3D Modeling of Highway Guardrails for Sight Distance Assessment

Safety barriers limit the severe consequences to occupants of vehicles leaving the roadway from colliding with obstacles, yet they may significantly reduce the available sight distance (ASD). A procedure was devised to accurately recreate highway guardrails in three dimensions (3D), fitting the barriers onto the curve roadsides. The effect of these devices on the reduction of the ASD was thus evaluated in a set of case studies comprising different curve radii overlapped with different vertical alignments and combined each with two safety barriers in two-lane rural roads. The 3D models of highway curves with the selected guardrails were created in a geographic information system. Then, a geoprocessing model was used to compute the ASD. The results made it possible to quantify the ASD reduction produced by the barrier with a higher containment level in relation to the highway design parameters, which can assist authorities in developing more comprehensive safety device standards

Risk-Based Calibration of Road Sag Vertical Curve Design Guidelines on Undivided Highways

Safety in highway geometric design is one of the main goals to be achieved. However, deterministic design criteria do not provide information concerning the risk associated with the design outputs proposed. To yield consistent safety levels, the sag vertical curve design model on undivided highways was calibrated using a reliability-based framework, which allows one to incorporate the uncertainty associated with the model variables. The sag curve design model contemplates the features of vehicle front lighting systems to compute the headlight sight distance (HSD), which must be equal to or greater than the stopping sight distance (SSD). A dataset of 34,238 case studies was generated. Each case study was associated with two values of the risk level, designated as the probability of noncompliance (Pnc), one per driving direction. A Monte Carlo simulation was selected to calculate the values of Pnc. Through a series of interpolating surfaces of the cloud of points, contour graphs and calibrated charts were depicted. The paper provides a new methodology to verify, design, and compare sag vertical curves, evaluating the risk level with the Pnc