Longitudinal Acceleration Models for Horizontal Reverse Curves of Two-Lane Rural Roads

Echaveguren, Tomás; Henríquez, Cristian; Jiménez-Ramos, Gustavo · 2020 · DOAJ

DOI: 10.7250/bjrbe.2020-15.463

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Summary

This study addresses the limitations of existing operating speed profile models for horizontal reverse curves (HRCs) on two-lane rural roads. Traditional models often assume constant acceleration and deceleration values derived from kinematic equations, ignoring the spatial correlation of speeds and the influence of road geometry. The authors aim to develop longitudinal acceleration-geometry models for light cars that account for these factors, thereby improving the accuracy of speed change estimations in HRCs. The research utilized field data collected from 23 HRCs in Chile, with 20 vehicle runs per curve. Data collection employed a 10 Hz GPS logger to record position, heading, speed, and longitudinal acceleration directly, avoiding indirect estimations. To isolate the effect of horizontal geometry, data were gathered under controlled conditions: daytime, dry weather, low traffic volume (AADT < 5000), flat terrain (slope < 4%), and good pavement conditions. The geometric dataset included curve radii, deflection angles, curve lengths, and tangent lengths. Data processing involved filtering with a Kalman filter, discretizing the HRCs into cross-sections, and clustering acceleration data points to analyze probability density functions (pdfs). Analysis revealed that acceleration and deceleration pdfs follow a Burr distribution, necessitating a Box–Cox transformation for proper model calibration. The models were calibrated using the 95th percentile of the acceleration pdf. The results confirmed that acceleration and deceleration rates are not constant but depend significantly on the radii of the entrance and departure curves of the HRC. This finding contradicts the assumption of constant acceleration used in simpler kinematic models and validates previous observations that speed changes are heterogeneous and geometry-dependent. The significance of this work lies in its contribution to more accurate operating speed models for HRCs. By establishing that acceleration and deceleration are functions of specific geometric parameters, the study provides a basis for better geometric design assessments. This enhances the ability of designers to evaluate speed homogeneity and safety, potentially reducing accidents caused by excessive speed changes. The proposed models offer a refined tool for understanding driver behavior in complex road geometries, moving beyond single-value approximations to geometry-specific predictions.

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• road geometry