Cover photograph sources (top to bottom): Minnesota Department of Transportation; Kittelson & 

Associates, Inc.; Georgia Department of Transportation; Federal Highway Administration; 

Kittelson & Associates, Inc. 

Notice 

This document is disseminated under the sponsorship of the U.S. Department of 

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The U.S. Government does not endorse products or manufacturers. Trademarks or 

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Quality Assurance Statement 

The Federal Highway Administration (FHWA) provides high-quality information to serve 

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i

Technical Report Document Page 

1. Report No. 

FHWA-HOP-15-023 

2. Government Accession No. 3. Recipient’s Catalog No. 

4. Title and Subtitle 

Use of Freeway Shoulders for Travel – Guide for Planning, 

Evaluating, and Designing Part-Time Shoulder Use as a Traffic 

Management Strategy 

5. Report Date 

January 2016 

6. Performing Organization Code 

7. Author(s) 

Jenior, P., Dowling, R., Nevers, B. (Kittelson & Associates, Inc.); 

Neudorff, L. (CH2M) 

8. Performing Organization Report No. 

18112 

9. Performing Organization Name And Address 

Kittelson & Associates Inc. 

300 M Street SE, Suite 810 

Washington, DC 20001 

10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

DTFH61-12-D-00049/5001 

12. Sponsoring Agency Name and Address 

U.S. 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 Jan 2016

14. Sponsoring Agency Code 

FHWA 

15. Supplementary Notes 

Jim Hunt (jim.hunt@dot.gov) served as the Government Task Manager

16. Abstract 

Part-time shoulder use is the conversion of shoulders to travel lanes during some hours of day as a 

congestion relief strategy. This strategy is also known as temporary shoulder use or hard shoulder running, 

and is typically implemented on freeways. Part-time shoulder use is a transportation system management 

and operations (TSM&O) strategy that uses shoulders to provide additional capacity when it is most needed, 

and preserves shoulders as refuge areas during the majority of the day. This guide covers planning, design, 

implementation, and day-to-day operation of shoulder use. It covers a wide variety of design and operational 

concepts for shoulder use, and describes how a performance based practical design (PBPD) process guides 

the planning of facilities with shoulder use. 

17. Key Words 

Shoulder Use, Hard Shoulder Running, 

Shoulder Lanes, Active Traffic Management, 

Performance-Based Practical Design 

18. Distribution Statement 

No restrictions. 

19. Security Classif. (of this report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified 

21. No. of Pages 

170 

22. Price 

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

CONVERSION FACTORS 
Table of Contents

i

TABLE OF CONTENTS 

INTRODUCTION..... ..................................................................................................................... 1

Purpose, Scope, and Target Audience ..................................................................................... 1 

Organization of Guide ............................................................................................................... 2 

CHAPTER 1. WHAT IS PART-TIME SHOULDER USE? ............................................................ 3

Shoulders and Shoulder Usage ................................................................................................ 4

Different Part-time Shoulder Use Concepts .............................................................................. 5 

Part-time Shoulder Use Guidance ............................................................................................ 6 

Examples of Part-time Shoulder Uses .................................................................................... 18 

CHAPTER 2. PLANNING, SCREENING, DECISION MAKING, AND PRELIMINARY 

ENGINEERING........... .............................................................................................................. 27

Part-time Shoulder Use Consideration in The Planning Process............................................ 27 

Planning for Operations .......................................................................................................... 30 

Environmental Decisionmaking Process ................................................................................. 30 

Preliminary Engineering .......................................................................................................... 34 

Performance Based Practical Design (PBPD) ........................................................................ 37 

PBPD and Objectives-Driven Decision-making ...................................................................... 39 

Determining Performance Objectives and Constraints ........................................................... 39 

TSM&O Strategies That Can Support Part-time Shoulder Use .............................................. 40 

CHAPTER 3. MOBILITY ANALYSIS ......................................................................................... 43

Shoulder Capacity ................................................................................................................... 43 

System Analysis.. .................................................................................................................... 45 

Operations Analysis ................................................................................................................ 46 

Reliability Analysis .................................................................................................................. 47 

Before/After Studies ................................................................................................................ 48 

CHAPTER 4. SAFETY ANALYSIS ............................................................................................ 49

Assessing Part-time Shoulder Use Safety .............................................................................. 49 

Observational Safety Studies .................................................................................................. 50 

Crash Prediction........... ......................................................................................................... 52 

Conclusions........ ................................................................................................................... 60 

CHAPTER 5. ENVIRONMENTAL ANALYSIS ........................................................................... 63

Air Quality Analysis ................................................................................................................. 63 

Greenhouse Gas Emissions Analysis ..................................................................................... 65 

Noise Analysis...... ................................................................................................................. 66 

CHAPTER 6. COSTS AND BENEFITS ANALYSIS .................................................................. 69

Life-Cycle Costs...................................................................................................69 

Monetizing Benefits ................................................................................................................. 73 

Conducting a Benefit/Cost Analysis ........................................................................................ 74 

Selecting the Optimum Project(s) ........................................................................................... 77
Table of Contents

ii

CHAPTER 7. DESIGN CONSIDERATIONS .............................................................................. 79

Geometric Design ................................................................................................................... 79 

Pavement Design .................................................................................................................... 94 

Drainage Design............ ....................................................................................................... 95 

Traffic Control Device Design ................................................................................................. 96 

ITS Design................. ........................................................................................................ 101 

CHAPTER 8. IMPLEMENTATION PROCESS ......................................................................... 107

Design Exception Process .................................................................................................... 107 

Legal Issues....... .................................................................................................................. 108 

MUTCD Experimental Approval Process .............................................................................. 109 

Stakeholder Engagement ..................................................................................................... 110 

Public Involvement ................................................................................................................ 112 

CHAPTER 9. DAY-TO-DAY OPERATION ............................................................................... 115

Maintenance......... ............................................................................................................... 115 

Incident Management ........................................................................................................... 115 

Law Enforcement. ................................................................................................................. 116 

Opening and Closing Part-time Shoulder Use Facilities ....................................................... 117 

APPENDIX A – CASE STUDIES OF SUCCESSFUL APPLICATIONS IN THE UNITED 

STATES............... .................................................................................................................. 119

Minneapolis-St. Paul, Minnesota – Bus on Shoulder ............................................................ 125 

Fairfax County, Virginia ......................................................................................................... 125 

Alpharetta, Georgia ............................................................................................................... 126 

San Diego, California ............................................................................................................ 126 

Middlesex County, New Jersey ............................................................................................. 127 

Seattle, Washington .............................................................................................................. 128 

Miami, Florida...... ................................................................................................................ 128 

Minneapolis, Minnesota – Dynamic Shoulder Lane .............................................................. 128 

Idaho Springs, Colorado ....................................................................................................... 130 

Boston, Massachusetts ......................................................................................................... 130 

APPENDIX B – SIGNING AND PAVEMENT MARKING EXAMPLES .................................... 133

Bus on Shoulder....... ........................................................................................................... 133 

Static Part-time Shoulder Use ............................................................................................... 139 

REFERENCES...... .................................................................................................................. 153

 
List of Figures

iii

LIST OF FIGURES 

Figure 1. Map. Part-time shoulder use locations in US, 2015. ..................................................... 19

Figure 2. Photo. Bus-on-shoulder operations in Minneapolis-St. Paul......................................... 20

Figure 3. Photo. Bus-on-shoulder operations on the left-shoulder in Chicago. ............................ 21

Figure 4. Photo. Static Bus-on-shoulder message sign on US 9 arterial in Old Bridge, New 

Jersey........................................................................................................................... 21

Figure 5. Photo. Previous Static Part-time shoulder use on I-66 in Northern Virginia ................ 22

Figure 6. Photo. Static part-time shoulder use on New Jersey Turnpike Newark Bay Extension 

with variable speed limit and changeable message sign. ............................................ 23

Figure 7. Photo. Part-time shoulder use in Germany. ................................................................... 23

Figure 8. Photo. High-occupancy-toll part-time shoulder use in Minneapolis-St. Paul. .............. 24

Figure 9. Illustration. National Environmental Policy Act Processing Options (Classes of 

Actions). ...................................................................................................................... 31

Figure 10. Illustration. Part-time shoulder use screening decision tree. ....................................... 35

Figure 11. Equation. Average Travel Time Rate .......................................................................... 47

Figure 12. Equation. Recurring Delay Rate. ................................................................................. 47

Figure 13. Equation. Incident Delay Rate. .................................................................................... 47

Figure 14. Equation. 95th-Percentile Travel Time Index. ............................................................. 48

Figure 15. Equation. Percent of Trips that Occur at Speeds Less than 45 mph. ........................... 48

Figure 16. Graph. Predicted crash frequency associated with increasing number of freeway lanes 

and narrowing the right shoulder. ............................................................................... 54

Figure 17. Graph. Predicted crash frequency on eight- and ten-lane freeways relative to Annual 

Average Daily Traffic, no change in shoulder width. ................................................. 55

Figure 18. Graph. Predicted crash frequency relative to Annual Average Daily Traffic and 

Number of Freeway Lanes, no change in shoulder width. ......................................... 55

Figure 19. Graph. Predicted crash frequency on eight-lane freeways with 14- and 4-foot right 

shoulder width relative to Annual Average Daily Traffic. ......................................... 56

Figure 20. Graph. Predicted crash frequency with and without narrow lanes and narrow 

shoulders on 4-lane freeways. ..................................................................................... 58

Figure 21. Graph. Predicted crash frequency with and without narrow lanes and narrow 

shoulders on 6-lane freeways. ..................................................................................... 58

Figure 22. Graph. Predicted crash frequency with and without narrow lanes and narrow 

shoulders on 8-lane freeways. ..................................................................................... 59

Figure 23. Graph. Predicted percent change in crash frequency when adding part-time shoulder 

use by narrowing all lanes........................................................................................... 60

Figure 24. Illustration. Typical part-time shoulder use add. ......................................................... 80

Figure 25. Illustration. Typical part-time shoulder use drop. ....................................................... 81

Figure 26: Illustration. Part-time shoulder use approaching major fork. ...................................... 82

Figure 27. Illustration. Path of parallel-style on-ramp traffic with part-time shoulder use. ......... 88

Figure 28. Illustration. Path of parallel-style off-ramp traffic with part-time shoulder use. ........ 89

Figure 29. Illustration. Parallel-style ramp with large convergence angle. Shoulder lane shaded.

..................................................................................................................................... 89
List of Figures

iv

Figure 30. Illustration. Parallel-style ramp with small convergence angle. Shoulder lane shaded.

..................................................................................................................................... 90

Figure 31. Illustration. Conflict between ramp and shoulder traffic with taper-style ramp. 

Shoulder lane shaded. ................................................................................................. 90

Figure 32. Illustration. Conversion of taper-style ramp to parallel-style ramp to remove conflict 

between ramp and shoulder traffic. Shoulder lane shaded. ........................................ 91

Figure 33. Illustration. Creation of inside merge with parallel-style two-lane on-ramp. Shoulder 

lane shaded. ................................................................................................................. 91

Figure 34. Illustration. Conflict between ramp and shoulder traffic with two-lane taper-style 

ramp with inside merge. Shoulder lane shaded. ......................................................... 92

Figure 35. Photo. Emergency Turnout, UK. ................................................................................. 93

Figure 36. Photo. Emergency Turnout, Georgia. .......................................................................... 93

Figure 37. Photo. MnDOT, regulatory sign for Bus-on-shoulder operation. ............................... 97

Figure 38. Photo and Illustration. Example of full gantry ATM deployment in Washington State 

(no part-time shoulder use). ...................................................................................... 104

Figure 39. Example Dynamic Part-time Shoulder Use Public Information Material ................. 113

Figure 40. Bus-on-shoulder sign placement, Minnesota. ........................................................... 133

Figure 41. Photo. FDOT regulatory sign for Bus-on-shoulder operation. .................................. 134

Figure 42. Photo. MnDOT on-ramp Bus-on-shoulder warning sign, right side of photo. .......... 134

Figure 43. Photo. Maryland SHA sign to manage right-turn lane conflict. ................................ 135

Figure 44. Photo. Caltrans word pavement markings for BOS operation. ................................. 135

Figure 45. Photo. NJDOT word pavement markings for BOS operation. .................................. 136

Figure 46. Photo. SR 522 arterial Bus-on-shoulder pavement markings, Washington state. ..... 136

Figure 47. Photo Illustration. US 9 arterial Bus-on-shoulder pavement markings, New Jersey. 138

Figure 48. Photo. Sign at start of part-time shoulder use segment, GA 400. ............................. 139

Figure 49. Photo. Warning sign along part-time shoulder use segment, GA 400. ..................... 140

Figure 50. Photo. Regulatory sign on on-ramp, GA 400 ............................................................ 140

Figure 51. Photo. Regulatory sign, I-H-1 mainline. .................................................................. 141

Figure 52. Photo. Regulatory sign, I-H-1 on-ramp. .................................................................... 141

Figure 53. Photo. Regulatory sign, I-H-1 off-ramp. ................................................................... 141

Figure 54. Photo. Updated regulatory sign, I-95 breakdown lanes. ........................................... 142

Figure 55. Illustration. Dynamic part-time shoulder use sign detail, I-95 breakdown lanes. ..... 143

Figure 56. Photo. Dynamic sign signifying the shoulder is closed to traffic, I-95 breakdown 

lanes. ......................................................................................................................... 143

Figure 57. Photo. Dynamic sign signifying the shoulder is open for use, I-95 breakdown lanes.

................................................................................................................................... 144

Figure 58. Photo. Regulatory sign, SR 29 mainline. .................................................................. 144

Figure 59. Photo. Mast Arm Dynamic Lane Control Sign, New Jersey Turnpike Newark Bay 

Extension................................................................................................................... 145

Figure 60. Photo. Dynamic Lane Control Sign on Gantry, New Jersey Turnpike Newark Bay 

Extension................................................................................................................... 145

Figure 61. Photo. Combination of static and dynamic signage, I-66 mainline. .......................... 146

Figure 62. Photo. Notice informing motorists of the lack of right shoulder during shoulder 

running operations, I-66 mainline. ............................................................................ 147
List of Figures

v

Figure 63. Photo. Static signage denoting permitted use of shoulder to exit during nonoperational hours of shoulder use, I-66 mainline...................................................... 147

Figure 64. Photo. Overhead regulatory sign, US 2. .................................................................... 148

Figure 65. Photo. Turnout sign sequence, I-66. .......................................................................... 149

Figure 66. Photo. Edge lines and “shldr lane” work markings on a part-time shoulder use section 

of I-H-1. .................................................................................................................... 149

Figure 67. Photo. Edge line markings at the start of part-time shoulder use segment, US 2. .... 150

Figure 68. Illustration. On- and off-ramp striping plans, I-93. ................................................... 151

Figure 69. Photo. On-ramp striping, I-93. .................................................................................. 151

Figure 70. Photo. Off-ramp striping, I-93. .................................................................................. 152

Figure 71. Photo. Off-ramp striping, I-66. .................................................................................. 152

 
List of Tables

vi

LIST OF TABLES 

Table 1. Feasibility checklist of design and operation concepts for part-time shoulder use. ....... 36

Table 2. Advantages and disadvantages of left and right part-time shoulder use. ........................ 37

Table 3. Example performance objectives for Performance Based Practical Design analysis. .... 40

Table 4. Transportation System Management & Operations strategies that can support part-time 

shoulder use. ............................................................................................................... 41

Table 5. Simulated part-time shoulder capacity.(18) ...................................................................... 45

Table 6. Freeway part-time shoulder use scenarios and crash prediction inputs. ......................... 57

Table 7. Air Quality tools and data needs. .................................................................................... 65

Table 8. Potential capital cost components. .................................................................................. 70

Table 9. Potential operations and maintenance cost components. ................................................ 72

Table 10. Benefit estimation parameters. ..................................................................................... 74

Table 11. Controlling criteria, minimum AASHTO values, and relationship to part-time shoulder 

use. .............................................................................................................................. 83

Table 12. Signing of static part-time shoulder use in US. ............................................................ 99

Table 13. Part-Time Shoulder Use Facilities in US. ................................................................... 120

Table 14. Non-Technical Success Factors of the I-35W Priced Dynamic Shoulder Lane. ........ 129

 
Introduction

1

INTRODUCTION 

Part-time shoulder use is a transportation system management and operation (TSM&O) strategy 

that allows use of the left or right shoulders as travel lanes during some, but not all, hours of the 

day. Use of the shoulder is typically restricted to certain classes of vehicles. It is one possible 

strategy for addressing congestion and reliability issues within the transportation system, and can 

be particularly cost-effective where alternatives to add lanes are infeasible, undesirable, or costprohibitive. In such situations, TSM&O alternatives, including part-time shoulder use, may be 

most appropriate for cost-effectively reducing delays and improving travel-time reliability. Parttime shoulder use is most cost-effective in constrained right-of-way conditions; however, there 

are certain minimum geometric clearances, visibility, and pavement requirements that must be 

considered before part-time shoulder use can be implemented. 

PURPOSE, SCOPE, AND TARGET AUDIENCE 

The purpose of this guide is to provide guidance for planning, designing, implementing, and 

operating part-time shoulder use. This guide provides guidance on factors that need to be 

considered in: 

● Deciding through a comprehensive Performance-Based Practical Design(PBPD) process 

if the part-time use of the shoulder is a viable alternative for meeting the current and 

projected goals of the region; 

● Determining the impacts and feasibility of implementing part-time shoulder use; and 

● Designing and operating part-time shoulder use to optimize safety and lane utilization. 

This guidance does not address the “part-time” use of a shoulder in work zones during 

construction (e.g., as part of a lane shift or lane closure), nor does it include the permanent, fulltime “conversion” of a shoulder into a travel lane. Full-time conversion of the shoulder 

constitutes the “permanent elimination” of the shoulder and needs to be addressed in that 

context. This guide does not address pedestrian and bicycle considerations because it is focused 

on freeway applications. Part-time shoulder use on other types of roadways in the U.S. has been 

limited to bus-only shoulder use on a handful of arterials, and this guide presents only limited 

arterial-specific considerations. 

The target audience for this guide consists of State Department of Transportation (DOT), toll 

agency, and Metropolitan Planning Organization (MPO) planners and designers. 

 
Introduction

2

ORGANIZATION OF GUIDE 

The guide is organized in the typical sequence of steps required to plan, design, implement, and 

operate part-time shoulder use. 

Part I of this guide addresses the planning steps for considering part-time shoulder use. 

● Chapter 1 introduces part-time shoulder use and shows images of various facilities with 

part-time shoulder use. 

● Chapter 2 provides planning considerations and screening criteria to help users assess if 

part-time shoulder use is feasible on a specific facility using a Performance Based 

Practical Design (PBPD) approach. 

Part II of this guide provides guidance on how to analyze part-time shoulder use. 

● Chapter 3 offers guidance on conducting operations analysis, including reliability 

analysis, of part-time shoulder use. 

● Chapter 4 provides guidance on assessing the safety impacts of part-time shoulder use. 

● Chapter 5 presents guidance on assessing the environmental impacts of part-time 

shoulder use, including air quality and noise. 

● Chapter 6 provides guidance on conducting benefit-cost analysis and computing the lifecycle costs of part-time shoulder use. 

Part III of this guide provides information on how to design, implement, and operate part-time 

shoulder use once a decision to use it has been made. 

● Chapter 7 identifies and describes the various design considerations for part-time 

shoulder use, including geometry, pavement, drainage, signing and marking, and ITS 

design. 

● Chapter 8 describes how the environmental approval process and the design exception 

process are handled for part-time shoulder use, how to coordinate with stakeholders such 

as emergency responders and maintenance personnel, and how to successfully conduct 

outreach to the general public prior to beginning part-time shoulder use. 

● Chapter 9 presents best practices for maintenance, incident management, and other dayto-day operational issues of part-time shoulder use. 

The appendices provide example applications of the guidance, along with case studies of 

successful applications of part-time shoulder use in the United States. 
What is Part-time Shoulder Use?

3

CHAPTER 1. WHAT IS PART-TIME SHOULDER USE? 

Part-time shoulder use is a transportation system management and operation (TSM&O) strategy 

for addressing congestion and reliability issues within the transportation system. It is a strategy 

that may be used as part of a congestion management process (CMP). There are many forms of 

part-time shoulder use or “shoulder running”; however, they all involve use of the left or right 

shoulders of an existing roadway for temporary travel during certain hours of the day. Part-time 

shoulder use has primarily been used in locations where there is recurring congestion due to lack 

of peak period capacity through the corridor, particularly where other alternatives to improve 

peak period operations are infeasible or cost-prohibitive (at least in the near term). In such 

situations, TSM&O alternatives, including part-time shoulder use, may be most appropriate for 

cost-effectively reducing delays and improving travel-time reliability. Part-time shoulder use is a 

form of Active Traffic Management (ATM) and modifies roadway conditions and controlsin 

this case the number of lanesin response to forecast or observed traffic conditions. It may be 

used in combination with other ATM strategies, such as overhead lane control signs, dynamic 

speed limits, and queue warning. Converting a shoulder to a full time travel laneknown as 

shoulder eliminationis fundamentally different than using a shoulder on a part-time basis as an 

ATM strategy. This strategy should be used with much greater caution, and involves additional 

considerations not presented in this guide. 

Although part-time shoulder use can be a very cost-effective solution, it may not be an 

appropriate strategy where minimum geometric clearances, visibility, and pavement 

requirements cannot be met, or it may have an adverse impact on safety. Part-time shoulder use 

is primarily used on freeways. There are multiple examples of how highway agencies have used 

the shoulders of roadways to address congestion and reliability needs and to improve overall 

system performance. These options vary in terms of the location of the shoulder (left/right 

shoulder options) used, vehicle-use options [e.g., bus only, high-occupancy vehicle (HOV) only, 

all vehicles except trucks], operating schedule, and special speed controls. In all of these options, 

the use is “temporary” for part of the day, and the lane continues to operate as a refuge/shoulder 

when not being used for these travel purposes. This condition is referred to as “part-time 

shoulder use” throughout this guide. 

The decision to pursue the option of part-time shoulder use should be made as part of a 

comprehensive Performance-Based Practical Design (PBPD) assessment of design and TSM&O 

options for achieving the agency’s performance objectives for the facility design and operations. 

First the physical feasibility of part-time shoulder use should be evaluated to determine if it is a 

feasible option, and a region should decide if part-time shoulder use is consistent with its longterm transportation goals and objectives. Then, a preliminary assessment should be made to 

identify one or more design and operations concepts for evaluation. This assessment, conducted 

under the overall umbrella of a PBPD process, should assess the operational and safety effects of 

part-time shoulder use to ensure it is indeed a cost-effective means for achieving the agency’s 

performance objectives for the facility. Throughout this evaluation, key planning and 

environmental, maintenance, operations, design, and emergency responder stakeholders should 

be involved to ensure a successful outcome. 
What is Part-time Shoulder Use?

4

SHOULDERS AND SHOULDER USAGE 

Part-time shoulder use may be an effective TSM&O strategy for operations and reliability of a 

facility in particular situations. In this context, part-time shoulder use is defined as follows: 

● The shoulder is used for travel only during those times of day when the adjoining lanes 

are likely to be heavily congested (e.g., during peak hours, when congestion is detected, 

or when general purpose lanes are closed for construction or incidents). 

● When not needed as an additional travel lane, the shoulder will be restored to its original 

purpose as a “shoulder,” and the basic physical characteristics of the shoulder are retained 

and recognizable. 

The term “part-time” does not require that the use of shoulders as a TSM&O strategy is “shortterm” and will be discontinued by some fixed date. Although part-time shoulder use may be used 

as an interim treatment while a conventional project (e.g., construction of additional lanes) 

awaits funding or completion, it may also be used indefinitely. 

This guidance does not address the “part-time” use of a shoulder in work zones during 

construction (e.g., as part of a lane shift or closure). The Manual on Uniform Traffic Control 

Devices (MUTCD) and agency-specific guidance on maintenance of traffic plans address such 

usages. Additionally, this guidance does not address the permanent, full-time usage of a 

shoulder as a travel lane. Such usage constitutes the “permanent elimination” of the shoulder and 

the creation of a new travel lane. This is a major design change and not a TSM&O strategy. 

Additionally, this guidance does not address the use of shoulders to remove slow-moving trucks 

from general purpose lanes on steep upgrades. This effectively converts the shoulder into a 

permanent truck-climbing lane. A handful of shoulders are open to slow moving trucks on rural 

and suburban freeways in the U.S. 

It remains the policy of the Federal Highway Administration (FHWA) that constructing 

and maintaining roadway shoulders along all major and minor arterials and freeways 

provides inherent value. Shoulder width is one of the controlling criteria that FHWA 

requires a formal written design exception if minimum design criteria are not met on the 

National Highway System.(1)

Aside from their structural benefits for pavement and drainage, shoulders provide refuge 

for vehicles in emergency situations, access for first responders, and an additional 

recovery area for drivers trying to avoid conflicts in the adjoining travel lanes. The 

safety benefits of shoulders are documented in the AASHTO Highway Safety Manual 

and other studies. Because of these factors, the decision to use shoulders for travel 

should be carefully considered and limited in both its application and time of usage. 
What is Part-time Shoulder Use?

5

DIFFERENT PART-TIME SHOULDER USE CONCEPTS 

The term “part-time shoulder use” covers a broad range of different design and operational 

options. In some cases, the particular physical limitations and conditions of the site ultimately 

drive these options, which in turn influence the design of the facility. Likewise, the travel 

demands and traffic characteristics of the corridor will very much influence the operational 

choices needed. Specifically, part-time shoulder use may be used to fulfill any number of 

“functions,” such as the following: 

● Reduce peak-period recurring congestion. 

o In lieu of a conventional add-a-lane capacity improvement. 

o As an interim treatment while a conventional widening or expansion project 

works through the planning/design/construction process. 

● Increase bus ridership by improving bus travel time and reliability. 

● Provide short-term benefits for a minimal cost compared to ultimate solution. 

● Mitigate the loss of general purpose lane capacity if a general purpose lane is converted 

to a managed lane such as an HOV lane. 

Given these various uses, a variety of part-time shoulder use options exist. Generally speaking, 

all of these options take advantage of the existing shoulder infrastructure and include a 

combination of treatments such as left/right shoulder option, vehicle-use option, operating 

schedule, and special speed controls, as listed below: 

● Left/Right Shoulder Option 

o Right shoulder 

o Left shoulder 

● Vehicle-Use Options 

o Open shoulder to transit vehicles only 

o Open shoulder as an HOV lane that permits carpools and transit vehicles to use it 

o Open shoulder as a HOT lane that allows vehicles to pay a toll to use it if they 

don’t meet HOV occupancy requirements 

o Open shoulder to all vehicles except trucks 

o Open shoulder to all vehicles 

o Open shoulder to slow moving trucks in rural mountainous areas 

● Operating Options 

o Dynamically open shoulder when certain congestion thresholds are reached (an 

ATM strategy referred to as “Dynamic Shoulder Use”) 

o Statically open shoulder during specified historical peak periods (time of day) 

● Speed Control Options 

o Same speed limit as other lanes (at posted speed limits). 

o Same speed as other lanes (at a reduced speed relative to normal posted 

speed limits) 
What is Part-time Shoulder Use?

6

o Lower speed limit than other lanes. 

PART-TIME SHOULDER USE GUIDANCE 

This section summarizes key guidance presented throughout this document. It is intended to 

provide readers with a concise summary of key information presented in the remaining chapters 

of this document. 

Planning, Screening, Decision Making, and Preliminary Engineering 

The evaluation of part-time shoulder use as a strategy for relieving congestion in a corridor 

should begin at the regional level as part of a planning process. Practitioners should consider 

part-time shoulder use if it is consistent with a region’s long-range plan, and congestion 

management process (CMP). More complex part-time shoulder-use projects, such as dynamic 

shoulder lanes, should also be consistent with the regional intelligent transportation system (ITS) 

architecture. More viable candidates for part-time shoulder use over “unmanaged” corridors 

include corridors monitored by a traffic management center (TMC), supported by a Traffic 

Incident Management (TIM) program, and generally highly managed. The National 

Environmental Policy Act (NEPA) should determine if part-time shoulder use is the preferred 

solution for a corridor, and preliminary engineering activities determine specific operating 

conditions. If congestion reduction (or transit service improvements in the case of BOS) is 

desired and traditional improvements are not feasible, part-time shoulder use may be the right 

solution for a corridor, and a NEPA process should be initiated. 

Implementation of part-time shoulder use typically occurs within the existing paved roadway 

area and primarily has the potential to impact environmental categories related to traffic volume 

and speed such as air quality, greenhouse gas emissions, and noise. However, some part-time 

shoulder use projects involve widening the shoulder, which creates the potential for impacts to 

many other environmental categories such as water quality, plants, animals, and socio-economic 

elements. Part-time shoulder use projects often receive a categorical exclusion (CE). 

FHWA generally consolidates these numerous types of part-time shoulder use into three 

types:(2) 

● Bus-only use of shoulders (Bus on Shoulder, or BOS) to improve bus travel time 

and reliability, 

● Static shoulder use for most vehicles during predetermined hours of operation, 

and 

● Dynamic shoulder use for most vehicles based on need and real-time traffic 

conditions. 

Vehicle-use restrictions vary by facility, but static and dynamic shoulder use is typically 

open to all vehicles except trucks. 
What is Part-time Shoulder Use?

7

Preliminary engineering activities should inventory the physical roadway conditions and 

consider the following: 

● Is shoulder width adequate, or can it be widened? 

● Are vertical clearances adequate? 

● Is the shoulder pavement structural capacity adequate in terms of drainage and 

rideability? 

● Is it feasible to provide supplemental emergency pull-off or refuge areas beyond the 

shoulder at reasonable intervals? 

● Is a sufficiently long segment available, or is an acute bottleneck being relieved? 

If the answers to these questions determine part-time shoulder use is feasible, a specific 

operating scheme can be selected. 

● Should the right or left shoulder be used? The right shoulder is used most often because it 

is usually wider than the left shoulder and thus easier to implement. Both shoulders 

should not be used. 

● What vehicles will the shoulder be open to? 

● If the shoulder is open to more than buses, should it be a static shoulder lane (fixed hours 

of operation) or dynamic shoulder lane (variable hours in response to traffic conditions)? 

● Will there be speed restrictions? 

Mobility Analysis 

The capacity of a shoulder used for travel depends on design features such as shoulder width, 

length of the segment used for travel, and speed limits. For example, I-66 in Virginia features a 

12-foot wide shoulder lane with a two- to four-foot wide paved “shoulder” beyond it, overhead 

dynamic lane control signs, and the same observed capacity as adjacent general purpose lanes. I93 in Massachusetts has shoulder lanes less than 12 feet wide, a one- to two-foot paved 

“shoulder” beyond the shoulder lane, limited dynamic signs, and generally older-style 

interchanges with more-constrained geometry than I-66. The shoulder on I-93 was observed to 

have only one-half to two-thirds the capacity of adjacent general purpose lanes. 

A simulation study found a “low quality” 10-foot-wide shoulder that is closed to trucks and only 

willing to be used by slightly more than half of drivers has a capacity of approximately 1,300 

vehicles per hour, and a 12-foot-wide shoulder with “normal freeway lane design standards” that 

all drivers are willing to use has a capacity of approximately 1,650 vehicles per hour. 

When analyzing a potential part-time shoulder use project, capacities should be set by first 

determining the approximate geometric dimensions of shoulder elements and then choosing a 

capacity value observed or simulated on a similar facility noted above. 
What is Part-time Shoulder Use?

8

Operations analysis of freeways is typically conducted with the procedures of the Highway 

Capacity Manual (HCM) or microsimulation. Both sets of tools can be adapted for analysis of 

part-time shoulder uses. 

The HCM does not provide for lane-by-lane analyses, so shoulders designated for part-time use 

must be combined with the general purpose lanes for the purpose of capacity analysis and the 

estimation of speed and delay. A proportional capacity reduction should be applied to all freeway 

lanes to account for the reduced capacity of the shoulder lane. Use of the FREEVAL software 

tool should be considered for part-time shoulder-uses projects encompassing multiple 

interchanges. Many microsimulation programs enable parameters to be adjusted on a per-lane 

basis, so capacity of the shoulder can be adjusted directly. 

Safety Analysis 

Experience in the U.S. to date has not identified major safety issues with part-time bus, static, or 

dynamic shoulder use that led implementing agencies to discontinue part-time shoulder use due 

to poor safety performance. Before/after crash studies of part-time shoulder use in the U.S. and 

internationally have not consistently indicated whether part-time shoulder uses has a positive or 

negative effect on crash frequency. 

An analysis of existing crash data, including crash type, the time of crashes, and the location of 

crashes should be the basis of a safety analysis of potential part-time shoulder use. Part-time 

shoulder use would likely reduce congestion-related crashes occurring during the hours part-time 

shoulder use would operate. Crashes related to erratic driver behavior, driver confusion, or 

suboptimal geometry may increase with part-time shoulder use. Assessment of the safety impacts 

of part-time shoulder use on a given facility should begin with a review of three or more years of 

historical crash data. The review should consider the crash type, temporal factors (e.g., time of 

day, day of week), and location. Congestion-related crashes, such as rear-ends occurring during 

times a shoulder would be open to travel, may potentially decrease with part-time shoulder use if 

congestion is reduced. Crashes related to erratic driver behavior or suboptimal geometry, such as 

run-off-road, fixed-object, or sideswipe crashes, may increase with part-time shoulder use. 

Crashes related to right-side ramp-freeway junctions may increase with part-time use of the right 

shoulder. The mere presence of crash types that may increase with part-time shoulder use should 

not prevent the application of part-time shoulder use, but a preponderance of those crash types 

indicates a given freeway may be a poor candidate for part-time shoulder use. 

The 2014 Supplement to the Highway Safety Manual (HSM), 1st Edition, provides crashprediction models for freeways and ramp terminals, but does not explicitly model part-time 

shoulder use. The HSM models would have limited utility in evaluating projects that involve 

only adding part-time shoulder use. For this guide, HSM models were used to conduct a 

comparative analysis of freeways with typical lane widths and shoulder widths and freeways 

with an additional lane in each direction, but narrower shoulder widths (and in some cases 

narrower lane widths). The HSM freeway crash-prediction models indicate that implementing 

freeway part-time shoulder use could have the following influence on crash frequency and 

severity: 
What is Part-time Shoulder Use?

9

● Reduce property damage only (PDO) crashes 

● Slightly increase fatal and injury (FI) crashes when converting existing 4- or 6-lane 

freeways 

● Have little to no effect on FI crashes when converting existing 8-lane freeways 

Environmental Analysis 

As with all federal-funded or permitted actions, the National Environmental Policy Act (NEPA) 

applies. The environmental categories most likely to be affected by part-time shoulder use 

include air quality, greenhouse gas emissions, and noise. 

Air Quality 

Given the variety of characteristics of shoulder use projects, generalizing the effect of shoulder 

use on air quality remains difficult. Shoulder use may reduce congestion, which is generally 

beneficial to air quality. Shoulder use also has the potential to increase traffic volume, which 

generally worsens air quality. There may also be no net effect on traffic characteristics that 

would affect air-quality pollution concentrations. 

Areas that do not meet, or previously did not meet, federal air quality standards are identified as 

“non-attainment” and “maintenance” areas, respectively. The Environmental Protection Agency 

(EPA) requires air quality analysis of federal transportation projects in these designated areas for 

the transportation-related pollutantsozone, nitrogen dioxide, carbon monoxide, and particulate 

matter per the transportation conformity rule (3). Shoulder-use projects are typically federal 

projects because they require design exceptions. Projects in metropolitan non-attainment and 

maintenance areas must be incorporated into regional emissions analysis associated with the 

region’s Transportation Improvement Plan (TIP) and long-range plan (MTP). Transportation 

conformity rules also require the analysis of potential localized emissions impacts where 

applicable. Non-attainment and maintenance areas have standing transportation conformity 

procedures in place that address how projects are handled to assess for conformity status 

(exempt/non-exempt) and whether a project-level analysis is required. These procedures may 

assist in assessing individual part-time shoulder-lane projects. 

Outside of non-attainment and maintenance areas, air quality analysis may be conducted as part 

of a NEPA analysis. For example, agencies may consider the following questions when deciding 

whether or not to conduct air quality analysis in these areas: 

● Is there concern about the project within the community? 

● Is the shoulder only open to buses, or will other vehicles have access? 

● If the shoulder is only open to buses, is service being added or will bus headways remain 

the same? 

● For PM impacts, are diesel vehicles being moved closer to sensitive roadside receptors? 
What is Part-time Shoulder Use?

10

● Is the project in a dusty area where dust will be stirred up when the shoulder opens each 

day? 

The degree of analysis conducted should be proportional to the project scope. Qualitative 

analysis without the use of modeling software is likely acceptable for low impact projects and 

more-complex analysis may provide useful information for projects with a higher potential for 

impact. 

Greenhouse Gas Emissions 

In some statescurrently California, Massachusetts, New York, and Washingtonanalysis of 

greenhouse gas (GhG) emissions is required for some transportation projects. Part-time shoulderuse projects in these states may require GhG analysis depending on the circumstances. 

Noise 

Noise analysis measures the noise impact when the predicted noise level approaches or exceeds 

the Noise Abatement Criteria (NAC) in 23 CFR 772 or represents a substantial increase over 

existing noise levels. Per 23 CFR 772, noise analysis is required for all Federal or Federal-aid 

Highway Projects authorized under Title 23, United States Code that are categorized as Type I or 

Type II. Type I projects include adding a travel lane such as during part-time shoulder use, and 

similar to air quality analysis, design exceptions required for part-time shoulder use will make 

these projects federal thus subject to 23 CFR 772. 

The level of noise analysis necessary will depend upon the type of part-time shoulder use. For 

BOS, noise analysis may be qualitative because the number of additional vehicles and changes in 

speed are small or nonexistent. For static and dynamic part-time shoulder use, noise analysis will 

typically be conducted in a manner similar to a conventional widening project. For the noise 

analysis, the location of the part-time shoulder use would affect the proximity to sensitive 

receptors. Left side part-time shoulder use is less likely to have noise impacts compared with 

right side part-time shoulder uses, which places the traffic closer to sensitive receptors. Noise 

analysis and determination of noise mitigation needs are focused on peak noise conditions. This 

may or may not correspond to peak volume conditions (when shoulders are typically open for 

travel), and analysis will determine if part-time shoulder use affects peak noise or not. Noise 

levels are determined by using the FHWA Traffic Noise Model (FHWA TNM).(4) 

If part-time shoulder use does increase peak noise, and there are impacts associated with it, noise 

abatement must be considered and implemented if found to be feasible and reasonable. The 

likelihood of noise issues is greater with use of the right shoulder than with use of the left 

shoulder, since the right shoulder places traffic closer to noise receptors. 

Costs and Benefits 

Compared to traditional capacity-adding projects, part-time shoulder use projects typically have 

lower initial construction costs and higher operations and maintenance costs due to the ongoing 

management of the shoulder and any associated ITS equipment. For this reason, a life-cycle cost 

should be computed for any part-time shoulder use project under consideration. A 10-, 15-, or 
What is Part-time Shoulder Use?

11

20-year time horizon should be considered. Shorter horizons may be appropriate if part-time 

shoulder use is being implemented as a temporary measure until larger capacity-adding project 

such as widening is completed. 

The following are costs that are often incurred with part-time shoulder use projects and should be 

incorporated into a life-cycle cost analysis: 

● Capital Costs 

o Activities associated with systems engineering 

o Shoulder reconstruction and widening 

o Bridge raising or widening, if required 

o Ramp treatments 

o Training 

o Emergency patrols 

o Public outreach and communications 

o ITS 

● Operations and Maintenance Costs 

o Compliance (additional police presence) 

o Driver training (for bus on shoulder) 

o Sweeps, including manual or video 

o ITS, including TMC operation and hardware maintenance 

o Roadway maintenance 

Benefit cost ratios are useful for comparing part-time shoulder-use projects to other alternatives 

on a corridor and other projects in a region. FHWA’s TOPS-BC tool was developed specifically 

for TSM&O projects such as part-time shoulder use and is one means of conducting a benefitcost ratio. 

Design 

Beginning and End Segments 

Logical termini should be established during project scoping and preliminary engineering 

consistent with NEPA guidance. Part-time shoulder use can begin and end along basic segments 

or at ramps. If the beginning or end of a static or dynamic shoulder use segment falls along a 

basic freeway segment, then it would desirably be located such that it is highly visible and easily 

comprehended to approaching drivers. Horizontal curves, crest vertical curves, and overpasses 

may limit a driver’s visibility of a downstream roadway, and dropping any type of lane, 

including a shoulder open to part-time travel, within or immediately beyond these features 

should be avoided if possible. Likewise, dropping any type of lane in or immediately beyond an 

area with extensive, complex signing or other features contributing to high driver workload 

should be avoided, if possible. The desirable locations for lane drops are also desirable locations 

to begin shoulder use. 
What is Part-time Shoulder Use?

12

Part-time shoulder use along basic freeway segments should include pavement markings at the 

beginning of the area designated for shoulder use that guide drivers from the adjacent general 

purpose lane onto the shoulder but also maintain continuity of the general purpose lane. Shoulder 

use ends along basic freeway segments are designed similar to shoulder use adds. A solid edge 

line is typically used to transition traffic from the shoulder back to the adjacent general purpose 

lane. 

Carrying part-time shoulder use through system interchanges is more complex due to conflicts 

with exiting and entering traffic. At major forks, the shoulder lane can be carried onto one of the 

forks. This is desirable if the ramps downstream of the fork have more lanes than the freeway 

approaching the fork. 

Georgia and Hawaii maintain static part-time shoulder use between (but not through) adjacent 

interchanges to create auxiliary lanes and mitigate the effects of closely-spaced entrance and exit 

ramps. In this case, lanes designated for shoulder use do not function as basic freeway lanes, and 

a drop onto a service interchange is necessary and inherent in the design. 

Lane Width 

For shoulders designated for part-time travel, a width of 12 or more feet is generally preferred. 

Narrower shoulders may be adequate depending upon the type of vehicles using the part-time 

shoulder lane, the available lateral offset to obstructions beyond the pavement edge, and if speed 

restrictions will be used when the shoulder is open. If trucks are prohibited from using the 

shoulder, then widths as narrow as 10 feet may be adequate. Shoulders less than 10 feet wide are 

not recommended for part-time shoulder use. 

A 10-foot shoulder may be inadequate for part-time shoulder use if the lateral offset to 

obstructions is less than 1.5 feet or a high volume of larger vehicles such as buses is anticipated. 

Opening the shoulder only when congestion is present and reducing the speed limit when the 

shoulder is open will likely to improve the safety of a narrow shoulder designated for part-time 

use. 

Shoulders less than 12 feet wide will typically require a design exception if they are designated 

for part-time shoulder use. If an entire roadway is repurposed, and general purpose lanes are 

reduced to less than 12 feet wide to accommodate part-time shoulder use (for any shoulder 

width), a design exception is also required. 

Shoulder Width 

It is desirable to leave several feet of pavement beyond the portion of the shoulder designated for 

part-time shoulder use to decrease the likelihood of vehicles departing the roadway and decrease 

pavement maintenance needs. Part-time shoulder use will require a design exception, since the 

remaining paved shoulder (beyond the portion of the shoulder designated for part-time shoulder 

use) will not meet the minimum width requirements. 
What is Part-time Shoulder Use?

13

Lateral Offset to Obstruction 

Lateral offset to obstruction is the distance from the edge of the traveled way to the nearest 

physical obstruction such as a median barrier, guard rail, bridge support, or bridge rail. The 

lateral offset between the edge of a lane designated for part-time shoulder use and an obstruction 

should be at least 1.5 feet. 

In practice, states have relocated guardrails and other obstructions (sign and lighting structures), 

and obtained design exceptions for segments adjacent to bridge rails/barriers and abutments or 

other concrete barrier where lateral offset to obstruction is less than 1.5 feet. 

Bridge Width 

Many bridges have narrower shoulders than the approach roadways. The minimum width of a 

bridge shoulder that could be designated for part-time shoulder use is 11.5 feet. This dimension 

provides 10 feet of the shoulder as an effective part-time lane and 1.5 feet of the shoulder as an 

effective lateral offset to obstructions. It is not necessary for a shoulder designated for part-time 

use on a bridge to be the same width as a shoulder designated for part-time use on the 

approaching roadway; however, it does need to be 11.5 or more feet wide. In these 

circumstances, design exceptions may be needed for shoulder widths less than 12 feet and/or if 

the lateral offset to obstruction dimension is not met. 

Stopping Sight Distance 

On the inside of horizontal curves, a shoulder designated for part-time use will be closer to 

guardrails or median barriers if they are present. This may reduce sight distance, and it may 

reduce it below AASHTO minimum design values. If this occurs, it may be appropriate to 

relocate the barrier causing the sight-distance obstruction, impose speed restrictions, or obtain a 

design exception. 

Cross Slope 

Cross slopes on shoulders are sometimes greater than adjacent general purpose lanes to facilitate 

drainage, creating potential issues for part-time shoulder use. An agency may need to round a 

grade break between the travel lane and the shoulder or reduce shoulder cross slope by adding 

pavement on top of existing pavement to modify the cross slope. 

Vertical Clearance 

Prior to implementing part-time shoulder use, agencies typically field measure the height of 

bridges along a route, and any substandard vertical clearances dictate vehicle restrictions. 

Ramp-Freeway Junctions 

Chapter 8 describes how to maintain part-time shoulder use through on- and off-ramps. Part-time 

shoulder use may be implemented on freeways with taper-style or parallel-style ramps. 

Maintaining part-time shoulder use through a two-lane entrance or exit ramp is more 
What is Part-time Shoulder Use?

14

challenging, and is not possible in some cases depending on the design details of the rampfreeway junction. Ramp meters are effective at mitigating potential conflicts in merge areas 

because they break up platoons of ramp traffic and make it easier for traffic using the shoulder to 

cross the ramp taper or enter the speed change lane. This benefit occurs even with BOS operation 

if on-ramps have meters, the meters should be active when the shoulder is in use. 

Turnout Placement and Design 

Providing periodic emergency refuge spaces for disabled vehicles beyond the shoulder is highly 

desirable with part-time shoulder use. Sometimes, gore areas or ramp shoulders at entrances and 

exits provide a refuge space large enough to store a vehicle. When this is not the case, or when 

ramp spacing exceeds a half-mile, emergency turnouts should be constructed desirably at halfmile intervals. Turnouts should be long enough and 16-or-more feet wide so a vehicle with poor 

control and in the process of breaking down can enter it and be out of the shoulder. They should 

also be long enough to enable a tow truck to park and load a broken-down vehicle. 

If turnouts cannot be constructed, such as on bridges or other constrained areas, part-time 

shoulder use can still be implemented, but there is a greater probability the shoulder will be 

blocked by disabled vehicles. Dynamic lane control signs should be given greater consideration 

on these facilities to enable closure of the shoulder in response to a disabled vehicle. 

Turnouts have fewer benefits and are generally not constructed on BOS facilities because buses 

can reenter a general purpose lane to pass a disabled vehicle without greatly affecting traffic flow 

on the freeway or bus travel time. 

Arterial Part-time Shoulder Use 

Similar to freeways, arterial shoulder widths of 10 or 11 feet are adequate for part-time use on an 

open section for a low volume of buses at lower, congested speeds, and a 12-foot shoulder is 

desirable for part-time shoulder use. A 10-foot lane should not be used for part-time travel if the 

lateral offset to obstructions is less than the 1.5-foot AASHTO standard or if curbs are present. If 

curbs are present, then vehicles should be able to remain entirely in the shoulder and maintain a 

1.5-foot separation between right side tires and the face of curb.

Signs 

The 2009 MUTCD(5) does not contain signs specifically intended for part-time shoulder use, 

although signs developed by agencies should be compliant with the MUTCD. The next edition of 

the MUTCD is expected to include signs for shoulder use. 

Primary static signs regulating part-time shoulder use, or the static portions of the dynamic signs, 

should be black on white. They may be supplemented with black-on-yellow warning signs. 

Signsstatic or dynamicshould be provided at the following locations, except for BOS 

operation: 

● At the beginning of the segment designated for part-time shoulder use 
What is Part-time Shoulder Use?

15

● At exit ramps, to manage the conflict of exiting traffic from general purpose lanes and 

through traffic in lanes designated for part-time shoulder use 

● At and on entrance ramps 

o To notify entering drivers that the shoulder may be used as travel lane 

o To manage the conflict between entering traffic and traffic on the shoulder 

● At recurring intervals between interchanges 

● At the end of the segment designated for part-time shoulder use 

Similar to exit ramps on a freeway, a series of signs provided in advance of a pull-off and at the 

pull-off itself is recommended to increase driver awareness of its existence. 

Signing on roadways with BOS operation is generally limited to static, ground mounted signs. 

Such signs should be installed along a roadway with BOS operation at regular intervals and near 

on- and off-ramps. There is typically no need for signs specifying hours of operation. Along a 

route, buses sometimes must merge back into a travel lane to avoid a narrow section of shoulder, 

often on or beneath a bridge. Black on yellow warning signs should be used if this is necessary. 

If dynamic signs are used, then they should, at a minimum, include dynamic lane controls 

indicating that the shoulder lane is currently closed, open, or will soon be transitioning to be 

closed. 

Pavement Markings 

On basic segments away from ramps, this is straightforward, and there is consistency across 

states: 

● The solid edge line typically used between the shoulder and adjacent travel lane remains 

in place. 

● A second solid line is used on the outside of the shoulder beside the edge of pavement. 

This line functions as an edge line for traffic using the shoulder. The second solid line 

should be continuous even when the shoulder narrows or has a physical barrier beside it, 

such as a bridge rail. 

● The two solid lines should be the same colorwhite for part-time use of the right 

shoulder and yellow for part-time use of the left shoulder. 

● Striping can create parallel or taper-style merges and diverges. 

The 2009 MUTCD limits use of diamond pavement marking symbols to HOV lanes, and they 

should not be used on shoulders open only to buses. 

Colored pavement 

The Section 3G of the 2009 MUTCD and an interpretation letter specify the use of colored 

pavements for the following situations: 
What is Part-time Shoulder Use?

16

● Yellow pavement for median islands separating traffic flows in opposite directions or left 

shoulders of divided highways or one-way streets or ramps(5)

● White pavement for channelizing islands or right-hand shoulders(5)

● Green pavement for bicycle lanes(6)

● Red pavement for streetcar and/or bus-only lanes on an experimental basis(6)

No color is designed for part-time shoulder use, and none should be used at this time unless a 

request to experiment is submitted to and approved by the MUTCD team. 

Implementation 

NEPA 

If part-time shoulder use projects make use of federal funding or require federal action, then they 

require NEPA evaluations. Most to date have received a categorical exclusion (CE) because they 

are typically implemented within the existing ROW and largely within the existing paved 

surface. 

Design Exceptions 

Implementing static or dynamic part-time shoulder use will typically require a design exception. 

By definition, part-time shoulder use decreases shoulder width (when the shoulder is open to 

traffic), and shoulder width is one of the controlling criteria with specified minimum values on 

the National Highway System. Part-time shoulder use often impacts other controlling criteria as 

well. A number of factors mitigate the substandard geometry created with a part-time shoulder 

use and may justify the design exception: 

● Reduced speeds, achieved through lower speed limits during periods of part-time 

shoulder use coinciding with congestion. 

● Annual average daily traffic (AADT) in ranges where Highway Safety Manual (HSM) 

analysis (summarized in CHAPTER 4) predicts a reduction in crashes with narrowing of 

the shoulder and addition of a lane. 

● Use on commuter facilities during commuting periods with a high percentage of 

familiar drivers. 

● Prohibition of trucks in shoulder lanes. 

● Enhanced monitoring of the facility with intelligent transportation systems (ITS) and/or 

patrol vehicles. 

● Variable lane controls allowing closure of the shoulder if it is blocked by a disabled 

vehicle. 

● Emergency turnouts. 
What is Part-time Shoulder Use?

17

The specific requirements of design exception requests vary by state. Design exceptions are 

typically submitted to and approved by FHWA Division Offices. Part-time shoulder use may 

have a relatively short implementation timeframe compared to conventional projects, so a design 

exception request should be prepared and submitted to FHWA as early as possible in the project 

development process. Most part-time shoulder use projects that have recently been implemented 

or are currently in the planning process are long-term implementations. Temporary approval is 

not recommended, since it may create the need for re-approval. 

Requests for Experiment 

Most part-time shoulder use projects have not required experimental traffic control devices. 

However, some more-complex part-time shoulder use projects, such as those with other ATM 

elements or extensive use of dynamic lane control signs, may require a request for 

experimentation. Chapter 8 describes the items that should be included in a request. 

Stakeholder Engagement 

As soon as a state DOT determines part-time shoulder use is desirable and feasible, they should 

reach out to stakeholders including planning, operations, design, maintenance, and executive 

leadership staff within a DOT; law enforcement; emergency responders; bus operators 

(particularly if the shoulder lane is only open to buses); MPO staff; and FHWA Division Office 

staff. Most agencies that have successfully implemented part-time shoulder use have formed 

working groups to ensure the needs of all stakeholders are incorporated into the concept of 

operations. Stakeholder involvement and educationassuming that some stakeholders may not 

be aware of the benefits and potential issues associated with part-time shoulder useis an 

ongoing process, and working groups should continue to meet during the early years of part-time 

shoulder use. Engaging executive leadership early is critical because policies may need to change 

and laws potentially prohibiting driving on the shoulder may need to be interpreted or changed. 

Public Engagement 

Successful implementation of the first part-time shoulder use project in a metropolitan area 

includes explicit and proactive outreach and education to the general public and should be 

undertaken consistent with state public information guidance. 

Best Practices 

The following case studies from around the nation have evidenced several practices that aid in 

the successful implementation of part-time shoulder use: 

● Maintenance of the shoulder is more similar to maintenance of general purpose lanes. 

● Part-time shoulder use is typically implemented on some of the highest volume and most 

congested freeways in a region. These roadways typically have incident management 

plans and infrastructure in place, and it can be adapted for part-time shoulder use. 

Emergency turnouts, service patrols, and CCTV are typically implemented during parttime shoulder use. 
What is Part-time Shoulder Use?

18

● On BOS facilities, shoulders can still be used by police to pull vehicles over. 

● A lane designated for static or dynamic part-time shoulder use should be inspected in 

entirety before each opening by “sweeping” (driving) the length of the facility or viewing 

CCTV if there is full camera coverage of the facility. 

● Although expert systems can electronically, rather than manually, sweep a facility, it is 

still necessary to have incident response vehicles on standby in the event that debris or 

disabled vehicles are identified and need to be cleared.

● Currently, no facilities in the U.S. use a fully-automated process to open and close the 

shoulder without a human making the final decision. 

EXAMPLES OF PART-TIME SHOULDER USES 

In recent years, part-time shoulder use has emerged as a cost-effective way to help alleviate both 

recurring and non-recurring congestion, exploiting limited improvements to the existing 

infrastructure. The earliest application of part-time shoulder use launched in the mid-1970s on 

Seattle’s SR 520 as a means to help remediate peak-hour congestion by letting HOVs jump a 

queue approaching a bridge leading to the city center. Since then, the range of applications for 

part-time shoulder use has grown to cover a wide variety of strategies and has seen 

implementation in more than 16 states. 

These applications, which are highlighted in the Appendix, often form in an ad-hoc manner, and 

there has been little consistency among applications to date. For example, some applications use 

the left shoulder and others use the right, some employ changeable message signs and some 

employ static displays. Strategies have been adapted to best fit the specific conditions of the 

corridor. One common theme throughout, however, has been the complexity of the project 

development processes necessary to implement part-time shoulder use. Coordination across 

multiple stakeholder groups, including state DOTs, state and local government officials, transit 

agencies (if applicable), MPOs, enforcement entities, and various safety and emergency response 

stakeholder groups is essential for successful implementation. Figure 1 illustrates states that have 

employed part-time shoulder uses. 
What is Part-time Shoulder Use?

19

Figure 1. Map. Part-time shoulder use locations in US, 2015. 

(Source: Kittelson & Associates, Inc.) 

The remainder of this section highlights trends and applications of part-time shoulder use, both 

domestic and international. Descriptions of the several part-time shoulder use locations and a 

complete list of known locations in the United States are located in the Appendix. 

Bus on Shoulder (BOS) Use 

Designed to improve transit reliability, bus-on-shoulder (BOS) operation allows authorized 

transit vehicles to use the shoulder to avoid congestion in the general purpose lanes. This 

application improves person-throughput along a corridor and incentivizes the use of mass transit. 

BOS is unique from other part-time shoulder use strategies, as low volumes on the shoulder 

(compared to opening the shoulder to general traffic) minimize the need for signing, pavement 

markings, and ITS equipment. BOS also minimizes the impacts for emergency response to 

incidents and storage of broken down vehicles. While most BOS applications utilize the right 

shoulder, systems in Chicago, Cincinnati, and Columbus utilize the left shoulder. Overall, twelve 

states currently use BOS strategies on their urban corridors: 

● California 

● Colorado 

● Delaware 

● Florida 

● Illinois 
What is Part-time Shoulder Use?

20

● Kansas 

● Maryland 

● Minnesota 

● New Jersey 

● North Carolina 

● Ohio 

● Texas 

● Virginia 

● Washington 

Additional information on BOS shoulder use in these states is included in the Appendix. 

BOS operation is primarily used on freeways, but is also used on arterials in several states. 

Figures 2 through 4 show BOS facilities. 

Figure 2. Photo. Bus-on-shoulder operations in Minneapolis-St. Paul. 

(Source: Metro Transit) 
What is Part-time Shoulder Use?

21

Figure 3. Photo. Bus-on-shoulder operations on the left-shoulder in Chicago. 

(Source: Pace Bus) 

Figure 4. Photo. Static Bus-on-shoulder message sign on US 9 arterial in Old Bridge, New 

Jersey. 

(Source: TCRP Report 151) 
What is Part-time Shoulder Use?

22

Static (Time of Day) Part-time shoulder use 

This strategy aims to reduce recurring congestion during peak periods by allowing all vehicle 

types to use the shoulder during fixed periods of the day. Though the predetermined hours of 

operation lend themselves to static message signs, dynamic signing may be used to reinforce 

restrictions or occasionally change them due to blockage of the shoulder, closure of general 

purpose lanes for construction, or major special events generating off-peak traffic. Overall, eight 

states currently use static part-time shoulder use: 

● Colorado 

● Georgia 

● Hawaii 

● Massachusetts 

● New Jersey 

● Virginia 

● Texas 

● Washington 

All of these applications are on freeways. Additional information on static part-time shoulder use 

in these states is included in the Appendix. Figures 5 through 7 show static part-time shoulder 

use, some of which implement dynamic lane control signs. The specific facility shown in Figure 

5I-66has since been converted to dynamic part-time shoulder use, although other static parttime shoulder use facilities remain in Virginia. 

 

Figure 5. Photo. Previous Static Part-time shoulder use on I-66 in Northern Virginia 

 (Source: Virginia Department of Transportation) 
What is Part-time Shoulder Use?

23

Figure 6. Photo. Static part-time shoulder use on New Jersey Turnpike Newark Bay 

Extension with variable speed limit and changeable message sign. 

 (Source: Kittelson & Associates, Inc.) 

Figure 7. Photo. Part-time shoulder use in Germany. 

(Source: Efficient Use of Highway Capacity Summary: Report to Congress, FHWA-HOP-10-023) 
What is Part-time Shoulder Use?

24

Dynamic (Traffic Responsive) Part-time shoulder use 

Rather than limit shoulder running to periods of estimated recurring congestion, dynamic parttime shoulder use allows for general purpose traffic to temporarily use the shoulder as a travel 

lane as needed based on real-time traffic conditions. Through ITS equipment, a Traffic 

Management Center (TMC) can monitor conditions on the corridor and open the shoulder for use 

as congestion arises or in anticipation of increased traffic (e.g., special event or emergency 

scenario). Dynamic signs actively inform motorists when the shoulder is open for use. Variants 

of this strategy have employed dynamic part-time shoulder use exclusively for (HOV) during 

peak periods to incentivize carpooling; these applications can also operate as HOT lanes, 

allowing single-occupant vehicles to utilize the shoulder for a fee based on traffic conditions. 

Currently there are two known dynamic part-time shoulder use installations in the US: one on 

I-35W in Minneapolis, and one on I-66 in Virginia that was converted from static part-time 

shoulder use in 2015. However, several statesincluding California, New Jersey, and 

Michiganare in the process of planning dynamic part-time shoulder use. Figure 8 shows 

dynamic part-time shoulder use in Minneapolis. 

Figure 8. Photo. High-occupancy-toll part-time shoulder use in Minneapolis-St. Paul. 

(Source: Minnesota Department of Transportation) 
What is Part-time Shoulder Use?

25

Unique Applications 

Part-time shoulder use is typically used on long segments of freeway encompassing multiple 

interchanges, and it has typically been installed as a long-term TSM&O strategy. However, it has 

also been used in other manners: 

● Massachusetts implemented part-time shoulder use on a portion of I-95/SR 128 in 1985. 

A portion of this facility has since been widenedeffectively replacing the shoulder with 

a full-time general purpose laneand part-time shoulder use was discontinued on this 

segment. Widening of the remaining section of I-95 is under design, and upon 

completion, part-time shoulder use will be eliminated from I-95. 

● Maryland allows buses to use the shoulder on a portion of US 29 to bypass queues at 

signalized intersections. The majority of intersections have been replaced with at-grade 

interchanges, and part-time shoulder use has been discontinued on the portions of US 29 

that no longer have signals. 

● Georgia and Hawaii do not carry part-time shoulder use through interchanges. When 

open, lanes designated for static part-time shoulder use function as auxiliary lanes 

between entrance and exit ramps. 

● New Jersey is currently utilizing static part-time shoulder use on the New Jersey 

Turnpike Newark Bay Extension portion of I-78 to mitigate the closure of an adjacent 

freewaythe Pulaski Skywayfor reconstruction. The part-time shoulder use will be 

discontinued when the Pulaski Skyway reopens. 

 

Planning, Screening, Decision Making, and Preliminary Engineering

27

CHAPTER 2. PLANNING, SCREENING, DECISION MAKING, AND 

PRELIMINARY ENGINEERING 

Part-time shoulder use is a TSM&O strategy for relieving congestion and improving peak period 

operation of a corridor. It should be considered if consistent with a region’s long-range plan and 

congestion management process (CMP). More-complex part-time shoulder use projects, such as 

dynamic part-time shoulder use, should also be consistent with the regional intelligent 

transportation system (ITS) architecture and viable to support with a traffic management center 

(TMC). The National Environmental Policy Act (NEPA) process is used to determine if parttime shoulder use is the preferred solution for a corridor, and preliminary engineering activities 

determine specific operating characteristics. Throughout these processes, a number of questions 

should be addressed, such as the following: 

● Is part-time shoulder use consistent with the goals and priorities identified in the 

Regional Plan and Congestion Management Process? 

● What is the transportation need in the corridor? 

● Should part-time shoulder use be considered as a reasonable alternative to meet a 

transportation need or as a component of an alternative? 

● Does the region have experience with transportation system management and operation 

(TSM&O) implementation? 

● Is part-time shoulder use feasible from a constructability standpoint? 

● Is real-time monitoring and incident response in place? 

● What are the impacts? 

● Does part-time shoulder use reduce cost compared to traditional projects? 

● How can lanes designated for part-time shoulder use be designed and operated to 

optimize benefits and mitigate any adverse impacts? 

PART-TIME SHOULDER USE CONSIDERATION IN THE PLANNING 

PROCESS 

Part-time shoulder use can be a cost-effective strategy for relieving congestion and improving 

operations. As such, it can be an important element in the overall planning of the region’s 

transportation system. Although it can be less expensive than other alternatives, part-time 

shoulder use can represent a sizable investment, which should be considered in a planning 

process within the context of regional goals and objectives. Likewise, the value also needs to be 

weighed against the other needs and goals a region may have. 

During the planning process, a number of issues should be examined to determine the viability of 

this strategy as an alternative for addressing the needs in the region. The extent to which these 

issues need to be addressed as part of the regional planning process varies depending on the 

scope and purpose of the project being considered. In some cases, the implementation of various 
Planning, Screening, Decision Making, and Preliminary Engineering

28

TSM&O options can change the dynamics of the transportation network in a region, but in 

others, the impacts may be more marginal and localized. As such, the amount of focus that needs 

to be given to each of these points should be commensurate with the scope and significance of 

the strategy. 

1. Regional Needs to Address Congestion, Reliability, and Safety Performance Issues. 

The regional planning process provides an opportunity to look at the transportation 

network as a whole and the performance of that network under different scenarios. It also 

points to the importance of having data to understand the current conditions and the 

future possibilities. This data provides the strongest justification for action, but also 

allows options to be evaluated in terms of their impact on performance. 

To the extent to which an objectives-driven, performance-based approach to planning for 

operations has been adopted, the consideration of part-time shoulder uses should also be 

part of the evaluation of other operational strategies that may also result in improving 

overall performance under multiple objectives. As an example, if data shows congestion 

is primarily a result of non-recurring problems, a look at other alternatives such as 

improved incident response in the area may be worthwhile. Likewise, the regional data 

can also provide a baseline for the region’s current congestion, reliability, and safety 

performance. In modeling future scenarios, this will also allow a basis for comparison, 

particularly when looking at a network level. 

2. Relationship to Other Planned Projects in the Region. A focus on a single problem 

(e.g., reoccurring congestion along a particular highway) may not provide a complete 

view of either the consequences of a particular action or the opportunities to leverage 

other planned projects. Such challenges and opportunities may include improvements 

such as interchange reconstruction, repaving projects, or new transit facilities in the area. 

In Transportation Management Areas, MPOs are required to maintain a Congestion 

Management Process (CMP), and this will coordinate potential projects, such as part-time 

shoulder use, with other planned projects. Likewise, if the region has developed a 

coordinated plan of TSM&O strategies, there may be an opportunity to connect those 

systems or at least coordinate their operation as part of a broader Active Traffic 

Management (ATM) or Integrated Corridor Management (ICM) system approach.

Another scenario relates to the staging of projects and the use of TSM&O strategies, such 

as part-time shoulder use, in the CMP as an interim solution while a longer-term solution 

is being developed. Because the long-term solution may include large capital 

improvements, the interrelationship between the TSM&O improvement and the ultimate 

project should be considered beforehand to avoid future conflicts. As an example, will 

implementation of the TSM&O strategy actually reduce the support needed for the longterm project? 

3. Support of Other Regional Goals. Although congestion, reliability and safety are the 

primary performance areas that are most often considered in the transportation planning 

process, many jurisdictions are promoting the use of an expanded range of indices that 

better reflect their overall goals for their community. As an example, Caltrans has 
Planning, Screening, Decision Making, and Preliminary Engineering

29

developed a Smart Mobility Framework for transportation planning in California.(7) The 

Framework is built around the following six “Mobility Principles:” 

o Location Efficiency 

o Reliable Mobility 

o Health and Safety 

o Environmental Stewardship 

o Social Equity 

o Robust Economy 

Other communities have incorporated similar elements into their planning processes, 

looking beyond what has traditionally been limited to transportation performance 

considerations. Some communities also incorporate conditions associated with natural or 

manmade disasters, such as evacuation, into their transportation planning. 

4. Maturity of TSM&O in the Region. Early in the planning process, it is important to 

consider what the region’s current TSM&O capabilities are and if they could be applied 

to the implementation of a part-time shoulder uses project. The Federal Highway 

Administration (FHWA) and the SHRP2 program have looked closely at the issue of 

“maturity” as it relates to the skills and experience that are needed to implement major 

TSM&O strategies, and they have developed “Capability Maturity Models” to describe 

the critical knowledge, skills, and abilities needed to make those deployments successful. 

Reaching the full potential of TSM&O is not primarily an issue of “technology” or best 

operations practices. Rather, the key is to put in place and manage specific supportive 

business and technical processes and supporting institutional arrangements—in essence, 

to “mainstream operations” into the institutional framework of the transportation agency. 

The SHRP2 L06 product, Institutional Architectures to Advance Operational Strategies, 

identifies the following six dimensions of organizational capability(8) 

o Business processes—Formal scoping, planning and programming, and budgeting 

(resources). 

o Systems and technology—Using systems engineering, systems architectures, 

standards (and standardization), and interoperability. 

o Performance—Defining measures, data acquisition and analytics, and utilization. 

o Culture—Technical understanding, leadership, outreach, and program legal 

authority. 

o Organization and staffing—Programmatic status, organizational structure, staff 

development, recruitment and retention. 

o Collaboration—Relationships and partnering among levels of government and 

with public safety agencies, local governments, MPOs, and the private sector. 

The implementation of part-time shoulder use can be challenging given the need for 

specialized skills and coordination across multiple disciplines and organizations. As such, 

an organization that is contemplating part-time shoulder use needs to first confirm it has 

developed TSM&O skills and has the experience to apply them to this kind of 

undertaking. 
Planning, Screening, Decision Making, and Preliminary Engineering

30

In addition to the organization’s own maturity, basic elements of an operational 

infrastructure should also be in place before part-time shoulder use, particularly morecomplex part-time shoulder use such as dynamic part-time shoulder use, is implemented. 

The infrastructure to conduct traffic surveillance and monitoring, as well as rapid 

incidence response are logical precursors to any temporary lane use strategy. These early 

TSM&O strategies will also provide decision makers with much better information 

regarding the performance issues on the system. 

The planning process provides the first opportunity to consider the viability of part-time shoulder 

uses as a means to respond to the region’s goals. As part of a performance-based planning 

process, relevant performance objectives are identified to define the basic “yardstick” the region 

wants to use in evaluating their capital programs and TSM&O strategies. If this process confirms 

that part-time shoulder use is a viable option, then the next question needs to focus on the 

feasibility of designing a facility to achieve or contribute to those performance objectives. 

PLANNING FOR OPERATIONS 

Planning for operations is “a joint effort between planners and operators to integrate 

management and operations strategies into the transportation planning process for the purpose of 

improving regional transportation system efficiency, reliability, and options”.(9) In the context of 

part-time shoulder use, a planning for operations process incorporates part-time shoulder use into 

the planning process as a tool for improving operations, similar to widening a road or 

constructing a new road. Static and dynamic part-time shoulder use should be broadly considered 

as congestion management strategies for freeways, and bus-on-shoulder (BOS) should be 

broadly considered as a bus reliability strategy. Incorporating part-time shoulder use into the 

planning process increases the likelihood of reasonable consideration under NEPA to meet a 

defined transportation need and ultimately implementing it. 

ENVIRONMENTAL DECISIONMAKING PROCESS 

NEPA requires and FHWA is committed to the identification and avoidance, minimization, or 

mitigation of potentially adverse impacts to the social, cultural and natural environment when 

considering approval of proposed transportation projects. In addition to evaluating the potential 

environmental effects, NEPA also takes into account the transportation needs of the public in 

reaching a decision that is in the best overall public interest. The FHWA NEPA project 

development process is an approach to balanced transportation decision-making that takes into 

account the potential impacts on the human and natural environment and the public’s need for 

safe and efficient transportation.

(10)

It is FHWA’s policy that(11)

● To the fullest extent possible, all environmental investigations, reviews, and consultations 

be coordinated as a single process, and compliance with all applicable environmental 

requirements be reflected in the environmental document required by this regulation. 
Planning, Screening, Decision Making, and Preliminary Engineering

31

● Alternative courses of action be evaluated and decisions be made in the best overall 

public interest based upon a balanced consideration of the need for safe and efficient 

transportation; of the social, economic, and environmental impacts of the proposed 

transportation improvement; and of national, state, and local environmental protection 

goals. 

● Public involvement and a systematic interdisciplinary approach are essential parts of the 

development process for proposed actions. 

● Measures necessary to mitigate adverse impacts are incorporated into the action. 

The types of NEPA processing options are shown in Figure 9. 

Figure 9. Illustration. National Environmental Policy Act Processing Options (Classes of 

Actions). 

(Source: NEPA and the Transportation Decisionmaking Process course, FHWA-NHI-142005) 

Part-time shoulder use often meets the criteria for a categorical exclusion (CE) because it is 

typically implemented within the existing ROW and largely within the existing paved surface. 

BOS projects and shorter static and dynamic part-time shoulder use projects that relieve acute 

bottlenecks are most likely to be a CE because of the relatively small effect they have on 

environmental resources, including social resources such as local or regional travel patterns. 

Larger projects that add part-time shoulder use over many miles and through multiple 

interchanges may have greater environmental impacts, possibly including social, traffic-related 

impacts, and may not be Ces. A review of the state’s Stewardship and Oversight agreement 

should be evaluated to determine the most appropriate NEPA approval action. 
Planning, Screening, Decision Making, and Preliminary Engineering

32

Likely Environmental Impacts 

Most part-time shoulder use projects have been implemented within the existing paved area of a 

road. Some, however, have involved widening the paved area of the roadway because the 

shoulder was not wide enough for a part-time lane. 

If the pavement is not widened, then some environmental effects related to traffic volume may be 

similar to that of a traditional widening improvement along an existing roadway alignment, and 

others will be lesser or non-existent. Effects on the environment associated with traffic 

volumespecifically the effects on air quality, greenhouse gas emissions, and noisemay need 

to be analyzed, and Chapter 5 describes how this should be done. In general, the analyses of 

impacts related to traffic volumes, such as air quality and noise analyses, would be similar to 

analyses conducted for a project that adds a travel lane. Part-time shoulder use would potentially 

increase peak-hour volumes and thus vehicle-miles traveled (VMT) and would affect average 

speeds and delays along the corridor. The environmental analysis will also need to reflect the 

specific type of part-time shoulder use being considered within its context of the larger roadway 

system and adjacent land uses. Depending upon the type of part-time shoulder use, as well as 

other treatments or strategies, such as the use of variable speed limits, the effects can vary. 

Many other environmental categories, such as water quality, plants, animals, and cultural 

resources, are unlikely to be affected if the pavement is not widened and are unlikely to require 

analysis. However, if the pavement is widened, a part-time shoulder-use project becomes more 

similar to a conventional widening project, and a much broader set of environmental categories 

should be assessed. A recent part-time shoulder use project on I-495 in Virginia involved 

widening the roadway by 4 feet. A summary of the analysis conducted for this projectwhich 

ultimately resulted in a CEis presented below. It should be noted that no two projects or 

project settings are the same, and impacts from part-time shoulder use will vary accordingly. 

I-495 Virginia Example 

In 2015, Virginia implemented part-time use of the left shoulder for approximately 2 

miles in the northbound direction on the Capital Beltway (I-495). The shoulder was 

added downstream of a managed-lane section to mitigate a bottleneck at the end of the 

managed lanes. The right shoulder was widened by four feet, and northbound lanes were 

shifted and narrowed from 12 to 11 feet. Static and overhead dynamic lane control signs 

are being installed, and two emergency turnouts are being constructed. The project was 

given a CE based upon the minimal impacts to the following:(12) 

● Socio-economic – No impacts. The project is in the existing ROW of the 

Interstate Highway System and potentially sensitive socio-economic groups and 

features (low income/minority populations, public recreational facilities, 

community services, bicycle and pedestrian facilities, etc. are not present) 
Planning, Screening, Decision Making, and Preliminary Engineering

33

● Section 4(f) and 6(f) – 4(f) properties are adjacent to the project but there will be 

no transportation “use” of them. 

● Cultural resources – A Section 106 effect determination of No Effect found the 

project as defined will not impact historical properties. 

● Natural resources – No impacts to Waters of the US are anticipated. 

● Agricultural/open space - No impacts because the project is in the existing ROW 

of the Interstate Highway System and no easements are present. Adjacent land is 

developed and residential. 

● Farmland – No impacts because the project is in the existing ROW of the 

Interstate Highway System and adjacent land is primarily residential. 

● Invasive species – Invasive species are likely present and soil disruption should 

be minimized to limit their spread. 

● Air quality 

o The project is incorporated in the MPO’s air quality conforming TIP and 

MTP. 

o A traffic study determined the project will have no impact on traffic 

volumes or vehicle mix. 

o The project is in a PM 2.5 non-attainment area, but is exempt because it 

is not expected to have a significant increase in the number of diesel 

vehicles because it is primarily providing capacity downstream of express 

toll lanes limited to 2-axle vehicles. 

o Mobile source air toxins – None due to the forecast of no impact on 

traffic volumes or vehicle mix. 

● Noise – A noise study was required and completed. Noise barriers were found to 

be feasible not reasonable. 

● ROW and relocations – No temporary or permanent property acquired. The 

physical widening of the shoulder was done within existing right-of-way. 

● Cumulative and indirect impacts – None. 

● Public involvement – One public information meeting was held, and the CE was 

made available for public review and comment. 
Planning, Screening, Decision Making, and Preliminary Engineering

34

PRELIMINARY ENGINEERING 

Preliminary engineering activities typically occur concurrently with NEPA and inform the NEPA 

decision-making process. Once planning activities determine part-time shoulder use is a desired 

mobility improvement for a given facility, a quick “checklist” review can be conducted to see if 

any design and operation concepts are feasible. As shown in Figure 10, the following criteria are 

assessed: 

● Does the paved shoulder width meet agency minimum widths for carrying traffic? 

o Would a lower speed limit or prohibiting trucks solve the problem? 

● Do bridges over the shoulder meet agency minimum clearance height requirements? 

o Is a special height restriction on shoulder lane users acceptable? 

● Does the shoulder pavement cross-section meet agency minimum depths for 

carrying traffic? 

o Is prohibiting heavy vehicles from using the part-time shoulder use an option? 

o Can the equivalent annual axle load be limited (for example, allowing only 

relatively infrequent heavy vehicle use of the shoulder, such as scheduled local 

buses)? 

● Is the drainage compatible with driving on the shoulder? 

o Are additional inlets or other drainage modifications needed to manage hydraulic 

spread and remove standing water from the shoulder? 

o Does the current drainage use a superelevation rate on the shoulder that will not 

support vehicle travel? 

● Is the segment long enough? 

o Is there a long enough segment to provide meaningful congestion relief? 

o If short, is the segment addressing an acute bottleneck? 

● Can safety concerns be resolved? 

o Can ramp merge visibility and merging distance issues be resolved? 

o Can substandard geometry be mitigated through lower speeds, vehicle 

restrictions, or ATM? 

o Can the concerns of emergency responders and maintenance personnel 

be resolved? 
Planning, Screening, Decision Making, and Preliminary Engineering

35

Figure 10. Illustration. Part-time shoulder use screening decision tree. 

(Source: Kittelson & Associates, Inc.(13)) 
Planning, Screening, Decision Making, and Preliminary Engineering

36

If assessment of a given facility with the decision tree in Figure 10 determines part-time shoulder 

use is generally feasible, then the checklist shown in Table 1 can be completed to determine 

specific type(s) of feasible part-time shoulder use. Information gathered during the assessment of 

the decision tree can be used to complete the feasibility checklist. For example, a region’s 

transportation goals may dictate whether the shoulder is open to buses, HOVs, or all vehicles 

except trucks, and pavement conditions and vertical clearances may dictate whether trucks are 

permitted to use the shoulder. 

Table 1. Feasibility checklist of design and operation concepts for part-time shoulder use. 

Feasibility Checklist for Use Options, Time of Day Options, Design Options 

Shoulder Design Type: Left side Right side Comments 

At Posted Speed Limit: Current Lower Current Lower 

Shoulder User Type 

 Bus Only 

 HOV’s Only 

 HOT Only 

 All But Trucks 

 All Vehicles 

Hours of Operation 

 Set Time of Day 

 Dynamic Hours 

HOT = High occupancy and toll paying vehicles. 

Note to User: please check off all usage options that are feasible (under the operating agency’s design and 

operations policies) and note whether a lower posted speed limit for part-time shoulder uses might affect 

that assessment. Provide comments to document rationale for assessment. 

A key element of Table 1 is the option of using the left shoulder or right shoulder. Unless there is 

an opportunity to remark all lanes on the freewaysuch as after a resurfacing projectthe 

choice of which shoulder to use may be determined based on a review of the existing shoulder 

width. Table 2 presents advantages and disadvantages of left and right shoulder lanes. Currently, 

the majority of U.S. part-time shoulder use facilities utilize the right side. 

 
Planning, Screening, Decision Making, and Preliminary Engineering

37

Table 2. Advantages and disadvantages of left and right part-time shoulder use. 

(Source: Kittelson & Associates, Inc.(2)) 

Design Alternatives Advantages Disadvantages 

Use of left 

shoulder 

 Left shoulder not used as much 

for emergency stops or law 

enforcement stops. 

 Least expensive if width is 

available. 

 Further from most large 

vehicles – trucks often 

restricted from left lane. 

 No conflicts with ramps (unless 

left exits/entrances present). 

 Usually requires restriping. 

 Potential sight distance 

problems with some median 

treatments. 

 Less likely to provide a 12 foot 

shoulder. 

Use of right 

shoulder 

 Often the easiest to implement 

because right shoulders are 

generally wider than left 

shoulders. 

 More likely to have large 

adjacent areas for turnouts . 

 Right shoulder is preferred area 

for emergency stops and 

enforcement. 

 Conflicts and sight distance 

challenges at merge and 

diverge areas of ramps. 

PERFORMANCE BASED PRACTICAL DESIGN (PBPD) 

PBPD is a broad concept applying to the entire project development process. It encompasses 

performance evaluations in the preliminary engineering phase of projects to guide NEPA 

alternative selections and, ultimately, geometric design decisions. PBPD encourages the 

evaluation of the performance impacts of highway design decisions in relation to the cost of 

providing various design features. While PBPD may lead to reductions in individual project 

costs, savings from projects can be redirected to other transportation projects and improvements 

such that overall system performance exceeds what would have been achieved otherwise; i.e., the 

goal is to have a well-performing highway system, rather than a scattering of high-performing 

highway segments.(14)

PBPD can be articulated as modifying a traditional design approach to a “design up” approach in 

which transportation decision makers exercise engineering judgment to build up the 

improvements from existing conditions to meet both project and system objectives. PBPD uses 

appropriate performance-analysis tools, and considers both short- and long-term project and 

system goals, while addressing project purpose and need.(15)

PBPD is consistent with FHWA’s objectives-driven, performance-based approach to planning 

for operations FHWA has provided substantial guidance including, Advancing Metropolitan 

Planning for Operations: The Building Blocks of a Model Transportation Plan Incorporating 

Operations – A Desk Reference”.(15) This Desk Reference offers a process for, as well as 

examples of, objectives-driven, performance-based approaches, and includes information related 

to part-time shoulder use. The Desk Reference details the ways in which TSM&O strategies, 

including part-time shoulder use, can be integrated into the planning process. 
Planning, Screening, Decision Making, and Preliminary Engineering

38

Notable attributes of PBPD are the following: 

● PBPD focuses on performance improvements that benefit both project and system needs. 

● Agencies make sound decisions based upon performance analysis. 

● By scrutinizing each element of a project’s scope relative to value, need, and urgency, a 

PBPD approach seeks a greater return on infrastructure investments. 

● PBPD strengthens the emphasis on planning-level corridor or system performance needs 

and objectives when planning, scoping, and developing individual projects. 

● PBPD can be implemented within the Federal-aid Highway Program regulatory 

environment utilizing existing flexibility. PBPD does not eliminate, modify, or 

compromise existing design standards or regulatory requirements. 

The keys to successful implementation of PBPD are the following(15)

● State department of transportation (DOT) executives embrace PBPD and communicate 

this support to all state employees and consultants. 

● State DOT PBPD champion leads implementation throughout all levels of the agency. 

● Agencies revise policies and guidance as appropriate to include the values of PBPD, thus 

securing a multi-disciplinary and comprehensive approach to delivering projects under 

PBPD. 

● Agencies encourage and empower engineers to exercise judgments on projects based on 

PBPD principles. 

● FHWA Division Offices support state DOTs in their implementation with early and close 

coordination. 

PBPD should consider multiple design and operating solutions, including part-time shoulder use, 

to find the combination that best addresses the project objectives. It is also useful for arriving at 

the best design and operation concept for part-time shoulder use. 

Part-time shoulder use is just one of many possible TSM&O treatments for cost-effectively 

improving the operation and reliability of a facility. Although it may be tempting to immediately 

assume that part-time shoulder use is “the solution,” looking deeper may reveal issues that were 

not originally anticipated or other alternatives that may better fit the circumstances. There are 

several design/operating concepts for part-time shoulder use. The decision to pursue the design 

of part-time shoulder use and the selection of the appropriate design/operating concept should be 

made as part of a comprehensive Performance-Based Practical Design (PBPD) assessment of 

design and TSM&O options. The assessment may be informed by systems engineering 

processes, with the ultimate goal of achieving the agency’s performance objectives for the 

facility design and operations. 
Planning, Screening, Decision Making, and Preliminary Engineering

39

PBPD AND OBJECTIVES-DRIVEN DECISION-MAKING 

Transportation decision-making typically occurs through a NEPA process and identifies a 

solution to an identified problem. Although part-time shoulder use can make sense in some 

situations, it can also have unintended consequences. Solving a problem at one location may 

create other problems in the future, or it may simply result in maintaining the status quo. A 

piecemeal approach may result in a suboptimal allocation of resources, as well as lost 

opportunities to do more. 

A performance-based approach to decision-making focuses not on the problem, but rather on the 

desired outcome. “Performance” is the ultimate objective measure of the system’s ability to 

satisfy or exceed user needs and expectations, particularly relating to congestion, reliability and 

safety. Understanding the factors affecting performance, and measuring those, allows decision 

makers to look beyond short-term solutions and take a longer-range view of system performance. 

By establishing performance objectives, a clear message is not only established in the planning 

and prioritization of projects, but those same performance objectives can guide the design and 

operations decisions further into the process. 

DETERMINING PERFORMANCE OBJECTIVES AND CONSTRAINTS 

An agency should work with its internal and external stakeholders to identify the performance 

objectives and constraints for the facility they are evaluating for possible part-time shoulder use. 

Table 3 presents potential performance objectives for a PBPD analysis. 
Planning, Screening, Decision Making, and Preliminary Engineering

40

Table 3. Example performance objectives for Performance Based Practical Design analysis. 

Dimension Performance Measures Example Objectives, to be achieved in 

opening year of project 

Mobility 

1. Throughput (VMT) 

2. Average Speed 

3. Delay per vehicle 

 Increase corridor throughput by 5% 

 Increase average peak period speed 

by 5% between point X and Y 

 Reduce average peak period delay by 

5% between point X and Y 

Reliability 

4. Planning Time Index 

(PTI) 

5. Percent Trips below 45 

mph 

 Reduce peak period PTI for trips 

from X to Y to below 3.0 

 Reduce percent of peak period 

corridor trips below 45 mph to < 

30%. 

Safety 

6. Crash rate 

7. Number of Fatalities 

 Reduce corridor crash rate by 5% 

 Reduce number of fatalities in 

corridor to zero 

Incident 

Management 

8. Incident Response Time 

9. Incident Clearance Time 

 Reduce response time by 5% 

 Reduce clearance time by 5% 

Maintenance 

10. Lane-hours closed for 

maintenance. 

11. Work zone crash rate 

 Reduce lane closures by 5% 

 Reduce work zone crash rates by 5% 

Environmental 

12. Emissions  Reduce specific pollutants emitted 

from vehicles by 5% in the peak 

period throughout corridor 

Resiliency 

13. Evacuation Time  Reduce the per capita time to 

evacuate individuals from an at-risk 

area by 25% 

Many of the objectives in Table 1 could be achieved with conventional widening or part-time 

shoulder use on a given facility. However, on many freeways, conventional widening may not be 

viable due to expected impacts identified in the NEPA process or fiscal considerations. Part-time 

shoulder use is most viable in comparison to conventional widening in constrained situations. 

TSM&O STRATEGIES THAT CAN SUPPORT PART-TIME SHOULDER 

USE 

Part-time shoulder use is not the only means for addressing recurring congestion, and part-time 

shoulder use often works more effectively when it is combined with other TSM&O strategies. 

The Congestion Management Process (CMP) and subsequent preliminary engineering activities 

can identify and refine which TSM&O strategies are appropriate and practical to implement in 

combination with part-time shoulder use on a given facility. Table 4 lists TSM&O strategies that 

can support part-time shoulder use. 
Planning, Screening, Decision Making, and Preliminary Engineering

41

Table 4. Transportation System Management & Operations strategies that can support 

part-time shoulder use. 

TSM&O 

Strategy 

Description (adapted from Transportation 

Research Circular E-C133) 

Support of Part-time shoulder 

uses 

Ramp 

Management

The application of control devices, such as 

traffic signals, signing, and gates to regulate 

the number of vehicles entering or leaving the 

freeway, or to smooth out the rate at which 

vehicles enter and exit the freeway. 

Potential mitigation for heavy 

merge volumes from a ramp into 

the shoulder.

Incident 

Management 

The systematic, planned, and coordinated use 

of human, institutional, electrical, mechanical, 

and technical resources to reduce the duration 

and impact of incidents, and improve the 

safety of motorists, crash victims, and incident 

responders. 

Strategies to notify drivers of 

incidents and clear them quicker 

can mitigate the loss of a shoulder 

refuge for disabled vehicles. 

Managed 

Lanes 

Highway facilities or a set of lanes where 

operational strategies are proactively 

implemented and actively managed to 

optimize traffic flow and vehicular and person 

throughput. These strategies typically involve 

pricing, vehicle eligibility, and access control 

(e.g. HOV, HOT, BOS). 

Managed lanes and lanes 

designated for part-time shoulder 

use can be added at the same time 

to maintain the existing number 

of general purpose lanes. The 

shoulder may already need to be 

restricted to certain types of 

vehicles due to its width and 

other physical conditions. 

Active 

Traffic 

Management 

(ATM) 

A comprehensive collection of strategies to 

dynamically manage recurrent and nonrecurrent congestion on the mainline based on 

prevailing and predicted traffic conditions. 

ATM includes the automation of dynamic 

deployment to optimize performance quickly 

and without delay that occurs when operators 

must deploy operational strategies manually. 

These include: dynamic speed limits, dynamic 

lane assignment, junction control, queue 

warning, among others. 

Adjusting speeds and lane 

assignments to prevailing 

conditions and notifying drivers 

of congestion or other incidents 

can mitigate speed differentials, 

substandard geometry, and the 

loss of a shoulder breakdown 

lane. 

Traveler 

Information 

A combination of strategies for enabling 

better traveler decision making throughout the 

trip chain – before, during, and near the end of 

a trip. Includes: 511, apps on Smartphones 

and tablet devices, CMS. 

Traveler information educates 

drivers on when shoulder is open 

and closed. 

Commercial 

Vehicle 

Operations 

and Freight 

Management 

A set of strategies tailored to the unique needs 

of commercial vehicle operation to promote 

efficient, seamless, and secure freight flows 

on the U.S. transportation system and across 

our borders. 

Information makes truck drivers 

aware of shoulder lane status and 

whether or not they may use the 

shoulder. 

Mobility Analysis

43

CHAPTER 3. MOBILITY ANALYSIS 

This chapter provides a brief overview of how to conduct an operations analysis and a reliability 

analysis of a freeway with static or dynamic part-time shoulder use. 

In general, part-time shoulder use improves the peak period operation of an existing freeway, but 

to a lesser degree than an additional general purpose lane. The results of operations analysis are a 

key metric in a performance-based practical design (PBPD) alternatives analysis process and are 

also inputs into other evaluation processes such as noise analysis, air quality analysis, and lifecycle cost analysis. Estimating specific operational conditions such as delay, travel time, and 

reliability is also a key component of performance management as reflected in Moving Ahead 

for Progress in the 21st Century (MAP-21).(16) The ability to quantify the operational benefits of 

part-time shoulder use will provide the ability to rank and prioritize part-time shoulder use 

projects among a region’s many other potential projects.

SHOULDER CAPACITY 

Operations analysis of part-time shoulder use with any technique requires the selection of a 

capacity for the lane designated for part-time shoulder use. One previous Federal Highway 

Administration (FHWA) study collected operational data from four part-time shoulder use 

facilities, and another simulated different part-time shoulder use configurations. (17, 18)

Collectively, the results indicate that utilization of the shoulder varies greatly and is influenced 

by the “quality” of the lane, as described below. 

The following operational characteristics of part-time shoulder use facilities have been observed:

(17)

● Virginia I-66 eastbound 

o The speed in the shoulder is approximately 5-10 mph lower than the speed in the 

adjacent general purpose lanes. 

o The capacity of the shoulder is the same as the adjacent general purpose 

lanesapproximately 2,000 vehicles per hour per lane. 

o The speed at capacity is approximately 55 mph. 

● Minnesota I-35W northbound 

o The shoulder is priced, and it is unclear if volumes reach capacity. 

o The maximum observed volume in the shoulder is 1,100 vehicles per hour, and 

the speed at this volume is 55 mph. 

o There was no significant change in adjacent general purpose lane speed after 

implementation of part-time shoulder use, suggesting that volume on I-35W 

increased. 

● Washington U.S. 2 eastbound 

o The volume using the shoulder when it is open is approximately one-third of the 

per-lane volume of adjacent general purpose lanes. 
Mobility Analysis

44

o The typical operating speed of traffic in the shoulder is approximately 50 mph, 

and the typical operating speed of traffic in the adjacent general purpose lanes is 

approximately 55 mph to 60 mph. 

o Observed speed-flow curves suggest the shoulder has an operating speed of 40 

mph at capacity, and the general purpose lanes have an operating speed of 50 mph 

at capacity. 

● Massachusetts I-93 

o AM peak period volume is approximately 1,000 vehicles per hour in the shoulder 

and 1,500 to 2,000 vehicles per hour per lane in the general purpose lanes. 

o Speed at capacity is 35-40 mph in the shoulder and approximately 55 mph in the 

general purpose lanes. 

The results indicate that design features influence shoulder capacity. The lane designated for 

part-time shoulder use on I-66 is 12 feet wide, has a paved shoulder several feet wide beyond it, 

has overhead dynamic lane control signs, and was observed to have the same capacity as 

adjacent general purpose lanes. The lanes designated for part-time shoulder use on I-93 in 

Massachusetts are less than 12 feet wide, have a one- to two-foot paved shoulder beyond the 

part-time shoulder use, use limited dynamic signs, and run through generally older-style 

interchanges with more constrained geometry than I-66. The shoulder on I-93 was observed to 

have only one-half to two-thirds the capacity of adjacent general purpose lanes. Additional 

background information on these part-time shoulder-use facilities can be found in the Appendix. 

Researchers for another study used a simulation model of the I-90/I-290 corridor in Buffalo, 

New York, to assess various part-time shoulder use configurations.(18) I-90/I-290 does not have 

part-time shoulder use, but it was added to a bottleneck area in the simulation model. The 

simulation models were run with various part-time shoulder length, shoulder design, demand, 

and incident levels. The results from the part-time shoulder length and shoulder design scenarios, 

listed below, are most applicable to future part-time shoulder-use studies: 

● Short, 1,000-foot part-time shoulder encompassing the length of the bottleneck. 

● Long, 1.5-mile part-time shoulder encompassing the length of the bottleneck and the 

queue prior to it. 

● A “low quality” part-time shoulder that is 10 feet wide, closed to trucks, and only willing 

to be used by 50% of drivers. 

● A “high quality” part-time shoulder is 12 feet wide with “normal freeway lane design 

standards” that all drivers are willing to use. 

Table 5 shows the simulated capacities of the four part-time shoulder use scenarios. 
Mobility Analysis

45

Table 5. Simulated part-time shoulder capacity.(18)

Part-time shoulder use Scenario Shoulder Capacity (vehicles 

per hour) 

Short and low quality 1,262 

Long and low quality 1,334 

Short and high quality 1,610 

Long and high quality 1,687 

The results are highly dependent upon simulation model settings selected by the researchers, but 

they suggest that part-time shoulder capacity varies greatly when a shoulder is substandard in 

width and other elements, making some drivers unwilling to use it. Length of a part-time 

shoulder use segment has a much smaller effect on utilization. 

In general, it appears part-time shoulder utilization and capacity is highly dependent on design 

features, and dimensions meeting or exceeding the AASHTO criteria described in Chapter 7 

should be provided when possible. Field-measured capacity ranges from 1,000 to 2,000 vehicles 

per hour, and a simulation study found capacity ranging from 1,250 vehicles per hour to 1,700 

vehicles per hour. (17, 18) Right part-time shoulders that continue through interchanges and have 

adequate ramp merge distances were found to have a higher capacity than those that do not. 

Right part-time shoulders that meet or exceed the standard width of 12 feet have a higher 

capacity than narrower shoulder lanes. Data on left part-time shoulder use is limited. 

The capacity of a standard width (12 feet) left part-time shoulder is expected to be similar to (and 

perhaps slightly lower than) that of the adjacent general purpose lanes. There may be some 

capacity reduction due to proximity to median structures, such as bridge piers and signposts, but 

there will be no effects of ramp traffic unless left-side ramps are present If the left part-time 

shoulder has limited access points connecting it to the general purpose lanes, then it will tend to 

have a capacity approaching that of a paint or barrier-separated high-occupancy vehicle (HOV) 

lane, which tends to be approximately 1600 vehicles per hour.(19, 20)

SYSTEM ANALYSIS 

System analysis is usually done in the context of a regional travel-demand model or as part of a 

post-process analysis of the demand model outputs to obtain more-precise estimates of 

operational performance measures such as speed, delay, and reliability and environmental 

performance measures such as motor vehicle emissions. The NCHRP 7-22, Planning 

Applications Guide describes a post-processing approach for obtaining improved system 

mobility performance estimates that can be adapted for the analysis of the system performance 

effects of part-time shoulder use on individual facilities.(21)

For systems analysis purposes, the capacity of a part-time shoulder should be considered to be 

half to three-quarters of that of a general purpose lane, based upon capacities presented in the 

previous section. 
Mobility Analysis

46

For system analysis purposes, the congested speed and the free-flow speed of a part-time 

shoulder can be assumed to be virtually the same as that for the general purpose lanes. 

Congestion in the general purpose lanes will generally encourage drivers to use the shoulder until 

the speeds are better balanced, unless a different speed limit takes effect during part-time 

shoulder use. 

OPERATIONS ANALYSIS 

Operations analysis of freeways is typically conducted with the procedures of the Highway 

Capacity Manual or microsimulation. Both sets of tools can be adapted for analysis of 

part-time shoulder use. 

Highway Capacity Manual 

The Highway Capacity Manual (HCM) does not provide for lane-by-lane analyses, so the 

shoulder must be combined with the general purpose lanes for the purpose of capacity analysis 

and the estimation of speed and delay. However, it is known that the shoulder will generally have 

a lower capacity than general purpose lanes, so a capacity reduction should be applied to all 

freeway lanes to account for this. Suppose a freeway with two lanes in one direction has a parttime shoulder added, and based on the design of the part-time shoulder, the capacity is expected 

to be half that of a general purpose lane. If the capacity of the general purpose lanes is 2,000 

vehicles per hour per lane, and the capacity of the shoulder is 1,000 vehicles per hour per lane, 

then the facility could be analyzed as three lanes with a capacity of 1667 vehicles per hour per 

lane. 

If the shoulder has a lower posted speed limit or design characteristics that are likely to cause the 

free-flow speed in the shoulder to be more than 5 mph different than the general purpose lanes, 

then the speed and delay may be computed separately for the general purpose lanes and the 

shoulder. The results are then weighted by volume to obtain an average speed and delay for the 

entire cross-section of the freeway. 

Analysis of long freeway facilities encompassing multiple interchanges becomes complicated 

due to the number of analyses involved (each basic segment, ramp freeway junction, and weave), 

as well as the potential for the effects of one segment to affect another and the potential for the 

effects of one time period to influence conditions at the start of the next time period. The 

FREEVAL software tool, developed by TRB, addresses these issues by allowing a user to input 

data for multiple segments and multiple time periods at once and accounting for relationships 

between them. However, the complexity of the tool makes it difficult for an analyst to make 

manual adjustments to for account different capacities in different lanes. 

Microsimulation 

Microsimulation is conducted with commercial software packages, and specific settings vary 

from one program to another. Many microsimulation programs enable parameters to be adjusted 

on a per-lane basis, and speeds, capacities, and driver behavior characteristics of lanes designated 

for part-time shoulder use and general purpose lanes can be set to different values. 
Mobility Analysis

47

Microsimulation settings could also restrict certain vehicles and certain drivers from using the 

shoulder. 

In general, microsimulation is an order of magnitude more complex than HCM analysis. 

However, modifying a simulation model to account for the unique properties of lanes designated 

for part-time shoulder use is more straightforward than modifying HCM analysis. 

RELIABILITY ANALYSIS 

The travel-time reliability for a freeway with or without part-time shoulder use can be estimated 

using the methods provided in the NCHRP 3-115 Updated Highway Capacity Manual with the 

capacity and speed adjustments presented in the previous section.(19) There are no reliability 

analysis procedures that specifically account for part-time shoulder use. 

In general, part-time shoulder use reduces congestion and would generally be expected to 

improve reliability. However, the degree to which this occurs will depend upon the frequency 

and duration of incidents that block the shoulder. Static and dynamic part-time shoulder use will 

have the same effect on peak-period reliability (assuming both are open during the peak-period), 

but dynamic part-time shoulder use will provide greater annual reliability because the shoulder 

can be opened on-demand in response to congestion. 

For planning and systems analyses, the following equations adapted from SHRP2-C11 can be 

used to estimate link-level reliability.(22) First, the average annual travel time rate (hours/mile) 

including incident effects is computed: 

Figure 11. Equation. Average Travel Time Rate 

where 

 TTIm = average annual mean travel time index (unitless) 

 FFS = Free-Flow Speed (mph) 

 RDR = Recurring Delay Rate (h/mi) 

 IDR = Incident Delay Rate (h/mi)(23) 

Figure 12. Equation. Recurring Delay Rate. 

Figure 13. Equation. Incident Delay Rate. 
Mobility Analysis

48

Where 

 S = peak hour speed (mph) 

 N = number of lanes in one direction (N = 2 to 4) 

 X = peak hour volume/capacity ratio 

Note: IDR equation is valid for X <=1.00. 

The 95th-percentile travel time index (TTI95) and percent of trips traveling at under 45 mph 

(PT45) then can be computed from the average annual travel time index according to the 

following equations. 

Figure 14. Equation. 95th-Percentile Travel Time Index. 

Figure 15. Equation. Percent of Trips that Occur at Speeds Less than 45 mph. 

where 

 TTI95 = the 95th percentile TTI; 

 PT45 = the percent of trips that occur at speeds less than 45 mph 

BEFORE/AFTER STUDIES 

Most before/after studies of facilities on which part-time shoulder use was implemented have 

identified positive operational outcomes. Data is primarily from Europe due to the limited 

number of recent U.S. installations. 

● On U.S. 2 in Washington State, peak period, peak direction delays on the 1.55-mile 

segment with part-time shoulder use decreased from 8-10 minutes to 1-2 minutes.(24)

● On the M42 motorway in the UK, average travel times increased because the speed limit 

was reduced. However, the variability of travel times was decreased 27-34 percent.(25) 

● In the Netherlands, part-time shoulder use increased capacity by seven to 22 percent, 

decreased travel times from one to three minutes, and increased through traffic volumes 

up to seven percent during congested periods.(26) 

● In Munich, Germany, part-time shoulder use created a 20-percent increase in peak hour 

capacity.(26)

● In the Hessen state of Germany, part-time shoulder use reduced congestion by 30 

percent.(27)

 
Safety Analysis

49

CHAPTER 4. SAFETY ANALYSIS 

Reducing congestion by allowing part-time shoulder use allows for greater headways between 

vehicles and reduces stop-start activity that is generally known to contribute to rear-end crashes. 

However, implementation of part-time shoulder use requires a compromise of other geometric 

design elements, including shoulder width (when the shoulder is open to traffic) and sometimes 

others such as lane width and lateral offset to obstructions such as median barriers, guardrails, 

and bridge rails. Although limited research is currently available to quantify the specific effects 

of part-time shoulder use, the relationship between these variables and crash frequency provides 

insight into the potential safety effects of part-time shoulder uses. 

The following sections draw on the best quantitative tools available and reference empirical 

studies in an effort to inform evaluations of future implementation.The first section of this 

chapter describes a general process for assessing the safety impacts of part-time shoulder use on 

a given facility. Subsequent sections present findings from past before/after safety studies of 

part-time shoulder use and crash prediction methods, both of which can be incorporated into the 

analysis of a specific facility. 

ASSESSING PART-TIME SHOULDER USE SAFETY 

Assessment of the safety impacts of part-time shoulder use on a given facility should begin with 

a review of three or more years of historical crash data. The review should consider the crash 

type, temporal factors (e.g., time of day, day of week), and location. Congestion-related crashes, 

such as rear-ends occurring during times the shoulder would be open, may potentially be reduced 

with part-time shoulder uses if congestion is reduced. Crashes related to erratic driver behavior 

or suboptimal geometry, such as run-off-road, fixed-object, or sideswipe crashes, may increase 

with part-time shoulder use. Crashes related to right-side ramp-freeway junctions may increase 

with right part-time shoulder use. The mere presence of crash types that may increase with parttime shoulder use should not prevent the application of part-time shoulder use, but a 

preponderance of those crash types indicates a given freeway may be a poor candidate for parttime shoulder use. 

The design of ramps and interchanges also informs the potential safety impacts of part-time 

shoulder use. There may be safety issues associated with on-ramps with high convergence 

angles, small merge areas, weaving sections, and other characteristics of older freeways. Twolane on- and off-ramps may also introduce safety issues. Additional information on the design of 

part-time shoulder use at ramp-freeway junctions is in the Geometric Design section of 

Chapter 7. 

The Crash Prediction section of this chapter provides additional guidance on quantitatively 

assessing how implementing part-time shoulder use (and modifying freeway cross-section) 

influences crashes. 
Safety Analysis

50

OBSERVATIONAL SAFETY STUDIES 

Experience in the U.S. to date has not identified major safety issues with bus, static, or dynamic 

part-time shoulder use that led implementing agencies to discontinue their use. However, few 

empirical studies have been conducted to evaluate the specific changes in crash frequency and 

severity as a result of implementing part-time shoulder use. Crash frequency has increased 

following some part-time shoulder use projects and decreased following others, suggesting the 

safety impact of part-time shoulder use is influenced by site-specific operational and geometric 

conditions. The results of empirical studies appear to be heavily influenced by operational and 

geometric conditions. The following sections summarize the most reliable studies that have 

evaluated crash history associated with part-time shoulder use. 

I-35W in Minnesota 

A Federal Highway Administration (FHWA) Study used Empirical Bayes analysis to conduct a 

before/after comparison of I-35W in Minneapolis.(28) The Empirical Bayes analysis of total 

annual crash rates (at all times of day) on I-35W in Minnesota showed a 28.4-percent increase in 

crashes after implementation of a priced dynamic part-time shoulder use. MnDOT indicated the 

increase in crashes on I-35W after implementation was partially related to the removal of an 

upstream bottleneck around the same time shoulder running was introduced, effectively 

increasing congestion on the segment with part-time shoulder use. 

SHRP 2 Project L07 related crash data to speed, volume, and density data from Seattle and 

Minneapolis/St. Paul. Density was identified as the independent variable. The SHRP 2 model 

indicates a non-linear increase in crashes as density increases, particularly at level-of-service 

(LOS) D or greater. 

Researchers applied the SHRP 2 L07 models to I-35W in Minneapolis, which indicated an 

increase in crash frequency of 22 percent could be expected with the increase in congestion 

experienced on I-35W. Therefore, the researchers related the I-35W Empirical Bayes analysis to 

the SHRP 2 L07 model prediction to indicate as little as 6.4 percent of the increase in crashes 

observed on I-35W could be related to the part-time shoulder use. 

Virginia 

Virginia conducted a safety analysis of a portion of I-66 with a left-side high-occupancy vehicle 

(HOV) lane and a right-side part-time shoulder use. The study only included “after” data with the 

HOV lane and part-time shoulder use in place, and focused on crash frequency differences 

between the hours when the part-time shoulder use was open and closed to traffic. The study 

found no significant differences in crash frequency in the study area. A typical factor, high 

annual average daily traffic (AADT) volume, and a natural causal factor, light conditions, 

especially combined with motorists’ aggressive lane change behaviors in merging and diverging 

areas, are presumably major factors influencing crashes in the study area.(29)
Safety Analysis

51

Colorado 

Kononov developed safety performance functions for freeways using data from Colorado and 

other states.(30, 31) Although the research did not specifically address part-time shoulder use, the 

findings have applications to the evaluation of other potential projects. On uncongested freeway 

segments, Kononov observed crash frequency increases only modestly as traffic increases until a 

critical traffic density is reached. Beyond this critical density, crash frequency increases much 

faster as traffic increases. When a lane is added to a freeway, there is a safety improvement due 

to the decreased density. However, if volume increases over time there is an increase in crash 

frequency. The additional lanes are able to process additional traffic, and Kononov also 

determined crash frequency increases more rapidly on freeways with more lanes. When 

considering part-time shoulder use, these findings suggest there will be a short-term crash 

reduction if part-time shoulder use decreases traffic density. If part-time shoulder use does not 

notably decrease traffic density [such as bus-on-shoulder (BOS) operation], then there may be no 

effect on crashes, or there may be an increase in crashes due to reduced shoulder widths, lane 

widths (if general purpose lanes were narrowed), and lateral clearances. 

International Experience 

Part-time shoulder use is more common in Europe than the U.S., and the European safety 

experience has been positive. A three-part study of the M42 motorway in the UK compared the 

following conditions: 

● 3 lanes per direction and no Active Traffic Management (ATM) (60 months) 

● 3 lanes per direction and variable speed limits (6 months) 

● 3 lanes plus dynamic part-time shoulder use in each direction and variable speed limits 

(36 months) 

The introduction of variable speed limits (without part-time shoulder use) decreased crashes per 

month from 5.08 to 3.17. The introduction of part-time shoulder use further reduced crashes per 

month from 3.17 to 2.25.(32) Variable speed limits are uncommon in the US at this time. 

Two other studies from Europe have identified positive safety impacts of part-time shoulder 

uses: 

● In the Hessen state in Germany, part-time shoulder use reduced congestion-related 

crashes.(27) 

● A study of multiple part-time shoulder-use locations in the Netherlands with 3 years of 

“before” data and 2 years of “after” data found a reduction in crashes at most sites due to 

reduced congestion. Two sites with close ramp spacing had an increase in crashes.(26) 

In Europe, part-time shoulder use is almost always accompanied by the construction of turnouts 

and a higher level of ATM than is typical in the U.S., including dynamic speed limits/lane 

assignment, full CCTV monitoring, and aggressive incident management. 
Safety Analysis

52

CRASH PREDICTION 

The 2014 Supplement to the Highway Safety Manual (HSM), 1st Edition, provides a structured 

methodology and specialized procedures to estimate the expected average crash frequency for 

various freeway facilities. It does not, however, explicitly model part-time shoulder use. 

The HSM freeway chapters provide safety performance functions (SPFs) for 4- to 10-lane 

freeway facilities that account for several variables influenced by part-time shoulder use, 

including the following: 

● Average Annual Daily Traffic (AADT), 

● Proportion of AADT during high-volume hours, 

● Number of through lanes, 

● Distance to median barrier, 

● Lane width, and 

● Shoulder width (left and right). 

The Enhanced Interchange Safety Analysis Tool (ISATe), developed by NCHRP Project 17-45, 

and the Interactive Highway Safety Design Model’s Crash Prediction Module apply the methods 

and models from the HSM freeway crash prediction chapters. These tools can be used to assess 

how changes to freeway cross-section influence crash frequency. 

The models reflect lane widths and shoulder widths and do not explicitly model shoulder use. 

Therefore, the predictive analysis assumes there is nothing inherent in a lane designated for parttime shoulder use that would change crash frequency relative to a general purpose lane of the 

same width, adjacent to a shoulder of the same width, on a freeway with the same AADT, and so 

forth. 

In order to account for the influence of congestion on crashes, when average freeway speed tends 

to decrease and headway is reduced, the crash prediction methodology accounts for “the 

proportion of the AADT that occurs during hours where the volume exceeds 1,000 vehicles per 

hour per lane (veh/h/ln).” 

Model Limitations 

A number of challenges and limitations are associated with conducting a predictive safety 

analysis of part-time shoulder use with HSM freeway models, including the following: 

● Models were developed with data collected on freeways with only full-time general 

purpose lanes. There is no differentiation between a general purpose lane and the 

shoulder, with all geometric dimensions being the same. 

● Models do not capture changes to ramp-freeway junction areas that occur with part-time 

shoulder use. 
Safety Analysis

53

● The HSM freeway model was calibrated only for right shoulder widths between 4 and 14 

feet. When a shoulder is open to traffic, the resulting “shoulder” between the part-time 

travel area and the edge of pavement is usually less than 4 feet and the HSM cannot 

model this. 

● Speed differential between vehicles in the shoulder and adjacent travel lane can vary 

depending on whether the shoulder is open to all traffic or restricted to specific users. 

● Lane changes and weaving maneuvers associated with on- and off-ramps and speedchange lanes are not accounted for in the basic freeway analysis. They can be analyzed 

separately, but the separate models also lack an explicit means of accounting for parttime shoulder use. 

● The HSM predicts crashes as a function of daily volumes and assumes a consistent crosssection throughout the day. Analyzing a shoulder in use for part of the day would require 

knowledge of the hours of operation and the percent of AADT during those hours. 

Models would be run twice, and a weighted average could be computed. 

● The model will not account for the transfer of crashes from outside of the study area to 

within the study area, a phenomenon that has been observed if part-time shoulder use 

alleviates upstream bottlenecks. 

● Improving freeway operation with part-time shoulder use may potentially transfer volume 

and crashes from adjacent alternate routes to the freeway. A slight increase in freeway 

crash frequency may accompany a larger decrease in network crash frequency. 

Despite these limitations, the HSM freeway models reflect trends related to freeway crosssection that provide insight into when part-time shoulder use may have a positive or negative 

impact on safety. The following sections present these trends. 

Model Evaluation of Number of Freeway Lanes and Shoulder Width 

The HSM freeway crash prediction model can be used to assess the change in crash frequency 

and severity associated with increasing the number of freeway lanes while reducing shoulder 

width. This is the closest the HSM can come to modeling part-time shoulder use, although it only 

changes lane widths and shoulder widths, and does not explicitly model shoulder use. The 

scenarios presented below, then, must assume there is nothing inherent in a shoulder that would 

change crash frequency relative to a general purpose lane of the same width, adjacent to a 

shoulder of the same width, on a freeway with the same AADT, and so forth. Several example 

applications of the HSM models are provided to demonstrate their use. 

The combined change in total crash frequency associated with increasing the number of freeway 

lanes while reducing right shoulder width from 14 to 4 feet, which is the range of right shoulder 

widths for which the model was calibrated, is shown in Figure 16. 

Figure 16 shows the safety effects of adding part-time shoulder use to 4-lane, 6-lane, and 8-lane 

freeways. The point at which each line crosses the 0% mark on the y-axis indicates the AADT 

threshold at which part-time shoulder uses would be expected to increase or decrease crash 

frequency. 
Safety Analysis

54

Figure 16. Graph. Predicted crash frequency associated with increasing number of freeway 

lanes and narrowing the right shoulder. 

Figure 16, like others in this section, assumes shoulder use is actually the addition of a full-time 

lane. This is not the case with part-time shoulder use, so crash frequency changes associated with 

part-time shoulder use would be a fraction of those depicted in Figure 16. 

The model predictions indicate that when congestion reaches a certain level (below the zero 

point on the y-axis in Figure 16), the crash reduction benefits of adding a lane are predicted to 

exceed the increase in crashes associated with reducing the width of the right shoulder. 

It is noted the AADT threshold for achieving a reduction in crash frequency for a 6- to 8-lane 

conversion is lower than that for an eight- to ten-lane conversion. This reflects the model 

prediction that an eight- to ten-lane conversion is expected to have a greater reduction in crashes 

than a six- to eight-lane conversion, as described in the Model Evaluation of Number of Freeway 

Lanes section below. 

Subsequent sections explore how number of lanes and shoulder width, individually without 

changing the number of lanes on the freeway, influence crash frequency and severity. 

Model Evaluation of Number of Freeway Lanes 

Using the HSM freeway models, the relationship between predicted crash frequency associated 

with converting an eight-lane freeway to a ten-lane freeway at various level of AADT was 

assessed. This is analogous to a conventional widening project where shoulder width remains the 

same after the addition of a lane. Figure 17 illustrates the predicted number of Fatal and Injury 

(FI) crashes and Property Damage Only (PDO) crashes associated with converting an eight-lane 

freeway to a ten-lane freeway at various level of AADT, while lane widths, shoulder widths, and 

all other model variables are held constant at default values. 

‐12%

‐10%

‐8%

‐6%

‐4%

‐2%

0%

2%

4%

6%

8%

50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000

Predicted Change in Annual Crash Frequency

Two‐way Annual Average Daily Traffic (veh/day)

8 to10‐Lane Freeway Conversion

6 to 8‐Lane Freeway Conversion

4 to 6‐Lane Freeway Conversion
Safety Analysis

55

Figure 17 indicates both FI and PDO crashes are expected to decrease with the conversion from 

an eight- to ten-lane freeway. 

Figure 17. Graph. Predicted crash frequency on eight- and ten-lane freeways relative to 

Annual Average Daily Traffic, no change in shoulder width. 

Figure 18 illustrates how total crash frequency is influenced by AADT and increasing the 

number of freeway lanes from four to six, six to eight, and eight to ten. 

Figure 18. Graph. Predicted crash frequency relative to Annual Average Daily Traffic and 

Number of Freeway Lanes, no change in shoulder width. 

0

5

10

15

20

25

Predicted Annual Crash Frequency

(crashes/year)

Two‐way Annual Average Daily Traffic (veh/day)

8 Lane Freeway ‐ PDO Crashes

10 Lane Freeway ‐ PDO Crashes

8 Lane Freeway ‐ FI Crashes

10 Lane Freeway ‐ FI Crashes

‐20%

‐18%

‐16%

‐14%

‐12%

‐10%

‐8%

‐6%

‐4%

‐2%

0%

60,000 70,000 80,000 90,000 100,000 110,000 120,000

Predicted Change in Annual Crash Frequency

Two‐way Annual Average Daily Traffic (veh/day)

8 to10‐Lane Freeway Conversion

6 to 8‐Lane Freeway Conversion

4 to 6‐Lane Freeway Conversion
Safety Analysis

56

As shown in Figure 18, the HSM freeway models predict a greater reduction in crash frequency 

for a 4- to 6-lane conversion than for an 8- to 10-lane conversion. 

Model Evaluation of Shoulder Width 

HSM freeway crash prediction models were applied to estimate the influence of reducing right 

shoulder width on 4-, 6-, and 8-lane freeways from 14 feet to the minimum model input of 4 feet, 

while holding all other model variables constant at default values. This isolates the effects of 

shoulder width from the effects of adding lanes. Figure 19 illustrates the predicted FI crash 

frequency associated with this change in right shoulder width on an 8-lane freeway. The trend is 

similar on 4- and 6-lane freeways. PDO crashes were omitted from Figure 19 because they are 

not sensitive to shoulder width in the 8-lane freeway model. The 4- and 6-lane freeway models 

predict slight increases in PDO crashes as right shoulder width decreases. 

Figure 19. Graph. Predicted crash frequency on eight-lane freeways with 14- and 

4-foot right shoulder width relative to Annual Average Daily Traffic. 

As shown in Figure 19, reducing the shoulder width from 14 to 4 feet (without adding a lane) is 

expected to increase FI crash frequency, assuming volumes and other variables are kept 

constant.This reinforces the previous finding that part-time shoulder use is most appropriate if it 

relieves congestion and thus reduces congestion-related crashes. 

Modelling Narrower Lanes and Narrower Shoulders 

Most projects involving the implementation of part-time shoulder use have not modified general 

purpose lanes. However, part-time shoulder use could be implemented by narrowing general 

purpose lanes and widening the shoulder to make it a more viable for travel. This section 

presents the predicted safety effects of this change for the specific scenarios shown in Table 6. 

0

2

4

6

8

10

12

14

Predicted Annual Crash Frequency

(crashes/year)

Two‐way Annual Average Daily Traffic (veh/day)

14‐foot Shoulder ‐ FI Crashes

4‐foot Shoulder ‐ FI Crashes
Safety Analysis

57

The alternatives without part-time shoulder use reflect default values from the prediction models. 

The alternatives with part-time shoulder use assume width reductions from existing travel lanes 

and shoulders to provide for an 11-foot shoulder lane. Scenarios with part-time shoulder use are 

modeled with two more travel lanes (one per direction) than the existing freeway cross-section. 

Like the previous analysis presented in this chapter, the scenarios only changed lane widths and 

shoulder widths and did not explicitly model shoulder use.

Table 6: Freeway part-time shoulder use scenarios and crash prediction inputs. 

Variable 

Alternative 

4-Lane Freeway 6-Lane Freeway 8-Lane Freeway 

without 

parttime 

shoulder 

use 

with 

parttime 

shoulder 

use 

without 

parttime 

shoulder 

use 

with 

parttime 

shoulder 

use 

without 

parttime 

shoulder 

use 

with 

part-time 

shoulder 

use 

Number of Lanes 4 6 6 8 8 10 

Lane Width 12 11 12 11 12 11 

Right Shoulder Width 10 4* 10 4* 10 4* 

Left Shoulder Width 6 3* 6 4* 6 5* 

* These are the narrowest shoulder widths for which the HSM has crash modification factors 

Note: Part-time shoulder use is modeled as six 11’ general purpose lanes beside narrower shoulders, in 

use 24 hours a day. 

Figure 20 through Figure 22 illustrate the predicted frequency of Fatal and Injury (FI) Crashes 

and Property Damage Only Crashes (PDO) for each freeway alternative shown in Table 6. 
Safety Analysis

58

Note: Part-time shoulder use is modeled as six 11’ general purpose lanes beside narrower shoulders, in 

use 24 hours a day. 

Figure 20. Graph. Predicted crash frequency with and without narrow lanes 

and narrow shoulders on 4-lane freeways. 

Note: Part-time shoulder use is modeled as eight 11’ general purpose lanes beside narrower shoulders, in 

use 24 hours a day. 

Figure 21. Graph. Predicted crash frequency with and without narrow lanes 

and narrow shoulders on 6-lane freeways. 

0

2

4

6

8

10

12

14

16

18

Predicted Annual Crash Frequency

(crashes/year)

Two‐way Annual Average Daily Traffic (veh/day)

PDO Crashes w/o Shoulder Use

PDO Crashes w/Shoulder Use

FI Crashes w/o Shoulder Use

FI Crashes w/Shoulder Use

0

5

10

15

20

25

30

Predicted Annual Crash Frequency

(crashes/year)

Two‐way Annual Average Daily Traffic (veh/day)

PDO Crashes w/o Shoulder Use

PDO Crashes w/Shoulder Use

FI Crashes w/o Shoulder Use

FI Crashes w/Shoulder Use
Safety Analysis

59

Note: Part-time shoulder use is modeled as ten 11’ general purpose lanes beside narrower shoulders, in 

use 24 hours a day. 

Figure 22. Graph. Predicted crash frequency with and without narrow lanes 

and narrow shoulders on 8-lane freeways. 

 

Figure 23 summarizes the scenarios shown in Table 6 and shows the safety effects of adding 

part-time shoulder use to 4-lane, 6-lane, and 8-lane freeways by narrowing general purpose lanes 

to 11 feet and reducing shoulder width. The point at which each line crosses the 0% mark on the 

y-axis indicates the AADT below which part-time shoulder use would be expected to increase 

crash frequency and above which part-time shoulder use would be expected to decrease crash 

frequency. 

The HSM freeway crash prediction models indicate that freeway part-time shoulder use, if 

similar to the three conversion scenarios presented in Figure 20 through Figure 22, could 

have the following influence on crash frequency and severity: 

● Reduce PDO crashes 

● Slightly increase FI crashes when converting existing 4- or 6-lane freeways 

● Have little to no effect on FI crashes when converting existing 8-lane freeways 

The analysis modeled part-time shoulder use as narrow general purpose lanes beside 

narrow shoulders and not explicitly as shoulder use because the HSM models do not 

explicitly include lanes designated for part-time shoulder use. 
Safety Analysis

60

 

Note: Part-time shoulder use is modeled as a reduction in general purpose lane width, addition of an 11’ 

general purpose lane, and reduction in shoulder width, in use 24 hours a day. 

Figure 23. Graph. Predicted percent change in crash frequency when adding 

part-time shoulder use by narrowing all lanes. 

CONCLUSIONS 

An analysis of existing crash data, including crash type, time of day, and the location of crashes, 

should be the basis of a safety analysis of potential part-time shoulder use. Congestion-related 

crashes occurring during the hours part-time shoulder use would operate will likely be reduced 

by part-time shoulder use. Crashes related to erratic driver behavior, driver confusion, or 

suboptimal geometry may increase with part-time shoulder use. 

Secondarily, the figures provided in this chapter provide ranges of AADT when part-time 

shoulder use is expected to have a positive or negative effect on crash frequency. 

Overall, there appears to be a link between changes in congestion and changes in safety 

performance when shoulders are narrowed to implement part-time shoulder use. The application 

of the HSM freeway crash prediction models indicate reducing congestion (by increasing 

capacity) can offset the increase in crashes associated with increasing the number of lanes while 

reducing lane and shoulder width. This finding is consistent with research conducted by 

Kononov et. Al. on Colorado’s freeways using a corridor-specific crash prediction model.(31) 

The empirical studies show that additional variables not specifically accounted for in the HSM 

prediction models could increase crashes associated with part-time shoulder use. Those factors 

include any differences between narrow general purpose lanes and a narrow part-time “lane” on 

‐20%

‐15%

‐10%

‐5%

0%

5%

10%

 ‐  50,000 100,000 150,000 200,000

Predicted Percent Change in Crash Frequency

Two‐way Annual Average Daily Traffic (veh/day)

Addition of

Shoulder Use to

4‐Lane Freeway

Addition of

Shoulder Use to

6‐Lane Freeway

Addition of

Shoulder Use to

8‐Lane Freeway
Safety Analysis

61

a shoulder, speed differential, influence of ramps, and upstream/downstream bottlenecks. 

Changes in barrier offset difference with and without part-time shoulder use can be modeled in 

the HSM, but were not included in the analysis presented in this chapter because of high 

dependence on site-specific conditions. There may be greater changes in crash frequency with 

part-time shoulder use if barriers are present and they cannot be moved further back from the 

roadway when part-time shoulder use is implemented. 

 

Environmental Analysis

63

CHAPTER 5. ENVIRONMENTAL ANALYSIS 

Although the National Environmental Policy Act (NEPA) process is described earlier, this 

chapter highlights how to consider and conduct an analysis for the three most 

likely/typical/common environmental issues associated with part-time shoulder use: 

● Air quality 

● Greenhouse gas emissions 

● Noise 

This chapter describes how an agency could or should go about assessing their impact on the 

feasibility of the project during the planning and NEPA stages and, later, addressing them during 

the environmental clearance stage. This chapter describes how and when these environmental 

analyses are conducted and discusses the potential effects of part-time shoulder use on air 

quality, emissions, and noise. This chapter identifies standard guides on conducting these 

analyses, and points out special considerations when evaluating the use of an existing paved 

shoulder (possibly with minor improvements) to allow use by cars and/or buses during peak 

hours on a regular basis. 

AIR QUALITY ANALYSIS 

Given the variety of characteristics of shoulder use projects, it is difficult to generalize the effect 

of shoulder use on air quality. Shoulder use may reduce congestion, which is generally beneficial 

to air quality. Shoulder use also has the potential to increase volume, which generally worsens 

air quality. There may also be no net effect on traffic characteristics that would affect air quality 

pollution concentrations. 

Nonattainment and Maintenance Areas 

Air quality analysis of federal transportation projects is required by the Environmental Protection 

Agency (EPA) in areas that do not meet, or previously did not meet, federal air quality standards, 

identified as “non-attainment” and “maintenance” areas, respectively. The definition of a federal 

project is broad and includes “any highway or transit project which is proposed to received 

funding assistance or approval through the Federal Aid Highway program or Federal mass transit 

program, or required FHWA or FTA approval for some aspect of the project, such as connection 

to an Interstate highway or derivation from applicable design standards on the Interstate system” 

is subject to transportation conformity. This definition, particularly the “derivation from 

applicable design standards,” will encompass most part-time shoulder use projects. Projects in 

non-attainment and maintenance areas must be incorporated into the region’s Transportation 

Improvement Plan (TIP) and, per the Clean Air Act, must demonstrate their consistency with the 

regional conformity determination and address potential localized emissions impacts. 

Conformity requirements cover four pollutants for which federal standards are setozone (O3), 

nitrogen dioxide (NO2), carbon monoxide (CO), and particulate matter (PM2.5 and PM10). 
Environmental Analysis

64

Areas that do not meet or previously did not meet federal air quality standards are identified as 

“non-attainment” and “maintenance” areas, respectively. Air quality analysis of federal 

transportation projects is required by the Environmental Protection Agency (EPA) in these 

designated areas for the transportation-related pollutantsozone, nitrogen dioxide, carbon 

monoxide, and particulate matter per the transportation conformity rule. Shoulder-use projects 

are typically federal projects because they require design exceptions. Projects in metropolitan 

non-attainment and maintenance areas must be incorporated into regional emissions analyses 

associated with the region’s Transportation Improvement Plan (TIP) and long-range plan (MTP). 

Transportation conformity rules also require the analysis of potential localized emissions impacts 

where applicable. Non-attainment and maintenance areas have standing transportation 

conformity procedures in place that address how projects are handled to assess for conformity 

status (exempt/non-exempt) and whether a project-level analysis is required. These procedures 

may assist in assessing individual part-time shoulder lane projects. 

More information on conformity can be found on these websites: 

FHWA Conformity Website: http://www.fhwa.dot.gov/environment/air_quality/conformity 

EPA Conformity Website: http://www.epa.gov/otaq/stateresources/transconf/index.htm 

Other Areas 

Outside of nonattainment and maintenance areas, air quality analyses may be conducted as part 

of a NEPA analysis. Agencies may consider the following questions when deciding whether or 

not to conduct air quality analysis in these areas: 

● Is there concern about the project within the community? 

● Is the shoulder only open to buses, or will a greater percentage of the fleet have access? 

● If the shoulder is only open to buses, is service being added or will bus headways remain 

the same? 

● For PM impacts, are diesel vehicles being moved closer to sensitive roadside receptors? 

● Is the project in a dusty area where dust will be stirred up when the shoulder opens each 

day? 

The degree of analysis conducted should be proportional to the project scope. Qualitative 

analysis without the use of modeling software is likely acceptable for low impact projects and 

more-complex analysis may provide useful information for projects with a higher potential for 

impact. 

Analysis Tools and Techniques 

For quantitative air quality analysis, conformity guidance should be used. Tools for quantitative 

analysis include the latest MOVES (Motor Vehicle Emissions Simulator) and EMFAC models. 

MOVES is used in all states, except California, which uses EMFAC. The models require inputs 

such as volumes and speeds, as shown in Table 7. 
Environmental Analysis

65

Table 7. Air Quality tools and data needs. 

Tool Inputs 

MOVES 

(Motor Vehicle Emissions Simulator) 

Vehicle Operating Mode: vehicle speed, vehicle 

acceleration, road grade, rolling resistance, vehicle 

mass 

Service Hours Operating: actual time a vehicle 

spends within certain operating modes (captures 

emissions from idling) 

EMFAC VMT-based emission model: daily VMT by vehicle 

speed (at 5 mph increments) and vehicle class 

More information on these tools can be found on these websites: 

U.S. Environmental Protection Agency, Motor Vehicle Emissions Simulator (MOVES): 

http://www.epa.gov/OMSWWW/ngm.htm 

California Air Resources Board, Emission Factor Model (EMFAC): 

http://www.arb.ca.gov/msei/categories.htm

When analyzing part-time shoulder use, practitioners may consider two unique aspects that differ 

from a conventional widening project: 

● During the hours the shoulder is closed to traffic, dust may accumulate on it, and this dust 

may be stirred up when the shoulder reopens each day. 

● Use of the right shoulder will place emission sources (vehicles) closer to sensitive 

receptors, if any are present. 

If a quantitative analysis is conducted for transportation conformity purposes, practitioners 

should follow EPA guidance for conducting hot-spot analysis for particulate matter and carbon 

monoxide, where applicable. 

GREENHOUSE GAS EMISSIONS ANALYSIS 

In some statescurrently California, Massachusetts, New York, and Washingtonanalysis of 

greenhouse gas (GhG) emissions is required for some transportation projects. Part-time shoulder 

use projects in these states may require GhG analysis, depending on the circumstances. 

Resources, such as the FHWA’s Handbook for Estimating Transportation Greenhouse Gases for 

Integration into the Planning Process, provide information on how to analyze on-road 

greenhouse gas emissions at the state and regional level. The majority of greenhouse gas (GhG) 

emissions from transportation are carbon dioxide (CO2) emissions from the combustion of 

petroleum-based products. Methods to reduce GhG emissions include improving traffic 

operating conditions, such as avoiding rapid acceleration and braking, reducing idling, and 
Environmental Analysis

66

reducing travel demand. MOVES and EMFAC (described in the previous section) are used for 

GhG emissions analysis. 

Similar to air quality, it is difficult to generalize the effect of part-time shoulder use on GhG 

emissions. A study of the M42 part-time shoulder uses pilot project in the UK captured this.(25) In 

general, regardless of part-time shoulder use, emissions on the M42 fall per mile as average 

speed increases from congested conditions to 40-50 mph where the fuel efficiency of engines is 

greatest and then rises as the average speed increases towards 70 mph and fuel efficiency falls. 

On a per-vehicle basis, the GhG emission benefit of part-time shoulder use was greatest in lower 

speed ranges when it reduced start-stop traffic. However, the effect is likely to be outweighed by 

additional emissions from higher speeds above the 40-50 mph range and changes in peak period 

traffic volume. The study concluded by stating “we expect that shoulder [use] will lead to an 

increase in traffic emissions compared to a ‘do nothing’ scenario. However, the impact of [parttime shoulder use] on traffic emissions is expected to be lower than the impact of road 

widening.” 

NOISE ANALYSIS 

The level of highway noise primarily depends upon traffic volume, traffic speed, truck volume, 

and to a lesser extent it depends on other factors such as topography and pavement type. 

The Federal noise regulation in 23 CFR 772 constitutes the Federal noise standard. For the 

purposes of meeting the requirements in 23 CFR 772, a noise analysis is required for all Federal 

or Federal-aid projects that are defined as Type I, per the regulation. Noise measurements are 

conducted to determine existing noise levels, and future levels are predicted using the FHWA 

Traffic Noise Model (TNM). A noise impact occurs when the predicted noise level approaches 

or exceeds the Noise Abatement Criteria (NAC) in 23 CFR 772, Table 1, or represents a 

substantial increase over existing noise levels. If noise impacts are determined, then noise 

abatement must be considered. If noise abatement is found to be feasible and reasonable, per 23 

CFR 772 and that state’s noise policy, then the noise abatement measure must be constructed. 

For the purposes of NEPA, a noise analysis may also compare the project noise level of a nobuild or no action condition to the existing noise levels. 

There are eight parts to the Type I definition, but there are only three that may encompass a parttime shoulder use project, depending on the type of shoulder and any restrictions and/or 

requirement for its uses. Those three parts include: 

● “The physical alteration of an existing highway where there is...substantial horizontal 

alteration. A project that halves the distance between the traffic noise source and the 

closest receptor between the existing condition and the future build condition.” 

● “The addition of a through-traffic lane(s). This includes the addition of a through-traffic 

lane that functions as an high-occupancy vehicle (HOV) lane, High-Occupancy Toll 

(HOT) lane, bus lane, or truck climbing lane.” 

● “Restriping the existing pavement for the purpose of adding a through-traffic lane or an 

auxiliary lane.” 
Environmental Analysis

67

Similar to air quality analysis, design exceptions required for part-time shoulder use projects will 

make these projects federal and, thus, subject to 23 CFR 772. 

The level of noise analysis necessary will depend upon the type of part-time shoulder use. For 

bus-on-shoulder (BOS), noise analysis may be qualitative because the number of additional 

vehicles and changes in speed are small or nonexistent. For static and dynamic part-time 

shoulder use, noise analysis will typically be conducted in a manner similar to a conventional 

widening project. For the noise analysis, the location of the part-time shoulder use would affect 

the proximity to sensitive receptors. Left side part-time shoulder use is less likely to have noise 

impacts compared to right side part-time shoulder use, which places the traffic closer to sensitive 

receptors. Noise analysis and determination of noise mitigation needs is focused on peak noise 

conditions. This may or may not correspond to peak volume conditions (when shoulder lanes are 

typically open), and analysis will determine if part-time shoulder use affect peak noise or not. 

Predicted noise levels are determined by using the FHWA Traffic Noise Model.(4) If part-time 

shoulder use does increase peak noise, and there are impacts associated with it, then noise 

abatement must be considered and implemented if found to be feasible and reasonable. 

Existing part-time shoulder use demonstrates the differences in noise analysis and mitigation 

needs. For example, part-time shoulder use on US 2 in Everett, Washington, was implemented 

on a bridge over wetlands. There were no sensitive receptors (i.e. land uses where noise would 

cause impacts) in the project area, so no noise analysis was conducted. Washington State is 

currently planning part-time shoulder use on another freewayI-90 east of Seattleand noise 

analysis was conducted because there were sensitive receptors. The analysis indicated the need 

for noise walls, which will be constructed as part of the part-time shoulder use project.(33)

Costs and Benefits Analysis

69

CHAPTER 6. COSTS AND BENEFITS ANALYSIS 

The previous chapters (3-5) address possible methods for estimating measures of part-time 

shoulder use performance in terms of mobility, safety, and environment, respectively. This 

chapter discusses how to compute the costs of part-time shoulder use over a project’s life cycle, 

how to monetize the potential benefits (or dis-benefits) discussed in previous chapters, and how 

to combine costs and benefits into a benefit-cost (B-C) ratio to simultaneously compare these 

performance measures. The B-C ratio is a useful tool in comparing alternative approaches for 

implementing and operating part-time shoulder use. 

A benefit-cost analysis is also an important consideration within the broader regional 

transportation planning process. Transportation planners and operations personnel will likely 

need to compare more traditional infrastructure projects (e.g., permanent widening, bottleneck 

removal) and Transportation System Management and Operations (TSM&O)-oriented strategies, 

including part-time shoulder use. Because both of these different types of projects are often 

competing for the same funds, a benefit-cost analysis provides a framework for prioritizing and 

ranking widely varying improvement types. 

This chapter provides information for computing life-cycle costs and developing a Benefit-Cost 

Analysis (BCA). Additional details on some of the BCA activities and processes can be found in 

the Federal Highway Administration (FHWA) Life-Cycle Cost Analysis Primer and the FHWA 

Operations Benefit/Cost Analysis Desk Reference.

(34, 35) 

LIFE-CYCLE COSTS 

Estimating the life-cycle costs of part-time shoulder use is often complex. This is particularly 

true of more-advanced part-time shoulder use, such as dynamic part-time shoulder use or static 

part-time shoulder use with dynamic signs. Compared with more traditional infrastructure 

improvements, TSM&O improvements such as part-time shoulder use typically incur a greater 

proportion of their costs as continuing operations and maintenance costs, as opposed to upfront 

capital costs. 

Much of the intelligent transportation systems (ITS) equipment associated with part-time 

shoulder use also typically has a much shorter anticipated useful life than many traditional 

improvements and must be replaced as it reaches obsolescence. Costs include deployment, 

implementation, and operations and maintenance plans. Failure to recognize and accurately 

forecast these costs may result in future funding or resource shortfalls, or the inability to properly 

operate and maintain deployed part-time shoulder use. 

The FHWA Operations Benefit/Cost Analysis Desk Reference recommends the following 

structure for organizing cost data: 

● Capital costs. The upfront costs necessary to prepare the shoulder pavement for traffic 

flow, provide refuge areas, modify signing and pavement marking, and procure and 

install ITS equipment. These costs will be shown as a total (one-time) expenditure and 
Costs and Benefits Analysis

70

will include the capital equipment costs, as well as the soft costs required for design, 

installation, and other systems engineering activities. Potential capital cost elements for 

part-time shoulder use are identified in Table 8. 

● Operations and maintenance costs. Those continuing costs necessary to operate and 

maintain the deployed part-time shoulder use, including ongoing labor costs for activities 

such as emergency patrols, additional law enforcement, and TMC staffing. These costs 

do not include wholesale equipment replacement when the equipment reaches the end of 

its useful life. These operations and maintenance costs will be presented as annual 

estimates. Likely operations and maintenance costs are listed in Table 9. 

● Replacement costs. The periodic cost of replacing and/or redeploying equipment as it 

becomes obsolete and reaches the end of its expected useful life. 

Table 8. Potential capital cost components. 

Component Description 

Activities associated 

with the systems 

engineering process

Concept of Operations and requirements documents, design and 

contract documents, testing and acceptance activities, construction 

engineering, and environmental assessments or environmental impact 

statements. 

Shoulder 

reconstruction and 

widening 

Repaving the shoulder, modifying drainage structures, 

adding/relocating guardrails, constructing turnouts, and complete 

reconstruction or minor widening of the shoulder.

Ramp treatments

Ramp widening and/or shoulder pavement improvement along ramps 

and in gore areas as may be required to provide continuity of the parttime shoulder use through interchanges. 

Training For existing / new operations staff, maintenance and law enforcement 

staff, and bus operators on Bus on Shoulder (BOS) facilities.

Emergency patrols Typically increased to compensate for the loss of a breakdown area.

Public outreach and 

communications 

campaigns

Part-time shoulder use will likely be new to the motoring public and an 

extensive public outreach program may be required 
Costs and Benefits Analysis

71

Continuation 

Component Description 

ITS

Most part-time shoulder use, except for BOS, has some degree of ITS. 

Major ITS cost components may include: 

 CMS and supporting sign supports and gantries – Static parttime shoulder uses facilities are increasingly being equipped with 

CMS, and dynamic facilities by definition must have CMS. Costs 

for CMS can vary greatly depending on spacing, mounting 

(overhead or ground-mounted), design (gantry or mast arm if 

overhead). Part-time shoulder uses with other Active Traffic 

Management (ATM) elements such as dynamic speed limits, 

dynamic lane assignment, and / or queue warning will require 

larger and more frequent CMS, increasing cost. 

 Overhead lane-use control signals – These are less expensive 

than CMS, but can only indicate whether a lane is open, closed, or 

(in some cases) about to close 

 Controllers – for operating CMS and for processing detector data. 

 Detection and CCTV – Dynamic part-time shoulder use or static 

part-time shoulder use that can be closed due to incidents will 

require some sort of detection and surveillance, up to full CCTV 

coverage of the shoulder and emergency refuge areas. If additional 

ATM elements such as dynamic speed limits, dynamic lane 

assignment, and queue warning are included, the system will likely 

require extensive detector subsystems. 

 Communications and power software – Dynamic part-time 

shoulder use with automated decision-making on the opening and 

closing of the shoulder will likely require additional software 

algorithms, including decision support systems that can assist 

operators with quickly inputting necessary information (e.g., 

confirm that a lane is closed, confirm that the shoulder is clear of 

any vehicles) and approving opening/closing. 

 Central Hardware / TMC Enhancements – Additional central 

hardware such as servers, communications modems, workstations, 

and video displays may be required at the TMC. This in turn may 

require alterations or enhancements to the TMC. 

Mobilization and contingency costs. 

 
Costs and Benefits Analysis

72

Table 9. Potential operations and maintenance cost components. 

Component Description 

Compliance 

It may be necessary to include the cost of additional police presence to help 

enforce the part-time shoulder use (e.g., not using the shoulder when closed) 

and related strategies such as variable speed limits. 

Driver 

Training 

Transit agencies using BOS facilities will need to conduct training for new 

bus drivers as they are hired or assigned to routes with BOS. 

“Sweeps” 

Many agencies with static or dynamic part-time shoulder use have a police or 

maintenance vehicle drive the length of the facility prior to each opening of 

the shoulder. 

ITS 

Most part-time shoulder use, except for BOS, has some degree of ITS. Major 

ITS operations and maintenance components may include: 

 On-going TMC Operation – Depending on the size and complexity of 

the part-time shoulder uses system, and the degree of automation and 

accompanying ATM, existing TMC operators’ workload might increase, 

and additional staff might be required. Training of new staff must also be 

included in the costing. 

 Updating and Maintaining Operating Procedures – Besides the 

additional labor costs associated with operations, there are other costs tied 

to operation of ATM strategies. These include updating standard 

operating procedures and the system rules based on operating experience. 

 Maintenance – This includes a consistent and continuing program of 

preventive and reactive maintenance of supporting ITS hardware in the 

field and at the TMC. This may require additional maintenance staff, 

spare parts, and on-going training. 

Roadway 

Maintenance 

Maintenance of lanes designated for part-time shoulder use is typically the 

same as maintenance of adjacent general purpose lanes and the incremental 

cost of maintenance (patching potholes, maintaining pavement markings, 

etc.) is minimal. Debris removal needs are more similar to regular travel 

lanes than regular shoulders. Snow removal is sometimes challenging in 

constrained areas such as under or on bridges after a major snowfall, and 

there may be costs related to this. 

Within each of the capital costs (Table 8) and operations and maintenance costs (Table 9), there 

are items that increase proportionally to the length of the facility and items that are only 

minimally affected by facility length. Costs such as driver training, public education, and 

“backbone” ITS infrastructure in a TMC are generally incurred regardless of facility length. 

Costs such as pavement preparation, CMS, and emergency turnouts are incremental, and largely 

a function of facility length. 

Structuring the cost data in this framework provides the ability to readily scale the cost estimates 

to the size of potential deployments. Presenting the costs in this scalable format provides the 
Costs and Benefits Analysis

73

opportunity to easily estimate the costs of expanding or contracting the size of the deployment 

and allows the cost data to be reutilized for evaluating other corridors. 

MONETIZING BENEFITS 

The computation of potential operational, safety, and environmental benefits of part-time 

shoulder use was discussed in previous chapters. This section describes how to monetize those 

benefits. The estimated benefits will likely be expressed in terms of reduced travel times, 

reduced delays, reduced number of crashes, and so forth, relative to existing conditions or a 

future no-build scenario. It will, therefore, be necessary to convert these various measures into a 

dollar value. State DOTs typically have such conversion values, or national averages may be 

used. Table 10 shows the values used by the FHWA TOPS-BC tool for various benefit 

parameters. 

TOPS-BC is a benefit-cost tool developed by FHWA for TSM&O projects. In addition to 

monetizing benefits, it can develop estimates of benefitsif they were not previously 

computedusing link volume (per analysis period) as a primary input, along with link length, 

number of lanes, link capacity, and free-flow speed. 

Many advanced TSM&O strategiesincluding part-time shoulder use and particularly part-time 

dynamic shoulder laneshave only been recently deployed in the U.S. Accordingly, estimates of 

the likely impacts and benefits resulting from these strategies may need to be based on limited 

empirical data of the actual benefits of the strategy within the analysis. Being conservative 

regarding the estimated benefits, and conducting a sensitivity analysis, should be considered. For 

part-time shoulder use, benefits are likely to be focused on improved operational performance. 

As discussed in previous chapters, there are no methods for reliably predicting crashes with parttime shoulder use, and environmental benefits may be positive or negative. 

Table 10 shows some of the performance measures that would be used in a benefit-cost estimate, 

and the societal cost of each per TOPS-BC. Many agencies have their own valuations for these 

parameters as well. 

 
Costs and Benefits Analysis

74

Table 10. Benefit estimation parameters. 

Benefit Specific Condition Valuation

Delay 

(per hour) 

“On the clock” travel $ 30.91 

Other auto travel $ 15.46 

Truck travel $ 30.91 

Crashes 

(per occurrence) 

Fatality $ 9,936,727 

Injury $ 73,973 

Property damage only (PDO) $ 2,539 

Fuel Use Per gallon (excluding taxes) $ 4.05 

Non-fuel Operating Costs 

(per VMT) 

Auto $ 0.25 

Truck $ 0.37 

Emissions 

(per ton) 

CO $ 77 

CO2 $ 41 

Nox $ 17,997 

PM10 $ 145,518 

VOC $ 1,259 

Noise 

(per VMT) 

Auto $ 0.0012 

Truck $ 0.0364 

Note: From TOPS-BC Tool, assuming 2015 dollars and a 2% inflation rate

The combination (e.g., mobility, safety, reliability, environmental) and subsequent monetization 

of benefits needs to be carefully planned and structured to avoid the double-counting of benefits. 

Double-counting can occur in situations in which there are overlaps in different benefits, or when 

a change to one benefit results in a direct change to another benefit. 

Another critical aspect of monetizing benefits is to annualize them, and then estimate the total 

dollar value of the benefits over the life cycle of the system. This life-cycle period must be the 

same as the analysis period used for the estimating costs, as discussed below. 

CONDUCTING A BENEFIT/COST ANALYSIS 

Once the life-cycle cost of a project has been determined and the project’s benefits have been 

monetized, a benefit-cost analysis can be conducted. 

Analysis Period 

It is essential that the analyses use the same period of timethe “analysis period”to assess 

life-cycle costs and benefits, and to compare the resulting benefit-cost ratios for different 
Costs and Benefits Analysis

75

alternatives and scenarios. The analysis period should be long enough to include the initial 

construction up to (and possibly beyond) the point where it becomes necessary to replace many 

of the ITS components, as these have a shorter lifespan than traditional infrastructure. The 

purpose of this approach is to spread out both the benefits and costs over an appropriate 

timeframe to allow for a meaningful analysis. For part-time shoulder use, a 10-, 15-, or 20-year 

time horizon should be considered. Shorter horizons may be appropriate if part-time shoulder use 

is being implemented as a temporary measure until a traditional widening project is completed. 

Inflation and Discounting 

An inherent issue in life-cycle benefit-cost analysis is the difficulty of making value comparisons 

among projects that are not measured in equal units. Even when values are stated in monetary 

units such as dollars, the values still may not be comparable, for at least two reasons: 

● Inflation. Expenditures typically occur at various points in the past or future and are, 

therefore, measured in different value units because of changes in price (e.g., a 1990 

dollar would, in general, have purchased more real goods and services in 1990 than 

would a 2010 dollar in 2010). A general trend toward higher prices over time, as 

measured in dollars, is called inflation. A general trend toward lower prices is called 

deflation. Dollars that include the effects of inflation or deflation over time are known as 

nominal, current, or data-year dollars. Dollars that do not include an inflation or deflation 

component (i.e., their purchasing power remains unchanged) are called constant or baseyear dollars.

● Discounting. Costs or benefits (in constant dollars) occurring at different points in 

time—past, present, and future—cannot be compared without allowing for the 

opportunity value of time. The opportunity value of time as it applies to current versus 

future funds can be understood in terms of the economic return that could be earned on 

funds in their next best alternative use (e.g., the funds could be earning interest) or the 

compensation that must be paid to induce people to defer an additional amount of current 

year consumption until a later year. Adjusting for the opportunity value of time is known 

as discounting. 

Analytically, adjusting for inflation and discounting are separate calculations. Future costs and 

benefits of a project should be expressed in constant dollars and then discounted to the present at 

a discount rate that reflects only the opportunity value of time (known as a real discount rate). 

Through the use of a real discount rate, the following transformations can be performed to 

facilitate comparison of the constant dollar costs of alternative transportation projects: 

● Relocation in Time. A single figure can be “moved” (transformed into an equivalent 

value) backward or forward in time, without altering its real value, known as its 

“present worth”.

● Annualized Cost. This is the average annual expenditure that would be expected to 

deploy, operate, and maintain the operations strategy and replace (or redeploy) any 

equipment as it reaches the end of its useful life. Within this cost figure, the capital costs 
Costs and Benefits Analysis

76

will be amortized over the anticipated life of each individual piece of equipment. This 

annualized figure is added with the reoccurring annual operations and maintenance cost 

to produce the annualized cost figure. This figure is particularly useful in estimating the 

long-term budgetary impacts of TSM&O deployments. 

● Present Value. Any combination of flows (finite or infinite) and lump sums can be 

summed into a single value at a single point in time. 

TOPS-BC 

A number of tools, many of them specific to certain agencies, exist for B/C analysis. The TOPSBC tool, developed by FHWA for TSM&O projects including part-time shoulder uses, is 

described in this section. 

TOPS-BC tool is a spreadsheet-based tool providing the following four key capabilities: 

● The ability for users to investigate the expected range of impacts associated with previous 

deployments and analyses of many TSM&O strategies. 

● A screening mechanism to help users identify appropriate tools and methodologies for 

conducting a benefit/cost analysis based on their analysis needs. 

● A framework and default cost data to estimate the lifecycle costs of various TSM&O 

strategies, including capital, replacement, and continuing operations and 

maintenance costs. 

● A framework and suggested impact values for conducting simple benefit/cost analysis for 

selected TSM&O strategies. 

A desk reference was developed in parallel with the tool. 

Part-time shoulder use is one of the strategies addressed by TOPS-BCidentified therein as 

“ATDM Hard Shoulder Running.” The user will likely need to modify default values and add 

inputs to meet the specifics of any particular location and application, for example: 

● The useful life, capital costs and annual costs for the “infrastructure-related components”.

● The useful life, capital costs and annual costs for the “incremental deployment 

equipment”. 

● Additional cost items for the two categories. Examples were listed earlier in this chapter 

in Table 8. 

● TOPS-BC calculates costs based on the user inputs of the “number of infrastructure 

deployments” and the “number of incremental deployments.” The infrastructure 

deployments (i.e., hardware, software, staff at the TMC, public outreach) can likely be set 

up as a single deployment. Incremental deployments may be set up as a single ITS 

location (e.g., lane control sign, support structure, controller, detector, and 

communications), although a “per mile” approach may work better if new 

communications infrastructure and/or some sort of shoulder work is required. With the 
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77

per-mile approach, the cost per mile for new communications and shoulder work would 

be included, along with the number of signs, support structures, controllers, detectors, 

cameras, etc., per typical mile. 

As was the case with estimating benefits, care should be taken to not double-count costs. For 

example, if part-time shoulder use is to be implemented with other ATM strategies (such as 

dynamic speed limits and dynamic lane assignmentwhat is shown in TOPS-BC as “speed 

harmonization”), then the supports, controllers, and communications for new signs may already 

be included in the other ATM costs, and should not be included for part-time shoulder use. 

SELECTING THE OPTIMUM PROJECT(S) 

Although a B-C analysis provides a robust and comprehensive framework for comparing the 

relative efficiency of different projects, strategies, and combinations of strategies, the resulting 

B-C ratios should not be the only piece of information that may be used in analyzing and 

prioritizing projects and strategies. Other considerations that should be addressed may include 

the following: 

● Regional goals and their relative priorities. If improved transit is of great importance, a 

BOS approach may be given greater consideration even if it has a low B-C ratio. If 

congestion frequently occurs outside of traditional peak periods, wideningalthough 

costlymay be more appropriate than part-time shoulder uses. 

● Roadway Use. Facilities that carry significant freight traffic, serve a large number of bus 

routes, provide access to and from special event venues, may be used for evacuations, 

and/or already have other types of ATM may have a higher priority for part-time shoulder 

uses. 

● Funding and time constraints. There may be budget constraints that preclude some 

projects, regardless of the B-C ratio. Similarly, it may be easier and faster to construct 

and implement strategies along one roadway relative to others and allow benefits to start 

accruing as soon as possible. 

● Political will and public acceptability. 

Design Considerations

79

CHAPTER 7. DESIGN CONSIDERATIONS 

Part-time shoulder use typically utilizes an existing shoulder; therefore, the design of a part-time 

shoulder use implementation project is typically less involved than the design of a full-time 

added lane. However, the same elements of roadway designgeometry, pavement, drainage, and 

signing and pavement markingare applicable to both full-time lanes and lanes designated for 

part-time shoulder use and require some level of attention prior to implementation. Preexisting 

pavement and drainage should be assessed before part-time shoulder use is implemented, and 

improvements or modifications may be necessary. Special signing and pavement markings are 

necessary for part-time shoulder use, and dynamic signs are often used. 

Designing for operations is “the collaborative and systematic consideration of management and 

operations during transportation project design and development” (36). In the context of part-time 

shoulder use, a designing for operations process incorporates design features needed for parttime shoulder usefull depth pavement, sufficiently wide shoulders and lateral offsets, space for 

turnouts, and so forthinto the design of a facility where there is a reasonable likelihood that 

part-time shoulder use would someday be implemented. Part-time shoulder use is typically 

implemented on older freeways in constrained environments, so the design project in which a 

designing for operations process is used may be a reconstruction project rather than a new 

facility. 

This chapter presents design considerations for part-time shoulder use in the context of existing 

design practices for facilities without part-time shoulder use and the experiences of states that 

have implemented part-time shoulder use. There is little quantitative research on design elements 

of part-time shoulder use, and much will be learned in this area in the coming years as new 

facilities are built and existing facilities age. 

GEOMETRIC DESIGN 

From a geometric design perspective, freeway part-time shoulder use can be subdivided into 

three types of segments: 

● Beginning and end segments 

● Basic freeway segments 

● Ramp-freeway junction segments 

This section presents geometric design considerations for each of these segment types, as well as 

design considerations for arterials with part-time shoulder use and emergency turnout areas. 

Part-time shoulder use may introduce design elements that are below the minimum criteria 

specified in AASHTO’s A Policy on Geometric Design of Highways and Streets (Green 

Book)(37) and design exceptions may be required. If the facility is an Interstate Highway, design 

elements in AASHTO’s A Policy on Design Standards – Interstate System(38) also apply. The 

Basic Freeway Segment section below presents design criteria that part-time shoulder use may 
Design Considerations

80

affect and require design exceptions. The process for obtaining a design exception is covered in 

CHAPTER 9. 

Beginning and End Segments 

Logical termini should be established during project scoping and preliminary design consistent 

with National Environmental Policy Act (NEPA) guidance. Part-time shoulder use can begin and 

end along basic segments or at ramps. If the beginning or end of static or dynamic part-time 

shoulder use is along a basic freeway segment, then it is desirable for it to be located such that it 

is highly visible and comprehended by approaching drivers. Horizontal curves, crest vertical 

curves, and overpasses may limit a driver’s visibility of a downstream roadway, and dropping 

any type of laneincluding part-time shoulder usewithin or immediately beyond these 

features, should be avoided if possible. Likewise, dropping any type of lane in or immediately 

beyond an area with extensive, complex signing or other features contributing to high driver 

workload should be avoided if possible. 

There are fewer considerations associated with adding a general purpose lane in comparison to 

dropping a general purpose lane because it requires no action on the part of the driver. However, 

starting part-time shoulder use requires a series of signs to indicate use restrictions and the point 

at which use of the shoulder becomes allowable. Therefore, the desirable locations for lane drops 

described above are also desirable locations to start part-time shoulder use. 

Beginning of Part-time Shoulder Use 

Part-time shoulder use added along basic freeway segments should have pavement markings that 

guide drivers from the adjacent general purpose lane to the shoulder, but also maintain continuity 

of the general purpose lane. Typically, a diagonal solid edge line provides a transition from the 

edge of the general purpose lane to the edge of the shoulder, and a dotted edge line connects the 

edge line adjacent to the general purpose lane before and after the transition to the part-time 

shoulder use. Striping for the beginning of part-time shoulder use is shown below in Figure 24. 

Figure 24. Illustration. Typical part-time shoulder use add. 

(Source: Kittelson & Associates, Inc.) 

Part-time shoulder use may also begin as an add “lane” from an on-ramp, with pavement 

markings supporting both ramp-to-general purpose lane and ramp-to-shoulder movements. At 

the end of the speed-change lane for a parallel style ramp, drivers from the on-ramp merge into 

the general purpose lane when the shoulder is closed and continue straight into the shoulder 

when it is open. This method of adding is most desirable at high-volume ramp locations where 

the merge of traffic from the on-ramp onto the freeway creates a bottleneck on the freeway. It is 

least desirable at locations where it is undesirable for a significant portion of on-ramp traffic to 
Design Considerations

81

use the shoulder, such when the shoulder is restricted to high-occupancy vehicle (HOV) traffic or 

an on-ramp with a high percentage of truck traffic. 

End of Part-time Shoulder Use 

The end of part-time shoulder use along a basic freeway segment is designed similarly to the 

beginning of part-time shoulder use. A solid edge line is typically used to transition traffic from 

the shoulder back to the adjacent general purpose lane, shown in Figure 25. 

Figure 25. Illustration. Typical part-time shoulder use drop. 

(Source: Kittelson & Associates, Inc.) 

In general, basic freeway lanes should not be trapped onto exit ramps because this is unexpected 

to drivers, and the same applies to part-time shoulder use. However, at large system 

interchanges, it is more common to drop lanes onto ramps because a large percentage of the 

traffic is exiting. If exit ramps and the part-time shoulder use are on the same side of the freeway, 

dropping the shoulder use onto the exiting ramp may be reasonable depending on traffic patterns. 

Other strategies at system interchanges include ending the part-time shoulder use at the same 

location where a general purpose lane is added (because general purpose lanes are often added in 

advance of system interchanges) and carrying the part-time lane through the system interchange 

if the exiting and entering ramps have one or two lanes are designed in a manner that will not 

create conflicts (see ramp-freeway junction section of this chapter). Carrying part-time shoulder 

use through system interchanges is complex due to conflicts with exiting and entering traffic and 

the role part-time shoulder use serves on the freeway network, and should be done with caution. 

System interchanges often change volume (to a significant degree) or number of basic lanes on a 

facility, and there is often a not a need for part-time shoulder use both upstream and downstream 

of a system interchange. 

At major forks, part-time shoulder use can be carried onto one of the forks. This is desirable if 

the ramps downstream of the fork have more lanes than the freeway approaching the fork. US 2 

in Washington State and SR 29 in New Jersey both have part-time shoulder use in one direction 

that terminate this way. SR 29, for example, has three general purpose lanes upstream of the fork 

and two two-lane ramps downstream of the fork. Figure 26 shows an example of part-time 

shoulder use used to remove a bottleneck upstream of a major fork. The part-time shoulder use in 

Figure 26 is on the right side and provides the second lane to the right side fork, terminating into 

a general purpose lane on the ramp. 
Design Considerations

82

Figure 26: Illustration. Part-time shoulder use approaching major fork. 

(Source: Kittelson & Associates, Inc.) 

Shoulder Use Between Interchanges Only 

Georgia and Hawaii use static part-time shoulder use between (but not through) adjacent 

interchanges to effectively create part-time auxiliary lanes and mitigate the effects of closelyspaced entrance and exit ramps. In this case, the shoulder is not functioning as a basic freeway 

lane, and a drop onto a service interchange is necessary and inherent in the design. 

Basic Freeway Segments 

Controlling design criteria and their minimum values from the AASHTO Green Book(37) and 

AASHTO’s A Policy on Design Standards – Interstate System are presented in Table 11.

(38)

When the Green Book has different values for different types of facilities, only the freeway 

values are presented because part-time shoulder use is typically implemented on freeways. 

Minimum values from both AASHTO publications are the same for many of the criteria, and are 

only noted separately if they differ. In one or both documents, some minimum criteria are 

required (“shall”) as opposed to desired (“should”). A design exception is needed if required 

minimum values are not met (on roadways on the National Highway System). States should 

work with their Federal Highway Administration (FHWA) Division Office when considering 

design exceptions on the National Highway System.

Existing design features often dictate part-time shoulder use dimensions. However, as discussed 

in 0, higher quality geometry meeting or exceeding AASHTO criteria, when possible, generally 

leads to higher utilization and capacity of the shoulder, compared to more constrained geometry. 
Design Considerations

83

Table 11. Controlling criteria, minimum AASHTO values, and relationship to part-time 

shoulder use. 

Controlling 

Criteria 

Minimum AASHTO Values(37, 38, 39) Affected by 

Part-time 

shoulder use 

Design Speed 

Chosen by agency. Shall be at least 50 mph in urban 

areas, should be 70 mph in rural areas, may be 50-60 

mph in mountainous areas 

No, unless 

agency choses 

to reduce it 

Lane Width Shall be 12 feet Possibly 

Shoulder Width 

(values for paved 

width presented) 

4-lane freeways – Right shoulder shall be 10+, left 

shoulder shall be 4+ feet 

6+-lane freeways – both shoulders should be 10+ feet 

Truck traffic exceeds 250 DDHV – 12+ foot shoulders 

on both sides should be considered 

Always 

Bridge Width 

Less than 200 feet long – Shall equal full paved width of 

approach roadway 

200+ feet long, Green Book – provide approach shoulder 

widths and median barrier if single structure. 

200+ feet long, Interstate Standards – offsets to parapet, 

rail, or barrier shall be 4+ feet from travel lane 

Likely 

Horizontal 

Alignment 

Varies based on design speed and maximum 

superelevation (see Green Book Table 3-7) Possible 

Superelevation Maximum of 6 to 12 %, should consider maximum of 6 

to 8 % where snow and ice are a concern Possible 

Vertical 

alignment 

Varies based on several elements (see Green Book 

Figure 3-43 for sag curves and 3-44 for crest curves) Never 

Grade Varies 3 to 6% by type of terrain and design speed (See 

Green Book Table 8-1) Never 

Stopping Sight 

Distance 

Varies based on design speed and grade (See Green Book 

Table 3-1 and 3-2) Possibly 

Cross slope 

Green Book – 1.5 to 2 % 

Interstate Standards – Shall be 1.5% minimum, desirably 

2%, may be 2.5% in areas of intense rainfall. Shoulder 

slopes should be in range of 2 to 6 % 

Possibly 
Design Considerations

84

Continuation 

Controlling 

Criteria 

Minimum AASHTO Values(37, 38, 39) Affected by 

Part-time 

shoulder use 

Vertical 

clearance 

Green Book – Shall be 16+ feet over lanes and shoulders 

in rural areas and at least a single freeway route through 

highly developed urban areas, shall be 14+ feet on other 

highly developed urban freeway routes 

Interstate Standards – Shall be 16+ feet over lanes and 

shoulders in rural areas and at least a single Interstate 

through urban areas, shall be 14+ feet on other urban 

Interstate routes 

Possibly 

Lateral offset to 

obstruction 

Green Book – refers to AASHTO Roadside Design 

Guide, which specifies a minimum width of 1.5 feet. 

Interstate Standards – Shall be consistent with shoulder 

width requirements 

Likely 

Structural 

capacity 

Green Book – Minimum HL 93 design loading structural 

capacity 

Interstate Standards – New bridges – HS 20, existing 

bridges – assess operating rating capacity for additional 

20 year service life 

Unlikely 

Discussion of how part-time shoulder use may affect these minimum values is presented in the 

following sections. Minnesota has developed state standards for bus-on-shoulder (BOS); these 

standards have been used by other states with BOS operation and they are presented in the 

following sections as well.(40)

Design Speed 

The selected design speed influences several geometric design criteria. The implementation of 

part-time shoulder use does not inherently change the design speed of the overall freeway 

facility. A lane designated for part-time shoulder use may have dimensions that are slightly 

below the minimum values set by the design speed (some of which may require a design 

exception), and the design speed could be reduced. This is rare and would occur in a situation 

such as a road with existing horizontal curves at the minimum radius and the shoulder having a 

radius that is 10 to 12 feet less than the minimum. 

Lanes designated for static and dynamic part-time shoulder use typically have the same speed 

limit as the rest of the facility on which they are located. If the shoulder is assigned a lower speed 

limit, or the shoulder is only open to traffic when facility operating speeds fall below posted 

speeds, then adjustments to selected design values may be acceptable. A variable speed limit 

could also be used to maintain the existing speed limit when the shoulder is closed and to lower 

the speed limit when the shoulder lane is open. Minnesota and some other states limit the speed 

of buses travelling in BOS lanes to 35 mph, and MnDOT has adopted 35 mph as the design 

speed of BOS lanes. 
Design Considerations

85

Lane Width 

A shoulder width of 12 or more feet is generally preferred for part-time shoulder use. A 12-foot 

shoulder creates a “shoulder lane” that is the same width as a typical general purpose lane. This 

dimension refers to the distance from the general purpose lane edge line to the edge of pavement. 

A second edge line is sometimes added near the edge of pavement to guide drivers on the 

shoulder and increase the delineation of the edge of pavement; however, pavement on both sides 

of a second edge line constitutes part of the shoulder. Research summarized in Chapter 3 of this 

guide has shown drivers are more likely to use 12-foot shoulders than narrower shoulders. 

Shoulders less than 12 feet wide may be adequate for shoulder use depending upon the type of 

vehicles using the shoulder when it is open and depending on the availability of lateral offset to 

obstructions beyond the edge of pavement. If trucks are prohibited from using the shoulder, then 

shoulder widths as narrow as 10 feet may be adequate. Shoulders less than 10 feet wide are not 

recommended for part-time shoulder use. 

A 10-foot shoulder may be inadequate if the lateral offset to obstructions is less than 1.5 feet or a 

high volume of larger vehicles, such as buses, is anticipated. Opening the shoulder only when 

congestion is present and reducing the speed limit when the shoulder is open are likely to 

improve the safety of a narrow shoulder during part-time shoulder use. 

Minnesota standards for BOS specify a minimum “shoulder lane” width of 10.0 feet and a 

minimum total shoulder width of 12.0 feet (implying a two-foot paved area between the second 

edge lane and edge of pavement). A lane width of 12.0 feet is required “in areas of new 

construction or reconstruction”. Massachusetts design criteria specify a width of 11 feet for 

“shoulder lanes” and also require a one- to two-foot paved area beyond the travelled portion of 

the shoulder (implying a minimum total shoulder width of 12-13 feet).(41)

Shoulder Width 

Designating the paved freeway shoulder for part-time travel use will typically require a design 

exception since there will typically be little or no untraveled shoulder beyond the portion of the 

shoulder used for part-time travel, and this will not meet the minimum width requirements. 

Bridge Width 

Many bridges have narrower shoulders than the approach roadways. The minimum width of a 

shoulder on a bridge that should be used as a travel lane is 11.5 feet. This dimension enables 

vehicles to remain 1.5 feet from the bridge rail and still have 10 feet of shoulder on which to 

maneuver. It is not necessary for the shoulder to be the same width on a bridge as on the 

approaching roadway, however, it does need to be 11.5 or more feet wide. Design exceptions 

may be needed for the narrow lane width. 

Minnesota standards for BOS lanes specify a minimum bridge [shoulder] width of 11.5 feet and 

a desirable bridge [shoulder] width of 12.0 feet. A width of 12.0 feet is required “in areas of new 

construction or reconstruction”. These standards effectively maintain a 10.0 foot shoulder lane 
Design Considerations

86

and a 1.5-foot paved lateral offset to the bridge rail, which is consistent with MnDOT’s BOS 

design standards. 

Horizontal Alignment 

A shoulder on the inside of a horizontal curve will have a smaller radius than the adjacent 

general purpose lane. However, the difference in radii is small, and it is unlikely to result in a 

radius below AASHTO minimum values. If AASHTO minimum values are not met, then a 

design exception could be obtained. In practice, states have not reported issues with horizontal 

curvature when implementing part-time shoulder use. 

Superelevation 

Through horizontal curves, the superelevation of shoulders may differ from the superelevation of 

adjacent general purpose lanes to facilitate drainage. In some cases, there may be a cross slope 

break on the shoulder, or the entire shoulder may be superelevated in the opposite direction of 

general purpose lanes to direct water to inlets. In practice, states have reported issues with this on 

left shoulders with concrete median barriers. Roadways designated for part-time shoulder use 

should not have superelevation breaks and shoulders on these roads should generally have the 

same superelevation as adjacent general purpose lanes. Small superelevation differences of 2% 

or less may be acceptable, with the break occurring on the edge line between the shoulder and 

general purpose lanes. 

Stopping Sight Distance 

On the inside of horizontal curves, traffic using the shoulder will be closer to guardrails or 

barriers if they are present. This may reduce sight distance, and it may reduce it below AASHTO 

minimum design values. If this occurs, it may be appropriate to relocate the barrier causing the 

sight distance obstruction or obtain a design exception. Minnesota addresses this issue by basing 

SSD of BOS lanes on 35 mph, the maximum speed at which buses are permitted to operate. 

Cross Slope 

Cross slopes on shoulders are sometimes greater than adjacent general purpose lanes to facilitate 

drainage, creating two potential issues. First, the algebraic difference between the shoulder and 

the adjacent travel lane may be too abrupt to safely accommodate vehicles transitioning between 

them. If it exceeds seven to eight percent, then an agency should consider rounding the grade 

break or prohibiting lane changes to and from the shoulder in the affected area.(42) Prohibiting 

movement between the shoulder and general purpose lanes would be most effective for BOS 

operation, with a small number of professional drivers needing to obey the restriction. Second, 

regardless of algebraic difference, if shoulder cross slopes are greater than the travel lane values 

in Table 11, then it is necessary to reduce shoulder cross slope by adding pavement on top of 

existing pavement to modify the cross slope or obtaining a design exception. If existing or 

modified cross slopes and the current drainage system create ponding on the shoulder and there 
Design Considerations

87

is no feasible means of addressing it, then the freeway is a good candidate for dynamic part-time 

shoulder use that can be closed during and after heavy rainfall or snowmelt. 

Vertical Clearance 

As shown in Table 11, AASHTO vertical clearance requirements are the same for travel lanes 

and shoulders. However, many bridges have lower clearances over shoulders because they predate current AASHTO policies or previously obtained design exceptions. In these cases, it is still 

necessary to ensure there is adequate vertical clearance for vehicles using the shoulder.

Part-time shoulder use generally prohibits trucks, which effectively eliminates the tallest vehicles 

from using the shoulder. During the preliminary engineering stage, a state DOT’s permitting 

group can typically provide information on the vertical clearance of bridges because they 

maintain an inventory for the purpose of providing permits for oversize/overweight trucks. Prior 

to implementing part-time shoulder use, agencies typically field measure the height of bridges 

along a route, and any substandard vertical clearances dictate additional vehicle restrictions 

beyond trucks. 

Lateral Offset to Obstruction 

Lateral offset to obstruction, called horizontal clearance in previous editions of the Green Book, 

is the distance from the edge of the traveled way to the nearest physical obstruction such as a 

median barrier, guard rail, bridge support, or bridge rail. The minimum width of 1.5 feet is 

automatically met on a full-standard freeway because minimum shoulder widths are greater than 

1.5 feet. However, the lateral offset between the edge of a shoulder and an obstruction may be 

less than 1.5 feet. In this case, it is necessary to move the obstruction or obtain a design 

exception. 

In practice, states have relocated guardrails and other obstructions (sign and lighting structures), 

and obtained design exceptions for segments adjacent to bridge rails/barriers and abutments, or 

other concrete barrier, where less than 1.5 feet or lateral offset is available. 

Other Criteria 

Vertical alignment, grade, and structural capacity are unlikely to be affected by part-time 

shoulder use. 

Ramp Freeway Junctions 

Ramp-freeway junctions are the locations at which ramps merge with and diverge from the 

mainline freeway. The types of ramps and their specific geometric characteristics will influence 

the details of part-time shoulder use design in these areas. This, in turn, influences the overall 

quality of operation, including the capacities of ramps and the shoulder lane. 
Design Considerations

88

One-lane Ramps 

Part-time shoulder use is generally compatible with one-lane ramps. Typical designs for the two 

basic types of ramp-freeway junctionsparallel and taperare shown in the sections below. 

Parallel Ramps: With parallel entrances and exits, entering and exiting traffic drives on a short 

speed change lane beside the outermost freeway lane (for right-side ramps) for several hundred 

feet before an exit gore or after an entrance gore. The speed change lane is essentially a striped 

portion of the shoulder. 

When part-time shoulder use is added to a facility with parallel ramps and open to traffic, the 

shoulder lane can tie into the existing speed change lanes. This effectively converts the parallel 

ramp into a taper ramp during the hours the facility is open. Figure 27 shows the path of ramp 

traffic on a parallel-style on-ramp. If the shoulder lane is closed, ramp traffic uses speed change 

lane and then maneuvers to the adjacent general purpose lane, as shown with shading in Figure 

27. If the shoulder lane is open, the speed change lane is part of the shoulder lane and on-ramp 

traffic no longer has an unimpeded path onto it. The ramp is effectively converted to a taperstyle. At the end of speed change lane, on-ramp drivers may maneuver into the adjacent general 

purpose lane or continue straight into the shoulder lane. Similar changes occur at parallel-style 

off-ramps, as shown in Figure 28. 

Figure 27. Illustration. Path of parallel-style on-ramp traffic with part-time shoulder use. 

(Source: Kittelson) 
Design Considerations

89

Figure 28. Illustration. Path of parallel-style off-ramp traffic with part-time shoulder use. 

 (Source: Kittelson) 

The operational effects of a part-time conversion of a parallel-style ramp to a taper-style ramp 

vary based on the geometric characteristics of the ramp and gore area. For example, a gore with a 

relatively large convergence angle will result in a short maneuver area at the end of an on-ramp 

when the shoulder lane is open, likely reducing capacity of the on-ramp and shoulder lane. A 

gore with a relatively small convergence angle will result in a longer maneuver area and have 

lesser impacts on capacity. This is shown in Figure 29 and Figure 30. 

Figure 29. Illustration. Parallel-style ramp with large convergence angle. Shoulder lane 

shaded. 

 (Source: Kittelson) 
Design Considerations

90

Figure 30. Illustration. Parallel-style ramp with small convergence angle. Shoulder lane 

shaded. 

 (Source: Kittelson) 

Taper Ramps: Taper-style ramps do not have speed change lanes, and ramp traffic effectively 

“crosses” the shoulder in a single maneuver. If a shoulder was opened to traffic and this 

configuration was kept in place, it would result in a conflict between shoulder lane traffic and 

ramp traffic, as shown for an off-ramp in Figure 31. 

Figure 31. Illustration. Conflict between ramp and shoulder traffic with taper-style ramp. 

Shoulder lane shaded. 

 (Source: Kittelson) 

To remove the conflict, the ramp should be converted into a parallel-style ramp with a speedchange lane. For an off-ramp, exiting traffic will maneuver onto the combined speed-change 

lane/shoulder lane prior to the exit as shown in Figure 32. Implementing shoulder use will 

already require that the shoulder be physically capable of carrying traffic, so the addition of the 

speed-change lane will typically require only pavement marking changes.
Design Considerations

91

Figure 32. Illustration. Conversion of taper-style ramp to parallel-style ramp to remove 

conflict between ramp and shoulder traffic. Shoulder lane shaded. 

 (Source: Kittelson) 

Two-lane Ramps 

Design of shoulder lanes through two-lane ramps is more complex than one-lane ramps, and 

some types of two-lane ramps are not compatible with shoulder use without major modifications. 

Parallel ramps: A parallel-style two-lane on-ramp has two speed-change lanes downstream of 

the entry gore that receive ramp traffic. Typically, they are different lengths, with the outer lane 

terminating before the inner lane. With shoulder use, the inner speed change lane will become 

part of the shoulder lane, as shown in Figure 33. When the shoulder lane is open, this will 

effectively create a taper-style two-lane on-ramp with an inside merge. Inside merges reduce 

ramp capacity and should be used with caution because they may be unexpected to drivers. They 

are most appropriate to use at locations where ramp and freeway drivers have good visibility to 

the gore and adequate time to prepare for the merge. 

Figure 33. Illustration. Creation of inside merge with parallel-style two-lane on-ramp. 

Shoulder lane shaded. 

 (Source: Kittelson) 

Design of a shoulder lane through a parallel-style off-ramp is similar to the design of the onramp shown in Figure 35. There are generally no issues associated with the loss of the inside 

speed-change lane when the shoulder lane is open and the creation of an “inside diverge”. 

Taper ramps: A taper-style two-lane on-ramp typically has an inside merge, and shoulder use 

will create a conflict between shoulder lane traffic and inside lane ramp traffic as shown in 

Figure 34. A similar conflict exists with taper-style two-lane off-ramps. Removal of this conflict 

is more complex than with single-lane ramp, and would typically involve adding a second speedchange lane downstream of the entry gore. In these cases, consideration should also be given to 

terminating the shoulder lane project upstream or downstream of the two-lane ramp, reducing the 
Design Considerations

92

ramp to a single lane, or implementing junction control to vary the lane configuration in response 

to traffic conditions. 

Figure 34. Illustration. Conflict between ramp and shoulder traffic with two-lane taperstyle ramp with inside merge. Shoulder lane shaded. 

 (Source: Kittelson) 

Turnout Placement/Design 

Based on experience in Massachusetts, Virginia, and the UK, refuge spaces for disabled vehicles 

should be located approximately every half-mile along a facility with static or dynamic shoulder 

use.(2) At this distance, a vehicle in the process of breaking down is generally able to reach the 

refuge. 

Sometimes, gore areas or ramp shoulders at entrances and exits provide a refuge space large 

enough to store a vehicle. When this is not the case or when ramp spacing exceeds a half-mile, 

emergency turnouts should be constructed. Turnouts should be long enough and wide enough 

that a vehicle with poor control and in the process of breaking down can enter it and be out of the 

shoulder lane. They should also be long enough to enable a tow truck to park and load a broken 

down vehicle. Turnouts should be a minimum of 16 feet wide to provide separation between a 

broken down vehicle and moving traffic in the shoulder, and additional width is desirable. 

Massachusetts uses turnouts that are 16 feet wide, 110 feet long, and have 300-foot tapers.(41)

Virginia’s turnouts are approximately the same width and have approximately the same taper 

length, but are several times longer than 110 feet. Virginia does not limit turnout lengths to a 

maximum distance, and paves existing flat areas along the roadside, if present, to increase 

turnout length. The UK uses shorter tapers, approximately 80 feet for the entrance and 150 feet 

for the exit.(2)

Turnouts should be used exclusively as refuge areas for disabled vehicles, and not for other 

purposes such as overnight truck park. States have not reported issues with this, but if they occur 

they should be addressed quickly with signing and law enforcement. 

If turnouts cannot be constructed, such as on bridge or other constrained areas, then part-time 

shoulder use can still be implemented, but there is a greater probability the shoulder will be 

blocked by disabled vehicles. Dynamic lane control signs should be given greater consideration 

on these facilities to enable closure of the shoulder in response to a disabled vehicle. Turnouts 

have fewer benefits and are generally not constructed on BOS facilities because buses can 

reenter a general purpose lane to pass a disabled vehicle without greatly affecting traffic flow on 
Design Considerations

93

the freeway or bus travel time. Figure 35 and Figure 36 show turnouts from the UK and 

Massachusetts, respectively. 

Figure 35. Photo. Emergency Turnout, UK. 

(Source: FHWA ATM Screening Guidelines) 

Figure 36. Photo. Emergency Turnout, Georgia. 

(Source: Georgia Department of Transportation) 
Design Considerations

94

Arterial Part-Time Shoulder Use 

There are few unique design considerations for part-time shoulder use on arterials. Arterials, 

particularly those in urban and suburban areas with recurring congestion, are less likely to have 

shoulders that are wide enough to be used as travel lanes, and increasing the shoulder width may 

be less feasible than on a freeway due to the potential presence of curb and gutter, roadside 

objects, or right-of-way constraints. 

All known arterial part-time shoulder use in the U.S. to date have been BOS. Similar to 

freeways, arterial shoulder lane widths of 10 or 11 feet are adequate on an open section for a low 

volume of buses at lower, congested speeds and a 12-foot shoulder lane is desirable. A 10-foot 

lane should not be used if the lateral offset to obstructions is less than the 1.5-foot AASHTO 

standard or if curbs are present. If curbs are present, then vehicles should be able to remain 

entirely in the shoulder and maintain a 1.5-foot separation between right side tires and the face 

of curb. 

Examples of signing and pavement marking treatments to accommodate right-turn lanes are 

shown later in this chapter. 

PAVEMENT DESIGN 

Part-time shoulder use places vehicles on a portion of the roadway that was not necessarily 

designed to carry through traffic instead of an occasional stopped vehicle, and an agency should 

assess shoulder pavement conditions prior to implementing part-time shoulder use. The first step 

in assessing the adequacy of existing pavement is to estimate the volume and type of vehicles 

that will use the shoulder. Part-time shoulder use is typically limited to certain hours of the day, 

reducing volume compared to adjacent general purpose lanes. Shoulders open only to passenger 

cars will result in only lighter vehicles using the shoulder, while shoulders open to buses will 

result in heavy vehicles using the shoulder. Bus volumes are relatively straightforward to 

estimate using known service schedules and expected hours of operation for the shoulder. 

Structural pavement needs for buses are related to the passenger load, and fully-loaded buses 

may have as much effect on pavement as a truck. The second step is to conduct a review of the 

existing shoulder pavement structural section and field assessment of pavement conditions to 

determine if the available pavement is adequate or if improvements are needed. 

If part-time shoulder use is intended to be temporary, such as until a widening project occurs or 

during construction on an adjacent route, then an agency may find it more economical to 

routinely conduct maintenance on a shoulder with pavement in poor condition rather than rebuild 

the shoulder. This strategy is less viable for longer-term part-time shoulder use.(42)

Rumble strips, if used, are typically placed in a position where the tires of a vehicle traveling on 

the shoulder would track over them. It will generally be necessary to remove existing rumble 

strips areas prior to implementing part-time shoulder use by milling and resurfacing, and relocate 

them if they are still desired. MnDOT reinstalled rumble strips on some freeways with BOS 

operation and placed them on the edge line or in the middle of the shoulder such that buses 

straddle them.(30)
Design Considerations

95

Minnesota’s experience is that BOS operation typically does not damage shoulder pavement. As 

of 2007, only one shoulder replacement in Minnesota was due to BOS operation, although others 

had been repaved, reinforced, or widened. Minnesota now requires a shoulder pavement depth of 

seven inches for BOS operation. Buses are limited to 35 mph on shoulders in Minnesota to 

minimize the speed differential with general purpose lanes, and Minnesota reports this also 

reduces wear and tear on pavement compared to higher speed operation.(42) More generally, the 

effects of bus speed on pavement wear and tear may vary depending on pavement type and 

condition. 

DRAINAGE DESIGN 

Like pavement condition, existing drainage conditions and facilities will need to be assessed 

prior to implementing part-time shoulder use. On open, uncurbed roadway sections it is unlikely 

drainage modifications would be needed prior to part-time shoulder uses. On closed section 

roadways with curb and gutter or other structures such as retaining walls or concrete median 

barriers that prevent water from running off the road, there are several issues that may be 

encountered. 

Catch basins located in the shoulder not only create potential safety issues and are uncomfortable 

to drive over, but most are not designed to handle a high volume of traffic driving over them. 

Minnesota encountered both of these issues after implementing BOS operation, and in response 

developed a catch basin design specifically for BOS operation.(42) The design brings the inlet 

flush with pavement and reinforces it with a concrete apron. Massachusetts moved inlets to the 

edge of pavement,(2) and Virginia relocated inlets on the BOS portion of I-66 that began 

operation in 2015.(43)

Some portions of a shoulder may have depressed areas to direct water towards catch basins or 

drainage channels (on open sections). These sections may be uncomfortable to drive over and 

require resurfacing and relocation of the associated drainage features to provide a smooth ride. 

Finally, ponding may occur on shoulders unintentionally (due to pavement imperfections or 

rutting of pavement(42)) or intentionally due to a design that stores water from a design rainfall on 

the shoulder. In most climates, these issues should be corrected by improving pavement or 

adding drainage structures prior to implementing part-time shoulder uses, especially part-time 

shoulder use by passenger cars. San Diego, which is located in a dry climate, had a BOS pilot 

project in the mid-2000s that did not improve the pavement, but instead did not allow use of the 

part-time shoulder use during heavy rain. 

In general, many drainage issues associated with part-time shoulder use are most likely to occur 

on arterials or older freeways. Freeways built in recent decades are less likely to have curbs, 

catch basins on shoulders, or other unusual drainage features that would require modification. 
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96

TRAFFIC CONTROL DEVICE DESIGN 

Signing and pavement marking needs vary greatly depending on type of part-time shoulder use. 

BOS, at one end of the spectrum, is typically implemented as unobtrusively as possible with 

minimal signing and no pavement marking. Extensive signing and pavement marking is 

detrimental to overall BOS operation because it leads some passenger car drivers to believe the 

shoulder is also open to them. Dynamic part-time shoulder use, at the other end of the spectrum, 

requires changeable signs to notify drivers when the shoulder is open. Static part-time shoulder 

use has been successfully implemented and operated for decades with static signs, but dynamic 

signs are becoming increasingly common on these facilities and have been added to several 

established part-time shoulder use facilities that previously had only static signs to give a higher 

degree of acknowledgement to drivers of the current operating condition on the shoulder. 

This section presents best practices for signing and pavement marking of part-time shoulder use, 

based on what states have done to date. The Manual on Uniform Traffic Control Devices 

(MUTCD) does not contain signs or pavement markings specifically intended for roadways with 

part-time shoulder use, but the principles of the MUTCD can be used to guide the development 

of such signs and pavement markings. 

Bus on Shoulder 

Signing and pavement marking needs for BOS facilities are minimal. States such as Minnesota 

and Virginia that have implemented BOS operation on multiple roadways at different times have 

determined fewer signs than initially anticipated are needed for BOS operation.(43, 44) Later 

implementations within these states have used fewer signs than the initial implementations. 

Limiting signing and pavement marking helps to make BOS operation inconspicuous and 

reduces the likelihood of the general public believing that they may use the shoulder.(45) TCRP 

Report 151 provides additional details on signs and pavement markings for BOS facilities. (42)

Signing 

Signing on roadways with BOS operation is generally limited to static, ground mounted signs. 

Most agencies have used black on white, rectangular regulatory signs similar to the R3-10 

through R3-12 series of preferential-only lane signs in the MUTCD. Such signs should be 

installed along a roadway with BOS operation at regular intervals (Minnesota uses one mile 

spacing) and near on- and off-ramps. They may be supplemented with “begin” and “end” banner 

plaques at the beginning and end of segments where part-time shoulder use is permitted. Most 

agencies with BOS operation allow buses to use the shoulder in response to traffic conditions 

rather than limiting use to certain times of day, so there is typically no need for signs specifying 

hours of operation. Minnesota experimented with several signs before settling on the sign shown 

in Figure 37. The word “authorized” is often used for BOS regulatory signs because part-time 

shoulder use is typically limited to certain transit agencies and/or certain bus drivers who have 

undergone training. 
Design Considerations

97

 Figure 37. Photo. MnDOT, regulatory sign for Bus-on-shoulder operation. 

(Source: Minnesota Department of Transportation)(42) 

Along a route, buses sometimes must merge back into a travel lane to avoid a narrow section of 

shoulder, often on or beneath a bridge. Black on yellow warning signs should be used if this is 

necessary. 

Along on-ramps, some agencies use a “watch for buses on shoulder” warning sign prior to the 

merge point. On arterials with BOS operation, some agencies use supplemental plaques on stop 

signs and yield signs on cross streets stating “stop for buses on shoulder” or “yield to buses on 

shoulder”. Use of warning signs on freeway on-ramps and arterial cross streets is recommended 

for BOS facilities. Additionally, when a portion of an arterial shoulder is striped as a right-turn 

lane, a warning sign or a regulatory sign instructing buses to yield to right turn traffic should be 

considered. 

Pavement Marking 

BOS operation can be implemented on many freeways with no additional pavement markings 

being added. Since the mid-1990s, Minnesota has not used any special pavement marking for 

BOS operation. 

The 2009 MUTCD limits use of diamond pavement marking symbols to high-occupancy vehicle 

(HOV) lanes, and they should not be used on shoulders open only to buses. Previous editions of 

the MUTCD allowed diamond pavement markings on other types of managed lanes. Minnesota 

installed diamond pavement marking symbols on shoulders open only to buses in the early 

1990s, but removed them because some passenger car drivers believed they indicated the 

shoulder was open to HOVs and began to use the shoulder as a lane. Word pavement markings 

such as “bus only”, “transit buses only”, and “transit only” may be placed on the shoulder. 

Arterials with BOS operation have greater pavement marking needs than freeways due to bus 

stops, side streets and driveways, right turn lanes, and other elements of access not present on 

freeways. Access may also increase the probability of a driver incorrectly believing the shoulder 
Design Considerations

98

is open to general traffic. Arterial BOS operation is less common than freeway BOS operation, 

with the majority of US facilities located in Washington State, New Jersey, and Minnesota. 

Pavement marking needs on BOS arterials is highly facility-specific, and examples from 

Washington State and New Jersey are highlighted in the Appendix. 

Static Part-time Shoulder Use 

Signing and pavement marking needs are greater with static part-time shoulder use than with 

BOS operation because the shoulder is open to the general public. Some static part-time shoulder 

use facilities utilize dynamic signs, and others have successfully operated with static signs. 

Signing and pavement marking of static part-time shoulder use is typically supplemented with 

some degree of ITS, although sometimes ITS is only used to deliver information to facility 

operators and not drivers. ITS is covered later in this chapter. 

Signing 

The key signing needs of a static part-time shoulder use facility are to notify drivers that the 

shoulder is sometimes used as a lane, and to provide the specific times the shoulder is open. Both 

needs can be met with static signs. However, dynamic signs offer two primary advantages over 

static signs. First, they can use words or symbols such as a green arrow or red ‘x’ to 

communicate whether or not the shoulder is open. This reduces the workload on drivers, who 

otherwise have to read a schedule on a sign, determine the current day and time, and then 

determine whether or not the shoulder is open. Second, dynamic signs allow facility operators to 

open or close the shoulder outside of scheduled hours. It is occasionally desirable to do this with 

a shoulder that is otherwise static in event of disabled vehicles on the shoulder, planned special 

events generating off-peak traffic, closures of some general purpose lanes for construction or 

maintenance, or inclement weather. If the project timeline and budget can accommodate dynamic 

signs, then they should be strongly considered due to the reduction in driver workload, reduced 

potential for lane status confusion, and flexibility to modify hours of operation. 

There are several factors to consider when choosing between static and dynamic signs for a new 

static part-time shoulder use installation: 

● Who uses the roadway? Is it primarily a commuter route or long distance travel route? 

● How complex is the part-time shoulder use segment? Are there system interchanges, 

other managed lanes, or features creating high driver workload? 

● How familiar are drivers with part-time shoulder use? Is it the first installation in the 

region, or are there others? 

● How quickly does the project need to be implemented? Is there time to install dynamic 

signs and communication to them? 

● What is the cost of dynamic signs? 

Primary static signs regulating part-time shoulder use, or the static portions of the dynamic signs, 

should be black on white. They may be supplemented with black-on-yellow warning signs. 
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99

Signsstatic or dynamicshould be provided at the following locations: 

● At the start of the part-time shoulder use 

● At exit ramps, to manage the conflict of exiting traffic from permanent lanes and through 

traffic in shoulder lanes 

● At and on entrance ramps: 

o To notify entering drivers that the shoulder may be used as travel lane 

o To manage the conflict between entering traffic and through traffic in shoulder 

lanes 

● At recurring intervals between interchanges 

● At the end of the part-time shoulder use 

Table 12 lists current static part-time shoulder use facilities in the U.S. and the type of signing 

used. Georgia plans to convert static signs on GA 400 to dynamic signs and is planning a second 

set of part-time shoulder use facilities that will initially have dynamic signs. Massachusetts used 

static signs on their part-time shoulder use facilities for nearly 25 years before adding small 

dynamic panels to them. Images of signs on the facilities listed in Table 12 are included in 

Appendix C. 

Table 12. Signing of static part-time shoulder use in US. 

State Facility Type of Signing 

CO I-70 Overhead dynamic 

GA GA 400 Ground-mounted static (planning conversion to dynamic) 

HI I-H-1 Ground-mounted static (Overhead dynamic signs on facility 

for adjacent reversible lane but not shoulder lane) 

MA MA 3, I-93, I95 

Ground-mounted static with dynamic panels 

NJ NJ 29, NJTPK 

NBE 

SR 29: ground-mounted static and portable dynamic, NJTPK 

NBE: overhead dynamic 

TX TX 161 Overhead dynamic 

VA I-66, I-264 Overhead dynamic and ground-mounted static 

WA US 2 Overhead and ground-mounted static 

NJTPK NBE – New Jersey Turnpike Newark Bay Extension 

Similar to exit ramps on a freeway, a series of signs provided in advance of a turnout and at the 

turnout itself is recommended to increase driver awareness of its existence. In 2007, Virginia 

modified turnout signing on I-66 from one small sign at the turnout itself to a sequence of typical 

freeway size signs, and this change has led to increased use of turnouts.(43) Turnouts can be 

signed with black on white regulatory signs (generally consistent with other signs related to parttime shoulder uses) or green guidance signs (consistent with exits). Preference will likely be 

determined in the next edition of the MUTCD. 
Design Considerations

100

Pavement Marking 

Pavement markings for static part-time shoulder use should provide effective guidance to drivers 

when the shoulder is both open and closed to traffic. On basic segments away from ramps, this is 

straightforward and there is consistency across states: 

● The solid edge line typically used between the shoulder and adjacent travel lane remains 

in place. 

● A second solid line is used on the outside of the shoulder beside the edge of pavement. 

This line functions as an edge line for traffic using the shoulder. The second solid line 

should be continuous even when the shoulder narrows or has a physical barrier beside it, 

such as a bridge rail. 

● The two solid lines should be the same colorwhite for part-time use of the right 

shoulder and yellow for part-time use of the left shoulder. 

Pavement markings at the start and end of part-time shoulder use segments and through ramp 

freeway junctions were discussed in the Geometric Design section of this chapter. Pavement 

markings at on- and off-ramps are more complex, and example markings were previously shown 

in Figure 27 through Figure 34. They vary based on the types of entrance and exit configurations 

described in the geometric design section of this chapter, and existing state ramp-freeway 

junction marking practices. In general, pavement markings in the vicinity of a ramp-freeway 

junction should provide a clear means for drivers on the mainline shoulder to pass through the 

ramp freeway junction, and they should also provide a means to transfer from the freeway to 

ramp or vise verse. Striping can create parallel or taper style merges and diverges. 

Colored Pavement 

The Section 3G of the 2009 MUTCD and an interpretation letter specify the use of colored 

pavements for the following situations: 

● Yellow pavement for median islands separating traffic flows in opposite directions or left 

shoulders of divided highways or one-way streets or ramps(5)

● White pavement for channelizing islands or right-hand shoulders(5)

● Green pavement for bicycle lanes(6)

● Red pavement for streetcar and/or bus-only lanes on an experimental basis(6)

No color is designed for part-time shoulder use, and none should be used at this time unless a 

request to experiment is submitted to and approved by the MUTCD team. 

Dynamic Part-Time Shoulder Use 

Dynamic part-time shoulder use requires dynamic signs to communicate whether or not the 

shoulder is open to traffic. Pavement marking needs for dynamic part-time shoulder use is no 

different than static part-time shoulder use. In both cases, pavement markings need to provide 

sufficient guidance to drivers when the shoulder is open and when it is closed. 
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101

ITS DESIGN 

Most part-time shoulder use facilities are accompanied by ITS, and dynamic part-time shoulder 

use requires it. ITS includes: 

● Speed sensors and cameras to help agencies monitor and manage the facility in real time 

● Electronic lane control signs (LCS) 

● Changeable message signs (CMS) 

● Driver information ITS treatments to communicate information such as when the 

shoulder is open to traffic 

● Regulatory and warning signs that must be turned on and off as the shoulder opens and 

closes 

The 2006 FHWA scanning tour of ATM systems in Europe identified several recommendations 

for active traffic management strategies on facilities with part-time shoulder use:(46)

● Changeable message signs to provide guide sign information and regulatory signs to 

adapt to the addition of the shoulder as a travel lane. The signing should be uniform, with 

adequate installation of sign gantries to provide operational information and to ensure it 

is in sight at all times. 

● Closed-circuit television cameras with sufficient coverage to verify the clearance of the 

shoulder before deployment. 

● Comprehensive incident management program, including advanced incident detection 

capabilities. 

This section addresses the potential ITS design treatments and associated issues. 

Signs 

Lane-Use Control Signals for Shoulder Use 

Dynamic part-time shoulder use requires electronic lane-use control signals (LCS) to display 

whether the shoulder is opened or closed to traffic or, optionally, transitioning from being open 

to closed Static part-time shoulder use facilities can benefit from LCS as well, as they allow 

occasional deviation from operating hours due to disabled vehicles, off-peak special events, or 

other nonrecurring events. 

The MUTCD (Section 4M.02 – Meaning of Lane Use-Control Signal Indications) identifies the 

following displays for lane control: 

● A steady DOWNWARD GREEN ARROW signal indication shall mean that a road user 

is permitted to drive in the lane over which the arrow signal indication is located 

● A steady RED X signal indication shall mean that a road user is not permitted to use the 

lane over which the signal indication is located. 
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102

● A steady YELLOW X signal indication shall mean that that a road user is to prepare to 

vacate the lane over which the signal indication is located because a lane control change 

is being made to a steady RED X signal indication. 

The MUTCD requires lane-use control signals to remain on and not be dark. In general, the 

YELLOW X has not been used for part-time shoulder use or for the broader dynamic 

applications. The initial applications of ATM in the United StatesSeattle, Washington and 

Minneapolis, MNhave used other yellow displays. Use of yellow displays other than an X is 

not consistent with the MUTCD and requires a request for experiment. Additional information 

on this process is included in CHAPTER 9. An ongoing FHWA study has been evaluating ATM 

sign displays and to identify potential gaps in the MUTCD in this regard. 

Changeable Message Signs 

In addition to lane control signs, changeable message signs (CMS) can be used to reinforce the 

open/closed status of shoulder or provide other information to drivers. High volume, urban 

freeways on which part-time shoulder use is typically implemented often already have CMS 

signs. 

Dynamic Speed Limits with Part-Time Shoulder Use 

Depending on the lane widths (both the shoulder and mainline), the types of vehicles allowed to 

use shoulder, the possible reduced sight distance around curves (as seen from the part-time 

shoulder use), the potential for reduced clear zone distances when part-time shoulder use is in 

operation, and the configurations of the mainline and ramp shoulders in the vicinity and through 

interchanges, it may be appropriate to reduce the speed limits during part-time shoulder use 

operation. If a state does not have the legal authority to vary speed limits, legislative changes 

may be needed so dynamic speed limits can be implemented. Enforcement of dynamic speed 

limits also presents challenges because the police must be informed in real time of the speed 

limit and have a record of speed limits used at all times for court purposes. 

Mainline Dynamic Lane Assignment and Dynamic Speed Limits 

The UK’s “Smart Motorway” concept (formerly known as “Managed Motorway”) includes the 

use of dynamic speed limits and dynamic lane assignment (with lane-use control signals) across 

all lanes, in addition to dynamic part-time shoulder uses. In Europe, dynamic part-time shoulder 

use is almost always deployed in conjunction with dynamic speed limits and dynamic lane-use 

control signals for all lanes along with queue warning. 

While this has not been the practice to date in the U.S., consideration should be given to this 

approach if dynamic part-time shoulder use is being installed, particularly along segments 

experiencing high frequencies of rear-end or side-swipe crashes. Additional information on 

identifying roadway segments where the application of dynamic speed limits and dynamic lane 

assignments may be cost effective can be found in the FHWA document Active Traffic 

Management (ATM) Feasibility and Screening Guide.

(47) 
Design Considerations

103

CMS Spacing – Static Part-time Shoulder Use 

States with static part-time shoulder use are increasingly using changeable signs to supplement 

the static signs regulating the hours of operation of the shoulder lane. This reduces driver 

workload by clearly communicating whether the shoulder is open or closed, and it provides 

flexibility to occasionally deviate from normal operating hours. If used, supplemental dynamic 

signs should be placed at the same locations as static regulatory signs displaying operating hours 

of the part-time shoulder use. Typically, this is at the start of the part-time shoulder uses segment 

and after on-ramps. 

CMS and LCS Spacing – Dynamic Part-Time Shoulder Use 

The effectiveness of any ATM approach requires that drivers recognize and understand they are 

driving on an actively managed facility. How this “continuum of information” is provided has a 

significant impact on dynamic part-time shoulder use costs, particularly if other ATM treatments 

are also provided. 

The initial deployments of ATM in the United Kingdom used gantries spanning the entire 

roadway with LCS displaying speed limits and lane control over each laneincluding the 

shoulder, where applicable. Larger CMS on the side displayed queue warning messages and 

other information. These gantries were spaced such that drivers could see the next gantry 

immediately after passing under a gantry, resulting in a gantry spacing of 600 meters 

(0.37 miles) to 1,000 meters (0.62 miles). The concern was that compliance would be less if 

gantries were spaced too far apart. The spacing of gantries for the Washington State and 

Minnesota ATM systems followed suit and are located at roughly 0.5-mile intervals on average. 

If only part-time shoulder use operation is implementedwith a cantilever sign and LCS over 

the shoulderthen this approach (sign approximately every 0.5 miles) is appropriate. However, 

if other ATM treatments such as mainline lane assignment and variable speed limits are 

deployed, then placing a LCS over every lane requires a gantry structure like the ones in Figure 

38, and this significantly increases project cost. In these cases, sign spacing greater than every 

0.5 miles may be appropriate. 
Design Considerations

104

Figure 38. Photo and Illustration. Example of full gantry ATM deployment in Washington 

State (no part-time shoulder use). 

(Source: CH2M) 

In the U.K., gantry spacing of 600 to 1000 meters used on early ATM facilities is now 

considered conservative, and experience indicates that greater gantry spacing may be adequate. 

The current U.K. philosophy is that spacing needs to be sufficient so that drivers know they are 

still on a controlled roadway. 

Cantilever signs that diagrammatically indicate lane status and gantry signs similar the one in 

Figure 38 were determined through a driver simulator trial to be comprehended equally well by 

U.K. drivers. The overall results suggested that cantilever signing is equal to gantry-mounted 

signing at instructing drivers to move out of a particular lane. 

The latest Smart Motorway design concepts from the U.K. Highways Agency for dynamic speed 

limits, dynamic lane assignment (including shoulders) and queue warning consist of the 

following:(48) 

● Driver information, including speed limits, lane availability and closures, and text 

legends (e.g., queue warnings) and pictograms is provided at intervals not exceeding 

1,500 meters (0.93 mile). This can be provided via gantry or cantilever signs (referred to 

as “verge-mounted”. 

● The first sign display downstream of an on-ramp is a gantry with lane signs (for 

displaying dynamic speed limit and dynamic lane assignment messages) over each lane 

and a CMS for other messages of a strategic nature. 

Based on the U.K. work, a “hybrid” approach has been developed for planned installations of 

dynamic part-time shoulder use and other ATM treatments in New Jersey and Pennsylvania 

consisting of gantries every mile, with cantilever dynamic speed limit signs (located on both 

sides of the roadway) between each set of gantries. 
Design Considerations

105

CCTV and Detection 

The aforementioned Smart Motorway design concepts from the UK Highways Agency also calls 

for full coverage of CCTV equipped with pan, tilt, and zoom. This allows viewing the entire 

length of the shoulder prior to initiating shoulder operations (i.e., verifying the clearance of the 

shoulder before deployment) and to identify and verify roadway conditions during incidents and 

other events. Many static part-time shoulder use facilities in the U.S. are manually inspected by 

police driving the corridor prior to the opening of the shoulder each day. This approach is less 

feasible for dynamic part-time shoulder use with varying hours of operation, and full CCTV 

coverage is recommended for dynamic part-time shoulder use. 

With dynamic part-time shoulder use, the software algorithms at a TMC determining when to 

open and close the shoulder will likely require a high density of detectors, measuring volumes 

(including the part-time shoulder use) and spot speeds (for each lane including the shoulder) at 

each gantry/sign location. These data are also used to vary speed limits and provide queue 

warnings if this is done on the facility. 

If there are weather-related concerns about part-time shoulder use, such as ponding of water, 

buildup of snow and ice, or reduced visibility due to fog, then consideration should also be given 

to the installation of road weather information sensors to determine the condition of the 

pavement and air. This information can be used to help determine whether the shoulder should 

be opened to traffic and to determine appropriate speed displays if variable speed limits are in 

place. 

 

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107

CHAPTER 8. IMPLEMENTATION PROCESS 

This chapter presents “how to” information to help agencies implement part-time shoulder use 

once a decision to use it has been made. The chapter will also help agencies still in the planning 

stages understand the steps generally taken to implement part-time shoulder use. 

DESIGN EXCEPTION PROCESS 

States are required to obtain design exceptions from Federal Highway Administration (FHWA) if 

the minimum values of the controlling criteria presented in the Geometric Design section of 

Chapter 7 of this Guide are not met on roadways that are part of the National Highway System. 

Part-time shoulder use may impact a number of the controlling criteria, and by definition it 

impacts shoulder width when the shoulder is open. AASHTO standards require a minimum 

freeway lane width of 12 feet and a minimum freeway shoulder width of 10 feet (except the left 

shoulder of 4-lane freeways, which has a minimum width of 4 feet). Therefore, unless an existing 

shoulder is at least 22 feet wide (or 16 feet wide in the case of a left shoulder on a 4-lane 

freeway), a design exception will be required when static or dynamic part-time shoulder use is 

implemented. Design exception practices for bus-on-shoulder (BOS) vary. 

The key piece of a design exception request is an explanation of why it is infeasible to meet 

AASHTO standards. Meeting standards on part-time shoulder use is equivalent to conventional 

widening, and part-time shoulder use is likely being considered because conventional widening 

is infeasible in terms of cost or right-of-way (ROW) requirements. 

Design exception requests should also include an evaluation of the implications of substandard 

features and how they are mitigated on a specific facility. In the case of part-time shoulder use, 

the following may mitigate substandard geometry: 

● Reduced speeds, achieved through lower speed limits of periods of shoulder operation 

coinciding with congestion. 

● Annual average daily traffic (AADT) in ranges where Highway Safety Manual (HSM) 

analysis, summarized in CHAPTER 4, predicts a reduction in crashes with narrowing of 

the shoulder and addition of a lane. 

● Use on commuter facilities during commuting periods with a high percentage of 

familiar drivers. 

● Prohibition of trucks from the shoulder. 

● Extensive monitoring of the facility with ITS and/or patrol vehicles. 

● Variable lane controls allowing closure of the shoulder if it is blocked by a disabled 

vehicle. 

● Emergency turnouts. 
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● The potential for a performance-based practical design (PBPD) approach where the 

savings associated with not constructing a conventional lane are used on other projects 

that improve network operations and safety. 

The specific requirements of design exception requests vary by state. Design exceptions are 

typically submitted to and approved by FHWA Division Offices, although they may allow 

approval on their behalf by state departments of transportation (DOTs) or local agencies.(50) Parttime shoulder use may have a relatively short implementation timeframe compared to 

conventional projects, so a design exception request should be prepared and submitted to FHWA 

as early as possible in the planning process. Design exception requests are typically reviewed in 

conjunction with the overall review and approval of the plans, specifications, and estimates, 

which may be relatively minor for part-time shoulder use.(50) 

FHWA approval process for part-time shoulder use has varied. In Massachusetts, approval was 

granted on a temporary basis when part-time shoulder use was first implemented in 1985 and 

renewed several times before permanent approval was granted in 2009.(49) 

Most part-time shoulder use projects that have recently been implemented or are currently in the 

planning process are long-term implementations. Temporary approval is not recommended 

because it creates the need for re-approval. 

Many states also have design standards, manuals, or laws that may need to be updated prior to 

implementing part-time shoulder use. Minnesota, which has nearly 300 miles of BOS facilities, 

developed standards for BOS facilities in the 1990s with input from their FHWA Division 

Offices.(44) The standards were incorporated into MnDOT’s design manual. Washington State, 

which is planning several part-time shoulder use and Active Traffic Management (ATM) 

installations, is developing an urban freeway retrofit guide with the help of their FHWA Division 

Office.(33) 

LEGAL ISSUES 

In some states, driving on the shoulder is prohibited by law, and implementation has required 

legislative action or new rulemaking and agreements to interpret existing laws. For example:(42)

● Minnesota amended their statutes in 2005 to “formalize” BOS operation. Previously, 

there was an agreement between the state patrol, Metro Transit, and the DOT. 

● Florida DOT created an inter-local agreement with the Miami-Dade Transit in which 

BOS was treated as a pilot project. 

● California defined shoulders as transit lanes to legally enable a BOS pilot project in San 

Diego in the mid-2000s (the project has since ended). 

● Georgia DOT authorized BOS as a demonstration project. 
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MUTCD EXPERIMENTAL APPROVAL PROCESS 

If “a new traffic control device or a different application of an existing device” is “not compliant 

with or not included in the MUTCD”, the state DOT considering its installation should submit a 

request to experiment to FHWA MUTCD team, and FHWA must approve the experiment before 

the control device is installed. 

Most part-time shoulder use projects have not used experimental traffic control devices. Control 

devices commonly used on part-time shoulder uses facilities that do not require experimental 

approval include the following: 

● Regulatory signs indicating the hours of operation of a shoulder lane 

● Warning signs on on-ramps or along part-time shoulder use segments that notify drivers 

of part-time shoulder uses 

● Signs indicating vehicle restrictions of part-time shoulder uses, such as no trucks or buses 

only 

● Green arrow and red “x” dynamic lane control signs 

● A second edge line between the outside of the shoulder and edge of pavement or median 

barrier 

● Dotted pavement markings at ramp-freeway junctions and the start and end of part-time 

shoulder use segments to guide drivers when the shoulder is open and closed 

However, more-complex part-time shoulder use projects, such as those with other ATM 

elements, may require a request for experimentation. 

The request for experimentation should originate with the State DOT and be sent to FHWA 

Headquarters with a courtesy copy to the FHWA Division Office. The FHWA must approve the 

experiment before it begins. All requests should include the following:(51) 

● A statement of the nature of the problem, including data that justifies the need for a new 

application. 

● A description of the proposed change, how it was developed, and how it deviates from 

the current MUTCD. 

● Any illustration(s) that enhances understanding of the device or its use. 

● Supporting data that explains how the experimental device was developed, if it has been 

tried, the adequacy of its performance, and the process by which the device was chosen 

or applied. 

● A legally binding statement certifying that the concept of the traffic control device is not 

protected by a patent or copyright. 

● The proposed time period and location(s) of the experiment. 

● A detailed research or evaluation plan providing for close monitoring of the 

experimentation, especially in the early stages of field implementation. The evaluation 
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plan should include before and after studies as well as quantitative data enabling a 

scientifically sound evaluation of the performance of the device. 

● An agreement to restore the experimental site to a condition that complies with the 

provisions of the MUTCD within 3 months following completion of the experiment. The 

agreement must also provide that the sponsoring agency will terminate the experiment at 

any time if it determines that the experiment directly or indirectly causes significant 

safety hazards. If the experiment demonstrates an improvement, the device or application 

may remain in place until an official rulemaking action occurs. 

● An agreement to provide semi-annual progress reports for the duration of the 

experimentation and a copy of the final results to the FHWA's Office of Transportation 

Operations within three months of the conclusion of the experiment. 

STAKEHOLDER ENGAGEMENT 

Successful deployment of part-time shoulder use requires a well-planned, interdisciplinary 

collaboration with a variety of different stakeholders, including planning, operations, design, 

maintenance, and executive leadership staff within a DOT; law enforcement; emergency 

responders; bus operators; MPO staff; and FHWA Division Office staff. 

A state DOT will typically be the agency that decides if part-time shoulder use is feasible, 

possibly in collaboration with a transit agency if BOS is under consideration. As soon as this 

determination is made, the state DOT should reach out to the stakeholder groups noted above and 

form a working group. Most agencies that have successfully implemented part-time shoulder use 

have formed working groups to ensure the needs of all stakeholders are incorporated into the 

concept of operations. Stakeholder involvement and educationassuming that some 

stakeholders may not be aware of the benefits and potential issues associated with part-time 

shoulder usesis an ongoing process and working groups should continue to meet during the 

early years of a part-time shoulder use facility’s operation. Engaging executive leadership early 

is critical because policies may need to change and laws potentially prohibiting driving on the 

shoulder may need to be interpreted or changed. 

For stakeholders who do not have a working knowledge of part-time shoulder use, implementing 

an education and outreach program during the early stages of the effort will help build trust in 

the proposed investments. This education and outreach effort can include peer exchanges, 

involving counterparts from other states or countries with shoulder running experience, as well 

as FHWA. 

The traveling public is also an important stakeholder, and their engagement is discussed later in 

this chapter. 

Incorporating and Mitigating Emergency Response and Incident Management Concerns 

Emergency responders frequently drive on shoulders to reach incident scenes and use shoulders 

to park while responding to incidents. Concerns over the potential loss of the ability to bypass 

congested traffic and remain out of the travelled way when responding to incidents need to be 
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addressed before part-time shoulder use is implemented, particularly for longer part-time 

shoulder use sections spanning multiple interchanges. 

Incident response plans developed during the planning of part-time shoulder use can mitigate 

these concerns. “Sweeps” of the shoulder before it opens and the construction of turnouts reduce 

the likelihood of the shoulder being blocked. A fleet of dedicated incident response vehicles 

positioned at multiple locations along the facility can also decrease incident response times. 

If dynamic signs are used, additional incident management and response options are available. 

Local emergency response agencies should be given the authority to order the closure of the 

shoulder and have a clear line of communication to the TMC for doing so. Closing the shoulder 

clears it of vehicles and provides emergency responders with an uncongested path to incident 

scenes. 

Incorporating and Mitigating Maintenance Concerns 

Maintenance concerns with part-time shoulder use typically relate to how the lane designated for 

part-time shoulder use should be maintainedmore similar to a shoulder or more similar to a 

travel lane, how existing maintenance activities will be impacted, and what new maintenance 

activities will be required. 

Agencies with part-time shoulder use have generally come to the conclusion that shoulders 

should be maintained in the same manner as other lanes, and nothing outside of typical 

maintenance operations needs to be done with regard to filling potholes, plowing snow, and so 

forth. Existing maintenance activities requiring stopping on the shoulder cannot occur when the 

shoulder is open but are otherwise unaffected. 

New maintenance needs vary greatly depending on the type of part-time shoulder use. BOS and 

static part-time shoulder uses with no additional ITS have virtually no additional maintenance 

needs beyond maintaining the shoulder as a lane. Extensive ITS hardware used for dynamic parttime shoulder use and other ATM systems likely require additional maintenance staff and staff 

training with regard to the specifics of the technology. 

Incorporating and Mitigating Bus Operator Concerns 

Minnesota began widespread implementation of BOS operation in the Twin Cities metropolitan 

area in the 1990s. Their methods of mitigating bus operator concerns are well-established and 

have served as a model for many other states that have subsequently implemented BOS. 

On routes designated for BOS, Minnesota limits BOS speed to 15 mph faster than adjacent 

traffic and an absolute maximum of 35 mph. This ensures BOS occurs in a relatively low-speed 

environment with low speed differentials. The choice to use the shoulder is up to each driver, 

although passengers sometimes complain if speeds are low enough to permit part-time shoulder 

use and drivers choose not to use it. Metro Transit, the largest bus operator in the Twin Cities, 

allows drivers who are uncomfortable driving on the shoulder to request transfers to other routes. 

The primary requirement for a bus using the BOS lanes is for the driver to have received 
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112

training. Transit agencies using the BOS lanes offer training several times a year, and new 

drivers are assigned to routes without BOS if they have not yet been trained. 

PUBLIC INVOLVEMENT

Similar to other innovative transportation projects, public outreach is a critical part of part-time 

shoulder use implementation. Successful implementation of the first part-time shoulder use 

project in a metropolitan area includes explicit and proactive outreach and education to the 

general public and should be undertaken consistent with state public information guidance. This 

would create opportunities to familiarize others with the concept of part-time shoulder use and 

the details of how it will work on a specific facility. How will drivers know if the shoulder is 

open or closed? What special signs will be used? Will the speed limit change? What should 

drivers do if they break down? Creating multiple forums to engage the public (including 

presentations at local council or board meetings, briefs at community organization functions, and 

project-specific open house meetings) results in opportunities to listen to community interests 

and share objective information about part-time shoulder use. 

Public outreach conducted during planning a part-time shoulder use project can inform and 

educate the public about proper use and benefits. Media campaigns through local newspapers, 

television, and public meetings can be effective methods of keeping the community informed. 

Once the part-time shoulder use project is open to the public, monitoring driver behavior and 

using law enforcement as necessary to promote proper use of the part-time shoulder use can aid 

driver acclimation. Figure 39 shows a postcard handout that has been used at public meetings in 

Michigan in preparation for an ATM installation. 
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Figure 39. Example Dynamic Part-time Shoulder Use Public Information Material 

(Source: Michigan Department of Transportation) 

The following communications and public involvement elements may be considered as part of 

the public outreach: 

● Expect opposition and confusion 

● Understand your non-technical audience 

● Define and identify success 

● Manage expectations 

● Demonstrate public accountability 

● Tell an engaging story 

Day-To-Day Operation

115

CHAPTER 9. DAY-TO-DAY OPERATION 

Part-time shoulder use has unique maintenance, incident management, and law enforcement 

needs. Early applications of part-time shoulder use in the U.S. were done with little or no 

intelligent transportation systems (ITS) support. As ITS technology has advanced, it has been 

increasingly integrated into part-time shoulder use operations. 

MAINTENANCE 

Maintenance of lanes designated for part-time shoulder use is more similar to maintenance of 

general purpose lanes than maintenance of a shoulder. Over time, agencies with part-time 

shoulder use have found it is most efficient to maintain the shoulder at the same level as general 

purpose lanes. There is no need to clean the shoulder with street sweepers, as the presence of 

traffic on the shoulder moves debris off of it similar to a general purpose lane. Conducting 

maintenance on part-time shoulder use segments that requires maintenance vehicles to stop on 

the shoulder will need to be conducted at times the shoulder is closed to traffic. On high volume 

freeways where part-time shoulder use is most commonly used, there may already be restrictions 

on maintenance during peak period when the shoulder lane would be open. 

After snowfall, part-time shoulder use is typically plowed after all general purpose lanes on the 

freeway have been plowed. This creates the potential for the shoulder to be closed during a 

period when it is scheduled to be open, although this usually has little effect on traffic operations 

due to reduced traffic volume during snow. Minnesota has found it beneficial to open the I-35W 

dynamic part-time shoulder use segment throughout the duration of a snowstorm because 

vehicles driving in the shoulder help to distribute salt that has been spread there. 

Reduced lateral offsets to obstructions may not provide sufficient space to push and store snow 

beside the shoulder. Minnesota and Massachusetts have not experienced issues with this, but 

Virginia has on I-66. On average, less often than once a year a storm produces enough snow that 

it cannot be fully plowed off of the shoulder in several constrained areas. Loaders and dump 

trucks are used to remove the snow from these areas in nighttime hours. The time and cost 

associated with this are high enough that it would not be feasible if Virginia received more snow 

and it was necessary to remove snow several times per year. 

INCIDENT MANAGEMENT 

Part-time shoulder use is typically implemented on some of the highest volume and most 

congested freeways in a region. These roadways typically have incident management plans and 

infrastructure in place that can be adapted for part-time shoulder use. Strategies for enhanced 

incident management on part-time shoulder use facilities include the following: 

● Emergency turnouts, discussed in the Geometric Design chapter, constructed 

approximately every half-mile unless other turnouts such as ramps are present. 

● Service patrols, especially for longer part-time shoulder use spanning multiple 

interchanges. 
Day-To-Day Operation

116

● CCTV coverage of shoulder lanes and turnouts. 

● Devices to detect slow or stopped traffic on shoulder lanes or in turnouts. 

● Dynamic lane control signs: 

o A shoulder can be closed for safety reasons if a disabled vehicle stopped on the 

shoulder 

o A shoulder can be closed to traffic so emergency responders can drive on it to 

rapidly reach a crash scene anywhere on the facility. 

Most static and dynamic part-time shoulder use facilities employ some of these strategies. Buson-shoulder (BOS) facilities, including those in Minnesota, typically do not have additional 

incident management specifically associated with BOS. 

LAW ENFORCEMENT 

The success of part-time shoulder use depends on the extent to which drivers comply with posted 

hours of operation or lane-use controls, as well as any vehicle restrictions. In Europe, agencies 

often use automated enforcement for temporary lanes. Such automated enforcement in the U.S. is 

uncommon outside of school and work zones, and there are legal restrictions on automated 

enforcement in many states. Accordingly, an increased traditional law enforcement presence will 

likely be needed on facilities with part-time shoulder use. Enforcement of BOS lanes is focused 

on use of the shoulder by non-buses, and enforcement of static and dynamic part-time shoulder 

use is more focused on use of the shoulder outside of hours of operation. 

With the increased likelihood of vehicles on the shoulder, including violators when the shoulder 

lane is closed, police conducting routine enforcement may want to target areas with downstream 

pull over opportunities such as exit ramps, emergency turnouts large enough for two vehicles, 

and so forth. Ultimately, law enforcement personnel should be engaged in the planning and 

design of shoulder lanes and specific design needs for local enforcement entities should be 

incorporated into the facility. 

Even without automated enforcement, installation of some of the hardware associated with it, 

such as presence and speed detectors, may be helpful to track compliance on a system level and 

help target areas for enforcement by police. On dynamic part-time shoulder use facilities, lane 

control technology may include mechanisms for providing real-time information to police 

officers in the field about the status of the shoulder, when it was opened/closed, and the current 

lane assignment displays (for patrol vehicles in locations where displays are not visible). This 

technology can also be used on a static shoulder lane facility with a high level of ITS 

infrastructure. 

On BOS facilities, shoulders can still be used by police to pull over vehicles, and bus drivers are 

trained to reenter general purpose lanes when a shoulder is obstructed. Police and bus operators 

in Minnesota have determined buses should reenter travel lanes approximately 500 feet upstream 

of a police car stopped on the shoulder, and bus drivers can estimate this distance in Minnesota 

based on the standard spacing of light poles along freeways.(44) 
Day-To-Day Operation

117

OPENING AND CLOSING PART-TIME SHOULDER USE FACILITIES 

The opening and closing of part-time shoulder use facilities in the U.S. open to more than buses 

is a largely manual process. A shoulder should be inspected in entirety before each opening by 

“sweeping” (driving) the length of the facility or viewing CCTV if there is full camera coverage 

of the facility. Any debris or disabled vehicles should be cleared prior to the scheduled opening 

time of the shoulder. If dynamic lane use control signs are present, then they can be used to keep 

the lane closed past the scheduled opening time if additional time is needed to clear the shoulder. 

Additionally, if an incident occurs while the shoulder lane is open and the shoulder becomes 

blocked, then the shoulder should be closed as soon as possible if dynamic lane assignment signs 

are present. Interagency agreements should be prepared prior to the implementation of part-time 

shoulder use to determine which agencies have the authority to instruct the TMC to close the 

shoulder. 

BOS lanes do not need to be inspected before opening, and most are not. If buses encounter 

obstructions on the shoulder, then they can merge into traffic to avoid them, and dispatchers can 

alert buses on part-time shoulder use routes of known obstructions. Additionally, many BOS 

lanes are used on an as-needed basis and there are no fixed hours of operation. 

The extensive ITS requirements and variable hours of operation of dynamic part-time shoulder 

use facilities make them well-suited for more automated opening and closing processes. Some of 

these processes may also be used for static part-time shoulder use if sufficient ITS infrastructure 

is in place. Agencies should be cautious with introducing too much variability into the operating 

hours of dynamic part-time shoulder use. For example, if a shoulder needs to be opened in the 

morning peak period for congestion reduction purposes nearly every weekday, it will be more 

predictable to drivers if it is opened at the same time every weekday (such as 7 a.m.) rather than 

different times (such as 6:50, 7:10, 7:15, etc.) based on minor variations in traffic from day to 

day. In this case, the benefits of dynamic over static part-time shoulder use would still be 

realized by the ability to extend the operating hours if high traffic volume was still present at the 

end of the typical a.m. peak period or occasionally open the shoulder at other times such as 

weekends. 

The long-term costs of an increased number of operators to continuously monitor dynamic parttime shoulder use and other ATM features, if they are present, may be greater than having 

software to assist with part-time shoulder use (and general ATM) operation. In Europe, some 

facilities with ATM are controlled by “an expert system that deploys the strategy based on 

prevailing roadway conditions without requiring operator intervention.”(46) Opening or closing a 

shoulder as a fully automated process is not recommended for the U.S. at this time because ATM 

is less common than in Europe. However, expert systems can be used to provide 

recommendations to human TMC operators, who then ultimately decide whether to open or close 

a shoulder based on the recommendation. Although expert systems can electronically, rather than 

manually, sweep a facility, it is still necessary to have incident response vehicles on standby in 

the event that debris or disabled vehicles are identified and need to be cleared. 

An expert systemalso known as a Decision Support System (DSS)continuously monitors 

data and other performance parameters collected from the field devices (e.g., speeds and 
Day-To-Day Operation

118

volumes; status of shoulder (blocked / clear); confirmed incidents, location, severity, number of 

lanes blocked, anticipated duration; scheduled events; weather and pavement conditions; 

equipment status; and time of day and day of week). Inputs from field devices will need to be 

supplemented with inputs from TMC operators, such as schedules of special events and police 

reports of incidents. Through a series of IF, AND, OR, and THEN logical statements, this DSS 

implements or recommends the most appropriate response plan. 

The logical statements typically involve comparisons of real-time parameters with various 

threshold parameters, such as comparisons of speeds and volumes with the time of day and 

known special events. Examples of outcomes from an automated system include: 

● Providing advisory messages to TMC operators 

● Switching sign displays 

● Switching text messages and contents on CMS 

● Sending a notification to others (e.g., State Police) 

● Automatically resetting signs to normal once an incident clears 

 
Appendix A – Case Studies of Successful Applications in the United States

119

APPENDIX A – CASE STUDIES OF SUCCESSFUL 

APPLICATIONS IN THE UNITED STATES 

A list of known part-time shoulder use applications can be found in Table 13. Though the 

application of part-time shoulder uses has been rather limited in some cases, it can be seen that 

this Active Traffic Management (ATM) strategy has been employed across most regions in the 

United States. The various examples highlighted in this section, which features corridors from all 

over the country and of vastly different implementation scales, evidence that under the 

appropriate conditions, part-time shoulder use is an effective strategy in reducing travel times 

and increasing overall network reliability and performance. 

Though part-time shoulder use is more-widely implemented in Europe, it is difficult to establish 

comparisons between ATM strategies employed in Europe versus those employed in the United 

States due to differences in driver behavior, political support, and transportation networks as a 

whole. No effort was made to inventory European facilities with part-time shoulder use, but 

noteworthy practices from Europe were provided through this guidance document. 
Appendix A – Case Studies of Successful Applications in the United States

120

Table 13. Part-Time Shoulder Use Facilities in US.

Continuation

Strategy Location Corridor Length (miles) Year Deployed Vehicle Type Usage Criteria Maximum Allowed Speed Lane W

(feet

Bus-onshoulder 

Minneapolis Metro Area Multiple 290 1991 Buses only 

24/7, when main line speed is under 35 mph 

Maximum of 

35 mph, and no 

more than 15 

mph faster than 

mainline 

10-1

Wilmington, Delaware US 202 0.3 Buses only 24/7 Miami, Florida SR 826 16 2005 Buses only 35 mph 10-1Miami, Florida SR 836 18 2005 Buses only 35 mph 10-1Miami, Florida Turnpike Buses only 

General purpose speeds drop below 25 mph 

Maximum of 

35 mph, and no 

more than 15 

mph faster than 

mainline 

10-1

depend

upon tr

volum

Miami, Florida SR-874, SR-878 9 2007 Buses only 

General purpose speeds drop below 25 mph 

Maximum of 

35 mph, and no 

more than 15 

mph faster than 

mainline 

10-1

depend

upon tr

volum

Montgomery County, Maryland 

US 29 4 Buses only M-F, 6-9am (SB), 3-8pm (NB) 

Mountainside, New Jersey 

US 22 

EB 1 Buses only 
Appendix A – Case Studies of Successful Applications in the United States

121

Continuation

Strategy Location Corridor Length (miles) Year Deployed Vehicle Type Usage Criteria Maximum Allowed Speed Lane W

(feet

Bus-onshoulder 

(con’d)

Middlesex County, New Jersey 

US 9 4 2006 Buses only M-F, 5-9am (NB), SB pm peak period 35 mph 

Falls Church, Virginia 

SR 267 

EB 1.3 Buses only M-F, 4-8pm 25 mph 12 

Columbus, Ohio I-70 10 2006 Buses only 

General purpose lane speeds drop below 35 mph 

35 mph 

Cleveland, Ohio I-90/SR 2 10 2008 Buses only 

General purpose lane speeds drop below 35 mph 

45 mph 

Cincinnati, Ohio I-71 10 2007 Buses only 

General purpose lane speeds drop below 35 mph 

45 mph 12 

Chicago, Illinois I-55 14 2011 Buses only 

General purpose lane speeds drop below 35 mph 

45 mph 

Raleigh, North Carolina I-40 12 2012 Buses only 

General purpose lane speeds drop below 35 mph 

35 mph 
Appendix A – Case Studies of Successful Applications in the United States

122

Continuation

Strategy Location Corridor Length (miles) Year Deployed Vehicle Type Usage Criteria Maximum Allowed Speed Lane W

(feet

Bus-onshoulder 

(con’d)

Kansas City, Kansas I-35 12 2012 Buses only 

General purpose lane speeds drop below 35 mph 

35 mph 

Seattle, Washington SR 522 2.2 1970 Buses only 24/7 

Buses allowed 

to operate at 

full posted 

speeds 

Seattle, Washington SR 99 

Static 

Alpharetta, Georgia GA 400 12 2005 All 

General purpose lane speeds drop below 35 mph 

35 mph max, 

speed 

differential 

with general 

purpose lanes 

below 15 mph 

Boston, Massachusetts 

I-93, I95, SR 3 45 1985 Passenger vehicles only M-F, 5- 10am, 3-7pm 65 mph (60 mph on SR 3) 10-1

Fairfax County, Virginia I-66 6.5 1992 All 

M-F, 5:30-11am (EB), 2-8pm (WB) 

55 mph 12 
Appendix A – Case Studies of Successful Applications in the United States

123

Continuation

Strategy Location Corridor Length (miles) Year Deployed Vehicle Type Usage Criteria Maximum Allowed Speed Lane W

(feet

Static 

(con’d)

Virginia Beach, VA I-264 3.5 1992 All 

M-F, 6-8am (EB), 4-6pm (WB) 

55 mph 10 

McLean, Virginia I-495 1.5 2015 All 7-11 am, 2- 8pm 55 mph 11 Everett, Washington US 2 EB 1.22 2009 All M-F, 3-7pm 60 mph 14 Honolulu, Hawaii I-H1 All Morning peak period Seattle, Washington US 2 1.55 All Evening peak period Same as general purpose lane Idaho Springs, Colorado I-70 EB 13 2015 

Passenger 

vehicles 

only 

Weekend peak periods 

Irving, Texas SR 161 3 2016 All M-F 6-10am, 2-7 pm 
Appendix A – Case Studies of Successful Applications in the United States

124

Continuation

Strategy Location Corridor Length (miles) Year Deployed Vehicle Type Usage Criteria Maximum Allowed Speed Lane W

(feet

Static 

(con’d)

Trenton, New Jersey NJ 29 1 Cars only M-F, 7-10am 

Same as 

general 

purpose lane 

13 

Newark, New Jersey I-78 EB 7 2014 All Peak periods 

Variable, but 

same as 

general 

purpose lane 

12 

Dynamic 

Minneapolis, Minnesota I -35W 2.5 2009 Dynamic priced Freeway free- flow speed 17-1Fairfax County, Virginia I-66 6.5 2015 All variable 12 
Appendix A – Case Studies of Successful Applications in the United States

125

MINNEAPOLIS-ST. PAUL, MINNESOTA – BUS ON SHOULDER 

Perhaps the foremost part-time shoulder use network in the country, the bus on shoulder (BOS) 

program in Minneapolis-St. Paul has allowed transit vehicles to travel on more than 290 miles of 

shoulder throughout the region since 1991. Though all 290 miles of shoulder have not been open 

since the program’s inception, the extent to which the program has grown has made itwithout 

a doubtthe most-extensive system in the United States. While many BOS systems arise out of 

the desire to increase transit reliability (and therefore its appeal to potential riders), the BOS 

system in Minnesota germinated out of a rather unique situation. 

In May of 1991, major flooding forced officials to close one of the bridges on I-35W, a primary 

means of travel in and out of the Twin Cities. In a state of emergency, the governor called a 

summit to help develop strategies for increasing throughput on the adjacent bridges while repairs 

were made to the I-35W bridge. Ultimately, it was decided that buses would temporarily be 

allowed to travel on the shoulder to improve subsequent traffic congestion. The quick turnaround 

and immediate success of the strategy prompted officials to begin testing bus shoulder running 

on other congested roadways in the Twin Cities area. The result was the development of a 

designated task team consisting of key stakeholders, such as Metro Transit and suburban bus 

operators, MnDOT officials, state police officers, and the Metro Council of Governments. 

Several central staff members at the DOT were selected to act as advocates for the program. 

Over the past decade, the task team has successfully advocated for the inclusion of BOS 

operations on hundreds of miles of freeways, primarily as part of larger construction or shoulder 

maintenance projects. MnDOT now has an overall program that looks annually at where 

shoulder running can be added on freeways.(42). A 1998 survey of the program estimated that the 

BOS system resulted in a bus travel time savings of 5 to 15 minutes depending on levels of 

congestion and route length. Respondents also saw the shoulders as a way to minimize their 

stress sitting in congestion and increase individual trip reliability. While safety has been 

identified as a primary concern by program officials and other key stakeholders, the mostconcerning safety issues for buses in the shoulders have been sideswipe crashes and mirror hits, 

which tend to be less severe crash types.(24) 

In 2009, MnDOT converted the right shoulder (previously used for BOS) into a general purpose 

lane on a section I-35W to maintain lane continuity into downtown as other portions of I-35W 

were widened. The left shoulder was converted to a dynamic priced lane. Buses and highoccupancy vehicles can use the lane for free, and single-occupant vehicles pay a variable toll.(52)

FAIRFAX COUNTY, VIRGINIA 

At the same time that a BOS system was being developed in Minneapolis-St. Paul, VDOT was 

establishing an alternative part-time shoulder use strategy for one of its most-heavily congested 

roadways. I-66, which extends radially outward from the Capital Beltway (I-495) in Northern 

Virginia, suffers from recurring congestion both during and outside of peak hours. To help aid 

peak-direction travel, VDOT converted the leftmost general purpose lane to an high-occupancy 

vehicle (HOV) lane and allowed general purpose traffic to use the shoulder to offset the decrease 
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in general purpose capacity. Static part-time shoulder use was opened in 1992 and was available 

for use by all traffic during specified peak periods on a 6.5-mile section of I-66 between I-495 

and US 50. These periods have been revised over the years to respond to changes in traffic, and, 

in 2015, a more-advanced active traffic management system with dynamic part-time shoulder 

use was installed. The shoulder is now opened whenever warranted by traffic conditions. A 2007 

investigation into system performance revealed that these shoulders operate at near capacity 

(V/C ratios: 0.90-1.0 eastbound, and 0.83-1.0 westbound), indicating the part-time shoulder use 

is able to help significantly augment throughput during the peak periods. A similar investigation 

was completed with regards to the safety effects of the part-time shoulder use; a negative 

binomial regression analysis using several years of crash data indicated the part-time shoulder 

use did not have any statistically significant effect on crash frequency.(24)

ALPHARETTA, GEORGIA 

In the northern suburbs of Atlanta, nearly 12 miles of part-time shoulder use has been developed 

on GA 400. The project has incrementally grown from BOS in one direction to static part-time 

shoulder use in both directions. Part-time shoulder use was initially operated only in the 

southbound direction during the AM peak and was only open to buses. Opened on September 12, 

2005, the project was championed by the GDOT and Georgia Regional Transportation Authority 

(GRTA), which operates express bus services in the area. The program was modeled after the 

successes of the Minneapolis-St. Paul BOS program but initially considered a temporary solution 

until the roadway could be permanently widened. The project development process included a 

bus ridership estimate using the regional travel demand model, benefit forecasts, and a field 

assessment of shoulder conditions. Both GRTA and Metropolitan Atlanta Rapid Transit 

Authority (MARTA), which operate four and eight buses per hour (respectively) on the BOS 

section of GA 400, report averages of five to seven minutes of travel time savings on their 

commuter bus routes. The routes end at a heavy rail station with direct access from GA 400. 

During peak congestion, up to 25 minutes were saved through the 12-mile corridor. The disparity 

of travel times between buses and general traffic later decreased due to the widening of GA 400. 

TCRP Report 151 states, as of 2012, no crashes related to BOS were reported in Georgia; no 

further safety information is provided in the report.(42) More recently, the southbound BOS was 

converted to general purpose part-time shoulder use, and northbound part-time shoulder use was 

opened. The part-time shoulder use only occurs on auxiliary lanes between interchanges and 

does not extent through interchanges.

SAN DIEGO, CALIFORNIA 

The San Diego Association of Governments (SANDAG) implemented BOS along five miles of 

I-805/SR 52, used by express bus route 960 in the mid-2000s. SANDAG agreed to a two-year 

pilot program with Caltrans to test BOS; it was initially envisioned as a temporary improvement 

until managed (i.e., HOV and HOT) lanes could be deployed or until the roadway was widened. 

In collaboration with SANDAG and local transit operators, BOS on I-805/SR-52 was opened in 

December 2005 by Caltrans. Several key findings were determined with a six-month assessment 

of the program: (42)
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● Safety 

o No crashes [As stated in TCRP Report 151presumably this refers to shoulderrunning buses only, as crashes in general likely happen on a freeway in a six 

month period of time]. 

o No issues related to enforcement or Caltrans maintenance. 

● Bus Travel Time and Reliability 

o Route 960 buses have 99 percent on-time performance. 

o Up to 5 minutes travel-time savings for buses during heavy congestion. 

● Freeway Level of Service and Maintenance 

o California Highway Patrol and Caltrans report no changes in freeway levels of 

service. 

o Transit operator indicates need for additional maintenance to remove debris on 

shoulders. 

● Structural Changes 

o 10-foot shoulder width is optimal. 

o Buses can safely operate in narrower shoulders, but it does slow operations. 

● Perceptions 

o 72 percent of bus drivers feel use of shoulders is safe. 

o 86 percent of bus drivers believe use of shoulders is a good idea. 

o 91 percent of passengers feel use of shoulders provides travel time savings. 

o 90 percent of passengers feel safe with buses on shoulders. 

The pilot program has since ended. However, another demonstration project is currently planned 

in the San Diego area on I-805/SR 94 from SR 54 to downtown.(53) 

MIDDLESEX COUNTY, NEW JERSEY 

Due to the success of BOS along US 22 in Mountainside, New Jersey (which is limited in scale 

and has existed for decades), New Jersey DOT opened a second BOS corridor along four miles 

of US 9 in Middlesex County. Opened in November 2006, the BOS was designed to serve over 

400 buses and 6,800 passengers during peak commute periods. The plan was a key element of 

the NJDOT’s Enhanced Bus Improvement Program, which is tasked with reducing delays and 

increasing travel-time reliability of bus services. Feedback from the program has been 

overwhelmingly positive from both passengers and bus operators alike; the latter responded 

positively to the use of 12-foot shoulder priority treatments. As of 2012, no crashes have been 

reported [As stated in TCRP Report 151presumably this refers to shoulder-running buses only, 

as crashes in general are likely to happen on an arterial in a six year period of time], and travel 

time savings on the order of three to four minutes have been seen during peak trips along the 4-

mile corridor.(42) 
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SEATTLE, WASHINGTON 

In order to help improve travel time, reduce the impacts of bottlenecks, and relieve congestion at 

a critical interchange, the Washington State DOT began opening the shoulder to all traffic along 

a 1.55-mile segment of US 2 near Seattle. WSDOT employed outreach efforts prior to 

implementation, which aided significantly in the development of the part-time shoulder use 

concept. It was determined the shoulder would only be open to traffic during the evening peak 

period, and restriping was undertaken to reduce weaving throughout the corridor. As a result of 

the additional throughput with part-time shoulder use, WSDOT considers it a permanent solution 

(at least for the near future) to solve the aforementioned issues along the corridor. Average 

delays for all vehicles have been reduced from 8-10 minutes to 1-2 minutes along the 1.55 mile 

stretch of US 2.(24) 

MIAMI, FLORIDA 

In 2002, residents of Miami-Dade County (MDC) developed the People’s Transportation Plan, 

which sought to improve mobility and reduce congestion throughout the county. Seventeen 

million dollars was committed under the plan to improve local bus services through the addition 

of routes, increased efficiency of service, and expansion of rapid transit services. 

Complementing this plan, the MDC MPO conducted an extensive, two-phased investigation into 

the feasibility of special-use lanes in the county. Phase I provided a high-level assessment of the 

applicability of various types of special-use lanes along several of MDC’s most-congested 

corridors. The primary outcome of this phase was the identification of rapid transit corridors 

comprised of Expressway Core routes. In Phase II of the study, these Expressway Core routes 

were further vetted for potential use with shoulder running schemes by the Center for Urban 

Transportation Research at the University of South Florida. The study outlined key operational 

characteristics required for the successful implementation of shoulder running in MDC. Based on 

several factors, including roadway characteristics, programmed corridor improvements, and 

proposed express transit, five corridors were ultimately identified as holding the most potential 

for a pilot bus on shoulder program. 

After further investigation by the MDC MPO, the SR 874 and SR 878 corridors were selected for 

the first BOS project. Consisting of approximately nine miles of freeway, buses were allowed to 

begin operating on the shoulders of these routes when the speed of general traffic fell below 25 

miles per hour. Four years after their opening in 2007, a 50-percent reduction in the number of 

late buses running along the BOS corridor was found. Key stakeholders in the program included 

the MPO, Office of the County Manager, Miami-Dade Transit, Miami-Dade Expressway 

Authority, Florida DOT and Turnpike Enterprise. Key stakeholders noted bus shoulder running 

was not the ideal solution to congestion, but it served as an effective means to help improve 

mobility and transit reliability throughout Miami-Dade County.(40) 

MINNEAPOLIS, MINNESOTA – DYNAMIC SHOULDER LANE 

Focused on reducing traffic congestion in the I-35W corridor and downtown Minneapolis, the 

Minnesota Urban Partnership Agreement (UPA) developed the first dynamic part-time shoulder 
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129

use application in the United States on I-35W. Opened in 2009, the “priced dynamic shoulder 

lanes” (PDSL) allow buses, vanpools, carpoolers (2+), and MnPass users to utilize the 17-19 foot 

left-shoulder during congested periods; it previously operated as BOS. The 2.5-mile length of 

shoulder features both static and changeable message signs every 0.5 miles to inform drivers 

when the shoulders are open, as well as the price per segment to utilize the PDSL. 

To implement this innovative system, the UPA relied on more than traditional technical analyses 

(e.g., operations, transit, and safety analyses); it also maximized the benefits of the institutional 

arrangements used to manage and guide the development of the initial proposal and 

implementation of the UPA projects, outreach activities, media coverage, and political and 

community support. The multi-agency organizational structure was essential for the initial 

implementation of this shoulder running application, and the subsequent processes, structures, 

media coverage, and staff competencies supported its development. Table 14 summarizes the 

non-technical success factors that were vital to the implementation of the PDSL, as well as other 

UPA projects on the I-35W corridor. 

Table 14. Non-Technical Success Factors of the I-35W Priced Dynamic Shoulder Lane. 

Questions Results Evidence 

What role did the following areas play in the success of the Minnesota UPA project 

deployment? 

1. People Effective 

Key elements included the multi-agency 

organization structure, support throughout the 

agencies, and neutral conveners. 

2. Processes Effective 

Forums, workshops, meetings, presentations, 

and newsletters were used to communicate 

with different groups. 

3. Structures Effective 

The strong agency working relationships 

supported the implementation of the UPA 

projects. 

4. Media Effective Played role of informing the public, rather 

than attempting influencing public opinion. 

5. Competencies Effective 

Agency personnel had the technical expertise 

and project management skills needed to 

successfully deploy the UPA projects. 

Does the public support the UPA strategies as effective and appropriate ways to reduce 

congestion? 

Supported

The reports from the various surveys of bus 

riders, commuters in the I-35W South 

corridor, and I-35W MnPASS customers 

indicate general support for the UPA 

strategies as effective and appropriate 

methods to reduce congestion. 
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Opened in both the northbound and southbound direction on I-35W, the PDSL have helped 

reduce congestion, improve travel-time reliability, and increased throughput along the corridor. 

A year after implementation, the PDSL (in conjunction with the I-35W HOT lanes) pulled an 

average of 50,000 to 60,000 month trips from the general purpose lanes and generated $74,000 to 

$102,000 in monthly revenue. Preliminary safety studies have shown that the addition of the 

PDSL do not appear to negatively affect safety.(54)

IDAHO SPRINGS, COLORADO 

Serving as the only east-west interstate in Colorado, the I-70 Mountain Corridor provides critical 

access for both localized and regional traffic from Denver to the mountains of West Colorado. 

As such, the corridor experiences heavy traffic demand, resulting in severe congestion and traffic 

delays in the eastbound direction. The 13-mile stretch of I-70 between Empire Junction and 

Idaho Springs, in particular, suffers from severe recurring congestion during peak periods. This 

four-lane section of highway would potentially benefit from traditional capacity improvements 

(e.g., road widening); however, strict physical constraints resulting from the surrounding 

mountainous terrain have forced the Colorado Department of Transportation (CDOT) to consider 

more context sensitive solutions. 

As a part of the CDOT’s comprehensive plan to improve travel along this corridor, a task force 

began investigating alternative solutions to help alleviate recurring congestion along I-70. 

Coordinating with representatives from the local community, including key community 

members, county and city officials, law enforcement, and historical and environmental protection 

advocates, CDOT formed Project Leadership and Technical Teams to gather valuable insights 

during the planning phase all the way through to final construction. These teams helped develop 

the guiding core principles for the alternatives analysis; this ultimately led to the development of 

a peak period shoulder running alterative in the eastbound direction. 

After fully vetting the operational and environmental viability of shoulder running between 

Empire Junction and Idaho Springs, CDOT proceeded with a plan to develop an optional, 

dynamically-tolled third lane on I-70. This scheme not only aims to alleviate congestion, reduce 

travel times, and increase throughput of the critical corridor, but it does so without expanding the 

existing roadway. Slated for completion in the fall of 2015, CDOT will open the left-shoulder for 

use during the peak periods, promoting a more-reliable travel experience for drivers by actively 

displaying prices for the tolled-shoulder via variable message signs. Though a static operation, 

the dynamic pricing of the lane will help maintain the travel time savings expected under 

shoulder use.(55)

BOSTON, MASSACHUSETTS 

One of the earliest part-time shoulder use operations in the country opened on several miles of I95 and SR-3 in 1985 outside of Boston. Prior to implementation, standstill traffic along these 

corridors prompted drivers to begin using the shoulder, despite a lack of permitted use. To help 

alleviate congestion along these corridors, the Massachusetts Department of Transportation 

(MassDOT) developed a static part-time shoulder use scheme on I-95 and SR-3 during the peak 
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travel periods (5 a.m. to 10 a.m. and 3 p.m. to 7 p.m. on weekdays) for passenger cars and trucks. 

Before this could be introduced, however, these corridors required a few minor improvements to 

accommodate the safe and efficient flow of traffic on the existing shoulders. 

Prior to implementation, MassDOT strengthened and relocated drainage structures on the 

shoulder, conducted minor repairs to pavement, widened shoulders to meet a 10-foot minimum 

(12-foot desired), and developed emergency breakdown turnouts at 0.5 mile intervals to facilitate 

incident management and emergency response. MassDOT also employed the assistance of the 

Massachusetts State Police, who travel the lanes each day prior to opening the shoulder for use to 

ensure motorists will be safe from debris. Though no specific performance measures are 

collected on the effect of the shoulder lanes, the early success of the shoulder lanes increased 

travel speeds along these corridors, prompting MassDOT to extend shoulder operations to 

additional sections of roadway. 

Since opening in 1985, part-time shoulder use in the Boston area have expanded to over 45 miles 

of roadway, including sections of I-93 north of the city. The infrastructure of these operations 

have also expanded, as pavement markings have been updated to reflect lessons learned, and 

signing plans have evolved to include both static and changeable message signs at the beginning 

and end of operations, as well as at freeway entrance ramps. The implementation of part-time 

shoulder use on these corridors, however, is only temporary. Prior to 2009, MassDOT was 

required to reapply for approval from Federal Highway Administration (FHWA) to implement 

the strategy every five to seven years until funding for permanent road widening was obtained. 

Since then, MassDOT has eliminated part-time shoulder use on half of the I-95 corridor after 

recent widening; it has plans to eliminate part-time shoulder use on the other half of I-95 within 

the next few years.(24) 

Appendix B – Signing and Pavement Marking Examples

133

APPENDIX B – SIGNING AND PAVEMENT MARKING 

EXAMPLES 

This appendix provides examples of signing and pavement marking from U.S. part-time shoulder 

use facilities. They are not necessarily compliant with the Manual on Uniform Traffic Control 

Devices (MUTCD) and are provided as examples of what states have done rather than guidance. 

CHAPTER 7 of this guide provides guidance on signing and pavement marking for agencies 

designing new part-time shoulder uses facilities, developed in part from the examples presented 

here. 

BUS ON SHOULDER 

Signing 

Figure 40 shows the layout of signs used for bus-on-shoulder (BOS) operation on freeways and 

arterials in Minnesota. 

Figure 40. Bus-on-shoulder sign placement, Minnesota. 

(Source: TCRP Report 151) 
Appendix B – Signing and Pavement Marking Examples

134

Figure 37 and Figure 41 show regulatory signs for BOS operation used in Minnesota and Miami, 

respectively. Miami’s signs have since been modified to remove the diamond symbol, which is 

now exclusively for high-occupancy vehicle (HOV) lanes per the 2009 MUTCD. 

 Figure 41. Photo. FDOT regulatory sign for Bus-on-shoulder operation. 

 (Source: TCRP Report 151) 

Figure 42 shows a typical MnDOT on-ramp warning sign for BOS operation. The white-onblack sign on the left side of the photo is a standard regulatory sign used on Minnesota regardless 

of whether or not the freeway has part-time shoulder uses. 

Figure 42. Photo. MnDOT on-ramp Bus-on-shoulder warning sign, right side of photo. 

 (Source: TCRP Report 151) 

Figure 43 shows a sign from the US 29 arterial in Montgomery County, Maryland, instructing 

buses to yield to right-turn vehicles at the start of a right-turn lane. 
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Figure 43. Photo. Maryland SHA sign to manage right-turn lane conflict. 

(Source: Kittelson and Associates, Inc.) 

Pavement Marking 

Figure 44 and Figure 45 show optional word pavement markings from a freeway in California 

and an arterial in New Jersey, respectively. 

Figure 44. Photo. Caltrans word pavement markings for BOS operation. 

 (Source: TCRP Report 151) 
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Figure 45. Photo. NJDOT word pavement markings for BOS operation. 

 (Source: TCRP Report 151) 

Arterials in Washington State and New Jersey are highlighted below to present examples of 

arterial BOS pavement markings in different contexts. 

SR 522 in Kenmore, Washington, is a highly developed arterial with numerous access points. 

A dotted edge line is used to indicate to passenger car drivers the shoulder is available as a rightturn lane in areas with many access points, and solid edge line is used in areas with fewer access 

points. Upstream of major access points, right-turn arrows are placed on the shoulder. 

Downstream of major access points, transverse white pavement markings are placed on the 

shoulder for approximately 50 feet followed by “transit only” word pavement markings. Figure 

46 shows pavement markings on SR 522, with red arrows pointing to markings noted above. 

Figure 46. Photo. SR 522 arterial Bus-on-shoulder pavement markings, Washington state. 

(Source: TCRP Report 151) 
Appendix B – Signing and Pavement Marking Examples

137

US 9 in Old Bridge, New Jersey, is a higher order roadway than SR 522, with fewer access 

points and a mixture of intersections and interchanges. A solid white edge line is used along the 

majority of the roadway. Approaching major intersections, the edge line transitions into the curb 

using dotted white pavement markings and the shoulder space becomes a right-turn lane, with 

lane line markings separating the right turn lane and through lanes. Downstream of major 

intersections, dotted white pavement marking transitioning from the curb to a solid white edge 

line is used to reestablish the shoulder lane. 

Figure 47 shows these pavement markings. The specific intersection shown in Figure 47 has 

jughandles, which provides space for a bus stop and turnout upstream of the intersection. This is 

a relatively unique configuration that cannot be easily replicated on many arterials. 
Appendix B – Signing and Pavement Marking Examples

138

Figure 47. Photo Illustration. US 9 arterial Bus-on-shoulder pavement markings, New 

Jersey. 

 (Source: TCRP Report 151)

 
Appendix B – Signing and Pavement Marking Examples

139

STATIC PART-TIME SHOULDER USE 

Signing 

Georgia 

Georgia 400 is a commuter freeway connecting Atlanta and its northern suburbs. BOS operation 

was implemented in the mid-2000s, and in 2012 and 2014, the southbound and northbound 

shoulders between three interchanges, respectively, were opened to all vehicles during peak 

periods. Part-time shoulder use does not extend through any interchanges and instead functions 

as an auxiliary lane between interchanges. GA 400 has black on yellow and white signs at the 

start of part-time shoulder uses segments noting the hours of operation (see Figure 48), and black 

on yellow warning signs along the part-time shoulder uses segments with the message “shoulder 

lane” and a 45 mph advisory speed limit plaque (see Figure 49). A black on white regulatory sign 

with the message “shoulder lane begins 1000 feet” is placed near the end of on-ramps, as shown 

in Figure 50. 

Figure 48. Photo. Sign at start of part-time shoulder use segment, GA 400. 

(Source: Georgia Department of Transportation) 
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140

Figure 49. Photo. Warning sign along part-time shoulder use segment, GA 400. 

(Source: Georgia Department of Transportation) 

Figure 50. Photo. Regulatory sign on on-ramp, GA 400 

(Source: Georgia Department of Transportation) 
Appendix B – Signing and Pavement Marking Examples

141

GDOT has a project underway to add dynamic signs to GA 400, and is planning another parttime shoulder use facility on I-85 that will open with dynamic signs. GDOT is adding dynamic 

signs to enable closure of the shoulder when disabled vehicles are stopped on it, and to more 

easily modify the set hours of operation. 

Hawaii 

Interstate H-1 in Hawaii employs static part-time shoulder use in the 

eastbound direction that operates during the a.m. peak period. Like 

Georgia’s shoulder lane, it functions as an auxiliary lane between 

interchanges and does not run through interchanges. Ground mounted, 

two-section black on white regulatory signs with the messages 

“shoulder lane 5 AM – 8 AM exc. Sat Sun Hol” and “no trucks or 

buses” are used along the route; an example is shown in Figure 51.

Similar signs are used at the start and end of segments and along ramps. 

Figure 52 shows signs on on-ramps and off-ramps. On I-H-1, signs are 

used on off-ramps because shoulder traffic is directed onto off-ramp 

shoulders to form a second exit lane rather than remaining on the freeway through interchanges. 

 

Figure 52. Photo. Regulatory sign, I-H-1 on-ramp. 

(Source: Google Maps) 

Figure 53. Photo. Regulatory sign, I-H-1 off-ramp. 

(Source: Google Maps) 

Figure 51. Photo. 

Regulatory sign,

I-H-1 mainline. 
Appendix B – Signing and Pavement Marking Examples

142

In addition to eastbound part-time shoulder use, I-H-1 also has a moveable zipper barrier that is 

used to reduce westbound lanes and increase eastbound lanes during the a.m. peak hour. I-H-1 

has dynamic signs to regulate use lanes created with the moveable barrier, but they do not 

communicate information related to part-time shoulder use. 

Massachusetts 

Massachusetts uses a mix of black on white regulatory signs and black on yellow warning signs. 

MassDOT initially implemented part-time shoulder use in 1985 with static signs at the start of 

part-time shoulder use segments, after on-ramps, and at the end of part-time shoulder uses 

segments. In the early months and years of operation, warning signs were added to on-ramps and 

“Mon - Fri” was added beneath the hours of operation; an example is shown in Figure 54. Prior 

to the addition of “Mon – Fri”, some drivers were using the shoulder on weekends. 

Figure 54. Photo. Updated regulatory sign, I-95 breakdown lanes. 

(Source: Massachusetts Department of Transportation) 

In 1999, MassDOT replaced the static signs, which were nearly 25 years old, on two of the three 

part-time shoulder use facilities. As part of the replacement, MassDOT added a dynamic panel to 

some of the static signs that displays “open” or “closed”. The primary purpose of adding the 

dynamic panel was to provide a clearer message to drivers. The dynamic panel also creates the 

opportunity to open shoulders outside of regularly scheduled hours, and MassDOT has done this 

when construction closes general purpose lanes. Figure 55 illustrates the signing detail of the 

new dynamic signing. 
Appendix B – Signing and Pavement Marking Examples

143

Figure 55. Illustration. Dynamic part-time shoulder use sign detail, I-95 breakdown lanes. 

(Source: Massachusetts Department of Transportation) 

These hybrid signs are located at the start of the permitted part-time shoulder uses lanes and after 

every on-ramp to the freeway where shoulder running is authorized. The dynamic messaging at 

the top of the sign is controlled remotely by the Incident Management Division in MassDOT’s 

Highway Operations Center. 

The varied messaging that can be displayed on these dynamic signs to inform travelers about the 

lane’s current functionality are shown in Figure 56 and Figure 57. 

Figure 56. Photo. Dynamic sign signifying the shoulder 

is closed to traffic, I-95 breakdown lanes. 

(Source: Massachusetts Department of Transportation) 
Appendix B – Signing and Pavement Marking Examples

144

Figure 57. Photo. Dynamic sign signifying the shoulder is open for use, 

I-95 breakdown lanes. 

(Source: Massachusetts Department of Transportation) 

New Jersey 

SR 29 in New Jersey employs static part-time shoulder use in the westbound direction that 

operates during the a.m. peak period. Ground-mounted black-on-white regulatory signs with the 

message “cars only may use shoulder 7 AM – 10 AM Mon-Fri” are placed along the route, as 

shown in Figure 58. Similar signs state the shoulder is only for access to SR 129, the right-hand 

side of a major fork at the end of the part-time shoulder use segment. There is one portable 

variable message sign at the start of the segment that supplements the static signs and informs 

drivers when the shoulder is open to traffic. 

Figure 58. Photo. Regulatory sign, SR 29 mainline. 

(Source: Google Maps) 
Appendix B – Signing and Pavement Marking Examples

145

The New Jersey Turnpike Newark Bay Extension currently employs part-time shoulder use to 

mitigate closure of the Pulaski Skyway, an adjacent facility, for reconstruction. Dynamic signs 

are used on the facility to open the shoulder during peak periods if traffic conditions warrant it. 

Some dynamic lane control signs are standalone (see Figure 59), and others are part of gantries 

with variable speed limit signs and variable message signs (see Figure 60) 

Figure 59. Photo. Mast Arm Dynamic Lane Control Sign, New Jersey Turnpike Newark 

Bay Extension. 

(Source: Kittelson & Associates, Inc.) 

Figure 60. Photo. Dynamic Lane Control Sign on Gantry, New Jersey Turnpike Newark 

Bay Extension. 

 (Source: Kittelson & Associates, Inc.) 
Appendix B – Signing and Pavement Marking Examples

146

Virginia 

Virginia’s initial static part-time shoulder use facilitiesI-66 in suburban Washington and I-264 

in Virginia Beachwere both implemented in the early 1990s and uses similar signs. The 

shoulders on I-66 were converted to dynamic part-time shoulder use in 2015, and signing 

changed. Both facilities used black on white regulatory signs. Overhead signs had a dynamic 

section that displayed a red “x” when the shoulder was closed to traffic and green arrow when it 

was open the traffic. Ground mounted static signs listed the hours of the operation and other 

regulatory information. The shoulder was opened and closed on a fixed schedule, but operators 

could override the schedule and change dynamic indications if special conditions warranted 

opening or closing the lane outside of scheduled hours. 

For travelers on the mainline, a combination of overhead and post-mounted signage denoted the 

start of permitted part-time shoulder uses, shown in Figure 61. Post-mounted signs displaying the 

hours of permitted shoulder use were spaced approximately every quarter mile throughout the 

corridor. Subsequent signs provided notice that there was no physical shoulder during the 

prescribed hours of shoulder use, shown in Figure 62. 

Figure 61. Photo. Combination of static and dynamic signage, I-66 mainline. 

(Source: Virginia Department of Transportation) 
Appendix B – Signing and Pavement Marking Examples

147

Figure 62. Photo. Notice informing motorists of the lack of 

right shoulder during shoulder running operations, I-66 mainline. 

(Source: Google Maps) 

While the shoulder was not in use, drivers were permitted to use the shoulder to exit the freeway 

a few hundred feet in advance of the gore point; Figure 63 illustrates the post-mounted, static 

signage used to inform motorist where they were permitted to begin exiting. 

Figure 63. Photo. Static signage denoting permitted use of shoulder 

to exit during non-operational hours of shoulder use, I-66 mainline. 

(Source: Virginia Department of Transportation) 
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148

Washington 

Part-time shoulder use was implemented on US 2 eastbound in Everett, Washington, in 2009 on 

a trestle crossing wetlands. WSDOT used static signs to reduce the project cost and initially 

planned to implement dynamic signs at a later date. As of 2015, the static signs are working 

effectively and WSDOT no longer plans to implement dynamic signs. The US 2 part-time 

shoulder use segment is a commuter-oriented facility on a bridge with few ramps and minimal 

curvature, signs, and other elements that would increase driver workload. This makes it a good 

candidate for having static signs only.(33) Figure 64 shows an overhead regulatory sign on US 2 

at the start of the part-time shoulder use segment. Ground mounted regulatory signs are used 

within the part-time shoulder use segment. 

Figure 64. Photo. Overhead regulatory sign, US 2. 

(Source: Google Maps) 

Washington previously allowed buses and HOVs (with three or more passengers) to travel on the 

shoulder of westbound SR 520 approaching Lake Washington at all times. It was frequently 

described as static part-time shoulder use, but it was not in the sense it was never available for 

emergency refuge and always open to traffic. The lane was signed with static black on white 

regulatory signs prior to its replacement with a general purpose lane in 2015 as part of a roadway 

widening project. 

Turnouts 

Figure 65 shows the turnout sign sequence current in use in Virginia. Massachusetts uses one 

small black on white sign at the start of the turnout and does not provide any advance signs. For 
Appendix B – Signing and Pavement Marking Examples

149

consistency with other types of roadside refuge areas such as slow moving truck turn offs on 

rural two-lane highways, the term “turnout” is preferred over “pull off”. 

Figure 65. Photo. Turnout sign sequence, I-66. 

 (Source: Virginia Department of Transportation) 

Pavement Marking 

Figure 66 shows the use of two edge lines on I-H-1 in Hawaii, with the outside edge line 

terminating at the start of the bridge. “Shldr lane” word markings are provided (see red arrow). 

Figure 66. Photo. Edge lines and “shldr lane” work markings on a part-time shoulder use 

section of I-H-1. 

(Source: Kittelson & Associates, Inc.) 
Appendix B – Signing and Pavement Marking Examples

150

At the start and end of part-time shoulder use segments, the line between the shoulder and the 

adjacent travel lane typically changes from solid white to dotted white to encourage travel 

onto/off of the shoulder. Sometimes diagonal solid or dotted lines are used to further guide the 

transition. Figure 67 shows pavement markings at the start of the part-time shoulder use segment 

of US 2 in Washington State. 

Figure 67. Photo. Edge line markings at the start of part-time shoulder use segment, US 2. 

(Source: Google Earth) 

Pavement markings at on- and off-ramp are more complex. They vary based on the types of 

entrance and exit configurations described in the geometric design section of this chapter, and 

existing state ramp-freeway junction marking practices. In general, pavement markings in the 

vicinity of a merge or diverge should provide a clear means for drivers on the mainline shoulder 

to pass through the ramp freeway junction, and they should also provide a means to transfer from 

the freeway to ramp or vise verse. Striping can create parallel or taper style merges and diverges. 

MassDOT uses parallel style entrances and exits on part-time shoulder use facilities. Figure 68 

illustrates the typical striping plans for part-time shoulder use at ramps on I-93 in Boston. The 

painted gore at on-ramps is used to terminate the exclusive use of the shoulder lane, allowing 

vehicles entering the freeway to drive on the shoulder for several hundred feet and then merge 

with the general purpose lanes. The acceleration lane for merging traffic is tapered down, and 

part-time shoulder use is resumed. Figure 69 shows an example of this merge; the solid white 

lines denote the shoulder, which reaches full-width after the acceleration lane is eliminated via 

the taper. 
Appendix B – Signing and Pavement Marking Examples

151

Figure 68. Illustration. On- and off-ramp striping plans, I-93. 

(Source: Massachusetts Department of Transportation) 

Figure 69. Photo. On-ramp striping, I-93. 

(Source: Massachusetts Department of Transportation) 
Appendix B – Signing and Pavement Marking Examples

152

At off-ramps, a single solid line is used to transition traffic from general purpose lanes onto the 

shoulder, allowing general purpose traffic to exit. Part-time shoulder use resumes beyond the 

painted gore; Figure 70 illustrates an example of this transition. 

Figure 70. Photo. Off-ramp striping, I-93. 

(Source: Massachusetts Department of Transportation) 

On I-66 in Virginia, the pavement markings for part-time shoulder use are carried through the 

on- and off-ramps. Vehicles from the general purpose lanes use a short portion of the shoulder to 

access the off-ramp, which is a taper-style design. Past the painted gore of the off-ramp, the 

shoulder lane again becomes a part-time lane. 

Figure 71. Photo. Off-ramp striping, I-66. 

(Source: Google Earth) 

 

 
References

153

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U.S Department of Transportation

Federal Highway Administration

O! ce of Operations

1200 New Jersey Avenue, SE

Washington, DC 20590

O! ce of Operations Web Site

www.ops.fhwa.dot.gov

February 2016

FHWA-HOP-15-023