The Effects of Traffic Mixes with 3-Wheelers on Performance of Unsignalized Intersections in Harar City
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Date
2018-04
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Publisher
AAU
Abstract
In heterogeneous traffic conditions, the performances of an intersection are described by vehicle
and driver characteristics which are different from traffic conditions in homogeneous conditions.
The absence of lane discipline results in vehicular movement that is influenced by the presence
of vehicles in the front as well as on the sides. This led to a complex traffic behavior and it
cannot be analyzed by using conventional microscopic and macroscopic traffic variables. In this
study the relationship between different vehicle compositions and the performance measurement
parameters for two roundabouts and one unsignalized T-intersection in Harar city are assessed
by application of gap acceptance procedures.
All data which describes actual condition of the intersections were collected to calibrate the
existing condition into gap acceptance procedures of highway capacity manual. Critical gaps
follow up times and passenger car equivalents representing the existing traffic conditions of the
study area are estimated. The analysis is made in 15minute interval over a range of 24
consecutive time series to indicate the trends of change of the performance of intersections in
relation to the change of vehicle compositions and flow characteristics. Highway capacity
manual 2000 was used for measurement of performances and multiple regressions was the
analysis method applied to indicate the effects of vehicle classes in the study
The results are interpreted by five performance measurement parameters. They are approach
capacity, degree of saturation, queue length, control delay and LOS. The model which indicates
the relationship between these parameters and the vehicle compositions are formulated in the
form of multiple linear regression equations with R
2
greater than 0.85 for most approaches of
the selected intersections. Cross validation was made on the models to estimate how accurately a
predictive model will perform in practice. Peak hour performances are compared with the
presence of bajaj vehicles and with bajajs replaced by minibus taxis.
Finally, the result indicates that some of the approaches of the intersections selected are
providing service closer or above the capacity during peak hour of traffic flows. Besides, the
presences of Bajajs were significantly affecting the performances of the intersection. A
replacement of bajaj vehicles by 12 seat minibus taxis indicates a very good improvement of
performances of the intersections in Harar city. For Arategna roundabout the average delay will
be reduced by 7 minutes per vehicle if bajajs are replaced by minibus taxis during peak hour.
The queue lengths will be reduced by 85 vehicles and the capacity will be increased by
396veh/hr for peak periods. Sillassie roundabout will be improved by decrease of average delay
by 95 sec/veh, decrease of queue length by 34 vehicles and increase of capacity by 531veh/hr
during peak hour if bajajs are replaced by minibus taxis. Thus, the effect of traffic mix with three
wheelers is very significant on performances of unsignalized intersections.
Description
Keywords
Unsignalized, Bajajs (3-wheelers), Roundabout, Composition, Delay, Performance, Intersection, Traffic Flow, Capacity