Determination of Passenger Car Unit and Capacity Loss at Curve Section of Two Lane Undivided Highway: A Case Study Of Balkhu-Chovar-Dakshinkali Road Section
Student: Tuphan Jijung K.C.
Supervisor: Prof. Dr. Thusitha Chandani Shahi
Submitted Date:
August, 2024
Abstract
Passenger Car Units (PCU) are used to quantify the impact of different vehicle types on a
traffic stream. In Nepal, where most national and feeder roads are two-lane highways with
heterogeneous traffic conditions. Factors such as lane width, horizontal alignment, gradient,
lateral clearance, and shoulder condition influence both PCU and roadway capacity.
Notably, the effect of radius of horizontal curves on PCU of different category vehicle and
capacity of highway has not been extensively studied in Nepal.
This study focuses on determining PCU values and roadway capacity at Straight and curve
section under heterogeneous traffic conditions for two-lane undivided highway. Data were
collected from five sections of the Balkhu-Chovar-Dakshinkali highway using a digital
video recorder, which was then analyzed to assess traffic characteristics and adopted
dynamic PCU method for PCU estimation. The fundamental speed-flow-density
relationships diagrams were drawn and were used to calculate roadway capacity.
The study found that PCU values for all vehicle categories increase linearly with increase
in radius of curves. The increase in PCU values was clearly observed in case of heavy
category vehicles however, there is no significant changes in PCU values for light vehicle
categories at curve sections. The PCU values for light category vehicles were slightly
increased and almost remain constant. The PCU values of Bus and Truck ranges from
5.2986 to 5.4333 and 3.3743 to 3.4450 on varying radius of curve from 32m to 151m
respectively. The maximum capacity of road at straight section was found 1451 PCU/hr at
chovar section for one direction which doesnot meet the capacity reported by Indo HCM (
1600PCU/hr for hilly terrain under ideal condition) for one direction. While the capacity
loss decreases as the radius of curves increases. For the curve with a radius of 32 meters,
the capacity loss observed was 25.27%, whereas for the curve with a radius of 151 meters,
the capacity loss decreased to 7.92%. The research emphasizes the impact of curve radius
on PCU and capacity loss of the highway.
Keywords
Traffic composition, Speed, Passenger Car Units, Volume, PCU, and Capacity