Highway Spiral Curve Length Function Based on the Discrepancy between Drivers’ Natural Steering Length and Spiral Curve Length

If the length of the spiral curve on a highway is too short or too long relative to the drivers’ natural steering length, it increases the drivers’ operational burden, affecting the smoothness and safety of vehicle steering. Ideally, the two should be properly matched. However, existing highway design standards lack a systematic method for calculating this desirable length. Driving simulation experiments conducted under various curve geometries revealed a roughly linear positive correlation between drivers’ natural steering length and the spiral curve length. However, adjusting the spiral curve length according to the difference between the two also changes the drivers’ natural steering length. Multiple adjustments can only gradually reduce the gap, making it difficult to precisely align them or maintain a consistent difference. Therefore, a method for construction the highway spiral curve length function based on the degree of discrepancy between the two is proposed. By controlling this discrepancy, the expected spiral curve length can be directly calculated, ensuring that drivers maintain a positive driving experience throughout the driving process. The study also aims to reduce construction costs associated with overly long spiral curves and contribute to the automation of highway alignment design.