This paper investigates potential Stopping Sight Distance (SSD) violation on divided highways at left horizontal curves overlapped with crest vertical curves. The authors previously developed a SSD control methodology that relates the 3D configuration to the dynamics of a vehicle moving along the roadway. This methodology is applied for the assessment of critical design parameters related to both demanded and available SSD values. Initially, utilizing control geometric and driver – obstacle values adopted by AASHTO 2011 design policy, SSD inadequacy areas were revealed. Subsequently, on the basis of an explanatory modeling approach for a number of geometry parameters, evaluation of SSD sufficiency was carried out in terms of the probability of SSD inadequacy and the prediction of the object height in order to grant SSD adequacy (amended object height). These models may be useful to researchers and practitioners aiming to evaluate the interaction of the utilized design parameters in terms of SSD inadequacy.@en

This paper presents a novel definition of drivers’ safety margins reflected in speed profiles on a tangent to curved road design. These safety margins are based on a vehicle dynamics model, which is implemented to assess the speed variation at impending skid conditions from tangent to curve on the basis of several parameters. This model returns the theoretical speed-distance curve corresponding to the driver’s maximum safe speed and acceleration when utilizing the outmost of the available vehicle horse power. On the basis of actual vehicle speed profiles, the model also returns the respective curve for the actual speed-distance i.e. the utilized share of vehicle horse power, which reflects the driver’s safety margin. Data from a driving simulator experiment are used to test the proposed methodology, explore driver’s speed profiles and the parameters affecting drivers’ safety margins. The results suggest that drivers’ safety margins towards the examined curve are considerable, with the majority of the drivers using less than 55% of the available vehicle horse power. Drivers can be grouped into “aggressive”, “moderate” and “conservative” speeding behaviour, each group exhibiting distinct initial speed, “breakpoint” distance and acceleration / deceleration patterns. Higher initial speed is positively correlated with more aggressive driving i.e. lower safety margins. On the contrary, a higher safety margin was associated with earlier deceleration before the curve. The proposed approach yields a continuous and objective assessment of driver speeding behaviour from tangent to curve and the related safety margins, both for individual drivers, as well as for groups of drivers with similar speeding patterns.@en

This paper investigates the safety margins of drivers along tangent to curved road sections. A vehicle dynamics model is presented, allowing to assess the vehicle speed variation at impending skid conditions from tangent to curve on the basis of several parameters. This model returns the theoretical curve corresponding to the driver’s maximum efficiency, i.e. the maximum safe speed and acceleration along the tangent to curve section when utilizing the outmost of the available vehicle horse power. On the basis of actual vehicle speed profiles, the model also returns the respective curve for the actual efficiency i.e. the utilized share of vehicle horse power, which reflects the driver’s safety margin. Data from a driving simulator experiment are used to test the proposed methodology and identify the parameters affecting drivers’ efficiency / safety margins. The results suggest that drivers’ safety margins towards the examined curve are considerable, with the majority of the drivers using less than 55% of the available vehicle horse power. Higher initial speed was positively correlated with driving efficiency i.e. lower safety margins. On the contrary, a higher safety margin was associated with earlier deceleration before the curve. Driver characteristics were not found to significantly affect the safety margins, except from age <35 years old who were associated with higher share of vehicle motion used. The proposed method has advantages over existing methods; it allows for a better understanding of driver speeding behaviour and a more objective and insightful calculation of the safety margin through the vehicle dynamics, along the entire road section from tangent to curve, which may assist in improving design and interventions at curves. Keywords: speed variation; safety margin; horizontal curve; driving simulator @en

An existing vehicle dynamics model was used to define design parameters up to which steady-state cornering conditions apply and consequently lift the restrictions of the point mass model. Besides a passenger car, the motion of a two-axle truck was examined as well for both loaded and unloaded conditions. In order to assess critical safety concerns in terms of vehicle skidding, a range of design speed values paired with control design elements from standard design guidelines as well as certain values of peak friction coefficients were used. The unloaded truck was found to be the most critical vehicle in terms of reaching a maximum constant speed, termed as safe speed. Furthermore, the authors provide modeling examples toward the development of a tool for practitioners to concurrently assess the impact of road geometry and friction in terms of defining the vehicle’s safe speed and, consequently, take certain actions. These actions include the adoption of acceptable arrangements for the above values, as well as scheduling accurate friction improvement programs.@en