Abstract
The main objective of this paper, based upon the extensive empirical research of free flow in local conditions, is to quantify the unfavourable impact of the flow structure on the road capacity using PCE (Passenger Car Equivalent) values as a function of longitudinal grade. Based on literature reviews and empirical research, it has been proved that the PCE value for all vehicle classes is directly correlated with the road gradient. The PCE values in free flow conditions have been determined for the approved vehicle classes. Based on the measured values, models for determining the average PCE value depending on the upward grade on two-lane roads have been developed. Comparison of the developed models in conditions of free traffic flow with the Highway Capacity Manual (HCM) models has shown lower PCE values in this research. Models for the percentage of PCE values PCE15%, PCE50% and PCE85% have also been established.
Highlights
Heavy vehicles hypothetically include all motor vehicles larger than passenger cars and the percentage of heavy vehicles differs on roads and depends on the distance of urban areas, availability of alternative routes and the like
The arithmetic mean of PCE values for LT, Heavy-Duty Vehicles (HDV), BUS, Auto Trains (AT) vehicle categories is grouped between values 2 and 3, except for the PCE value for AT vehicle category which is higher than 4
Deviation of PCE value for AT vehicle category from PCE values determined in other vehicle categories is higher with the increase of a longitudinal road gradient
Summary
Heavy vehicles hypothetically include all motor vehicles larger than passenger cars and the percentage of heavy vehicles differs on roads and depends on the distance of urban areas, availability of alternative routes and the like. As the vehicle length increases, the vehicle will occupy larger road space which will lower the maximum traffic density value. This will have direct negative impact on the resulting road capacity. HCM-2000 [3] confirms that bad weather conditions can significantly reduce capacity and exploitable speed and deals with issues like where and how to take these effects into consideration These are all very important factors which disturb the PCE values. Based upon the extensive empirical research of free flow in local conditions, the main goal of this paper is to quantify the unfavourable impact of the flow structure on the road capacity using the PCE (Passenger Car Equivalent) values as a function of longitudinal grade.
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