Developing mathematical model to estimate the brake sight distance according to several variables

Features of the engineering design of the road, obstacles to sight on the sides of the road, the condition of the pavement surface, climatic conditions affect road safety and sight distance requirements. The dominant factor to get the traffic safety related to the moment when the braking system is activated, and the end is the complete stop of the vehicle. Although the AASHTO policy of geometric design of roads has taken into consider condition, effect of the vehicle’s speed and the coefficient of friction between its wheel tire and the road surface in addition to the slope of the latter, but several variables, (such as the quality and condition of the rubber, road surface condition, vehicle option, etc. ), control this distance, even by a small amount, as it has an effective effect on the sensitivity of the matter with some millimetres of the safe stopping distance. Therefore, it became necessary to discuss and research in finding an updated mathematical equation to calculate the braking sight distance BSD. Field tests were carried out with two types of vehicles and on roads with different types of pavements at wet and dry surface conditions. The purpose was to measure the distance of BSD at different operational speeds through which the necessary data is obtained to achieve the required sample size with the selected statistical analysis to estimate an acceptable and reliable mathematical equation. The data were arranged in Microsoft Excel and analyzed using the multiple-regression SPSS program. The results showed significant relationship of the variables, in current study, and BSD and predicted model in an acceptable correlation factor of more than 80%. The validity of this model was also examined with other data from previous studies, which had a strong correlation coefficient over 90%.