Traffic Analysis Tools Volume IX: Work Zone Modeling and Simulation
A Guide for Analysts
Section 2.0 provided a detailed discussion of the myriad factors that influence which type of transportation modeling approach to choose. As observed earlier, the need to conduct a work zone analysis can occur at any stage during the project life cycle including Planning, PE/Design, and Construction. This breadth of application is evident in Table 1 which lists each of the case studies and where during the project life-cycle the analysis took place. Of the 13 project application case studies, seven occurred during Planning, four during PE/Design, and two during Construction. Clearly, the need for work zone analyses is not limited to a single stage. Thus it becomes important to develop a strategic methodology to applying transportation modeling approaches throughout the work zone project life-cycle.
To that end, this section deals with establishing a strategic methodology for work zone analysis in order to maintain analytical consistency when work zone planning and analysis spans the project life-cycle. As mentioned previously, the benefits of establishing a strategic methodology for work zone analysis are much greater than what could be achieved through the deployment of a number of components operating in isolation. Thus, strengths and weaknesses of strategic methodologies that utilize more generalized transportation analysis tools (e.g., sketch-planning and HCM) to screen projects for issues and then commit to more detailed transportation analysis tools are contrasted against other strategic methodologies where one (or more) transportation analysis tools are initially developed in detail in the Planning stage and utilized consistently as the project evolves. Three general strategic methodologies are presented in Figure 10 and described below:
- Mono-Scale—The mono-scale methodology features a single transportation analysis tool applied consistently throughout the project life-cycle. This is represented by the single bar in the figure. Michigan DOT’s SEMSIN is an example of a Mono-Scale methodology.
- Screening—The screening methodology utilizes a series of transportation analysis tools throughout the project life-cycle, in an attempt to match the best transportation analysis tool to the specific decision being supported. This is portrayed by the vertically segmented bar in the figure with each segment representing a different transportation modeling approach being used based upon the project life-cycle stage. The Wisconsin DOT: Transportation Management Plan Development Process is an example of a Screening methodology.
- Multi-Scale—The multi-scale methodology involves the deployment of multiple transportation modeling approaches in an integrated and strategic way to support decision making throughout the project life-cycle. This is portrayed by the horizontally segmented bar in the figure with each segmented representing a modeling approach to be used based upon the need rather than the project life-cycle stage. The Woodrow Wilson Bridge Reconstruction is an example of a Multi-Scale methodology.
Just as no single transportation analysis tool is right for all work zone analyses, no single work zone analysis methodology represents the single best match for all projects. Sections 3.1 through 3.3 provides discussion about the strengths and weaknesses of these various strategies relative to the analysis factors (primarily the agency resources and performance measures) discussed in Section 2.0.
Figure 10 Comprehensive Work Zone Analysis Methodologies
The mono-scale methodology features a single transportation analysis tool applied consistently throughout the project life-cycle. The advantage of this methodology is that model consistency is essentially guaranteed throughout the project life-cycle. Resources invested in developing the tool and its supporting data are passed along as the project proceeds. The disadvantage of this methodology is that a single tool may be well-suited to support some types of decisions but not well-suited to others. For example, a mono-scale methodology using microscopic simulation of the immediate work zone area may capture detailed elements of traffic control (work zone geometry and traffic signal operations) but have only limited capability to predict impacts from diversion on parallel routes. A mono-scale methodology may be an attractive option if a calibrated, well-maintained model of the work zone impact area is already in hand. If there is not a good match between the transportation modeling approach and model type in-hand, and there are some resources in hand to extend or enhance the analysis, a multi-scale methodology can be considered.
|Michigan DOT: Southeastern Michigan Simulation Network|
Development of Michigan DOT’s SEMSIM Network was undertaken, in part, to leverage the up-front costs associated with developing a microscopic simulation network across multiple projects as well as multiple stages within the project life-cycle. The Michigan DOT Detroit Metro Region expended lots of resources (both time and money) in developing the initial application of the SEMSIM Network for the Ambassador Gateway Bridge MOTSIM during the PE/Design stage and will continue to use the network as needed during construction. The same network was expanded to use for two other projects, I-75 Trade Corridor and I-94 Rehab, which are in the Planning and PE/Design stages, respectively. More information can be found in the Michigan DOT: Southeastern Michigan Simulation Network case study.
This methodology is characterized by the use of simpler tools using archived data to screen work zone projects to determine which may warrant more in-depth analysis. This concept has been used to allocate resources for work zone analysis when looking across a number of projects to identify potential mobility impacts. For single projects this includes the use of simpler transportation modeling approaches such as sketch-planning and HCM in early project phases and the use of a more complex transportation modeling approaches (if warranted) later in the project.
The advantages of this methodology include the focusing of agency resources (institutional, financial, and technical) on projects or issues that have the most potential mobility impact. It can be difficult early in project development or when looking across many projects to accurately identify where significant congestion is likely to be induced by work zone activity. The screening method allows for a uniform method to find the locations, times, and projected impacts as early as possible so these issues can be dealt with before the work zone decision engine has generated significant momentum.
The disadvantage of this methodology is that the high-level screening transportation analysis tools used in earlier stages may not produce consistent predictions of impacts with more detailed tools used in later stages. The detailed analysis in later stages may reveal a nuance to the problem that may be contradictory to the direction the analysis with the screening tool has directed the decision engine. For example, using archived data in the planning stage, a screening tool may indicate that mid-day lane closures will not result in congestion. Thus, scheduling and application decisions later made in the PE/Design stage may count on a 4-6 hour window for mid-day work zone activity. However, a more detailed analysis with field traffic counts (e.g., travel demand data) collected specifically for the project in the PE/Design stage could indicate that unacceptably long delays are likely to result from mid-day lane closures.
|Wisconsin DOT: Transportation Management Plan Development Process|
The Wisconsin DOT has established a screening approach in order to provide traffic engineers and planners in the various regional offices guidance on the selection of an appropriate transportation modeling approach. The screening approach developed by Wisconsin DOT is used to filter through those projects requiring more in-depth analysis (what they classify as Type IV and III work zones). If a project does require in-depth analysis (typically the use of microcopic or mesoscopic simulation tools) then a secondary model scoping worksheet is employed to further determine data needs and requirements.
To further reinforce the use of overall work zone analysis and the application of transportation models throughout the project life-cycle, Wisconsin DOT developed a training course which includes an exercise in applying transportation analysis models for a simple bridge replacement project beginning in the planning stage.More information can be found in the Wisconsin DOT: Transportation Management Plan Development Process case study.
This methodology deploys several tools in combination from project planning through construction, and any inconsistencies between models are identified and resolved throughout the process. This type of methodology is effective for looking at a complete range of issues using the most appropriate tool with the added value of cross-validation among tools and data types. The disadvantage of this methodology is that the agency resources (the technical staff, funding, and scheduling) are significant as well as the required data (specifically its quality and availability). This type of methodology is likely to be deployed only on the largest projects with a large work zone impact area, longer duration, and significant resources devoted to mobility impacts mitigation.
|Woodrow Wilson Bridge Replacement|
Planning for the reconstruction of the Woodrow Wilson Bridge began in the 1990s with record of decision on the locally preferred alternative made in November 1997. Construction began in October 2000 with final design completed in June 2003. Construction of the bridge is planned to be completed in December 2009. All throughout this time, transportation models were being used for both the design of the facility itself as well as the design of the work zones to be implemented as part of the construction. The use of transportation models for work zone analysis primarily occurred during the construction stage as refinements to the staging of the various work zones were required. During this time, the transportation consultants used a variety of modeling approaches depending upon the requirements of the TMP, available data, and required performance measures. More information can be found in the Woodrow Wilson Bridge Replacement case study.