Investigating the Start-Up Lost Time for Selected Signalized Intersections of Addis Ababa
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Date
2019-11
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Addis Ababa University
Abstract
In Transportation, Signalized Intersections are an important nodes of traffic movement and this
node are designed and their performance evaluated based on the adopted standards. In this
respect, most of the parameters that are used for design and capacity evaluation of Signalized
Intersection are taken from Highway Capacity Manual (HCM) which was developed by
Transportation Research Board in Washington, D.C. Accordingly, the default values will not
represent the actual condition of the traffic for a specific study area. To this effect, calibration of
the values should need to be the major task for researchers and traffic agencies. Lost time is one
of the key parameters used to estimate an optimum cycle time. It is a very sensitive parameter and
small variation of lost time may cause large changes of cycle time.
Different studies show a great deal of variations in start up lost time and saturation flow. This
indicates a lack of stability and this is acknowledged in the HCM. Due to these instabilities, HCM
recommends that local data collection be performed to produce more accurate estimates of local
start-up lost time and saturation flow.
In this Study, experimental research is carried out for estimating the start-up lost time and the
contributing factors affecting its value. For this purpose, observations were carried out on four
selected signalized intersections in Addis Ababa City. Data was collected by a video recording of
traffic flow at four selected signalized intersections of Addis Ababa city. Recorded data were
analyzed for start-up lost time by extracting the information of time headway of the vehicles. In
this research a more accurate way of estimating Start Up Lost Time is proposed by developing
applicable and replicable models.
The analysis showed that the overall estimated mean of start-up lost time is 2.513 Sec for all
observed sites with a different mix of traffic and Geometric condition as well as from the analyzed
intersections the ideal intersections were selected as per HCM recommendation and it shows that
the mean start up lost time for an ideal intersections is 2.383 Sec and t test showed that the mean
start up lost time is significantly different with the HCM recommendation of 2sec per phase. Start
Up Lost Time data for eleven vehicular compositions were fitted to a probability distribution.
Lognormal, Weibull and Johnson Transformed were found to be best fitted probability distribution
for the Start Up Lost Time. Regression Analysis was conducted by Multiple Linear Regression
technique to predict Start Up Lost Time. From regression analysis Mix of Traffic (Vehicular
Composition), Approach Grade, Lane Width, Approach Width, Green Time, Type of Movement,
Lane Position for Maneuvering and Saturation Headway were the factors that affect start up lost
time and found statistically significant to predict Start Up Lost Time.
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Keywords
Start Up Lost Time, Saturation Headway, Signal Timing, Model and Signalized Intersection