Sequential Monte Carlo (SMC) is a set of methods allowing us to approximate virtually any sequence of probability distributions. SMC are very popular in physics where they are used to compute eigenvalues of positive operators, the solution of PDEs/integral equations or simulate polymers. SMC is also applied vastly in construction management to provide stochastic solutions in scheduling and planning.
It is a computerized tool for modeling a stochastic process where the input data are randomly determined by certain statistical distributions. In such a simulation, the computer generates large sets of outputs after running a large number of iterations with random inputs. These outputs are then statistically analyzed to measure their uncertainties and risks. The major parts of a Monte Carlo simulation method involve a probability distribution function, a random number generator, and a sampling rule (Bayraktar and Hastak 2009).
Monte Carlo simulation was developed in the 1940s and became available under the help of personal computers and associated software, e.g. Primavera Risk, Primavera
Crystal Ball, @RISK for Projects and so on. Monte Carlo has been involving in many industrial, scientific, logistical and social fields in many years. Recently project managers have used Monte Carlo to simulate the project completion date and the project cost estimate. Through computing the Critical Path Method schedule many times, Monte Carlo simulation can determine the project completion date on the basis all possible combinations of the uncertain activity durations. In Monte Carlo simulation, the project model is computed many times (iterated) with the input values (e.g., activity durations) chosen at random for each iteration from the probability distributions of these variables. Monte Carlo simulation follows certain steps:
1. Creation of the quantitative model of the form of y=ƒ(x1, x2, ... ,xn), 2. Selection of the random variables xi1, xi2, …, xin,
3. Evaluation of the model and output storage in yi,
4. Repeat steps (b) and (c) as many times needed (for i=1 to k), 5. Analysis of results.
Su et al. (2006) suggested Monte Carlo simulation to use in decision-making models to overcome the inherent deterministic aspect of benefit- cost analysis method. As explained in the previous sections, they combined BCA with Monte Carlo simulation to get more reliable alternative assessment tool (Su et al. 2006).
2.10 Chapter Summary
This chapter provided an extensive literature review of the decision making process in the front-end phase of major transportation projects, as well as existing decision support systems and gap analysis in the existing approaches. It also overviewed the basic concepts of Bayesian belief network and multi-criteria decision making
methods and theories that will be utilized for developing the created framework in the course of this research. The following chapter will describe in detail the current state-of- the-practice of the decision-making procedure in the U.S. based on the findings and analysis of a questionnaire survey conducted at DOT’s and also reviewing the current regulations and published guidelines.
STATE-OF-THE PRACTICE 3.1 Introduction
The objective of this chapter is to provide an overview of the process of decision- making in major transportation projects in the relevant agencies of the U.S. and present methods and frameworks through which planning experts achieve the prioritized alternative as well as the assessing indicators and factors. Transportation decision-making performs at several levels of government in the U.S. Transportation planners work across all modes of transportation, and with environmental resource agencies, tribes, and interested parties as defined by law.
State Departments of Transportation (State DOTs), Metropolitan Planning Organizations (MPOs), and transit agencies develop the transportation planning in different levels and then, USDOT surface transportation agencies reviews these plans MPOs are organizations that carry out transportation planning at the regional level. Any urbanized area with a population of more than 50,000 has an MPO (USDOT 2015). The policy at MPO is set by a board of local elected officials and includes long-range plans and short-range programs of future transportation improvements. Several stakeholder groups, such as nonprofit, community-based, and environmental organizations as well as general public, provide input for MPO’s policies, plans, and overall program direction. There are other agencies such as tribal governments, local governments, transit agencies and Regional Transportation Planning Organizations (consist of local governments outside of metropolitan areas) that come together and coordinate with State DOTs in planning process (USDOT 2015).
Highlighted points of transportation planning process through DOTs extracted from USDOT website are summarized as follows:
One of the major metrics in project prioritization process in DOTs and MPOs is
commonly an effective project performance with meaningful, measurable and monitorable performance measures.
“There is no one size fits all approach to project prioritization. Each MPO must
work with regional stakeholders to develop a prioritization process that addresses the region’s specific goals, resources, and needs. Participating MPOs use different approaches and criteria to evaluate, prioritize and select projects for long-range plan. Some prioritization processes are more detailed and technical, while others reflect broader policy priorities.”
Most of the transportation agencies conduct some type of benefit-cost analysis in
order to prioritize projects. To develop a meaningful prioritization process it is better to use a mix of quantitative and qualitative tools and analysis. In some types of projects, it can be difficult to accurately measure their costs and benefits, therefore quantitative analysis may not score them well. It is important to build qualitative factors into the prioritization process by providing supplementary information for projects whose benefits and costs may be difficult to quantify.
“Weighting of project prioritization criteria should be left to the discretion of each
agency’s decision-making boards”.
Transportation agencies often tend to focus their prioritization efforts on projects
that add new capacity and on funding sources that they have direct decision- making authority over, especially on regionally significant projects that add new
highway or transit capacity in the region. There is also tendency in prioritization analysis for funding sources that these agencies have discretion over, such as Federal Congestion Mitigation and Air Quality funds and Surface Transportation Program.
Preservation and maintenance of the existing system is a focus for all
transportation agencies, but these areas are typically funded on a programmatic basis, rather than as individual projects.
“Transportation modeling is extremely important for providing guidance on the
anticipated outcomes of investments.” (USDOT 2015).
3.2 Legislations and procedures for decision making in major transportation