Modeling critical overturning criteria for single vehicle run-off-road crashes for Bangladesh context

Abstract

Road traffic accidents and the consequent deaths are the most concerning issue in the transportation sector of the world. Being a developing country Bangladesh is not an exception. The road safety situation in Bangladesh is very severe by international standards. Accident and casualty statistics of 13 years (1998-2010) shows that overturning accident is about 9% of total accidents and is responsible for 15% of total fatalities. Analysis in Microcomputer Accident Analysis Package (MAAP5) demonstrates that overturning of vehicles to the left or right of carriageway on straight or curved road comprises of about half of the single vehicle Run-Off-Road (ROR) crashes in Bangladesh. Running off road may not be the sole result of driver performance, rather it is due to the result of complex interaction among vehicle loading pattern, tire characteristics, improper super elevation, cross slope, vehicle speed etc. Shoulder or pavement edge drop-off, discontinuity in shoulder, ill-maintained road/shoulder surface also imposes potential safety hazards. When left wheels go onto the shoulder, the drop-off causes tilting of vehicle and in effect the resultant moment increases that tends to overturn the vehicle. Vehicle speed and overloading condition are the other factors that may affect the stability of vehicles. While the vehicle is in motion, it undergoes continuous jerking and vibration effect from the potholes and rough road surface. If the loading is loosely fastened and is of high height, bulging and shifting of load occurs. Due to this, the horizontal component of CG gradually shifts towards the direction of roadway slope that makes a vehicle more prone to overturn. High centre of gravity height may worsen the situation. Considering these facts, in this research work, an analytical model is developed which relates these factors with ROR crashes and establishes critical condition for overturning in terms of rollover threshold. The rollover model deals with shoulder drop-off as special geometric feature, vehicle speed as driver behavior, gross weight, overall height and load bulging as vehicular features. Some guidelines are also provided based on the model analysis. Though ROR crashes involving buses result in more fatalities and casualties, considering importance of freight transportation, the model covers only heavy truck features. Matlab/SimuLink is used for the simulation of the model.