Vol 6, No 5 (2015) > Civil Engineering >

Median-type Adjustment Factor for Road Capacity Calculation

Martha Leni Siregar, Heddy R, Agah, Fadhliya Afifa Arifin


Abstract: A median is required for
a two-way road to separate the opposite traffic and prevent head-on collisions.
In road capacity calculation, the median factor contributes in terms of its
existence regardless of the difference in median types. Road capacity is
determined by a number of geometric factors such as road types, width of
carriageway, shoulder/curb characteristics, and the presence/absence of
medians, etc. The contributions of these factors are represented by the
coefficients in the capacity calculations. Despite the different types of
medians, the Indonesian Highway Capacity Manual (IHCM) does not adopt different
coefficients to accommodate the effects in the capacity. The aim of this study
is to obtain an adjustment factor for road capacity calculation based on median
types. The method of this study adopts video recordings of real traffic moving
along three different types of medians: raised medians, fenced medians, and
line medians. As it is assumed that the effects of different median types are
expressed in the vehicles’ safety distances from medians, the capacity of the
road will also vary by types of medians. The adjustment coefficients for roads
with raised medians, fenced medians, and line medians obtained are: 0.79, 0.78,
and 0.81, respectively. The results of this study confirm that in addition to
the presence of the medians, the types should essentially be considered in
calculating the road capacity. The result of this study will contribute to the
enrichment of the road capacity calculation in the IHCM.
Keywords: Drivers’ hazard perception; Median; Median-type adjustment factor; Road capacity; Vehicle-to-median distance

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