Traffic Analysis Tools Volume IX: Work Zone Modeling and Simulation
A Guide for Analysts
This document is the second volume in the FHWA Traffic Analysis Toolbox: Work Zone Modeling and Simulation series. The intent of this volume (TAT Volume IX) is to provide guidance to the analyst, researcher, or manager in charge of conducting a specific work zone analysis project or who has been charged with developing an overall work zone modeling program or approach. This volume is not intended to be a specific how-to guide on using transportation analysis tools. This volume complements Traffic Analysis Tools Volume VIII: Work Zone Modeling and Simulations - A Guide for Decision-Makers, which was published with the intent to provide local decision-makers with a broad, fundamental understanding of how transportation analysis tools can be used to support work zone decision making throughout the complete project life cycle. These documents are rooted in an overall philosophy that "one size does NOT fit all" with respect to the best transportation modeling approach, that is, no single transportation analysis tool or strategic methodology is the right answer for all work zone analyses.
Similarly, it is important to recognize that using modeling and simulation tools for work zone impacts analysis may not be necessary for every project. The sophistication of the impacts analysis needs to be matched to the complexity and expected degree of impacts of the project. Work zone impacts analysis may involve a high-level, qualitative review for some projects, and a detailed, quantitative analysis using modeling and/or simulation tools for other projects. An agency should use modeling and simulation tools as helpful and appropriate for supporting its overall efforts to conduct work zone impacts analysis and making decisions to manage the impacts of projects
The results from analyzing work zone impacts can serve to improve decision making as well as improve overall understanding of the relationships between the many forces affecting work zone decision making: mobility, financial, environmental, safety, and user costs. Critical to the work zone decision-making process is that a work zone analysis should never be used to make key decisions but instead developed as a trusted resource for understanding the potential mobility impacts and using this information to inform key decisions. The informative value of analysis is directly related to how well the analyst has considered both the context for analysis (decisions to be supported and relevant performance measures) and the context for validation (data and staff resources). The job of the work zone analyst extends beyond merely conducting an analysis and reporting results; instead the work zone analyst provides decision-makers with a broader understanding that connects the findings of the analysis within the decision-making context.
TAT Volume IX includes numerous case study examples, discussion and analysis designed to provide the prospective work zone analyst with information pertaining to:
- Developing An Appropriate Analytical Approach
- Identifying opportunities for analysis throughout the project life-cycle
- Managing technical risk
- Incorporating lessons learned from case studies analyzing both simple and complex projects
- Specific Project Applications
- Constructability—Constructability is defined as the optimum use of construction resources throughout the project life-cycle to achieve project objectives in a cost-effective manner. Opportunities to integrate mobility impacts assessment into constructability analyses, when identified and considered jointly, can often lead to innovative and high-payoff approaches minimizing mobility impacts and maximizing return on project investment.
- Scheduling—Transportation modeling approaches have the potential to provide analysts and decision makers with better information on how to time lane closures and other construction-related roadway capacity reducing measures to best reduce work zone mobility impacts. Scheduling activity can occur on a broad time scale, from assessing various alternative multi-year, multi-season approaches to scheduling hourly lane closures.
- Transportation Management Plan Design and Evaluation—Developing a Transportation Management Plan (TMP) is a critical component of many work zone projects. The use of transportation analysis tools can better evaluate the array of TMP options available to a transportation agency in order to identify the most effective options (or combination of options) with best potential to mitigate disruptions caused by roadway construction.
The use of transportation analysis tools enables a decision-maker to better understand the impact a proposed alternative will have on the transportation network. The categorization of transportation modeling approaches found in TAT Volume VIII and Volume IX is based upon the FHWA Traffic Analysis Toolbox (2). The FHWA TAT organizes the available tools into six categories: Sketch-Planning and Analytical/Deterministic Tools (HCM-Based), Travel Demand Models, Traffic Signal Optimization, Macroscopic Simulation, Mesoscopic Simulation, and Microscopic Simulation. A brief description of each category is provided here:
- Sketch-Planning/HCM — Specialized tools utilizing traffic count data and capacity analyses to predict transportation systems impact.
- Travel Demand Models — Mathematical models that forecast future regional travel demand based on current conditions, and future projections of household and employment centers.
- Traffic Signal Optimization — Optimization tools used to develop signal timing plans for isolated signal intersections, signalized arterial corridors, and signal networks.
- Macroscopic Simulation — Models based on deterministic relationships of the flow, speed, and density of the traffic stream. Macroscopic model simulations assess traffic conditions on a section-by-section basis rather than by tracking individual vehicles and treat traffic flows as an aggregated quantity; they do not model the movement of individual vehicles on a network.
- Mesoscopic Simulation — Intermediate approaches tailored for larger networks associated with Macroscopic and Travel Demand Models but preserving some aspects of the detail of Microscopic Simulation. Mesoscopic models estimate congestion effects based on the flow of vehicles across a link over time, but typically do not represent individual lanes on the link.
- Microscopic Simulation —These tools simulate the movement of individual vehicles based on car-following and lane-changing algorithms and other parameters associated with individual driver behavior. Microscopic Simulation models update the position of individual vehicles every second (or fraction of a second) as they move through a network by lane for every link the vehicle traverses.
TAT Volume VIII includes a detailed discussion of the various transportation modeling approaches available to analysts in order to analyze work zone impacts (1). In Figure 1, these transportation modeling approaches are placed on a continuum from simple to complex. Above the continuum are specific examples of transportation analysis tools that have been used to conduct a work zone analysis (these examples do not represent all of the product choices). Simpler tools include the categories of HCM and sketch-planning while the more complex tools include macro, meso, and microscopic simulation software. The spectrum includes seven examples of commonly-used transportation analysis tools used to assess the impacts of roadway construction projects. A wider range of transportation analysis tools across the spectrum are described in more detail on the TAT website (2).
Figure 1 Work Zone Modeling Spectrum
It is important to clarify some terminology used throughout the document. First, a transportation modeling approach is defined as one of the six model classifications identified in the work zone modeling spectrum (sketch planning/HCM through microscopic). Second, a transportation analysis tool is a specific computer program that is classified as one of the transportation modeling approaches. These tools are either freely available for download and use or through a commercial vendor. Finally, a work zone analysis is the process of an analyst using a transportation analysis tool to generate results for use by decision makers.
Which transportation modeling approach is best suited to a particular work zone analysis? This document is intended to be a guide to assist analysts with answering this question, carefully considering the many factors associated with a specific transportation modeling approach or analysis tool. These factors include work zone characteristics, transportation management plan strategies, available data archives, agency resources and modeling capabilities, and work zone performance measures. Choosing a transportation modeling approach is generally a tradeoff among these five categories of factors. However, the key to successful work zone analysis does not begin or end with just transportation modeling approach selection, but rather in the successful integration of data and tools to provide a meaningful assessment of work zone impacts relevant to one or more key project decisions.
In essence, the sophistication of the analysis needs to be matched to the complexity of the project. For example, developing a microscopic simulation model would probably be "overkill" for a simple bridge replacement project on a minor rural highway. Similarly, a sketch planning tool alone would probably be insufficient for a comprehensive analysis of the impacts of a high-volume urban freeway-to-freeway interchange replacement project.
Figure 2 shows how the work zone decision making process, which consists of Planning, PE/Design and Construction, was developed based upon the FHWA publication Work Zone Impacts Assessment: An Approach to Assess and Manage Work Zone Safety and Mobility Impacts of Road Projects.
Figure 2 Work Zone Decision-Making Process
While the decision-making process is important and transportation analysis tools have a potential role in all three stages of the project life-cycle, more important to the discussion at hand are the types of decisions that need to be made. These decisions are represented by three inter-related decision types that drive the overall work zone decision-making process as a three-part work zone decision-making engine (Figure 3). The decision-making engine concept is represented by three decision areas including Scheduling (circle on top denoted with an "S"); Application (circle on the bottom left with an "A"); and Transportation Management Plan (circle on the right with "TMP"). Adjacent to each circle is a smaller circle used to indicate a relative level of finality regarding the decisions within each category. For example, in Figure 3, all of the decisions regarding the Application have been made indicating there is little, if any, room to make adjustments or refine those decisions. In contrast, the decision regarding TMP is shown approximately 25 percent complete indicating that many of these decisions have not yet been finalized, implying considerable flexibility potentially remaining in this area.
Figure 3 Work Zone Decision-Making Engine
All of the three circles are connected indicating each decision type does not operate in isolation but is influenced by decisions made in other areas. Thus, a decision made about the application (e.g., cast-in-place concrete) may dictate the scheduling of the work (e.g., to work in warmer-weather months) which in turn impacts the transportation management plan that could be implemented. In summary, the decision-making engine shown in Figure 3 conveys four key pieces of information:
- The decision making process is dynamic.
- Decisions made in one category (scheduling, application, or traffic management) impacts decisions in other categories.
- Decisions made in earlier stages of the project life-cycle will have an impact in later stages.
- Once momentum is gained early in the planning process it becomes more difficult to deviate from that course of action later in the process.
A critical component for TAT Volume IX is the inclusion of case studies to demonstrate how different transportation agencies have applied transportation analysis tools for the purpose of work zone impacts assessment. The case studies appear in various elements of the document with varying levels of detail in their description. First, a brief summary of the case studies is provided in this section. Second, the case studies are used as specific examples throughout the document to highlight various aspects of the factors that go into developing a modeling approach (Section 2.0) or the process that a transportation agency has established to guide analysts in selecting a modeling approach (Section 3.0). Third, a summary of each case study is provided in the Case Studies section with references to additional reports and contacts for each case study.
A total of 17 case studies have been included in this volume (13 project applications and 4 strategic modeling approaches) and are shown in Figure 4 below. The 17 case studies have been categorized as either Project Applications or Strategic Modeling Approaches and are indicated by the diamond and fill, respectively, in the figure. The case studies that are included in this document were selected based upon access to the analysts and/or decision makers, availability of reports and data regarding the work zone application, geographic diversity, and project application (uniqueness). A summary of the categories and brief description are provided following the figure.
Figure 4 Case Study Locations
Project Applications — Project applications are specific examples of work zones associated with roadway construction projects that have used a transportation analysis tool to conduct a work zone analysis as part of the overall decision-making process.
- Caltrans I-15 Pavement Reconstruction Project (CA I-15) — Application of an HCM-based constructability tool and mesoscopic simulation model during the design stage to address construction staging and mobility impacts.
- Glacier National Park: Going to the Sun Road Rehabilitation Project (GNP) — Application of a sketch-planning tool in the planning stage to help assess scheduling and constructability issues surrounding a high-profile, multi-year construction project.
- Michigan DOT: Ambassador Gateway Bridge MOTSIM (MI AMB) — Application of a microscopic simulation model during the final stages of design and beginning of construction in order to address maintenance of traffic issues.
- Michigan DOT: I-94 Rehab MOTSIM (MI I-94) — Leveraged the Ambassador Gateway Bridge microscopic simulation model (see above) as part of the initial design stage in order to address constructability, staging, and maintenance of traffic.
- Michigan DOT: I-75 Trade Corridor MOTSIM (MI I-75) — Leveraged and built upon the overall process developed as part of the Ambassador Gateway Bridge microscopic simulation model (see above) to address mobility, constructability, and staging from the planning stage forward.
- Nova Scotia, Canada: Reeves Street (NS-Reeves) — Application of a sketch planning tool for a simple work zone which includes a detour route.
- Utah DOT I-15 Reconstruction Design-Build Evaluation (UT I-15) — Use of a travel demand model to determine the impact of selecting an innovative contracting technique (design-build) in terms of mobility, cost effectiveness, and safety.
- Wisconsin DOT Work Zone Signal Optimization — Two examples of work zone signal optimization applications for work zones including a hypothetical case study used for training and a real-world application involving the Daniel Webster Hoan Memorial Bridge.
- Woodrow Wilson Bridge Reconstruction: Lane Closure Analysis (WWB-LCA) — Application of an HCM-based tool to address contractor requests for additional lane closures during the construction stage.
- Woodrow Wilson Bridge Reconstruction: Roadway Operations Analysis (WWB-ROA) — Application of a microscopic simulation tool during the construction stage to determine the optimal design of a traffic switch connecting old roadways to new alignments.
- Woodrow Wilson Bridge Reconstruction: Roadway Closure Analysis (WWB-RCA) — Application of a sketch-planning tool during the construction stage to determine impact of significant lane closures and full closures for extended weekend work.
- Yosemite National Park: Yosemite Village Roadway Reconstruction (YOS) — Application of a sketch-planning tool during the design stage to determine work zone staging and constructability.
- Zion National Park: Entrance Booth Reconstruction (ZION) — Application of a sketch-planning tool during the design stage to determine construction scheduling.
Strategic Modeling Approaches — Strategic modeling approaches are examples of agencies setting up a systematic process to facilitate rapid assessment of work zone impacts and to ensure best practices when more complex modeling approaches are warranted.
- Maryland SHA Lane Closure Analysis Program (MD-LCAP) — The Maryland State Highway Administration developed the Lane Closure Analysis Program (LCAP) to support state traffic engineers with a structured method to analyze work zone impacts.
- Michigan DOT: Southeastern Michigan Simulation Network (MDOT-SEMSIN) — Michigan DOT has developed a relatively complex microscopic simulation network and nalysis process whereby decision-makers can leverage previous analyses for current work.
- New Jersey Turnpike Authority: Lane Closure Application (NJTA-LCA) — The New Jersey Turnpike Authority established an approach whereby a simple GIS-based tool was developed to assist personnel in determining optimal timing of routine roadway maintenance work for the simplest of work zones.
- Wisconsin DOT: Transportation Management Plan Development Process (WisDOT) — The Wisconsin DOT has established a formal Transportation Management Plan Development Process which includes a decision-tree on recommended tools to use based upon certain work zone characteristics. In addition, for the most high-profile work zones requiring detailed microscopic simulation analysis, they have also established a review process to ensure the proper use of these complex tools.
TAT Volume IX is structured around three broad categories of decisions associated with selecting and using a transportation modeling approach for better understanding work zone impacts on roadway construction projects: factors associated with conducting a work zone analysis; various strategic methodologies in addressing work zone analyses; and how to ultimately identify and develop a comprehensive transportation modeling approach for work zone analysis. Each of these three categories builds upon each other taking the reader from very detailed and finite elements associated with work zone analysis in general (do I have enough data or financial resources?) through the general concerns and questions that need to be addressed when ultimately deploying the transportation modeling approach.
The organization of the document reflects these three broad categories of considerations and is organized as follows:
- Section 2.0 Work Zone Analysis Factors — Provides a detailed discussion regarding five categories of work zone analysis factors that should be considered when deciding whether or not to conduct a work zone analysis and those data elements necessary to successfully conduct a work zone analysis. Section 2.0 includes a number of tables that provide a summary of the transportation modeling approach best suited based upon the factor being discussed. The summary tables are based upon the suitability classification system developed in TAT Volume I and are slightly modified as needed for each of the work zone analysis factors being discussed (2).
- Section 3.0 Establishing a Strategic Methodology for Work Zone Analysis — Presents three strategic methodologies to systematically incorporate transportation modeling into the overall work zone decision-making process.
- Section 4.0 Identifying a Transportation Modeling Approach for Work Zone Analysis — Provides a framework and process that can be used to select an overall transportation modeling approach appropriate for the given circumstances.
- Section 5.0 Summary and Synthesis — Provides a synthesis of the document.
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