Traffic Analysis Tools Volume IX: Work Zone Modeling and Simulation
A Guide for Analysts
The intent of this work zone modeling and simulation guide for analysts is to provide practical guidance on the identification and development of a transportation modeling approach for work zone analysis. The guidance is grounded in a detailed understanding of the key work zone factors in developing a transportation modeling approach (Section 2.0). This understanding is considered jointly with a strategic methodology for work zone analysis (Section 3.0). These two elements provide the foundation for a worksheet-driven exercise to assist the analyst in the development of transportation modeling approach for a specific work zone analysis project (Section 4.0). Throughout this process, a series of case study examples were used to illustrate how analysts have successfully identified modeling opportunities, mitigated technical risk, and conducted work zone impacts analyses to support key decisions across a range of considerations, including constructability, scheduling and TMP design, and evaluation.
What the preceding discussion and case study examples demonstrate is that work zone decision-making is an evolutionary process. Any work zone analysis should be linked to a specific decision with the knowledge that decisions made early in the project life-cycle have a large impact on future decisions. Placed within the context of analyzing work zone impacts, the further along in the project life-cycle one is, the lower the relative opportunity for transportation models to have a role in supporting the decision-making process. As seen in Figure 14 below, the decision-making evolution process combines the work zone decision-making process along with the work zone decision-making engine. Below it, represented by two polygons, are the tradeoffs that are made between modeling opportunities and data requirements as the decision-making process evolves over time.
Figure 14 Work Zone Decision-Making Engine Process
In the end, the options available to an analyst in deploying a transportation modeling approach decrease as more decisions are made regarding application techniques, scheduling, and TMP strategies. For example, once planning is complete and the decision to conduct a full-closure has been made, the use of a transportation modeling approach to help mitigate the mobility impacts is limited in that the decisions to be supported are much narrower. However, as seen in many of the case studies, the use of a transportation analysis tool may still be warranted regardless of the project life-cycle stage.
TAT Volume IX highlighted four key points that are important to consider when an analyst is deciding upon which transportation modeling approach to ultimately develop and use:
- Work zone decision-making is an evolutionary process which supports a number of key questions to be answered. — As seen in Figure 14 and discussed throughout this document, work zone analysis evolves over time as the roadway construction project moves forward from Planning to PE/Design to Construction and key decisions need to be supported. For example, during the planning stage, the work zone analysis may focus on numerous TMP alternatives and the key question is centered upon which alternatives are feasible given certain criteria. Later, a new set of questions may need to be answered that places more constraints on the feasible list of TMP alternatives (e.g., available funding or political pressure). Thus, as the overall project moves forward it is always evolving and the use of a transportation modeling approach is always predicated on certain key decisions that have to be made.
- Data requirements are a driving force behind developing a transportation modeling approach — Section 2.0 provides a detailed discussion of the many different factors that need to be considered when selecting a transportation modeling approach. For example, selecting an approach may be constrained by agency resources in terms of budget and staff resource. Or, the tool selection may be driven by the utilization of a cutting-edge TMP strategy such as variable speed limits through a work zone which requires a detailed vehicle-based evaluation. Regardless, it is a complex issue to unravel. However, what each of these examples shows is that data requirements are an important factor to consider. As seen in Figure 14 above, data requirements increase as the project evolves from planning to construction thereby placing constraints on the use of a transportation modeling approach. Thus, as the project evolves and different questions need to be answered, so too will different data need to be used/collected which may create both constraints and opportunities in developing a transportation modeling approach.
- Identifying a Strategic Methodology early in the project life-cycle can mitigate future work zone analysis problems — As discussed in Section 3.0, three strategic methodologies were presented representing various modeling opportunities for work zone analysis: mono-scale, screening, and multi-scale. These methodologies serve as a foundation on which transportation modeling approaches could be incorporated into the overall work zone decision-making framework. As shown in the Figure 14, the opportunity associated with choosing a transportation modeling approach is much greater early on in the project life-cycle. For example, during the planning stage relatively few decisions have been made and the availability and use of a transportation analysis tool are fairly large. his is in contrast to the construction stage at which time the application technique, scheduling, and TMP have been finalized and the opportunity to select a transportation analysis tool and for it to generate useful information are much more limited. However, by identifying a strategic methodology in the beginning of the project life-cycle, the work zone analysis opportunities do not necessarily decrease over time but rather grow as the model can be leveraged and applied to more work zone analyses as warranted or needed.
- Developing a transportation modeling approach is unique to each work zone analysis — While many people desire a prescriptive “cookbook” method to direct them in determining which transportation modeling approach to use, making that determination based solely upon one particular factor is problematic. What this document demonstrates is that there are many factors that go into developing a transportation modeling approach. For example, the Woodrow Wilson Bridge, a Type I work zone, used both simple HCM methodologies and complex microscopic simulation tools. Thus, the use of the worksheets developed in Section 4.0 are intended as a tool to guide analysts and provide a framework with which to better conceptualize and address the complexities associated with conducting a work zone analysis. Some agencies have developed specific procedures to guide the analyst in the development of an appropriate modeling approaches (such as the Wisconsin DOT Transportation Management Plan Development Process discussed in the case study), and these systematic approaches can both speed the modeling approach development process as well as ensure consistency when different staff consider projects independently.
Ultimately, the questions for many analysts boils downs to which transportation analysis tool should I use? Where do I get the data from? And, how do I overcome my institutional issues? These are difficult questions to answer and it is not the intent of this document to specifically address them given that each circumstance is unique. However, the following provides some direction on where one can turn to for help.
- Individual Transportation Analysis Tool Resources — It is not the intent of this document to provide guidance on the use or application of any one specific transportation analysis tool. Rather, this guidance is intended to help an analyst identify a certain transportation modeling approach for work zone analysis. There are many unique transportation analysis tools available under each modeling approach. Often, these tools are constantly changing as capabilities are added as well as being routinely updated and tweaked. Also, new tools become available on a regular basis. Recently, many commercial vendors have begun offering hybrid models that span more than one class of tools such as mesoscopic models that also operate on the microscopic level. For more information on using an individual transportation analysis tool refer to the following:
- FHWA Traffic Analysis Toolbox (TAT): The Traffic Analysis Tools Program was formulated by FHWA in an attempt to strike a balance between efforts to develop new, improved tools in support of traffic operations analysis and efforts to facilitate the deployment and use of existing tools. The TAT provides a detailed description of traffic modeling tools. http://ops.fhwa.dot.gov/trafficanalysistools/index.htm.
- McTrans: Center for Microcomputers in Transportation (McTrans) serves as a resource for the distribution and support of microcomputer software in the highway transportation field. McTrans provides expert technical advice, information exchange and a wide range of transportation-related software at very reasonable costs. http://mctrans.ce.ufl.edu/
- Data Collection — Data collection is routinely cited as a barrier to using transportation modeling. As the expression goes: “garbage in, garbage out”. With the increasing use of sensors located throughout the transportation system, the ability to cost effectively collect traffic data has increased. Often, much of the required data has probably already been collected and simply requires contacting another department within the agency. Some examples are as follows:
- Many transportation agencies have permanent count stations on Interstate and arterial roadways from which traffic count data is routinely collected, cleaned, and archived. A case in point is the Minnesota Department of Transportation Traffic Forecasting & Analysis unit which makes its data available on its website (http://www.dot.state.mn.us/traffic/data/html/traffic.html).
- Another opportunity for data collection is the use of portable traffic counters. The Federal Lands Highway Division purchased a number of counters for the sole purpose of data collection for transportation modeling. See the Yosemite National Park: Yosemite Village Roadway Reconstruction case study for more information.
- For major roadway reconstruction projects the use of real-time monitoring may yield useful data. This occurred as part of the Woodrow Wilson Bridge project where a traffic data collection effort was undertaken to establish a formalized process for collecting and archiving traffic data as part of the project for use in future studies and analyses. See the Woodrow Wilson Bridge Reconstruction case study for more information.
- Addressing Institutional and Policy Issues — Institutional polices can often be a significant driver in developing a transportation modeling approach. The discussion on Institutional Arrangements (Section 2.4.1) lists four areas general areas that can impact transportation modeling: culture, leadership, data management, and contracting. Many progressive transportation agencies have addressed these areas and the FHWA has available numerous resources addressing the subject. Another institutional area that needs to be addressed is work zone policies that have been created. For example, many agencies now have restrictions on lane closures in work zones, available work hours, maximum user delay, etc. These policies, created by the transportation institutions, have an impact on the overall usefulness of a transportation modeling approach. For example, a policy limiting the maximum user delay may negate the results of a model that demonstrate a larger maximum user delay for a shorter duration is a better choice overall for a construction project. While many of these policies are developed with good intentions, the use of a transportation analysis tool may contribute to the development a more refined approach. For more information on work zone policy issues refer to the following FHWA material concerning the Final Rule on Work Zone Safety and Mobility:
- Implementing the Rule on Work Zone Safety and Mobility (HTML, PDF) — Provides a general overview of the Rule, as well as guidance, examples, best practices, tools, and resources to help implement the Rule's provisions.
- Work Zone Impacts Assessment: An Approach to Assess and Manage Work Zone Safety and Mobility Impacts of Road Projects (HTML, PDF) — Provides guidance on developing procedures to assess and manage work zone impacts of road projects, as well as examples and practices of how agencies are currently assessing and managing work zone impacts.
- Developing and Implementing Transportation Management Plans for Work Zones (HTML, PDF) — Provides information about developing and implementing Transportation Management Plans (TMP), including information on how and where a TMP fits into project-level processes and procedures, a list of components that can be considered for inclusion in a TMP, descriptions of work zone management strategies, and examples and practices of how agencies are currently using TMPs.
- Work Zone Public Information and Outreach Strategies (HTML, PDF) — Provides tips, examples, and practices on designing a public information and outreach campaign for work zones and offers a variety of strategies that can be used in a campaign.