A Performance-Based Highway Geometric Design Process (2016) / Chapter Skim
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C-1 Demonstration of Cost-effectiveness Approach to Horizontal Curve Design Policy Horizontal curvature has a proven effect on substantive safety performance and operational performance. This Appendix demonstrates how the knowledge base can be applied to develop a more performance-based approach to geometric design processes and criteria for horizontal curvature.
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C-2 A performance-Based Highway Geometric design process Table C-1 shows the alignment design values for an array of central angles from 15 degrees to 90 degrees. As the curve radius changes, the amount of alignment that is tangent versus curved changes.
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Horizontal Curve Analysis C-3 • 1,500 foot radius 0.2231 miles length of curve (PC' to PT') ; 0.901 miles total tangent length (PC to PC' + PT' to PT)
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0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Pr ed ic te d Cr as he s ( to ta l c ra sh es p er y ea r) AADT (vehicles per day)
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Horizontal Curve Analysis C-5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Pr ed ic te d Cr as he s ( to ta l c ra sh es p er y ea r) AADT (vehicles per day)
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C-6 A performance-Based Highway Geometric design process 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Pr ed ic te d Cr as he s ( to ta l c ra sh es p er y ea r) AADT (vehicles per day)
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Horizontal Curve Analysis C-7 4,000 vpd 7,000 vpd 10,000 vpd 500 to 1,000 0.06 0.104 0.149 500 to 1,500 0.083 0.144 0.206 500 to 2,000 0.096 0.168 0.24 1,000 to 2,000 0.036 0.064 0.091 1,000 to 3,000 0.054 0.095 0.136 Change in Radius of Curve Predicted Reduction in Crashes for Central Angle of 45 degrees Table C-3. Predicted changes in annual crashes for changes in radius (from Table C-2)
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C-8 A performance-Based Highway Geometric design process benefits over a 50 year life would range from $200,000 for lower-volume, moderate curvature to $1,200,000 for higher-volume, sharper curvature (per values in Table C-4)
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Horizontal Curve Analysis C-9 $0.61 per mile operating cost cited in the Interim Report (from AASHTO) and computed over a 50 year service life.
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