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FHWA Home / Safety / Geometric Design / Publications / Mitigation Strategies For Design Exceptions

The Design Exceptions

 

The design speed selected for the highway was 65 mi/hr (100 km/h).

Grade

For the selected design speed and mountainous terrain, the design criteria specified 5 percent maximum grades. Grades exceeded 5 percent for approximately 4.5 miles (7.3 km), or about 52 percent of the project length, with significant lengths exceeding 7 percent. The steepest grade reached 7.9 percent.

Horizontal Alignment

For the selected design speed, the minimum radius was 1,434 feet (437 m) with maximum superelevation of 6 percent. There were 11 horizontal curves that could not be flattened to this extent. The sharpest of these had a radius of 590 feet (180 m) and a corresponding design speed of 40 mi/hr (60 km/h). Five of the curves had radii with corresponding design speeds of 45 mi/hr (70 km/h).

Shoulder Width

Design criteria specified shoulder widths of 8 feet (2.4 m) for rural arterials with traffic volumes of more than 2000 vehicles per day. Six-foot (1.8-m) shoulders were used.

 

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Page last modified on April 1, 2019
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