Tangent-to-curve transition on two-lane rural roads based on continuous speed profiles

[EN] In the road geometric design process, speed variation along the road segment is one of the most popular criteria to evaluate road consistency, hence the importance of estimating operating speed and its variations. Most of the estimation models are based on speed spot data collection, usually assuming some hypotheses like operating speed remains constant at curves and speed variations take place entirely at preceding tangent. This paper presents the results of the study of the deceleration phenomenon using a new methodology based on data collection by global positioning system devices. By means of this new methodology, not only new and more accurate models can be developed, but also the previous hypotheses can be checked and new studies can be carried out. Tangent-to-curve speed variations have been evaluated, comparing the 85th percentile speed differential (85V) and the differential of the 85th percentile operating speed (V85), analyzing the percentage of deceleration length that takes place at curves, and developing two deceleration models with radius of horizontal curve and parameter of transition curve as explanatory variables.