2.0 Overview of the Transportation Analysis Process

The Intermodal Surface Transportation Efficiency Act (ISTEA), the Transportation Equity Act for the 21st Century (TEA-21), and the Federal/State Clean Air legislation have reinforced the importance of traffic management and control of existing highway capacity. As transportation agencies deploy more sophisticated hardware and software system management technologies, there is an increased need to respond to recurring and nonrecurring congestion in a proactive fashion, and to predict and evaluate the outcome of various improvement plans without the inconvenience of a field experiment.

Out of these needs, traffic analysis tools emerge as one of the most efficient methods to evaluate transportation improvement projects. This document addresses quantifiable traffic operations analysis tools categories, but does not include real-time or predictive models. Traffic analysis tools may include software packages, methodologies, and procedures, and are defined as those typically used for the following tasks:

• Evaluating, simulating, or optimizing the operations of transportation facilities and systems.
• Modeling existing operations and predicting probable outcomes for proposed design alternatives.
• Evaluating various analytical contexts, including planning, design, and operations/construction projects.

Figure 1 presents an overview of the transportation analysis process, along with its various evaluation contexts and the types of traffic analysis tools that are typically used in each context. Typically, transportation analysis needs result from the policies and objectives of State/regional/local transportation plans and programs. A transportation improvement (project) goes through several phases, including planning, project development, design, implementation, and post-implementation operational assessment and modification. As shown in figure 1, each of these phases requires different analytical methodologies and tools. A project’s early planning stage usually involves the application of sketch planning or travel demand modeling techniques. These methodologies help agencies screen the different transportation improvements, resulting in the selection of a few candidate transportation improvements. Later stages (such as project development or post-implementation modifications) usually involve the application of more rigorous and detailed techniques, such as traffic simulation and/or optimization. The role of traffic analysis tools is further explained in the following chapter.

Figure 1. Overview of the transportation analysis process.

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