Traffic Analysis Tools Volume IX: Work Zone Modeling and Simulation
A Guide for Analysts
The preceding two sections provided a detailed overview of the factors that influence the development of a transportation modeling approach and three strategic methodologies applied to maximize value from work zone analyses. Once an analyst has a better understanding of the factors influencing an overall work zone analysis, the next step is to consider two critical questions:
- Does it make sense to move forward with work zone analysis for a given project?
- What criteria should be used to select an actual modeling approach for a project?
The following two sub-sections discuss each of these questions in more detail. Section 4.1, Deciding to Analyze or Not Analyze, provides a framework to better understand the technical risk and rewards associated with ultimately deciding to deploy a transportation modeling approach. Section 4.2, Characterizing Case Studies by Transportation Modeling Approach, uses the same framework to classify the transportation modeling approaches utilized in the selected work zone analysis case studies. Finally, Section 4.3, Developing a Transportation Modeling Approach, provides a set of worksheets to guide an analyst in developing an appropriate transportation modeling approach and strategic methodology.
In order to better understand which work zones warrant analysis, and to what extent, an analytical work zone decision framework was created. Figure 11 provides a notional representation of this framework for the work zone analyst considering the complex tradeoff between analytical opportunity and technical risk. Managing these two concepts is based on two high-level considerations shown on the two axes of Figure 11 the level of detail required to support decision-making on the X-axis (Level of Detail), and resources available to conduct a work zone analysis on the Y-axis (Resource Availability). The axes were developed based upon the five categories of work zone analysis factors discussed in Section 2.0 whereby resource availability incorporates data and agency resources, and level of detail incorporates work zone characteristics, desired TMP strategies, and required work zone performance measures. Effectively managing this tradeoff between analytical opportunity and technical risk is one of the most important responsibilities of the work zone analyst. Failure to realistically account for technical risk is the most frequent underlying issue when analytical efforts fail to meet the expectations of both analysts and decision-makers. This failure can manifest itself in failure to meet schedule, budget overrun, or an abandonment of the technical approach even after the expenditure of significant agency resources.
Figure 11 Analytical Work Zone Decision Framework
As seen in Figure 11, when significant data and staff resources are available, there are many more options in matching a transportation modeling approach with the decisions to be supported. When resources are limited, however, the analyst must consider whether a less detailed analysis using a simpler tool is adequate to the requirements of the analysis. If the mis-match between the necessary level of detail and resource availability is high enough, the corresponding technical risk may be so high that a drastic re-consideration of modeling approach may be appropriate.
In some cases, the technical risk of attempting to conduct a work zone analysis with little reliable data or too few resources may outweigh the benefits of conducting it. In these cases, there is a risk that rushed or poorly-informed work zone analyses will provide highly inaccurate or misleading assessments of mobility impacts. Such analyses are to be avoided, since they not only represent a waste of project resources, but also because they may entrench institutional mistrust of transportation analysis tools and analytical results, even in cases where well-calibrated models do provide meaningful results.
The decision about what transportation modeling approach to select for a work zone analysis is secondary to the decision to deploy a transportation modeling approach at all. However, once the decision is made to use a transportation analysis tool, the question turns to which tool is best suited given my circumstances? The difficult part is balancing the available resources (time, money, data, etc.) with the desired level of detail (e.g., ability to model one-lane/two way operations using historic traffic counts for a Type I project).
Given the fact that each work zone analysis will be different, developing a comprehensive checklist or decision-tree will never be adequate enough in selecting “the right tool”. However, the case studies included in this document illustrate generally successful examples of managing technical risk as a part of an overall modeling approach. Using the Analytical Work Zone Decision Framework discussed previously, all of the 13 project application case studies and two of the strategic modeling case studies were placed on the framework to indicate how each ranked in terms of level of detail needed (low-medium-high) and available resources (low-medium-high). As shown in Figure 12, what the case studies reveal is a diverse mix of transportation modeling approaches based upon the level of detail needed and available resources.
Figure 12 Analytical Work Zone Decision Framework—Case Studies
From these case studies, a number of clusters can be created based upon the modeling approach chosen. These clusters are shown in Figure 13 and characterize the modeling approaches observed across the case studies based upon relative availability of resources and required detail for analysis. Figure 13 should not be considered specific recommendations but rather a reflection of the diversity of approaches developed by the analysts across the case studies. The transportation modeling approach clusters are highly consistent with the work zone modeling spectrum presented in Figure 1. As one moves along the modeling boundary bisecting the areas of significant technical risk and modeling opportunities, the complexity of the transportation modeling approaches increase. When both resource availability and the level of detail needed are low, the most appropriate transportation modeling approaches are likely to be sketch-planning and HCM methodologies. As resources increase, the available transportation modeling approaches increase and include macroscopic models for pipe network forms and travel demand models for those analyses with a grid network form. As the requirement for detail increases, the available transportation modeling approaches shift to mesoscopic and microscopic modeling tools. Mesoscopic applications include both pipe and network forms. Microscopic modeling tools are applied alone or as a part of a multi-scale approach, where the model is designed to be used strategically throughout the project life-cycle in conjunction with other tools.
Figure 13 Analytical Work Zone Decision Framework—Modeling Approaches
The preceding two sections established a strategic framework which can be used identify a specific transportation modeling approach. Some analysts, however, would like a tool to assist with identifying an appropriate transportation modeling approach and strategic methodology. To that end, the following two worksheets were developed to provide an analyst with a tool to conduct a detailed assessment of a work zone analysis project and ultimately identify a transportation modeling approach and strategic methodology. These worksheets are intended to be used as a tool to guide an analyst and should not be considered the final decision in choosing a specific transportation modeling approach. In other words, this is an additional input into the overall decision-making process.
The two worksheets are discussed below and include instructions for filling each out. Using the worksheets requires the analyst to have read through this document and have a good understanding of a work zone analysis project.
The scoping worksheet should be used to document the various components of a work zone project that need to be analyzed using a transportation analysis tool. The scoping worksheet is based primarily upon Section 2.0, Work Zone Analysis Factors. The following instructions provide more detail on how to fill-in the scoping worksheet.
- Key Decisions — List the Key Decisions that need to be supported using the transportation modeling approach. References on the importance of articulating key decisions to be supported:
- Section 1.2, Work Zone Analysis Decision Making
- Work Zone Characteristics — Identify the Type, Network Configuration, Size, and Analysis Area Dimension of your work zone analysis project. Refer to Section 2.1 for more information on definitions.
- Agency Resources — Under each heading mark the following and refer to Section 2.4 for more information on definitions:
- Institutional: Circle those institutional categories which have been addressed by your agency.
- Technical Staff: Circle whether the technical expertise to run the transportation analysis tools resides in-house, via consultant or both.
- Funding: Indicate the amount of funding available. $ = $10,000 and $ = $100,000
- Time to Analyze: Circle the amount of time available to conduct the analysis
- short = Less than 2 months
medium = 3 months to 6 months
long = Greater than 6 months
- short = Less than 2 months
- Performance Measures
- Measures of Effectiveness: Fill in each circle based upon the classification system indicated. Refer to Section 2.5 for more information and definitions.
- Precision of Results: Indicate on the bar whether the Key Decisions that need to be supported are either a rough estimation or a detailed assessment.
- Data — Indicate the following and refer to Section 2.3 for more information and definitions.
- Type: Indicate availability.
- Source: Indicate which data is available through archived or primary sources.
- Quality: Indicate availability.
- Transportation Management Plan Strategies — Indicate which transportation management plan strategies need to be included in the analysis based upon the classification system indicated. Refer to Section 2.2 for more information and definitions.
- Fill-in Scoring Worksheet
The scoring worksheet should be used after the scoping worksheet has been filled in. The following instructions provide more detail on how to fill-in the scoring worksheet.
- Develop a Transportation Modeling Approach — This table should be filled in using the classification system indicated in the bottom left corner of the table. Each heading refers to a certain work zone factor from this document (Section 2.0) the analyst will need to reference in order to indicate whether the transportation modeling approach is appropriate. Based upon the scoping worksheet, the analyst should fill out each cell after reviewing the discussion and summary table for each section. The following provides a reference to the sections in the document:
- Work Zone Characteristics: Section 2.1 Work Zone Characteristics
- Agency Resources: Section 2.4 Agency Resources
- Performance Measures: Section 2.5 Work Zone Performance Measures
- Data: Section 2.3 Data
- Transportation Management Plan: Section 2.2 Transportation Management Plan Strategie.
- Summary — Once each of the cells for each work zone factor is filled in, the analyst should provide an overall ranking (using the same classification system as in Step 1 above) for each transportation modeling approach. The analyst should rely on visual inspection of the results to indicate whether the transportation modeling approach is appropriate or not.
- Identify a Strategic Methodology — This section asks three basic questions regarding the work zone analysis to assist the analyst in identifying one of the three Strategic Methodologies discussed in Section 3.0 Establishing a Strategic Methodology for Work Zone Analysis.
- Answer — Once the three previous steps have been completed both a Transportation Modeling Approach and Strategic Methodology should become evident. The space provided in the Answer section should be used to describe and justify the analyst’s reason for choosing each.
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