Traffic Analysis Toolbox Volume XII:
Work Zone Traffic Analysis – Applications and Decision Framework
2.0 Establishing a Methodology for Work Zone Traffic Analysis
A WZTA can serve as a critical tool for work zone management and decision-making. This type of analysis provides a valuable resource for understanding the various impacts of particular work zone strategies. Evaluation of these impacts aids an agency in creating the optimal combination of work zone strategies and construction project management decisions that can optimize the efficiency of the construction work and minimize costs to the agency, road user, and society.
This chapter describes the methodology for developing and implementing a WZTA. The sections provide a sequential order for approaching WZTA, including the following:
- The first section defines the WZTA’s goals and objectives;
- The second section defines or sets performance targets that serve as a measure of the work zone strategies’ effectiveness towards achieving the established goals and objectives;
- The third section provides some suggested work zone alternatives or strategies that are commonly used to mitigate work zone impacts on safety, mobility, and constructability of a project;
- The fourth section provides a methodology for narrowing down alternatives that will best serve the goals and objectives of the project;
- The fifth section provides project coordination for work zone traffic management; and
- The last section discusses typical steps in an MOTAA and decision framework.
2.1 Identifying Work Zone Analysis Goals and Objectives
One of the main components of developing a work zone traffic analysis plan is to define the goals and objectives of the analysis. Setting goals and objectives serves several purposes. By establishing a set of goals and objectives, an agency is forced to evaluate the traffic impacts, benefits, and costs of their work zone project. Using these results, they can direct their resources to those strategies that will help them minimize costs or maximize benefits, mitigate traffic impacts, and improve safety within the work zones. Second, it provides a direction to guide the analysis and the decisions made towards a set of expected and desired results. Third, it sets an established target to determine the effectiveness of potential work zone strategies.
Typically, an agency will have an overall mission statement or policy in regards to work zone traffic management, which explains the agency’s vision with respect to maintaining the safety, mobility, and quality of work within the work zones. An agency’s goals and objectives will typically be guided by this vision statement. Safety, mobility, and constructability are often at the core of an agency’s vision statement.
- Safety – An agency’s work zone policy or vision statement for safety will include considerations for both users and workers within and around the work zone. Examples of safety goals can include reducing crashes and/or reducing worker fatalities and injuries at the construction site.
- Mobility – This pertains to facilitating efficient travel conditions through or around a work zone area with a minimum delay compared to baseline travel (preconstruction) conditions, while maintaining optimal construction duration/timeframe and not compromising safety.
- Constructability – This refers to efficient and effective planning, designing, and building of projects while minimizing impacts on mobility and safety. For agencies, such goals may include optimizing construction duration, minimizing construction costs, or reducing negative economic impacts on the surrounding community.
Examples of Agency Vision Statements
Creating a work zone traffic impact mitigation strategy requires finding the most cost-effective strategy.
New York State DOT
- To provide a high level of safety;
- To minimize congestion and community impacts by maintaining levels of service close to or at preconstruction levels; and
- To provide contractors with adequate access to the roadway to complete the work efficiently while meeting quality requirements of the contract.
The Maryland State Highway Administration (SHA) is committed to maintaining optimum worker safety while having traffic traveling smoothly and safely through and around work areas at all times. (Work Zone Safety and Mobility. Maryland State Highway Administration (MD SHA), Maryland. Accessed January 11, 2012.) Careful consideration of work zone impacts should begin during planning and continue through design, construction, and post-construction review.
Figure 2. Maryland Strategic Emphasis Areas for Work Zone Safety and Mobility
(Source: Maryland State Highway Administration, 2012.)
Developing Project Goals and Objectives
Strategic goals and performance objectives should be established in accordance with the work zone vision. The goals should directly correlate to the work zone safety, mobility, and constructability concerns and needs of the agency. The performance objectives then drive the selection of work zone alternatives or strategies that are designed to meet the established goals.
Before setting the specific goals and performance objectives, the agency should review project details, such as the design, plans, scope, and environmental documents for important safety, mobility, and constructability constraints and considerations that help form the basis of the goals and objectives. Examples of safety, mobility, and constructability considerations include:
- Worker and road user safety;
- Impacts to emergency response; and
- Injury/fatality crash rates.
- Road user costs;
- Average Daily Traffic (ADT);
- Delay or queue length;
- Truck percentages;
- Lane closure hours;
- Transit operational impacts;
- Bike/pedestrian access; and
- Detour availability and impacts.
- Duration of construction;
- Number of construction stages;
- Maintenance considerations;
- Environmental constraints; and
- Business and residential impacts.
The goals and objectives can be qualitative and/or quantitative. A qualitative goal may be to promote public awareness and motorist travel information of work zone traffic conditions. A quantitative goal may be to reduce work zone delays by X percent within a certain time period. If quantitative, it also may be necessary for an agency to conduct data collection efforts and a preliminary analysis to identify the specific areas of concern that may potentially need mitigation. There may be several areas of concern the agency may like to analyze or mitigate. However, the number of concerns may exceed the agency’s monetary and time resources, thus it may be necessary for the agency to prioritize which specific project design or work zone strategies should be analyzed. The agency also can qualitatively evaluate the impacts of the project’s particular work zone characteristics as a way of prioritizing. For instance, the New Jersey DOT Traffic Mitigation Guidelines for Work Zone Safety and Mobility rate project characteristics based on if they will have high, medium, or low impacts. The impact rating helps New Jersey DOT determine the particular mitigation strategies needed to achieve their goals of maintaining work zone mobility and safety. Figure 3 shows a sample impact matrix developed by the agency. (Traffic Mitigation Guidelines for Work Zone Safety and Mobility. New Jersey Department of Transportation, New Jersey, October 2007. Accessed January 11, 2012.)
Figure 3. New Jersey DOT Project Impact Matrix
Source: New Jersey Department of Transportation, 2008.
Example Goals and Objectives
Once the project details and plans have been reviewed and any preliminary analysis has been completed, the particular goals and associated performance objectives should be established. Goals and performance objectives will vary depending on project characteristics, agency policies, and resources. The following serves as example goals and corresponding performance objectives:
- Goal 1 – Keep work zone congestion at preconstruction levels.
- Objective 1 – Optimize lane closure strategies; evaluate impact of detours; alternative work schedules (i.e., nighttime, weekend work).
- Goal 2 – Reduce work zone-related crashes by X percent.
- Objective 2 – Determine impacts of traffic incident management strategies, intelligent transportation systems (ITS) strategies, enhanced monitoring on crash rate.
- Goal 3 – Promote public awareness.
- Objective 3 – Keep the public apprised of Maintenance of Traffic (MOT) plans and their projected impacts.
New Jersey identified a potential list of work zone goals and objectives:(Traffic Mitigation Guidelines for Work Zone Safety and Mobility. New Jersey Department of Transportation, New Jersey, October 2007. Accessed January 11, 2012.)
- Provide work zone speed reductions of 10 mph compared to preconstruction speed limit;
- Reduce traffic volumes by X percent;
- Decrease average daily traffic by Y vehicles during peak period;
- Maintain level of service (LOS) D or better;
- Reduce expected delay by Z percent;
- Keep average delay per vehicle to less than X minutes during the peak period;
- Maintain vehicle or person throughput by increasing auto occupancy and transit ridership;
- Promote public awareness;
- Keep congestion no worse during construction than before;
- Mitigate community impact;
- Maximize safety of workers and the traveling public; and
- Keep road user costs below X dollars per day.
Concurrent with setting goals and objectives is selecting the appropriate analysis tool, discussed in Chapter 3. The type of analysis tool can vary from simple to complex and also will depend on the type of project, the goals, and available data and resources.
2.2 Selecting Measures of Effectiveness (MOE) and Thresholds
Once goals and objectives have been established, measures of effectiveness (MOE) or thresholds should be set to determine the performance standards for the safety, mobility, and constructability of the work zone. The MOEs or thresholds selected should be customized to the agency’s goals and project characteristics. The MOEs and thresholds set a minimum performance standard that the objectives must meet or exceed. They also will help in evaluating the different objectives or alternatives as a way of determining which strategies best fit the goals of the project. For instance, for Goal 1 listed in the Example Goals and Objectives from Section 2.1, “keep work zone congestion at preconstruction levels,” an MOE could be LOS, delay, travel time, or road user costs. Based on the MOE(s) selected, the agency will select an analysis tool to determine the LOS, delays, travel time, or road user costs of the work zone area prior to construction. Then, each of the proposed alternatives can be analyzed using the selected analysis tool and compared against the results of the preconstruction scenario.
Selecting an MOE will depend on the goals, project characteristics, and agency resources. However, determining an appropriate MOE or threshold also will require some analysis of the existing conditions within the work zone area. For instance, the agency should have some data supported knowledge regarding the transportation facility’s average daily traffic (or hourly volumes), applicable intersection counts, ramp metering and signal control timings, travel times, delays/queue lengths, bottleneck locations and severity and roadway capacity. These provide background information regarding the current performance of the roadway facility. It also provides a way of determining the performance standards the agency may want to meet or improve upon prior to construction.
The FHWA recently released a primer on work zone safety and mobility performance measurement. (Ullman, G.L., and T.J. Lomax. A Primer on Work Zone Safety and Mobility Performance Measurement. Publication FHWA-HOP-11-033, Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., September 2011.) It describes various work zone MOEs, and provides guidance to help agencies select and implement measures that make sense for their own work zone programs.
Example MOEs and/or Thresholds
The following provides some examples of performance measures used to determine the appropriate traffic mitigation strategies to use in work zone projects.
Maryland State Highway Administration (MD SHA)
MD SHA uses mobility thresholds that are calculated according to their Work Zone Lane Closure Analysis Guide. MOEs, according to the guide, include LOS, intersection control delay, and arterial travel time based on the type of facility being analyzed.
The Ohio DOT has two levels of MOEs that particular strategies are measured against. The first is defined by lane closure duration and the other uses queue thresholds.
- Permitted Lane Closure Map (PLCM) – Each Ohio district is required to prepare a permitted lane closure map (PLCM) that specifies the allowable times a lane may be closed on a freeway within that district. The predefined times are determined based on work zone capacity. For any proposed lane closures that do not meet the PLCM, the district must analyze the impacts on motorists.
- Queue Thresholds Analysis – A quantitative queue analysis should be performed for those lane closures proposed outside of PLCM allowable times. This analysis compares existing queues with expected queues caused by the lane closure. A vehicle will be considered part of a queue if its average operating speed is approximately 10 mph or less. The district may use analysis tools, such as QUEWZ-92, Synchro/SimTraffic, CORSIM or similar programs to model the expected queues. The allowable queue thresholds are defined below:
- For queues less than 0.75 mile, the work zone impacts are acceptable.
- For queues greater than 0.75 mile and less than 1.5 miles, the work zone impacts are acceptable if the queue exceeds 0.75 mile for 2 hours or less. Where queues are expected to exceed 0.75 mile for any period of time, additional advanced work zone warning signing should be specified.
- For queues longer than 0.75 mile for more than 2 hours or longer than 1.5 miles for any period of time, the work zone impacts are unacceptable.
For any individual project, the most cost-effective mitigation strategy (or combination of strategies) should be selected. To determine the most cost-effective mitigation strategy, Wisconsin DOT uses Road User Costs (RUC) as the MOE. The agency also sets a particular RUC threshold that the project’s cost for mitigations strategies must meet. For any individual project, the agency costs for mitigation should be less than 10 percent of the monetary value of the RUC associated with the construction. This is equivalent to a benefit/cost ratio of 10 or higher for mitigation activities.
2.3 Identifying MOT Alternative Strategies
MOT alternative strategies can be evaluated and fit several categories, including the following:
- Construction Approach – These strategies minimize traffic disruption by optimizing construction duration or by ensuring that the road has sufficient capacity during peak travel periods. Strategies within this category include:
- Staging/sequencing of construction phases;
- Lane closure and ramp closure alternatives;
- Alternative work schedules, such as night work or weekend work; and
- Innovative contracting.
- Traffic Control Operations – These strategies increase safety and capacity. Strategies within this category include:
- Speed limit reductions;
- Truck restrictions;
- Signal timing, coordination, and phasing improvements;
- Reversible lanes; and
- Physical barriers.
- Public Information – These strategies can include public outreach efforts to inform the community about the project, as well as the provision of traveler information regarding travel conditions at the work zone. Strategies within this category include:
- Public outreach efforts through community meetings, newsletters/pamphlets, and project web sites;
- Dynamic message signs;
- Highway advisory radio;
- Telephone hotlines (i.e., 511); and
- Closed-circuit television (CCTV).
- Incident Management and Enforcement – These strategies work to efficiently plan for, detect, respond, and clear incidents that can occur within the work zone area. These strategies can include:
- Incident management plans;
- Traffic management centers and the use of ITS technologies for advanced detection and response technologies;
- Emergency service patrols; and
- Enhanced police enforcement.
- Travel Demand Management (TDM) – This includes strategies that shift motorists from driving alone to multi-occupant modes in order to reduce congestion along the work zone, especially during critical travel periods. TDM strategies for work zones include:
- Rideshare incentives;
- Transit incentives and improvements;
- High-occupancy vehicle (HOV) facility provisions and improvements; and
- Park-and-ride provisions.
The selected MOE and related threshold(s) can be used to filter out MOT alternatives that do not meet certain criteria, will not minimize traffic impacts, or will make traffic conditions worse.
2.4 Conducting Fatal Flaw Analysis
Fatal flaw analysis determines if an individual alternative has one or more defects that prevent it from being successfully implemented. One of the key inputs to a fatal flaw analysis is the establishment of clear goals and objectives for the work zone project. Using these as a guide, a multidisciplinary team reviews the proposed alternatives and performs an initial screening of the identified alternatives. This screening identifies those alternatives that deviate from the stated goals in a significant manner, and determines if that deviation is substantial enough to remove the alternative from further consideration before more detailed analyses are completed. While this review may result in the elimination of alternatives, it also can result in refinement of the proposed alternatives. However, care must be taken not to cut too deeply with the fatal flaw analysis process, as some of the more innovative strategies that may utilize unconventional approaches could be lost in this manner.
2.5 Identifying Needed Coordination Between Projects
An important step that should be considered during the planning and design stages of the project development process is the identification of coordination between projects, other infrastructure improvements or maintenance activities, and agencies. Project coordination strategies are a critical part of the work zone traffic analysis process, as they can contribute to the reduction of traffic impacts and project duration. Project coordination can begin with discussions with other transportation and public works agencies and other stakeholders that may be impacted by the work zone. While coordination makes intuitive sense, the reality of work zone projects often involves a number of different agencies, contractors, funding sources, stakeholders, etc. that may pose logistical challenges for coordination efforts. In creating a work zone traffic analysis plan or a transportation management plan for a particular highway maintenance, reconstruction, and/or rehabilitation project, the following coordination strategies and considerations may be employed:
- Coordination between Construction Projects – This coordination strategy involves considerations for nearby state, local, and regional projects that may be occurring concurrently. This strategy involves coordinating, phasing, and scheduling these multiple projects in a way that will minimize delays and impacts on motorists, businesses, and neighborhoods, while reducing potential construction delays for all projects. This coordination effort also may involve assessing the potential combined impacts of the multiple projects at the corridor level in order to identify potential conflicts between projects and other coordination opportunities.
- Coordination with Special Events and Major Traffic Generators – Considerations for special events and major traffic generators that may be impacted by or could impact the project under consideration also are essential for reducing mobility and safety impacts. Construction schedules and sequencing, alternate routes, and other work zone strategies can be structured and coordinated with these events and traffic generators in mind in order to minimize disruption to motorists, businesses, and neighborhoods.
- Utilities Coordination – Coordinating and scheduling utility work within and around the work zone project is critical in minimizing disruptions to utility work and the overall construction duration. Coordinating the construction work with utility work also can identify additional utility improvements, roadway work and utility and traffic device installations (i.e., detectors, cameras, metering) that can be done concurrently with the work zone project. Consolidating the various improvements can reduce the need for future work zones and minimize road user disruptions.
- Right-of-Way and Permit Coordination – This type of coordination strategy involves considerations for right-of-way needs and issues that may impact construction duration.
- Coordination with Other Transportation Infrastructure Improvements and Maintenance Activities – This involves coordination with non-highway transportation facilities and associated agencies. Such facilities would include transit, railroads and intermodal facilities. As with other coordination efforts, this also will help to minimize mobility and safety impacts network- or regionwide.
2.6 Steps in the Maintenance of Traffic Alternatives Analysis (MOTAA) and Decision Framework Process
Figure 4 presents the steps involved in the application of a maintenance of traffic alternatives analysis (MOTAA) and decision framework. They vary depending on the agency work zone policies and resources. While work zone traffic analysis can vary in complexity, there are common components applied by various agencies in their work zone alternatives analysis and decision-making procedures. These common elements are described below. The common components or steps in an MOTAA and decision framework have been categorized into the various project stages that may occur in project planning and data collection, impact analysis, decision-making criteria, impact mitigation, and monitoring and post-implementation.
Figure 4. MOTAA and Decision Framework Flowchart
Planning and Data Collection
During this stage of the alternatives analysis, agency staff develops an analysis approach using existing conditions information, project characteristics, and traffic and/or economic data within and around the work zone. Considerations involved in this stage could include:
- Determination of Goals and Objectives – This step answers questions such as what is the purpose of the analysis or what are the priority impacts that need to be mitigated? Section 2.1 provides examples and further information on setting work zone goals and objectives.
- Project Scoping – This step involves reviewing the project characteristics and work zone strategies in order to gain a better understanding of the potential mobility and safety impacts within the work zone, as well as impacts on nearby projects, businesses, and neighborhoods.
- Determine Criteria, Thresholds, or Measures of Effectiveness – This step involves determining performance measures by which to compare proposed alternatives against. The selected thresholds vary based on the goals and objectives of the agency. Section 2.2 provides further information and examples of how to select and develop the thresholds or measures.
- Determine appropriate analysis tool(s) – Using the information gathered from the data collection efforts and existing conditions data, an appropriate analysis tool that matches the level of complexity of the project could be selected at this stage of the project. Chapter 3 of this guide provides detailed information on how to select the appropriate analysis tool based on the work zone’s characteristics.
Most highway projects go through some type of impact analysis to determine any negative impacts the project may have on the mobility, safety, and environmental conditions of the study area, as well as the surrounding community, corridor, or region. At this stage of the project, the various work zone alternatives also can be analyzed for their mobility, safety, environmental, and financial impacts within and beyond the work zone area. This analysis will contribute to selecting the appropriate set of work zone alternatives or strategies that will minimize impacts while maintaining or reducing the project duration and costs. The steps involved in the impact analysis may vary depending on the selected analysis tool. Common components may be as follows:
- Perform Analysis – How the analysis is performed will depend on the type of tool utilized. Chapter 4 of this document provides further information on performing the analysis.
- Calibration and Validation of Model – If the selected analysis tool requires modeling, an existing condition or preconstruction model is typically created. This preconstruction model, often called the “no-build” model, provides the baseline for the mobility and safety performance of the roadway facility. The calibration and validation process ensures that this baseline model accurately reflects the existing travel conditions and patterns on the ground.
- Obtaining Model Outputs – The model outputs also will vary depending on the type of tools and analysis selected. For instance, simulation tools may produce outputs, such as delay, travel time, and volumes. Sketch-planning tools may include measures, such as LOS or a benefit/cost ratio.
The decision-making criteria an agency may choose to apply in determining the recommended alternative (or combination of alternatives) may be greatly influenced by the goals and objectives, the data collection efforts, and the level and complexity of their impact analysis. The typical steps involved in this stage of the project often include the following:
- Determining whether the alternative(s) meets the thresholds or decision framework criteria; and
- Selecting the alternative(s) with the least impacts or the best fit for the criteria established.
For further information on developing a decision-making framework, refer to Chapter 5 of this document.
This stage of the project and the alternatives analysis depends on the results of the impact analysis and the decision-making criteria stage. The alternatives analysis indicates the types of impacts to expect from the recommended alternative or combination of strategies. The impact mitigation stage identifies the potential mitigation strategies that can aid in further reducing the impacts. Further analysis may be conducted to determine which combination of mitigation strategies may prove to be most efficient and cost-effective. Types of mitigation strategies can include public information, traffic control devices, travel demand management, and traffic operations measures.
Monitoring and Post-Implementation
The monitoring and post-implementation efforts include monitoring the performance of the work zone and the effectiveness of the recommended alternatives and/or mitigation strategies during the duration of the construction period and after. Developing a monitoring plan can serve as a way to determine the effectiveness of the work zone traffic analysis and the alternatives analysis process by determining impacts and mitigating mobility and safety issues. The results of the monitoring efforts and post-implementation analyses also can serve as feedback to improve the agency’s current analyses and decision-making methodologies.
PDF files can be viewed with the Acrobat® Reader®.