Efficient freight transportation is an essential for a strong economic
system. A rapid growth of freight demand, however, lessens the
efficiency of provided infrastructure. In order to alleviate this
problem effectively, evaluation studies have to be performed in order to
invest the limited budget for the best of social benefits. In addition
to many difficulties on making a decision for each project investment,
it is made harder by the complimentary and substitution effects that
happen when considering transportation project together. Current
practices, however, limit number of project combinations in order to
avoid numerous tests. The best project combination may have never been
realized.
This dissertation proposes network design models which can automatically
create project combinations and searching for the best. The network
design models have been studied for the passenger movements and focus on
highway expansions. In this dissertation, the focus is shifted to the
freight movements which involve multimodal transportation improvements.
Our freight network design model is developed based on the bi-level
optimization model. The development then involves two components. The
first task is to set the freight investment problems within the bi-level
format. This includes finding a suitable freight flow prediction model
which can work well with the bi-level model. The second task is to
provide a solution algorithm to solve the problem.
The dissertation sets the framework of the freight flow network design
model, identifies expecting model issues, and provides alternatives that
alleviate them. Through a series of developments, the final model uses
the shipper-carrier freight equilibrium model to represent freight
behaviors. Capacity constraints are used as a mean to emphasize limited
services since the reliability issues, an important factor for freight
movements, cannot be captured by steady state traffic assignment. A case
study is implemented to allocate a budget for improvements on the
California highway network. The transportation modes are selected by the
shipper model which can be trucks, rails, or the multimodal
transportation. The results shown that the proposed network design model
provided better solutions compared with traditional ranking methods. The
solution algorithm can manage the problem with reasonable project
alternatives. However, the computation expense increases rapidly with
increasing number of project alternatives.
