dc.description.abstract |
Traffic performance of a road section is expressed in terms of Level of Service (LOS). The
Highway Capacity Manual (HCM) developed by the Transportation Research Board of the
National Academies of Science in the United States provides procedures to determine LOS
based on analysis of capacity of a road. It divides the quality of flow into six levels ranging
from level A to F. These definitions of quality are based on measures of effectiveness of the
road which include speed, travel-time, density and delay.
Road development authorities in Sri Lanka are adopting the methodologies given in the HCM
due to the lack of guidelines specific for the country. However, the HCM methodologies may
not depict the correct traffic performance of roads owing to the nature of the mix of vehicle
types in the traffic stream, the lack of lane discipline and irregular road side activities. This
may lead to incorrect decisions in planning, designing, maintenance, rehabilitation, and
operation of roads. Therefore, it is necessary to study traffic performance in Sri Lanka, and to
evaluate the transferability of methods used in other similar countries in order to develop
appropriate and applicable approach to mix traffic Condition. Subsequently, in order to
evaluate traffic performance, it is important to study about operational characteristics of
traffic stream. In a pilot study under this work, capacity of a road was found to be affected by
the traffic composition and control condition. Therefore, characteristics of vehicle
composition in different capacities have been considered and study was focused to two waytwo
lane roads.
Different size, power, and maneuverability performance of vehicles cause significant level of
friction to the movement of other vehicles in a mix traffic stream. For an example, in a high
traffic volume stream, a large proportion of motorized two wheelers and three wheelers are
able to move with speeds closer to their free speeds due to the ability of utilizing smaller gaps
in the traffic stream, while the large-size vehicles are subjected to significant speed reduction.
Characteristics of fundamental traffic flow parameters (Speed, Density and Flow) in traffic
streams with different compositions of vehicles were studied. One-Sample Kolmogorov
Smirnov test was performed to check normality of speed of collected data samples under prevailing conditions and it has shown that speed distribution is significantly deviate from
normality (P-value < 0.05) under different compositions and traffic volumes. It is observed
that speed distribution shows bi-modal distribution in roads which
wheelers and three wheelers. One-way analysis of variance (One-way ANOVA) tests was
carried for speed characteristics of group of two wheelers, three wheelers and four wheelers.
Null hypothesis (Ho) that there will be no significant difference between different groups of
vehicle speed sample means was rejected with 95% confidence level (P-value < 0.05).
Therefore, vehicle composition has described as separate groups of two wheelers, three
wheels and four wheelers. Modified continuity equation for heterogeneous driver population
was used to calculate densities of traffic streams. Different traffic flow models which
used to model two-lane traffic flow behavior had been tested under prevailing conditions.
Greenshield traffic flow model has showed strong correction between flow and speed and it
was chosen to develop speed-flow models. Finally, empirical speed - density and speed -
flow curves were developed for different compositions of vehicles in order to evaluate the
capacity variations under mix traffic condition. |
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