Kajian lapangan telah dijalankan di bulatan sederhana, dengan diameternya bernilai 42.5
m. Dari kajian ini, taburan kekerapan jurang yang diterima dan jurang yang ditolakkan
telah didapati berdasarkan klasifikasi kenderaan. Kelas 3 kenderaan tidak termasuk
dalam kajian ini kerana data yang diperolehi tidak mencukupi untuk perbincangan lanjut.
Bagi kenderaan Kelas 1, purata jurang yang diterima perolehi ialah 14.45 s manakala
bagi jurang yang ditolak ialah 2.69 s. Sementara itu, purata bagi jurang diterima dan
ditolak bagi kenderaan Kelas 2 ialah 10.24 s dan 1.87 s masing-masing. Bagi Kelas 4
kenderaan dan Kelas 5 kenderaan, nilai purata jurang yang diterima adalah 13.12 s dan
12.70 s masing-masing, manakala purata jurang ditolak yang diperolehi bernilai 2.03 s
dan 2.84 s masing-masing. Selain itu, nilai sela kritikal lorong cantuman untuk Kelas 1
kenderaan adalah 5.75 s pada sesi pagi manakala pada sesi petang adalah 4.49 s dan
mempunyai nilai keseluruhan 4.82 s. Manakala bagi kenderaan Kelas 2, nilai yang
diperolehi adalah 4.48 s pada waktu pagi, 6.25 s pada waktu petang dan nilai keluruhan
6.00 s. Kelas 4 kenderaan mempunyai nilai sela kritikal yang paling tinggi dalam
kalangan jenis kelas kenderaan lain-lain, iaitu 7.21 s pada waktu pagi, 5.74 s pada waktu
petang dan nilai keseluruhan 6.34 s. Kenderaan Kelas 5 mempunyai nilai sela kritikal
waktu pagi, petang dan keseluruhan dengan nilai 4.71 s, 3.00 s dan 3.67 s. Susulan masa
ditentukan dan kesan kenderaan-berikut yang berbeza kes-kes diterima dikaji
juga. Susulan masa diperolehi bagi kenderaan Kelas 1 adalah 2.67 s dan jauh lebih tinggi
daripada Kelas 5 kenderaan, iaitu 1.09 s. Bagi gabungan kenderaan Kelas 1 dan Kelas 5
kenderaan, susulan masa pula menunjukkan arah aliran menurun iaitu nilai purata 1.52 s.
Fenomena menjelaskan bahawa kenderaan Kelas 5 cenderung untuk mengikuti lebih
dekat meskipun jenis kenderaan dalam barisan adalah berbeza.
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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.
Study on gap acceptance behavior of vehicles at roundabout / Chin Wei Ai