Office of Operations
21st Century Operations Using 21st Century Technologies

Efficient Use of Highway Capacity Summary
Report to Congress

Executive Summary

Chapter 1: Background

This report was developed to summarize the implementation of safety shoulders as travel lanes as a method to increase the efficient use of 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 transportation 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 in the 2008 Technical Corrections Act. The issues that need to be considered include design, traffic control devices, performance measures, potential safety benefits, maintenance concerns, enforcement roles and processes, incident response, training for personnel, costs, liability and legal issues, and public outreach and education. Careful consideration of these issues can help ensure a shoulder use deployment is effective without having negative impacts on safety and operations.

Document Overview

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.

Chapter 2: Context and Findings

The report documents usage of shoulders as travel lanes in both the United States and three European countries.

Shoulder Lanes—The American Experience

In the United States, the primary use of shoulders has been as a safety refuge area. The limited shoulder use as a travel lane has been primarily reserved for special users of the roadway system, most often transit vehicles. Some shoulder use dates back to the 1970s, and many installations have been in operation for more than 10 years to address congestion on urban corridors. Agencies have seen bus use of shoulders as a low-cost and quick strategy to improve bus operations and reliability without having to acquire additional right-of-way and invest additional large sums of money into the infrastructure. The length of these deployments varies depending on location, ranging from a more than 290-mile comprehensive network in the Minneapolis-St. Paul metropolitan area to deployments less than 1 mile in length used to serve as a queue jump for transit in Delaware. The operational strategies often depend on the congestion on the general purpose lanes and often require speed restrictions of the transit vehicles using the shoulders. Overall, experience using shoulders for interim use has been positive in the United States, and more agencies are considering the strategy to address growing congestion on their urban freeway networks. In fact, several States have deployed temporary shoulder use for all vehicles on congested corridors with success. Another application that is much more difficult to research and document is the number of locations where an existing shoulder has been narrowed or taken away to allow for widening with an extra permanent travel lane. This method is more commonly used in roadway work zones to maintain the existing number of travel lanes during construction. However, it has been applied in some permanent forms as well. In the United States, usage can be broken out into the following categories:

  • Bus-only use on shoulders
  • Converted shoulders used as permanent lanes
  • Temporary use of shoulders for either general purpose traffic or managed lanes
  • Emergency (Hurricane) Evacuation Routes

Shoulder Use—The European Experience

In Europe, part-time shoulder use is a congestion management strategy typically deployed in conjunction with complementary traffic management strategies – such as variable speed limits (speed harmonization) and/or ramp metering – to address capacity bottlenecks on the freeway network. European implementers include The Netherlands, Germany, and Great Britain. The strategy provides additional vehicle-moving capacity during times of congestion and reduced travel speeds. The use of the exterior shoulder during peak travel periods has been used in Germany since the 1990s. When travel speeds are reduced, dynamic signs over or next to the shoulder indicate that travel on the shoulder is permitted.

A complete series of traffic signs indicate operations related to temporary shoulder use, including one with a supplemental speed limit indication (used when overhead gantries are not present).

These signs and the overhead lane messages are blank when travel on the shoulder is not permitted. Temporary shoulder use is permitted only when speed harmonization is active and speed limits are reduced, thus providing an operating environment only when speeds are managed below posted levels.

Generally, implementation of temporary shoulder use is at the discretion of the traffic management center operator, although traffic volumes help determine the need for the strategy. A typical installation in Europe incorporates a number of unique roadway features, which can include:

  • Lightweight gantries.
  • Lane control signals.
  • Dynamic speed limit signals.
  • Dynamic message signs.
  • Automated enforcement technology.
  • Closed-circuit television cameras.
  • Enhanced lighting.
  • Roadway sensors.
  • Emergency roadside telephones.
  • Advanced incident detection.
  • Intensified incident management.
  • Emergency refuge areas or pull-outs beyond the shoulder.

Operation of the system is handled by the regional control center, with operators on hand to monitor the system and initiate the modified operations as necessary. Specifically, operators use closed-circuit television cameras (CCTVs) mounted on lightweight sign gantries or separately to check for incidents and stalled vehicles in the shoulder before activating the system.

Chapter 3: Critical Issues

The primary concern related to shoulder use involves its impact on operations and safety. The purpose of this project was to assess the deployments of shoulder use in the United States and determine the impacts on, the experience with, and the addressing of the following safety issues:

  • Conflicts at access ramps.
  • Sight distance.
  • Conflicts with motorists pulling onto the shoulder for emergency purposes.
  • Loss of use of the shoulder for emergency refuge.
  • Need for bus driver training.
  • Speed differential between the general purpose lanes and the shoulder.
  • Effect on general purpose lane users.
  • Return merge distance adequacy.
  • Debris hazards on shoulder.
  • Reduced bridge clearance.
  • Drainage.
  • Operational efficiency.
  • Crash experience.

By providing a summary of this information and data related to shoulder use experience, it is expected that the project can assist FHWA with developing guidance on the subject and identifying what, if any, research needs to be conducted to address unknowns related to the operational strategy and its potential long-term and widespread use in the United States.

Agencies need to consider a wide range of issues when determining whether shoulder use is appropriate for a particular corridor or region. Experience both overseas and domestically provides a wealth of experience from which agencies can learn to make informed decisions. From the European perspective, part-time shoulder use is only used during congested periods when queues begin to build at bottlenecks in the system. Moreover, this treatment is almost always deployed in conjunction with speed harmonization. The intent is to reduce the speeds along the corridor and smooth out driver performance and reduce the likelihood of collisions. (1) Furthermore, European agencies have realized both safety and mobility benefits as a result of these projects. While American deployments have been limited, the experience has generally been positive. However, safety benefits have not been conclusive. The issues that need to be considered include design, traffic control devices, performance measures, potential safety benefits, maintenance concerns, enforcement roles and processes, incident response, training for personnel, costs, liability and legal issues, and public outreach and education. Careful consideration of these issues can help ensure a shoulder use deployment is effective without having negative impacts on safety and operations.

Another area needing further analysis is the topic of left shoulder use versus right shoulder use. Domestically, almost all applications of part-time shoulder use have occurred on the right side, while shoulder conversions to permanent lanes have tended to be more prominent on the left side. Each application has a different subset of design and operational considerations to analyze.

Chapter 4: Case Studies

Detailed Case Study reviews were made of the following locations:

  • The Netherlands
  • Germany
  • Great Britain
  • Virginia
  • Minnesota
  • Massachusetts
  • Washington

Chapter 5: Final Remarks

This report was developed to summarize the implementation of safety shoulders as travel lanes as a method to increase the efficient use of 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 shoulder usage on highway safety and/or accidents during operations was reviewed as well. The report provides critical information that the 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 in the 2008 Technical Corrections Act.

Agencies need to consider a wide range of issues when determining whether shoulder use is appropriate for a particular corridor or region. Experience both overseas and domestically provides a wealth of experience from which agencies can learn to make informed decisions. From the European perspective, temporary shoulder use is only used during congested periods when queues begin to build at bottlenecks in the system. Moreover, this treatment is almost always deployed in conjunction with dynamic lane control signing and speed harmonization. Furthermore, European agencies have realized both safety and mobility benefits as a result of these projects. While American deployments have been limited, experience has been positive, though safety benefits have not been conclusive. The issues that need to be considered include design—such as the treatment at interchanges and auxiliary lanes, drainage, emergency refuge areas, rumble strips, and Intelligent Transportation Systems (ITS) components; traffic control devices; and operational and safety performance measures. In addition, maintenance concerns, enforcement roles and responsibilities, incident response procedures, personnel training, costs, liability and legal issues, and public outreach and education are issues that should be examined. Careful consideration of these issues can help ensure that a shoulder use deployment is effective without having negative impacts on safety and operations.

The following results can be taken away from this summary:

  • The use of buses on shoulders has generally significantly benefited transit trip time reliability in those corridors where it has been implemented.
  • There have been shoulder use projects that have shown bottleneck relief at spot locations.
  • Incident data provided from the U.S. seems to be inconclusive at this point. There are safety benefits provided from the European applications. However, the shoulder use is only a part of a much larger investment in ATM technology and resources to manage them.
  • There have been longer incident clearance times in areas that don't have shoulders available to move incidents off the highway. Also, responders don't have the benefit of traveling the shoulder to reach the incident scene.
  • European usage of hard shoulder running has always been accompanied by additional ATM strategies such as dynamic lane control signals and variable speed limits. These additional support strategies have generally been lacking in U.S. applications.

As a result of the information gained from this study, consideration should be given to the following:

  • The FHWA should consider developing clearer agency guidance on the use of shoulders. This would need to be a joint effort from the Offices of Infrastructure (Design), Safety, and Operations (including how the Manual on Uniform Traffic Control Devices (MUTCD) relates to shoulder use lanes). The lack of existing U.S. performance data would also point to the need for more research in this area.
  • Hard shoulder running was one of the ATM strategies recommended for implementation in the U.S. from a recent international scan. As FHWA and American Association of State Highway and Transportation (AASHTO) develop guidance on ATM, they should clarify guidance on temporary shoulder usage. This would include comparing the differences in current U.S. usage to that of the European countries.
  • Research and modeling for temporary shoulder use is lacking at this time. This could be covered in research being developed for the ATM program.
  • The results of the NCHRP/AASHTO/FHWA Domestic Scan on Maximizing Flow on Existing Highway Facilities should be considered in the development of shoulder use guidance

(1) Mirshahi, M., et al. Active Traffic Management: The Next Step in Congestion Management. Alexandria, VA: American Trade Initiatives, 2007. FHWA-PL-07-012. Return to footnote 1.

Office of Operations