Obstructions on horizontal curves: Analysis of exact equation to render the radius explicit

A major shortcoming of the exact equation for calculating the clearance distance to obstructions on horizontal highway curves is that, if the radius is required for a specified sight and clearance distance, the designer must resort to trial and error methods. This article analyses the degree of error incurred by applying the Taylor theorem to the exact equation. By expanding the cosine term in the latter to only three terms an extremely accurate equatin is obtained, rendering the radius explicit.