Modeling on the effect of geometric and traffic parameters on speed-flow-geometry relationship for urban roads in Johor Bahru street network

Abstract

Urban roads are essential transportation facilities and require a sound planning and design. It serves as major routes and access points to the land uses situated in the urban area. In an effort to overcome issues involving the accurate prediction of traffic flow operation due to the increasing traffic flow and wide range of urban roads’ features, this study examines the speed-flow relationship for the complex conditions of urban road facilities. The main aim of this study is to develop new empirical models of speed-flow-geometry relationship for urban roads. A multilinear regression analysis technique was used to develop new models with varying cross-sectional and longitudinal parameters of urban roads. The parameters considered in the modelling are average travel speed (ATS), traffic volume, median existence, lane number, roadside friction, driveways access density, intersections density, and traffic calming device density. Data for the study were collected at 197 urban streets in Johor Bahru using moving observer method. Using a correlation matrix, it was found that the values of Pearson correlation (r) related to the ATS were 0.41, 0.36, 0.30, 0.28, and 0.25 for road side friction, access density, intersection density, traffic flow, and median existence, respectively (at 95% confidence level). All the five developed models were statistically significant with R2 values ranging from 0.64 to 0.98 (at 95 % confidence level). Furthermore, for models of road’s category of one number of lane and without a median, the ATS increased by 5 km/h when they occurred in low roadside friction comparing to that of high roadside friction conditions. Intersection density and traffic calming density were found to reduce the ATS by the same values of coefficients in the model of road’s category with high roadside friction. Accordingly, the ATS reduced by 1 km/h as the number of intersection and traffic calming devices increased by 13/100 m. For models of road’s category of two numbers of lanes and high roadside friction, the only two longitudinal parameters that significantly predicted the ATS were traffic calming devices and access driveways with similar values of coefficients, depending on the median existence conditions. Furthermore, for the roads without median and high roadside friction, the ATS decreases by 1 km/h as the number of traffic calming increases by 2/100 m. However, for the roads with median and high roadside friction, the ATS decreases by 1 km/h as the number of access driveways increases by 5/100 m. The main application of these models is the ability to be used as a planning and design tool for urban roads. This is because they could be used to predict the overall reduction of speed of traffic flow according to the current or planned view of the surrounding geometric and traffic parameters of urban roads. Findings from this study suggested that there is a need to review the models provided in the MHCM to include a wide range of parameters affecting the speed-flow relationship on urban roads.