The Extension Study on the Evaluating of the Spot Speed Distribution at Horizontal Alignment on Two-Lanes Rural Arterial Highway

The rising number of accidents has been associated with inconsistencies in the geometric design of highways. To evaluate design inconsistency, estimation of 85th percentile speeds associated with horizontal geometric is vital important. Significant variations in the operating speeds of consecutive elements indicate inconsistencies in the alignment. Therefore, to enhance the safety of the road it is crucial to produce road design that permits and encourages operating vehicles at uniform speed. This research investigates and expands the use of operating speeds in the analysis of design consistency. Series of regression equations were developed to predict the operating speeds of passenger vehicles in Malaysian’s road. The conventional method for designing is using the design speed process which ensures design consistency are involved. Once the design speed is selected, it guides the selection of values for geometric design elements. The study was carried out by analyzing the speed characteristics on daytime at 3 different segments along the Horizontal cure (i.e. Transition at entering of curve, Middle of Curve and Transition at leaving of curve) and it was discovered that vehicles travelling on transition entering curve tend to travel at higher speed than on the middle and on transition leaving curve. Based on the preliminary finding, further testing on middle of curve at night-time was carried out to find significant effect under Mesopic and Photopic visual condition. The speed data measurement is based on Spot Speed Data at specific points and location using Laser Gun Detector. It was also found that the existing speed limit of the selected road stretches is lower than the 85th percentile speed. The 85th percentile speed is a commonly used measure to decide speed limit on a road. Also, the different in the mean speed on the contrast sensitivity under mesopic and photopic condition was determine using t-test. Further discussion on the analysis will be presented in the data and result analysis.