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Purpose This paper evaluates all the available transition curve types related to road and railway alignments and proposes a new, well verified, transition curve type that combines the accuracy of clothoid curve and the simplicity of cubic parabola curve. Method A methodology similar to clothoid's curve formation is used to introduce a new transition curve type called "of clothoid Symmetrically Projected Transition Curve (SPTC). All three transition curve types are being compared to each other, for a variety of transition length value versus Radius value combinations. The cubic parabola is a simple function of the form of y=f(x). Clothoid is a transition curve in the form of x=f(l), y=f(l), having as main characteristic the linearity of curvature variation versus its length. A new transition curve will be defined in the form of y=f(x) having also as main characteristic the linearity of curvature variation versus its projection length on axis X. By using the same calculation procedure as the clothoid, the new transition curve will be fully defined. A relation similar to (1) was used as base, by defining a parameter Α similar to the one used in the clothoid. The new curve will be called Symmetrically Projected Transition Curve (SPTC). Results Some remarkable results that derived from transition curves comparison are: There are no significant differences between the 3 curves in the area of short transition lengths. For long transition lengths, cubic parabola is diverging from the other 2. The deviation of the cubic parabola from the other curves for large values of Χ, ratios Χ/Α >0.7, as well as the

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Objective The present paper focuses on the investigation of motorcycle riders' behavior at curved road sections by introducing a new methodology based on global positioning system (GPS) technology. In the frame of the research, the determination of the optimum regression curve between the curve radius' and the corresponding velocities, was investigated. Design Within the context of the paper field measurements were conducted, with the use of appropriate velocity recording equipment in order to confirm the efficiency of the proposed methodology. The measurements were conducted taking into account various factors that potentially influence riders' behavior such as the different light conditions, the difference on riding experience level, the familiarity of the riders with the routes, the presence of pillion and the different road environments, such as width/condition of the road pavement, roadside land use, right/left hand curves etc. Setting The experimental environment that served the needs of the experiment was mountain Pelion in Magnesia region in Greece and was based upon four primary conditions: the location, the type of the road, the weather conditions and finally, the time and date that the experiment would be conducted. Participants The validation of the proposed methodology was performed by recruiting two motorcyclists. Their selection was based on demographic, psychometric and experience criteria.Results The research showed among others, that the regression curves could be used as a curve classification mean. Moreover, a significant variation was detected on the riders' behavior when carrying a pillion related to their experience levels.