavy vehicles at signalized intersections is being under-estimated. If this is the case, then capacity is being over-estimated and intersections are not being adequately designed. The primary objective of this thesis was to determine appropriate heavy vehicle PCE values to apply for signalized intersection. In this thesis, PCE values were classified by six different categories of heavy vehicle sizes and performances (minibus, pick-up, midibus, truck, bus and large truck) . Additionally, a general PCE value with only one heavy vehicle category was developed for planning purposes and/or a less detailed analysis. The road traffic systems, travel patterns and other traffic characteristics are different for each country due to differences in geometric patterns of a country, available transport facilities for commuters, rate of development in the transport sector and so on. Consequently, many standard relations and factors used in one region may not be suited for others. Therefore, an issue comes up to determine the different traffic engineering parameters which are appropriate to local urban transport system characteristics. The second objective of this thesis was to determined the passenger car equivalent (PCE) at signalized intersections for the Istanbul City in Turkey where traffic characteristics are completely different from any other cities of the world.The development of the PCE values was based on the relative headway concept, as defined in the HCM. The results of this study are based on field data collection. Two location determined, one observer has colleted headways and vehicle type for lane. First location is Ali Sami Yen Stadium intersection in Mecidiköy, Büyükdere street. The second locations is İMES E in Dudullu, Necip Fazıl street. All data has collected under dry-weather conditions and during morning peak hours. Observations have made between 25 March – 22 October 2014. In the context of this study, the headway values , in the direction of Mecidiyeköy-Zincirlikuyu leg of the intersection, that is in front of the old Ali Sami Yen Stadium, and in the direction of Dudullu-Ataşehir leg of the intersection, that is in front of IMES E door on the Necip Fazıl Boulevard, in Dudullu district, are measured in terms of vehicle type. During the measurement, both vehicles, where in front and behind, are recorded, thus the headway for the different types of vehicles in front or behind, are classified separately.Measurments has done separately for the lanes at two intersection, as a result, 4 number of data series obtained( Ali Sami Yen Stadium left lane, Ali Sami Yen Stadium right lane, IMES E door left lane, IMES E door right lane). First of all fitness to normal distribution has been research each data series, by by means of χ2 test. For two series, in which both of them fit normal distribution, has been research BOtE value could be specified for the two series by t test. For the two series, in which at least one serie does not fit to the normal distribution, practically by combining the series, general BOtE values are specified by means of the K-W (Kruskal-Wallis) test.Obtained values are evaluated for the 3 different approaches of headway method, separately.The first approach has been developed by Miller in 1968. The approach based proportion of the headway of heavy vehicle and headway of car.The second approach has been developed by Molina in 1987, after than same approach simple version used 2007 by Cruz-Casas. The approach based proportion of the extended value, which is achieved from adding the retarder effect to the vehicle in behind, to the headway of heavy vehicles and the headway of car.The third approach; proportion of the values, which are achieved from the correction of combinations, depending upon the number of observations.In consequence of the study, the BOtE values, which are achieved from these different approaches, are given. The BOtE values achieved by practically combined total data;The first approach; minibus 1.20, pick-up 1.14, midibus 1.73, truck 1.55, bus 1.48, articulated large truck 2.82.The second approach; minibus 1.38, pick-up 1.46, midibus 1.97, truck 1.84, bus 2.18, articulated large truck 3.55.The third approach; pick-up 1.24, truck 1.85, bus 2.22.