Comparison of Alternative Junction Designs For Light Rail Transit Grade Crossings
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Date
2018-10
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Addis Ababa University
Abstract
Light rail transit is a relatively new mode of transport for Ethiopia. Hence, rigorous research
needs to be done in order to identify and work out flaws in the system. Most of the road-rail
intersections within Addis Ababa LRT corridors are built as grade separated intersections.
However, certain intersections such as Sealite Mehret and CMC roundabout meet the LRT
line at grade. Research done up to now on these areas, points out significant problems with
respect to traffic congestion. The main causes of congestion in this area that are related to the
LRT line are: frequent LRT crossing and interruption of traffic flow, high pedestrian volumes
at stations near the roundabouts that impede entry and exit flows, lack of U turn areas along
the LRT corridor, which transfers high volumes of U turning vehicles to the roundabouts,
which in turn adds to congestion of the roundabouts. Performance evaluation of the
roundabouts under current traffic conditions was done during peak and off – peak periods.
Results indicate approach delays of over ten minutes for both locations during peak periods.
However, during off – peak periods the roundabouts perform above level of service C.
The goal of this study is to propose alternative solutions to mitigate each cause of congestion
and to see if adequate performance can be achieved without grade separation at the selected
locations: Sealite Mehret and CMC roundabouts. In order to fulfill this goal necessary data
were collected at the study areas. Then the alternatives were designed and modeled using
VISSIM simulation software.
The alternatives considered are signalized intersection, signalized roundabout, installation of
pedestrian signals and diverting U turns to other locations. Comparing these alternatives
based on queue length, travel time, intersection delay and level of service under current
traffic conditions, showed that the best alternatives for both locations are signalized
roundabout and signalized intersection.
Up on comparing signalized roundabout and signalized intersection alternatives under
forecasted traffic conditions, analysis results showed that both options have similar travel
times and delay. Both alternatives are viable options. However, since signalized roundabout
alternative provides the option of functioning as a normal roundabout during off peak
periods, and reduces risk of right angle crashes, signalized roundabout is preferred.
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Keywords
Signalized roundabout, LRT grade crossing, VISSIM