Evaluation of the sight distance adequacy on highway horizontal curves with single or multiple obstacles requires determination of the minimum sight distance on the curve. The current method of establishing such a minimum is to plot the sight distance profile for the given curve and obstacle. Approximate relationships have been developed for establishing the sight distance profile. However, there is no explicit, exact solution available for determining the minimum sight distance on the curve. Exact formulas have been derived to relate the available sight distance to the circular curve parameters, lateral clearance of the obstacle, its location along the curve, and the locations of observer and object. These relationships are then used to derive closed-form solutions of the minimum sight distance. To facilitate practical use, values of the minimum sight distance are established for typical ranges of the curve parameters, lateral clearance, and obstacle location. Values of the maximum lateral clearance, which is required in design, are also provided. The methodology and results should be valuable in the operational and cost-effectiveness analysis of highway locations with restricted sight distances.
Abstract