4.2 Project Development Stage (PDS)

Traffic and safety analysis procedures are applied to a wide range of projects. The PDS refers to a project’s position on the project timeline (i.e., is the project in the beginning, middle, or end stage?). The PDS defines the level of effort necessary to complete an analysis and could also influence the analysis tools used, depending on project complexity, scope, schedule, and cost. A project’s PDS can be classified as either the Planning stage, Preliminary Schematics stage, or Final/Approved Schematics and Design stage. General characteristics of each PDS are provided later in this chapter. The general impact of PDS on tool selection is shown in . This figure generally describes the impact that the PDS has on tool selection but may not be applicable to every project.
Analysis with a low amount of detail calls for accurate input data but is not as finely detailed or coded as that necessary for highly detailed analysis. In terms of network, a low-detail analysis typically involves general link-node representation and longer segments with lane and posted speed information. Highly detailed analysis calls for accurate input data that is finely detailed or coded. It involves longer segments broken up into multiple segments. It depicts lane variations, geometric configuration, curvature, turning movement, and additional details.
Figure 4-1: Tool Selection by Project Development Stage
Figure 4-1: Tool Selection by Project Development Stage

4.2.1 Planning-Stage

A Planning-stage analysis is typically a lowdetail analysis applied to projects at an early development stage. While a Planning-stage analysis is low-detail, it uses accurate data and as much data as available for the study. Per the HCM, Planning-stage analyses are “directed toward broad issues such as initial complication identification, long-range analyses, and regional and statewide performance monitoring.” While Planning-stage analysis is often applied to high-level projects and large areas, it could also be applied to specific locations and projects that use many data inputs.
Planning-stage analyses:
  • Are conducted for projects such as short- or long-range studies, master plans, strategic plans, and alternatives analyses;
  • Help estimate high-level project cost;
  • Identify questions to be answered in later stages of analysis;
  • Rely on available data sources and supplement unknown inputs with default values; and
  • Use screening tools, TDM outputs, or other planning stage tools to select viable alternative for further analysis
    • Screening tools that can be implemented include general service volumes, CAP-X, and other spreadsheet-based tools
  • May use tools that are deterministic (report same results, given same inputs) and macroscopic (evaluate traffic stream as compared to individual vehicles); and
  • May use tools that are stochastic (account for randomness) and mesoscopic (evaluates both traffic flows/streams and individual vehicles)

4.2.2 Preliminary Schematics-Stage

Preliminary Schematics-stage analysis is a medium-detail analysis applied to projects at a middle development stage. Per the HCM, Preliminary Schematics-stage analyses are “conducted to support planning decisions related to roadway design concept and scope and when alternatives analyses are performed.” Compared to a planning-stage analysis, the preliminary schematics-stage may have the project broken down into smaller components for individual analysis. Projects in the preliminary schematics-stage may also include more data that was not included in the planning-stage analysis.
Preliminary Schematics-stage analyses:
  • Are conducted for projects such as alternatives analyses, preliminary design, and existing intersection/corridor evaluation;
  • Answer key questions to determine scope and benefits of further study, if needed;
  • Use tools that may need more detail input;
  • May use tools that are deterministic (report same results, given same inputs) and macroscopic (evaluate traffic stream as compared to individual vehicles); and
  • May use tools that are stochastic (account for randomness) and mesoscopic (evaluates both traffic flows/streams and individual vehicles)

4.2.3 Final/Approved Schematics and Design Stage

Final/Approved Schematics and Design-stage analysis is a high-detail analysis that is often performed with more data than projects in other stages of development. While study limits for projects in this stage could be broad or narrow, they are well defined.
Final/Approved Schematics and Design-stage analyses:
  • Are conducted for projects beyond the preliminary design stage;
  • Answer questions generated by previous stages of analysis;
  • Often necessitate substantial amounts of data to be collected; and
  • May use tools that are stochastic (account for randomness) and microscopic (evaluate individual vehicles). The use of microsimulation (microscopic) tools depends on the scope, complexity, traffic operational conditions, and MOEs of the project

4.2.4 Multi-Stage Analysis

Multi-stage analysis is a combination of analysis stages, often applied in sequence. As with alternatives analysis, study limits are well-defined and narrowed to permit increased detail. For example, if a project used CAP-X (a Planning-stage analysis tool) to determine intersection configurations and then modeled in Vissim (a design stage analysis tool) to determine the preferred intersection configuration, that would be considered a multi-stage analysis.
Multi-Resolution Modeling (MRM) involves tools with different traffic analysis resolutions (Sketch-level or macroscopic, HCM-based (mesoscopic), and microsimulation (microscopic)). It could include assessing a sketch-level or macroscopic trip table to determine overall trip patterns. It could also include using HCM-based (mesoscopic) analysis to understand impact of mitigation strategies on groups of vehicles at a lane-by-lane level or packets of vehicles in large networks. Lastly, a multi-stage analysis could potentially include microsimulation (microscopic) analysis of individual driver behavior and the impacts of traffic control strategies. shows the MRM framework.
Partial multi-resolution models, involving macroscopic and microscopic models for networks experiencing medium to low levels of congestion, may not be able to model largescale traffic demand reroutes. This could result in macroscopic/TDM output results that may not properly represent the congestion for the various alternatives and could require further analysis using engineering judgement or different analysis techniques.
Multi-Resolution Modeling Frameworks
Figure 4-2: Multi-Resolution Modeling Frameworks