Different types of vehicles have different impacts on traffic streams. Traditionally these impacts have been expressed in terms of passenger cars as the common unit, which is used to convert a heterogeneous traffic stream into a hypothetical passenger car stream. However, due to significant proportion of motorcycles in traffic streams in Asian countries, it is more reasonable if the common unit is motorcycles (MCU). Many methods exist for determining the common unit such as headway method, Walker method, semi-empirical method, multiple regression method, density method, etc. Most of them estimate the common unit upon a homogeneous traffic concept, such as strict lane discipline. However, the urban road system in Asian carries heterogeneous traffic, where roadways are shared by many traffic modes with different physical sizes. Because vehicles may not follow lane discipline, the homogeneous traffic concept has a limited application. This study introduces the effective space concept to estimate MCU for heterogeneous traffic, which is considered to be the most applicable to Asian road system. This concept correlates the flow rates of motorcycle traffic only and mixed traffic streams that are equivalent in terms of the drivers perception of the level of service (LOS). Because the variables that are used to define LOS reflect the factors that influence the drivers perception, the same variables are applied to estimate motorcycle unit. LOS on a segment of highway is defined in terms of speed, volume and density. Therefore, speed and effective space are the key factors in order to estimate MCU in this study. Three locations in Hanoi, Vietnam are used for data collection. It is noted that the sample sizes at all locations are the same and data are collected at high traffic volumes. In order to estimate effective spaces and mean speeds of different types of vehicles, it is necessary to apply the software SEV, developed in the traffic lab for this specific purpose. The concept for validating the proposed formula is coming from the speed-flow curve. It is understandable that if the mean stream speeds at different time intervals are the same, the volumes (after converting into MCU) must be the same. Therefore, after calculating mean stream speeds at different time intervals, if mean stream speeds are the same and the volumes at those intervals after converting into MCU are the same, the methodology of calculating MCU is correct. The proposed method of motorcycle unit estimation is validated based on the validation data set at those study locations. The sensitivity analysis also applied to determine whether the MCU values are optimum or not. The MCUs obtained from this study compares with 110%, 105%, 95%, 90% of those estimated values. The result shows that the proposed formula gives the lowest different volumes, meaning that calculated MCUs values are accepted. The findings of the present study can be used to assist the design of roadways as well as traffic operation systems in order to improve the capacity of highways. The speed variation of traffic on the main roadway would be reduced leading to fewer conflicts and improved speeds for the traffic stream. The information presented here also can be applied to develop the level of service, as well as estimate the traffic capacity in urban road system in Asian countries. For the covering abstract see ITRD E137145.
Samenvatting