# Treating Uncertainty in the Design of Horizontal Curves

*by*Prianka N. Seneviratne, Utah State Univ, Logan, United States,

M. Nazrul Islam, Utah State Univ, Logan, United States,

**Document Type:**Proceeding Paper

**Part of:**Infrastructure: Planning and Management

**Abstract:**A model based on expected total cost minimization approach is developed for determining optimal horizontal curvature for highway sections. Expected total cost is defined as the sum of the construction costs and the expected cost of accidents. Construction cost is treated as a deterministic function of curvature while the expected cost of accidents is determined in relation to the amount by which required (demand) curvature differs from design (supply curvature. It is shown that the optimal degree of curvature is highly sensitive to the skewness of the probability distribution of the required curvature. This distribution is derived from the fundamental relationship between speed and degree of curvature while treating speed to be a random variable. The optimal value is shown to change in direct proportion to skewness of the speed distribution.

**Subject Headings:**Curvature | Construction costs | Skewness | Probability distribution | Highway and road design | Traffic accidents | Occupational safety

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