Traffic Analysis Toolbox Volume XII:
Work Zone Traffic Analysis – Applications and Decision Framework

1.0 Background and Objectives of this Guidebook

1.1 Overview of Work Zone Traffic Analysis Guidance

Work Zone Traffic Analysis (WZTA) is the process of evaluating and determining the mobility and safety impacts within a transportation construction, maintenance, or rehabilitation project. Establishing a procedure for analyzing work zone mobility and safety impacts aids agencies in the planning, decision-making, design, and financial aspects of the project. In order to establish an effective and comprehensive process, the work zone traffic analysis plan should address broader considerations of mobility and safety impacts that go beyond the work zone itself. An agency’s WZTA procedure should, therefore, include the following considerations:

• Impacts on mobility and safety of the project at corridor, network, and regional levels;
• Impacts on nearby facilities;
• Impacts on emergency management/incident management;
• Impacts on neighborhoods;
• Impacts on public property and services;
• Impacts on affected businesses and developments;
• Impacts on the environment; and
• Impacts of concurrent projects located near project.

Components of a Work Zone Traffic Analysis

The structure of a WZTA procedure will vary depending on the agency performing the analysis, as well as the size and complexity of the project. A WZTA plan will typically include the components listed below. More detailed guidance on developing a methodology for analyzing work zone traffic impacts is provided in Chapter 2 of this document.

• Goals and objectives of the Analysis Plan.
• Identification of construction design, staging, and phasing plans and alternatives.
• Analysis of work zone impacts. This section of the WZTA plan defines how the mobility and safety impacts of the alternatives will be calculated. This section will, therefore, define the analysis outputs, performance measures, and thresholds used for the analysis.
• Impact mitigation strategies that will address or minimize mobility and safety impacts of alternatives. These strategies can include public information, traffic control devices, travel demand management, and traffic operations measures.
• Decision framework for choosing a recommended alternative. The criterion or process of choosing the recommended alternative or combination of alternatives using data and information from the traffic impact analysis results and mitigation strategies assessment.

Role of Work Zone Traffic Analysis

As previously mentioned, the development of a WZTA can have multiple benefits for agency staff as they proceed through the planning, development, and implementation of a project. It enables agencies to understand the potential mobility and safety impacts of the project and identify the optimal alternative or combination of alternatives that will minimize impacts while keeping cost low and construction process efficient. The following details other benefits and uses of the WZTA process:

• Assisting agency staff in allocating resources more effectively and gaining the best value for the money.
• Improving construction management and scheduling. WZTA has the potential to improve the coordination and management of multiple projects and construction schedules to minimize overall impacts.
• Developing ways of monitoring and managing work zone impacts during construction.
• Conducting performance assessment pre- and post-construction. Evaluating the performance measures of a work zone prior to, during, and post – implementation helps provide data and information that aids agency staff in improving and updating work zone policies, procedures, and practices in the future.

Purpose of the Work Zone Traffic Analysis Guide

The purpose of this document is to provide a WZTA applications manual. This guide will be a useful resource for practitioners in understanding the analytical methods involved in conducting and developing a WZTA. The prior Federal Highway Administration (FHWA) work zone guidance, Traffic Analysis Tools Volume VIII and Traffic Analysis Toolbox Volume IX, provided guidance on the appropriate consideration of analytical tools in work zone planning and management, and the selection of a modeling approach based on these tools. (Hardy, M., and K. Wunderlich. Traffic Analysis Toolbox Volume VIII: Work Zone Modeling and Simulation – A Guide for Decision-Makers. Publication FHWA-HOP-08-029, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., August 2008. Hardy, M., and K. Wunderlich. Traffic Analysis Toolbox Volume IX: Work Zone Modeling and Simulation – A Guide for Analysts. Publication FHWA-HOP-09-001, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., March 2009.) This particular guide will focus on the work zone applications of these tools. It will provide a step-by-step guide customized to the selected tool and type of work zone project.

1.2 Role of Traffic Analysis Tools for Work Zone Applications

Work zone project types can span from simple flagging to complex corridor reconstruction projects. Additionally, work zones are temporal and can often take different forms over the project duration, depending on the construction staging plans. Measuring mobility and safety impacts may be dynamic, depending on these factors, therefore, making calculations and analyses more complex. There are a variety of different analysis tools that vary in complexity of features and functions. The sophistication of the analysis should be matched to the complexity of the road projects and the potential impacts. There is no one tool that can fit all work zone types. Traffic analysis tools can provide work zone mobility performance measures, such as duration and severity of congestion, queue lengths, and estimated volumes, which can be used to further analyze safety, economic, environmental impacts.

The FHWA’s work zone analysis framework is presented in Chapter 3 of the Traffic Analysis Tools Volume VIII. (Hardy, M., and K. Wunderlich. Traffic Analysis Toolbox Volume VIII: Work Zone Modeling and Simulation – A Guide for Decision-Makers. Publication FHWA-HOP-08-029, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., August 2008.) The components of the framework are reflective of the program delivery process: 1) System Planning; 2) Preliminary Engineering (PE)/Design; and 3) Construction; however, the types of decisions that need to be made are more important than specifically where in the program delivery process it is. These decisions are represented by three interrelated decision types that drive the overall work zone decision-making process as a decision-making engine:

1. Scheduling Decisions – Decisions impacting when work zone activity will occur, ranging from the selection of time of day to days of week to time of year. Analysis tools can be used to determine the optimal construction phasing/staging plan that will be cost-effective and time efficient.
2. Application Decisions – Decisions pertaining to the construction technique to be used within the work zone (e.g., a decision to use cast-in-place techniques rather than a precast approach). Analysis tools can play a role in determining which construction design strategies can minimize both mobility and safety impacts while improving construction time efficiency and cost-effectiveness. Analysis tools also can provide insight on impacts to road users, neighboring developments, and nearby projects.
3. Transportation Management Plan Decisions – Decisions that determine how traffic will be managed while work zones are in place. This includes issues of temporary traffic control, public information, and transportation operations. Analysis tools can determine how to best manage traffic in work zones by aiding agencies in identifying the optimal use and combinations of transportation management strategies.

The decision-making engine concept is visually represented in Figure 1, with each decision type represented by one of the three circles. (Hardy, M., and K. Wunderlich. Traffic Analysis Toolbox Volume VIII: Work Zone Modeling and Simulation – A Guide for Decision-Makers. Publication FHWA-HOP-08-029, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., August 2008.) 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 (TMP) that could be implemented.

S – Scheduling; A – Application, and TMP – Transportation Management Plan. Adjacent to each circle is a smaller circle used to indicate a relative level of finality regarding the decisions within each category.

Figure 1. Work Zone Analysis Strategies Decision-Making Engine

(Source: Hardy and Wunderlich, 2008.)

Chapters 3 and 4 in this document provide more information regarding selecting the appropriate analysis tool(s) and how the different tools can be applied for work zone project alternative analysis.

1.3 Organization of this Report

The purpose of this guide is to provide a useful resource for practitioners in understanding the analytical methods involved in conducting and developing a work zone traffic analysis. This document is organized as follows:

• Chapter 1 provides background and objectives of this guidebook and introduces the rest of the document;
• Chapter 2 describes the methodology for developing and implementing a work zone traffic analysis;
• Chapter 3 presents a process on how to select the appropriate type of traffic analysis tool to determine the impacts of a work zone;
• Chapter 4 presents key considerations when applying various modeling tools for work zone traffic analysis;
• Chapter 5 provides guidance on developing and applying a Maintenance of Traffic Alternatives Analysis (MOTAA) decision framework;
• Chapter 6 presents guidance on how to reconcile inconsistencies and conduct sensitivity analysis;
• Chapter 7 presents a mix of quantitative and qualitative factors that may be considered in an MOTAA process;
• Chapter 8 presents the essential components of a MOTAA Report; and
• Chapter 9 presents case studies to demonstrate the MOTAA process.