الفهرس 
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Abstract
This study presents the behaviour of vehicles at mid-block median U-turn openings in multilane divided urban roads based on gap acceptance in Egypt. Most of the median openings in
Egypt are uncontrolled. In this study, models are proposed for calculating U-turn capacity
using both field and gap acceptance approaches. This study estimates the critical gap or lag,
accepted gaps, and vehicle merging time in U-turn opening. The capacity of median openings
mainly depends on the critical gap and follow-up time of U-turn vehicles. Hence, a thorough
investigation into the gap acceptance behaviour of U-turn vehicles was carried out. A
field approach depends on data collection and was performed on eight different sites in ElObour and Benha cities in Egypt. Data collection was done during peak hours using a video
recording technique at the selected sections. Sections were chosen to be free from gradients,
curves, and on-street parking. In addition, Eight factors were considered; five related to the uturning vehicle (age, gender, vehicle type, queue length, and wait time); three related to the
conflicting traffic (gap size, speed, and vehicle type). The results showed that those factors
had an effect on the decision in the following descending order: gap size, speed, wait time,
conflicting vehicle type, queue time, gender, u-turning vehicle type, and age. The significant
factors included gap size and speed. Both field and gap acceptance approaches were used to
estimate the capacity of U-turn movement. The field approach was done using regression
analysis and investigated to estimate the capacity of U-turn movement. Different factors that
might affect the estimated capacity were studied in this approach. Finally, we found that the
parameters that affect gap acceptance, including critical gap, move-up time, driver age, and
percentage of females, were studied for suitability to be included in the calculation of the
capacity model. The method is based on a gap-acceptance approach that was created and
refined in Germany. The capacity of each nonpriority stream is calculated using Siegloch’s
formula.
Results from both approaches have been used to derive a regression model to estimate the
capacity of U-turn movement at the median opening and calculate the distance between two
U-turns for each road.