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Vertical alignment design is an important phase in the highway
geometric design process. Even with today''s array of
sophisticated computer software, determining the vertical
alignment of a highway remains an art and relies mostly on the
judgement of experienced engineers. The work becomes even more
complicated when climbing lanes come into play. Speed of heavy
vehicles is a major consideration in highway vertical alignment.
Long and/or steep slopes are usually carefully avoided to
maintain the speeds of heavy vehicles at a minimum allowed
level. At locations where this is hard or costly, lower speeds
can be accepted with the deployment of a climbing lane. While
climbing lanes relax the limits on steep slopes, and thus
potentially reduce earth and construction costs, the additional
lane itself consumes land and cost as well. In practice, it is
up to the design engineer to evaluate between the choices, and
determine how the climbing lane should be deployed. Typically
no systematic effort is employed to optimize the design. In
this research, we develop a mixed integer programming model that
determines optimal highway vertical alignment and climbing lane
allocation simultaneously. Application of the model is
demonstrated by several numerical examples. The results are
promising and appear to be on the right track.
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