Analysis of trajectory transection rate on four-lane divided rural highway curves.

Objective: The study aims to develop continuous trajectory profiles along curves with minimal error. It also focuses on formulating a percentage trajectory transection rate model as a function of geometric parameters (e.g., radius and curve length) for through and passing maneuvers on four-lane divided highways. Additionally, the study sought to identify the critical maneuver between through and passing on horizontal curves of four-lane divided highways.

Methods: A total of 15 horizontal curve sites on a four-lane divided rural highway in plain terrain were selected. An instrumented vehicle, equipped with a GPS data logger and cameras, was used for data collection. Naturalistic driving data from 34 drivers' trips across the curves were collected for analysis, ensuring free-flow conditions. This dataset was used to develop continuous trajectory profiles, with GPS positioning errors minimized by calibrating the profiles at the Point of Curvature (PC) and Point of Tangency (PT) using the vanishing point method. Moreover, multiple linear regression technique was used to develop the mean percentage trajectory transection rate models i.e., for through (PTTR_{μC_T}) and passing (PTTR_{μC_P}) maneuvers.

Results: The trajectory profiles were effectively developed using the vanishing point method, which restricts the mean absolute error to 16 cm. The developed models revealed that curve length significantly influences PTTR in through maneuvers, while deflection angle, approach tangent length and curve length are the most critical factors in passing maneuvers. Notably, curve length emerged as a common predictor for both maneuvers. Additionally, a 15% higher trajectory transection rate was observed in passing maneuvers.

Conclusions: Combining geometric features such as curve length, deflection angle, and approach tangent length provides a more comprehensive understanding of drivers' trajectory behavior, especially during passing maneuvers. The developed models can serve as a supplemental tool in geometric design to minimize lateral deviations and trajectory transitions across horizontal curves on four-lane divided highways. Passing maneuvers are riskier than through maneuvers, often involving lane changes and unpredictable paths. This highlights the need for roadway departure safety measures such as raised pavement markings, centerline rumble strips, and passing restrictions at specific curves.