Design of Horizontal Curves for Roadways
The geometric design of roadways is the part of highway engineering that is concerned with how the physical elements are positioned, dependent on standards and constraints. The main objectives are to optimize safety and efficiency while also minimizing environmental damage and costs. Engineers aim to design roadways to provide access to business, schools, residences, accommodate travel, and serve broader community goals. There are three types of geometric roadway design elements which include alignment, profile, and cross-section.
Alignment is defined as a series of horizontal curves and tangents. The horizontal alignment of the road consists of straight sections called tangents which are connected by horizontal curves. The radius or tightness and deflection angle define circular curves. The horizontal curve is designed by determining the minimum radius based on the speed limit, objects that may obstruct the view of drivers, and the curve length.
Engineers use AASHTO (American Association of State Highway and Transportation Officials) standards to ensure the design of a roadway is comfortable and safe. If there are objects that obstruct the view of a horizontal curve or corner, engineers need to make sure there the driver can see far enough to stop or accelerate if needed. To ensure safety around horizontal curves that have a small radius with high speed, the elevation of a bank is increased.
When there are sudden changes in road conditions, accidents become more frequent. Design consistency in roadways helps to reduce the areas where a driver might find certain road segments to change unexpectedly such as a sharp curve at the end of a long section. Other efforts are created for design consistency in areas where there are significant changes in a predicted area. Enhancing road signs for curves that have a smaller radius than the previous curves help to catch the attention of drivers and improve the concept of design speed.
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