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Use of Narrow Lanes and Narrow Shoulders on Freeways: A Primer on Experiences, Current Practice, and Implementation Considerations

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United States Department of Transportation Federal Highway Administration

U.S. Department of Transportation
Federal Highway Administration
Office of Operations
1200 New Jersey Avenue, SE
Washington, DC 20590


August 2016


This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

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The Federal Highway Adminstration (FHWA) Office of Operations is pleased to present this publication titled "Use of Narrow Lanes and Narrow Shoulders on Freeways: A Primer on Experiences, Current Practice, and Implementation Considerations" (Narrow Lanes Primer).

Freeways in major urban areas are increasingly challenging due to physical and fiscal constraints. Performance-Based Practical Design (PBPD) solutions — linked with Operations strategies — offer a means of reducing freeway congestion in a manner that is achievable in today's resource constrained environment. PBPD modifies the traditional "top down, standards first" approach to a "design up" approach where engineering judgement is used to build up a roadway from existing conditions to a state where project and system objectives can be cost-effectively achieved.

In urban settings where those physical or fiscal constraints prevent adding full-width lanes with full shoulders, applying PBPD approaches to provide additional capacity by adding lanes that are slightly narrower than standard or reducing shoulders below width are sometimes viable options. The slight reduction in efficiency from narrower individual lanes or shoulders can be more than offset by the capacity gain of an additional lane. Operations strategies — including enhanced incident management and Active Traffic Management (ATM) strategies such as dynamic speed limits, dynamic lane assignment, and traveler information — can be coupled with the narrow lane and shoulder treatments to further improve operational and safety performance.

Early applications of narrow lanes and narrow shoulders in the 1970s and 1980s typically added general purpose lanes. More recent applications of narrow lanes and narrow shoulder use have enabled the implementations of managed lanes or part-time shoulder use within the existing footprint of a freeway. Some applications have also narrowed lanes or shoulders for short distances to eliminate bottlenecks.

The primer includes case studies of narrow lanes and narrow shoulders and provides insights on opertional, safety, and travel time reliability effects of implementing narrow lanes and narrow shoulders. This is one of two primers developed to highlight the linkage between PBPD and Transportation Systems Management and Operations (TSMO). The other primer focuses on Complete Streets. The FHWA Office of Operations is supporting these Primers through related technical assistance. If you have any comments on this material or seek further assistance, please contact Jim Hunt or Greg Jones from the FHWA Office of Operations.

Robert Arnold
Director Office of Transportation Management
Office of Operations, FHWA

Technical Documentation Page

1. Report No.

Publication #: FHWA-HOP-16-060

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Use of Narrow Lanes and Narrow Shoulders on Freeways: A Primer on Experiences, Current Practice, and Implementation Considerations

5. Report Date

July 2016

6. Performing Organization Code

7. Author(s)

Neudorff, L. (CH2M), Jenior, P., Dowling, R., Nevers, B. (Kittelson & Associates, Inc.)

8. Performing Organization Report No.


9. Performing Organization Name and Address

901 New York Ave NW
Washington, DC 20001

Under contract to:
Kittelson & Associates, Inc.
300 M Street SE, Suite 810
Washington, DC 20001

10. Work Unit No. (TRAIS)

11. Contract or Grant No.


12. Sponsoring Agency Name and Address

United States Department of Transportation
Federal Highway Administration (FHWA) Office of Operations
1200 New Jersey Avenue, SE
Washington, DC 20590

13. Type of Report and Period Covered

Technical Report
Informational Report
Sept 2014 to May 2016

14. Sponsoring Agency Code


15. Supplementary Notes

Jim Hunt ( served as the Technical Manager for FHWA

16. Abstract

Congested freeways are often located in urban areas with constrained environments and/or rights-of-way where significant widening of the roadway is not practical due to adjacent developments and land use, physical constraints, along with limited availability of funding. Among the strategies for increasing freeway capacity in such constrained environments — and thereby reducing congestion and improving operations — is to add a travel lane within the existing roadway footprint by reducing the widths of the existing lanes and/or shoulders. The additional lane may be utilized by all traffic at all times, as a special use or managed lane that is open only to specific types of vehicles or movements (e.g., High Occupancy Toll (HOT) lane, exit only lane), or only during selected times of the day and/or when congestion warrants opening the lane (e.g., temporary shoulder use). Narrow lanes and shoulders may be applied to add capacity on the freeway mainline and in interchange areas including ramps.

This primer provides information to policy makers, transportation agency managers, designers and operators on the use of narrow lanes and narrow shoulders to improve capacity within an existing roadway footprint. Much of the information contained in the primer is presented in the broader context of both Performance Based Planning and Programming (PBPP) and Performance — Based Practical Design (PBPD). Primer contents include case studies on the use of narrow lanes, issues and approaches for analyzing the operational and safety impacts of narrow lanes and narrow shoulders, and the role of transportation systems management and operations (TSMO) in support of narrow lanes operations.

17. Key Words

Performance-Based Practical Design, Lane Width, Freeway Design, Shoulder Width

18. Distribution Statement

No restrictions.

19. Security Classification (of this report)


20. Security Classification (of this page)


21. No of Pages


22. Price

Form DOT F 1700.7 (8-72)
Reproduction of completed page authorized.

Table of Contents

[ List of Acronyms and Symbols ]

[ SI Conversion Factors ]

List of Figures

List of Tables

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