Abstract
Experimental investigation was conducted on a 24 km long segment of the two-lane state road to collect the driver behavior data. The research involved 20 drivers driving their own cars equipped with the GPS device. Considering the impact of path radius and speed on the side friction demand, the design consistency on horizontal curves was evaluated by determining the margins of safety. The analysis showed that the vehicle path radii were mainly smaller than curve radius, on average for 12%. Regression analysis indicated that the percentage difference between the curve radius and vehicle path radius is not affected by the speed, speed differential and geometric characteristics of the curve and surrounding elements. Two different margins of safety were analyzed. One is the difference between maximum permissible side friction (based on design speed) and side friction demand, while another is the difference between side friction supply (based on operating speed) and side friction demand. Generally, demands exceeded supply side friction factors on curves with radii smaller than 150 m, whereas “poor” conditions (in terms of Lamm’s consistency levels) were noted for curves under approximately 220 m. Both values are very close to the critical radius below which higher accident rates were observed according to several accident studies. Based on the results of the research, it is proposed to use a 12% smaller curve radius for the evaluation of margin of safety and that curves with radii smaller than 200 m should be avoided on two-lane state roads outside the built-up area.
Highlights
Motorized road transport is one of the important characteristics of modern civilization which, with all the benefits that provides, has a human cost
Considering the impact of path radius and speed on the side friction demand, the design consistency on horizontal curves was evaluated by determining the margins of safety
At the entering to the selected road segment, drivers are asked to participate in the research, so the global positioning system (GPS) device is placed on the vehicle and the vehicle is released at the exit checkpoint
Summary
Motorized road transport is one of the important characteristics of modern civilization which, with all the benefits that provides, has a human cost. Driving performance measurements comprise of vehicle trajectory, speed profile, longitudinal deceleration and lateral acceleration (Cafiso, La Cava 2009) They are direct consistency indicators since they point to the deviations between the driver behavior and real highway’s geometric and operational features. Most of previous design consistency and road safety studies were based on operating speed whereas only a few researchers were studying the impact of real vehicle path radii on vehicle stability. At the entering to the selected road segment, drivers are asked to participate in the research, so the GPS device is placed on the vehicle and the vehicle is released at the exit checkpoint This methodology ensures collecting a large amount of data which is appropriate for developing different models based on speed. Similar data collection methodology was performed in this study with a detailed description presented below
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