Compatibility Between the Takeover of a Conditional Automated Vehicle and the Horizontal Alignment of a Small-radius Off-ramp from a Highway
This study aims to examine the compatibility between the driver's behavior after a takeover in automated driving and the horizontal geometric design of a small-radius off-ramp from a highway.The takeover scenarios at the highway exit were constructed based on a driving-simulation platform,and a driving-simulation experiment was conducted.The independent variables of the experiment were the driving mode(manual driving,takeover),the horizontal-curve radius of the ramp(50 m,70 m,90 m),and the traffic density(5 pcu·km-1 per lane,45 pcu·km-1 per lane).Twelve scenarios were constructed.Thirty people participated in the test,and their gaze behavior and the vehicle's motion state during the test were recorded.The pupil diameter,speed,standard deviations of the gaze yaw,gaze pitch,and lane position,and minimum time to collision(TTC)were selected,and the effects of various factors on each indicator were examined.Finally,based on the test results,the corresponding indicators were selected to build a comprehensive fuzzy compatibility model.The takeover compatibility was estimated under a combination of different ramp horizontal-curve radii and traffic densities.The results show that,compared with manual driving,the pupil diameter and gaze-yaw deviation of drivers increase,and the longitudinal and lateral stabilities of the vehicle are impaired in takeover scenarios.As the curve radius increases or the traffic density decreases,the pupil diameter of the driver decreases,and the longitudinal stability of the vehicle is enhanced.The change in the horizontal-curve radius has a greater impact on the vehicle's motion state than the driver's gaze behavior.In scenarios with a traffic density of 45 pcu·km-1 per lane,the ramp horizontal-curve radius has a marginally diminishing effect on the takeover compatibility.The combination of a low ramp radius and high traffic density amplifies the adverse effects on the takeover compatibility.With a low traffic density(5 pcu·km-1 per lane),the compatibility can reach"high",even if the ramp radius takes the limit value.With high traffic density(45 pcu·km-1 per lane),the compatibility can reach"high"only when the ramp radius approximates the highest standard in current practical-engineering applications.Based on the takeover-compatibility levels,various approaches from the perspectives of humans,vehicles,and infrastructure can be adopted to improve drivers'takeover performance.The results of this study provide guidance for enhancing the safety of takeovers at highway exits.
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