  Finding an optimal alignment connecting two end-points in a specified
corridor is a complex problem that requires solving three interrelated
sub-problems, namely the horizontal alignment, vertical alignment and earthwork
optimization problems. In this research, we developed a novel bi-level
optimization model combining those three problems. In the outer level of the
model, we optimize the horizontal alignment and in the inner level of the model
a vertical alignment optimization problem considering earthwork allocation is
solved for a fixed horizontal alignment. Derivative-free optimization
algorithms are used to solve the outer problem. The result of our model gives
an optimal horizontal alignment in the form of a linear-circular curve and an
optimal vertical alignment in the form of a quadratic spline. Our model is
tested on real-life data. The numerical results show that our approach improves
the road alignment designed by civil engineers by 27\% on average, resulting in
potentially millions of dollars of savings.
