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This paper introduces a new piecewise regression methodology that can be used when linear regression fails to represent data. Effort can be saved to determine the best non-linear model shape using this methodology. Therefore, in this paper a nonlinear relationship is introduced using only one independent variable by a simple and direct way. The new approach depends on dividing the data set into several groups and then estimating the best line or segment for each group to perform a continuous broken line. The locations of breakpoints are determined by minimizing the sum of squared errors while the number of segments is determined by maximizing the adjusted coefficient of determination. The proposed approach can be used in many transportation applications such as trip generation models, zonal trip rates, nonlinear correlation coefficient, accident modeling, and traffic characteristics models. The proposed approach was tested against many practical examples and found that it can describe most of the transportation relationships properly and can decrease the number of variables used in the transportation modeling process. The proposed approach can be extended in the future to get the nonlinear relationship using more than one independent variable to cover the rest of transportation applications.

The aim of this study is to evaluate the effect of strengthen of soil under concrete slab on its thickness. Rigid pavement strength depends on the rigidity of concrete slab in addition to the effect of soil strength. This research tries to study strengthen of soil under rigid pavement using different compositions of coarse and fine aggregate. The term which expresses soil strength in the AASHTO design equation is the value of the modulus of subgrade reaction (K). Various compositions of fine and coarse aggregate have been tested in the lab. Each sample has been analysed in term of sieve analysis and California bearing ratio (CBR). Using CBR value for each sample and AASHTO equation, the modulus of subgrade reaction has been estimated. Using the estimated value of modulus of subgrade reaction and AASHTO design method for rigid pavement the slab thickness has been estimated for each case. Results have been analysed to get the effect of best composition of coarse and fine aggregate under rigid pavement.

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