Median-type Adjustment Factor for Road Capacity Calculation

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.

Drivers’ hazard perception, Median, Median-type adjustment factor, Road capacity, Vehicle-to-median distance

AASHTO, 2011. A Policy on Geometric Design of Highways and Streets. Washington DC, American Association of State Highway and Transportation Officials

Bella, F., 2013. Driver Perception of Roadside Configurations on Two-lane Rural Roads: Effects on Speed and Lateral Placement. Accident Analysis and Prevention, Volume 5, pp. 251–262

Departemen Pekerjaan Umum, 1997. Manual Kapasitas Jalan Indonesia 1997. Jakarta: Direktorat Jenderal Bina Marga

Departemen Pekerjaan Umum, 2004. RSNI Geometri Jalan Perkotaan (RSNI T-14-2004). Jakarta : Badan Standardisasi Nasional

Gaca, S.A., Tracz, M., 2012. Two Lane Roads with Multifunctional Median Lane. In: SIIV–5th International Congress – Sustainability of Road Infrastructures Procedia – Social and Behavioral Sciences, Volume 53, pp. 801–810

Hobbs, F.D., 1973. Traffic Planning and Engineering. Birmingham: Pergamon Press

Pignataro, L.J., 1973. Traffic Engineering. New Jersey: Prentice Hall

Rusmawan, T., 2011. Pengaruh Median dengan Pembatas Beton terhadap Jenis Kecelakaan di Jalan Tol. Jakarta: Universitas Indonesia

Siregar, M.L., 2015. Hazard Driven Drivers’ Behaviours towards Vehicle-to-median Safe Distances. Makara Journal of Technology, Volume 19(1), pp. 5–10

Tay, R., Churchill, A., 2007. Effect of Different Median Barriers of Traffic Speed. Canadian Journal of Transportation, Volume 1(1), pp. 56–66

Underwood, G., Ngai, A., Underwood, J., 2012. Driving Experience and Situation Awareness in Hazard Detection. Safety Science, Volume 56, pp. 29–35

Wanga, Y.G., Chena, K.M., Ci, Y.S., Huc, L.W., 2011. Safety Performance Audit for Roadside and Median Barriers using Freeway Crash Records: Case Study in Jiangxi, China. Scientia Iranica, Transactions A: Civil Engineering, Volume 18, pp. 1222–1230