Study on gap acceptance behavior of vehicles at roundabout
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Date
2019-06
Authors
Chin Wei Ai
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Abstract
Field study was carried out at a medium-sized roundabout, with value of 42.5 m in
diameter. Frequency distribution of accepted gaps and rejected gaps were found out
based on vehicle classification from this study. Class 3 vehicles are not included in the
study as data obtained is insufficient for further discussion. For Class 1 vehicles, the
mean of accepted gaps obtained was 14.45 s while for rejected gaps was 2.69 s. The mean
of accepted gaps and rejected gaps for Class 2 vehicles was found to be 10.24 s and 1.87
s respectively. For Class 4 vehicles and Class 5 vehicles, mean accepted gaps of 13.12 s
and 12.70 s respectively were obtained, while rejected gaps of 2.03 s and 2.84 s were
found. Critical gap was identified and analysed according to vehicle classification and
time session too. For Class 1 vehicle, critical gap during morning session was 5.75 s
while during evening session was 4.49 s and have an overall value of 4.82 s. Critical gap
with value of 4.48 s in the morning and 6.25 s in the evening was found for Class 2
vehicles with higher value of overall critical gap of 6.00 s as compared to Class 1 vehicles.
Class 4 vehicles had the highest value of critical gap among the other classes of vehicles,
which was 7.21 s in the morning, 5.74 s in the evening and an overall value of 6.34 s. For
Class 5 vehicles, lowest value of critical gap, 3.67 s was obtained with 4.71 s for morning
session and 3.00 s for evening session. Follow-up time was determined and effects of
different vehicles-following cases on accepted gap were studied too. Follow-up time of
Class 1 vehicles was 2.67 s which is significantly higher than that of Class 5 vehicles
which was 1.01 s. Different vehicles-following cases such as combination of Class 1 and
Class 5 vehicles, the time interval determined was 1.35 s in the morning and 1.69 s in the
evening, which then resulted in a mean value of 1.52 s. This shown that Class 5 vehicles
tend to follow closer despite vehicle types and thus shorten overall follow-up time.