Efficient Use of Highway Capacity Summary
Report to Congress
Chapter 1: Background
This report was developed to summarize the implementation of safety shoulders as travel lanes as a method to more effectively use existing highway capacity. Its purpose is to provide a succinct overview of efforts to use left or right shoulder lanes as temporary or interim travel lanes. As part of this summary, information related to the impact of that shoulder usage on highway safety and/or accidents during operations was reviewed as well. The intent of the report is to provide critical information that the Federal Highway Administration (FHWA) can use to formulate guidance for agencies on providing temporary shoulder use as a means of increasing roadway capacity. The study that resulted in this report was conducted at the request of Congress through the 2008 Technical Corrections Act.
This document is divided into five chapters that discuss in detail the results of the study and the critical issues and findings related to the use of shoulders for increasing capacity during congested travel periods. The titles of each chapter and major topics covered are highlighted below.
- Chapter One - Background: Provides an overview of the document including its scope and purpose, intended audiences and uses, and background information on the roles that planning and project development play in the decision to use a shoulder as a travel way to increase capacity and enhance mobility.
- Chapter Two - Context and Findings: Discusses the concept of shoulder use within the context of active traffic management (ATM) and summarizes the domestic and foreign experience with this operational strategy and those that are complementary to its deployment.
- Chapter Three - Critical Issues: Gives a brief overview of the critical issues that need to be addressed when considering the use of shoulders for temporary capacity increase on congested freeways.
- Chapter Four - Case Studies: Provides case studies of European and domestic applications of shoulder use.
- Chapter Five - Final Remarks: Includes final remarks related to the document and its use and provides a complete list of references used in the development of this document.
The intended audience for this report is transportation professionals and agencies at the State, regional, and local levels involved in transportation planning, project development, and operations who may be considering the temporary use of a highway shoulder to increase capacity on a congested facility, be it for special users or general purpose traffic. It is anticipated that the information provided in this document will offer valuable insight for professionals and ensure that they carefully consider all aspects of shoulder use from the planning, design, operational, and safety perspectives prior to implementation. Moreover, agencies might factor potential shoulder use into the planning process as a potential operational strategy where capacity increases are limited. The report will also lay the groundwork for supporting project development efforts once the planning process is complete.
As modified and enhanced by the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), the modern transportation planning process works to improve the transportation system and investment decision making associated with transportation projects. (2) Based on the paradigm shift from construction to system preservation, ISTEA identified critical issues related to transportation planning, including but not limited to:
- Linking transportation to the economic, mobility, and accessibility needs of the country.
- Emphasizing the participation of key stakeholders in the transportation planning process.
- Recognizing the constraints limiting expansion.
- Protecting the human and natural environments while providing accessibility to transportation services.
- Linking transportation planning to the air quality objectives in the Clean Air Act amendments and State air quality plans. (3)
The transportation plan (also known as the long-range transportation plan, metropolitan transportation plan, regional transportation plan, etc.) is a statement of the way in which the region plans to invest in the transportation system. (4) This 20-year document, which must be updated on a periodic basis (typically every 5 years, but every 3 years for nonattainment and maintenance areas), sets the stage for transportation investment in the region by mapping general strategies for improving the safe and efficient movement of people and goods throughout the area. Operational strategies, which might include temporary use of shoulders during peak periods or measures such as managed lanes, can be part of this plan.
The transportation improvement program (TIP) is a short-range document related to the transportation plan. Covering a minimum 3-year period of investment, this fiscally constrained document identifies the immediate high-priority projects and strategies as outlined in the transportation plan and advances them for implementation. (4) In short, the Metropolitan Planning Organization (MPO) takes those projects in the transportation plan and lays out which of them can realistically be undertaken with the limited resources available over the next several years. The TIP is incorporated into the statewide transportation improvement program (STIP) and must conform to the state implementation plan (SIP) for improving air quality for projects to move forward to implementation.
The elements of the metropolitan transportation planning process include public involvement, planning factors, management systems input, major investment studies (MIS), the air quality conformity process, and the financial plan. Ways in which temporary shoulder use for capacity increases and other operational strategies may impact these elements are as follows:
- Public involvement when planning operational improvements helps ensure that all of the social, economic, and environmental consequences of investment decisions are considered and that the MPO has the broad support of the community.
- The goals and objectives of various operational strategies easily fit within the general planning factors in the transportation planning process.
- Congestion management systems might consider shoulder operational strategies, whose goals and objectives work in concert with the system, to maximize the efficiency potential for the transportation network.
- Incorporating shoulder use operational strategies as potential solutions in the major investment study can help address the factors influencing project solutions while efficiently and effectively meeting the needs of the community.
- Shoulder use strategies that involve pricing may present transportation agencies with an opportunity to capitalize on innovative techniques to balance financing with regional goals.
Figures 1 and 2 outline the basic steps in the general planning process and the Transportation Improvement Plan process. These figures indicate where the critical consideration of operational strategies such as temporary shoulder use fits into the process. Regional planning and corridor- and facility-level planning through the MIS process are all part of developing the 20-year regional transportation plan. Once projects get placed on the TIP and the STIP, they move to implementation. It is important to note that the MPO, FHWA, and the Federal Transit Administration (FTA) check for conformity with the SIP at the plan, TIP, and project levels. Once again, public involvement throughout the entire planning process cannot be overlooked. It helps an MPO develop a comprehensive plan for transportation improvements that is responsive to the community and its needs.
Incorporating shoulder use for capacity increases into the planning process requires agencies to consider various planning-related issues from a slightly different perspective. While all of the planning considerations listed below are general transportation factors that can apply to virtually any mode, they are listed here within the shoulder use context. Throughout the entire planning process, the MPO should consider these issues when assessing shoulder use strategies as potential solutions to the region's transportation needs and when formulating the plan and TIP. The typical shoulder use planning considerations include but are not limited to the following:
- Geometric design and cross-section.
- Decision making needs and traffic-control devices.
- Environmental justice.
- Evaluation and monitoring.
- Funding and financing.
- Incident management.
- Interoperability and technology components.
- Public outreach and education.
- Legal and institutional challenges.
- Operational flexibility.
- Pricing as an option.
In many areas temporary use of shoulders has been implemented as a low-cost interim solution. Whereas the ultimate plan is a much more costly widening project or reconstruction, given the need to develop transportation plans that are fiscally constrained, there might be more opportunities for operational-based, lower-cost projects in the near term.
One area that is lacking is historical data for use in traditional planning models. To that extent, additional modeling and research efforts are needed to fill this gap in data.
During project design, agencies must engage in even more detailed planning and design to ensure that all aspects of shoulder use operational strategies are considered and assessed for a particular facility. Design standards dictate project design. By their very nature, temporary shoulder usage projects run contrary to most design standards for highways since they have a requirement for shoulders. Therefore, almost any project proposing to use the shoulder as a travel lane is going to involve a design exception. These design exceptions will need to be analyzed on a case-by-case basis with particular emphasis given to the safety elements of the roadway. This will involve geometric design elements of the roadway, traffic volumes and congestion, and crash history. Careful consideration of these issues at the facility level can help ensure that the shoulder use operational strategy is effective in meeting the goals and objectives for the corridor, enhance operational flexibility, and optimize use over the life of the project. These parameters include but are not limited to the following:
- Design vehicle.
- Design speed.
- Access control, design, and spacing.
- Signing and pavement markings.
- Driver information.
- Acceleration and deceleration distance.
- Vertical clearance.
- Lateral clearance.
- Toll collection.
- Incident management.
- Design flexibility for future needs.
The careful consideration of the parameters shown above are important factors when planning a facility and should be considered in project's development.
After identifying and assessing the design parameters and additional shoulder use considerations for a facility, the MPO and stakeholder groups need to assess the specific operating strategy(ies) for a facility. The factors to consider in this assessment include but are not limited to the pricing approach, time period variations and their impact on hours of operation, enforcement issues, incident management, evaluation and monitoring, marketing, and operations during construction. After careful assessment of all of these issues, the agencies can identify the most appropriate strategy or combination of strategies for a facility.
This document summarizes the implementation of safety shoulders as travel lanes as a method to increase the performance of the existing highway's capacity. Its purpose is to provide a succinct overview of efforts to use left or right shoulder lanes as temporary or interim travel lanes.
This chapter presents an introduction to the report, outlines the basic steps of the general planning process and where the critical consideration of shoulder use operational strategies fits into that process, and discusses design considerations. The reader should also have an appreciation of the shoulder use planning considerations that should be specifically addressed at the regional, corridor, or facility level in the process. Additionally, this chapter discusses the project development process as impacted by the consideration of shoulder use operational strategies. It presents the general steps in this process and offers insight into how an agency might incorporate shoulder use operational strategies to best meet the needs of the community at the corridor and facility levels. The reader should understand the importance of public and agency input, project identification and shoulder use assessment and project design.
(2) Research and Innovative Technology Administration. Intermodal Surface Transportation Efficiency Act of 1991. [Online] Federal Highway Administration, 1991. http://ntl.bts.gov/DOCS/istea.html. Return to footnote 2.
(3) Federal Highway Administration/Federal Transit Administration. A Guide to Metropolitan Transportation Planning Under ISTEA: How the Pieces Fit Together. Washington, D.C.: U.S. Department of Transportation, 1995. FHWA-PD-95-031. Return to footnote 3.
(4) Transportation Planning Capacity Building Program. The Metropolitan Transportation Planning Process: Key Issues. Washington, D.C.: Federal Highway Administration/Federal Transit Administration, 2004. FHWA-EP-03-041. Return to footnote 4.