006_FHWA_Maintaining_Pavement_Markings.pdf

Methods for Maintaining Pavement Marking Retroreflectivity

FHWA-SA-22-028 | July 2022

Notice

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

Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

Unless otherwise indicated, the source of all tables, graphics, and photos in this document is FHWA.

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Trademarks or manufacturers’ names appear herein only because they are considered essential to the objective of this document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Form

1. Report No.

FHWA-SA-22-028

2. Government Accession No.

3. Recipient’s Catalog No.

4. Title and Subtitle

Methods for Maintaining Pavement Marking

Retroreflectivity

5. Report Date

July 2022

6. Performing Organization Code

7. Author(s)

Adam M. Pike, Cathy Satterfield, Greg Schertz, Joseph

Cheung, and Kathy W. Falk

8. Performing Organization Report

No.

9. Performing Organization Name and Address

Texas A&M Transportation Institute

The Texas A&M University System

College Station, TX 77843-3135

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

Contract DTFH61-10-D-000024

12. Sponsoring Agency Name and Address

Office of Safety

Federal Highway Administration

1200 New Jersey Avenue, S.E.

Washington, DC 20590

13. Type of Report and Period

Covered

14. Sponsoring Agency Code

15. Supplementary Notes

Research performed in cooperation with the U.S. Department of Transportation and the Federal

Highway Administration. Project Contracting Officer’s Technical Representative: Cathy Satterfield, Federal Highway Administration, Office of Safety

16. Abstract

In response to a congressional directive, the Federal Highway Administration established a standard for minimum maintained pavement marking retroreflectivity levels that are incorporated in the Manual on

Uniform Traffic Control Devices (MUTCD). This document, referenced in the MUTCD, describes retroreflectivity maintenance methods that, when implemented as intended, provide agencies with a flexible means of being in conformance with the standard. These methods were developed specifically for longitudinal pavement markings (i.e., center lines, lane lines, and edge lines) although some of the methods could also be applicable to other types of markings. Agencies can use the information in this report to help determine which retroreflectivity maintenance method or combination of methods best suits their needs.

17. Key Words retroreflectivity, traffic control devices, pavement markings, pavement marking maintenance, maintenance methods, minimum retroreflectivity, retroreflectometer

18. Distribution Statement

No restrictions.

19. Security Classif. (this report)

Unclassified

20. Security Classif. (this page)

Unclassified

21. No. of Pages

22. Price

N/A

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

July 2022 ii

SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km

AREA

in square inches 645.2 square millimeters mm ft square feet 0.093 square meters m yd square yard 0.836 square meters m ac acres 0.405 hectares ha mi square miles 2.59 square kilometers km

VOLUME

fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft cubic feet 0.028 cubic meters m yd cubic yards 0.765 cubic meters m

NOTE: volumes greater than 1000 L shall be shown in m

MASS

oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")

TEMPERATURE (exact degrees) o F Fahrenheit 5 (F-32)/9 Celsius o C or (F-32)/1.8

ILLUMINATION

fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m cd/m

FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi

AREA

mm square millimeters 0.0016 square inches in m square meters 10.764 square feet ft m square meters 1.195 square yards yd ha hectares 2.47 acres ac km square kilometers 0.386 square miles mi

VOLUME

mL milliliters 0.034 fluid ounces fl oz

L liters 0.264 gallons gal m cubic meters 35.314 cubic feet ft m cubic meters 1.307 cubic yards yd

MASS

g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T

TEMPERATURE (exact degrees) o C Celsius 1.8C+32 Fahrenheit o F

ILLUMINATION

lx lux 0.0929 foot-candles fc cd/m candela/m

0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce per square inch lbf/in

*SI is the symbol for th International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. e

(Revised March 2003) https://www.fhwa.dot.gov/publications/convtabl.cfm

July 2022 iii

July 2022 iv

TABLE OF CONTENTS

Chapter 1. Introduction

Purpose

Background

Maintaining Pavement Marking Retroreflectivity Performance

Report Organization

Chapter 2. Overview of the Methods

Introduction

Objectives of the Methods

Pavement Marking Visibility and Retroreflectivity

Acceptable Pavement Marking Retroreflectivity Maintenance Methods

Measured Retroreflectivity Method (See Chapter 3)

Nighttime Visual Inspection Methods

Service Life Based on Historical Data Method (See Chapter 6)

Service Life Based on Monitored Markings Method (See Chapter 7)

Other Methods

Techniques Not Recommended as Pavement Marking Retroreflectivity Maintenance

Methods

Sun-over-the-Shoulder Technique (Not a Recommended Method)

Comparison Panel Technique (Not a Recommended Method)

Lane Line Count Technique (Not a Recommended Method)

Windshield Marking Technique (Not a Recommended Method)

Control Markings Technique (Not a Recommended Method)

Comparison Light Box (Not a Recommended Method)

Chapter 3. Measured Retroreflectivity Method

Introduction

Background

Inspector Training

General Procedures

Detailed Procedures

Linking Measurements to Retroreflectivity Levels

Advantages

Concerns

Chapter 4. Consistent Parameters Nighttime Visual Inspection Method

Introduction

Background

Inspector Training

General Procedures

July 2022 v

Detailed Procedures

Linking to Maintained Retroreflectivity Levels

Advantages

Concerns

Chapter 5. Calibrated Pavement Markings Nighttime Visual Inspection Method

Introduction

Background

Inspector Training

General Procedures

Detailed Procedures

Linking to Retroreflectivity Maintenance Levels

Advantages

Concerns

Chapter 6. Service Life Based on Historical Data Method

Introduction

Procedures

Current Practice

Linking Service Life to Retroreflectivity Maintenance Levels

Advantages

Concerns

Chapter 7. Service Life Based on Monitored Markings Method

Introduction

Procedures

Linking Service Life to Retroreflectivity Maintenance Levels

Advantages

Concerns

Chapter 8. Frequently Asked Questions

What Markings Are Subject to the Minimum Maintained Retroreflectivity Levels?

Is a Retroreflectometer Required to Use the Pavement Marking Retroreflectivity

Maintenance Methods Described in This Report?

Is an Inventory Necessary?

Does an Inspector Need to Be at Least 60 Years Old?

Can I Use Any Vehicle for the Nighttime Inspection Methods?

Are Annual Inspections Frequent Enough?

Is Documentation of My Inspections Required?

What If I Cannot Restore All Markings According to the Replacement Schedule?

Am I Allowed to Use Resources or Take Actions outside My Written or Documented

Method and Still Be Considered in Compliance?

July 2022 vi

References

Appendix A: Final Rule—Pavement Marking Retroreflectivity MUTCD Text

Appendix B: Method Development

Getting Started

Maintenance Methods

Deciding Which Roads and Markings to Include in the Method

Method Development: Measured Retroreflectivity

Method Definition

Method Needs

Method Implementation

Examples

Method Development: Consistent Parameters Nighttime Visual Inspection

Method Definition

Method Needs

Method Implementation

Examples

Method Development: Calibrated Pavement Markings Nighttime Visual Inspection

Method Definition

Method Needs

Method Implementation

Examples

Method Development: Service Life Based on Historical Data

Method Definition

Method Needs

Method Implementation

Examples

Method Development: Service Life Based on Monitored Markings

Method Definition

Method Needs

Method Implementation

Examples

July 2022 vii

LIST OF FIGURES

Figure 1. Text. MUTCD maintaining minimum pavement marking retroreflectivity

Figure 2. Diagram. 30-meter geometry

Figure 3. Photo. Measuring retroreflectivity with a handheld instrument

Figure 4. Photo. Typical mobile pavement marking retroreflectivity measurement instrument

Figure 5. Text. Headlamp aiming procedure.(22)

Figure B1. Diagram. Roadways to be included in the method

Figure B2. Diagram. Roadways included in method and evaluated this year

Figure B3. Diagram. Example of monitored markings map

LIST OF TABLES

Table 1. Range of pavement marking service life estimates.(26)

Table B1. Maintenance method information and data needs

Table B2. Spreadsheet example of roadway database for measured retroreflectivity

Table B3. Example inspection data collection sheet for consistent parameters nighttime visual inspection

Table B4. Spreadsheet example of roadway database for consistent parameters nighttime visual inspection

Table B5. Example survey data collection sheet for calibrated pavement markings nighttime visual inspection

Table B6. Spreadsheet example of roadway database for calibrated pavement markings nighttime visual inspection

Table B7. Hypothetical example of expected pavement marking service life (Do not use these values—example only)

Table B8. Spreadsheet example of roadway database for service life based on historical data (hypothetical data)

Table B9. Spreadsheet example of roadway database for service life based on monitored markings

July 2022 viii

ABBREVIATIONS AND ACRONYMS

AASHTO American Association of State Highway and Transportation Officials

AASHTO Guide American Association of State Highway and Transportation Officials

Roadway Lighting Design Guide, 7th Edition

ADT average daily traffic

ANSI American National Standards Institute

CFR Code of Federal Regulations

FAQ frequently asked question

FHWA Federal Highway Administration

GIS geographic information systems

IESNA Illuminating Engineering Society of North American

LTAP Local Technical Assistance Program

MUTCD Manual on Uniform Traffic Control Devices

RRPM raised retroreflective pavement marker

July 2022 1

CHAPTER 1. INTRODUCTION

Purpose

On August 5, 2022, the Federal Highway Administration (FHWA) published a final rule that incorporated a standard for maintaining minimum retroreflectivity levels for pavement markings into Section 3A.03 of the Manual on Uniform Traffic Control Devices (MUTCD) (see figure 1 and Appendix A). This document, referenced in the MUTCD, describes retroreflectivity maintenance methods that, when implemented as intended, provide agencies with a flexible means of conforming to the standard. This document includes a number of potential methods because different agencies have varying levels of staffing, equipment, budgets, road systems, and expertise.

It is not the purpose of this report to provide information on the initial installation of markings and does not address initial retroreflectivity levels. The report provides information about methods to help agencies ensure pavement markings are replaced before they reach the end of their useful service life and no longer meet nighttime driving needs. This report also includes background information on pavement marking retroreflectivity.

Background

Reducing transportation-related fatalities and serious injuries across the transportation system is the first of four goals listed in FHWA’s Strategic Plan.(1) In 2019, 36,096 people died in motor vehicle traffic crashes in the United States.(2) While only a quarter of travel occurs at night,(3) about one-half of traffic fatalities occur during nighttime hours.(4) This translates to a nighttime fatality rate that is approximately three times greater than that of daytime. There are many reasons for this disparity, such as reduced visibility, impaired driving, and fatigue. One way to address the visibility of roadway delineation is to evaluate the retroreflectivity of in-service pavement markings and replace pavement markings that are no longer performing at their intended level by implementing effective retroreflectivity maintenance methods.

Retroreflection (more commonly referred to as retroreflectivity) is a special type of reflection where light reflecting off a surface is redirected back toward the source. For the case of pavement markings, light from vehicle headlamps is reflected from the markings back toward the vehicle, making the markings appear brighter to the driver than they would be otherwise.

Pavement marking retroreflectivity can be measured and is a key indicator of the nighttime visibility of pavement markings. Maintaining pavement marking retroreflectivity to a level that meets nighttime driver needs is consistent with FHWA’s goal of improving safety on the

Nation’s streets and highways. Many safety and operational strategies depend on pavement marking visibility that meets the needs of drivers. Furthermore, recent research shows reduction in both daylight and nighttime crashes with the presence of markings and increased probability of crashes for very low retroreflectivity values, thereby indicating there are nighttime safety benefits of maintaining longitudinal pavement marking retroreflectivity.(5–8)

July 2022 2

Figure 1. Text. MUTCD maintaining minimum pavement marking retroreflectivity.

Section 3A.03 Maintaining Minimum Retroreflectivity

Standard:

01 Except as provided in Paragraph 5, a method designed to maintain retroreflectivity at or above 50 mcd/m2/lx under dry conditions shall be used for longitudinal markings on roadways with speed limits of 35 mph or greater.

Guidance:

02 Except as provided in Paragraph 5, a method designed to maintain retroreflectivity at or above

100 mcd/m2/lx under dry conditions should be used for longitudinal markings on roadways with speed limits of 70 mph or greater.

03 The method used to maintain retroreflectivity should be one or more of those described in

“Methods for Maintaining Pavement Marking Retroreflectivity” (see Section 1A.11) or developed from an engineering study based on the values in Paragraphs 1 and 2.

Support:

04 Retroreflectivity levels for pavement markings are measured with an entrance angle of 88.76 degrees and an observation angle of 1.05 degrees. This geometry is also referred to as 30-meter geometry. The units of pavement marking retroreflectivity are reported in mcd/m2/lx, which means millicandelas per square meter per lux.

Option:

05 The following markings may be excluded from the provisions established in Paragraphs 1 and 2:

A. Markings where ambient illumination assures that the markings are adequately visible;

B. Markings on streets or highways that have an ADT of less than 6,000 vehicles per day;

C. Dotted extension lines that extend a longitudinal line through an intersection, major driveway, or interchange area (see Section 3B.08);

D. Curb markings;

E. Parking space markings; and

F. Shared-use path markings.

Support:

06 The provisions of this section do not apply to non-longitudinal pavement markings including, but not limited to, the following:

A. Transverse markings;

B. Word, symbol, and arrow markings;

C. Crosswalk markings; and

D. Chevron, diagonal, and crosshatch markings.

07 Special circumstances will periodically cause pavement marking retroreflectivity to be below the minimum levels. These circumstances include, but are not limited to, the following:

A. Isolated locations of abnormal degradation;

B. Periods preceding imminent resurfacing or reconstruction;

C. Unanticipated events such as equipment breakdowns, material shortages, and contracting problems; and

D. Loss of retroreflectivity resulting from snow maintenance operations.

When such circumstances occur, compliance with Paragraphs 1 and 2 is still considered to be achieved if a reasonable course of action is taken to resume maintenance of minimum retroreflectivity in a timely manner according to the maintaining agency’s method(s), policies, and procedures.

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Improvements in pavement marking visibility will also support FHWA’s efforts to be responsive to the needs of older drivers whose visual capabilities are declining. This is important because the number of older drivers is expected to increase significantly in the coming years. In 2019,

54.1 million drivers in the United States were at least 65 years old.(9) The U.S. Department of

Transportation estimates that there will be more than 72 million licensed drivers 65 years and older by 2030.(10) In addition, there is an increased interest in pavement marking visibility for automated vehicle guidance.

When pavement markings were first used about 100 years ago, they were hand-painted along the center lines of dangerous curves and were not retroreflective. Since then, there have been many improvements in pavement markings, such as adding optics (typically glass beads) to provide nighttime visibility. Now pavement markings provide more safety benefits than ever. Recent studies, as well as those more than a half-century old, have continuously shown that adding edge lines to rural two-lane highways can reduce crashes and fatalities. More recent research findings demonstrate that benefits can be achieved using pavement marking edge lines with pavement widths as narrow as 18 feet and traffic volumes as low as 400 vehicles per day.(11) Other recent pavement marking research findings are included in a 2015 FHWA synthesis including topics such as the effects of pavement marking width and retroreflectivity.(12)

The opening statements of the MUTCD define the purpose of traffic control devices and the principles for their use. Traffic control devices, including pavement markings, are meant to promote highway safety and efficiency by providing for the orderly movement of all road users.(13) (The MUTCD is incorporated by reference in 23 CFR 655.601 and is available on

FHWA’s website at http://mutcd.fhwa.dot.gov.)

To ensure consistent application, the MUTCD describes the characteristics of and warranting criteria for pavement markings.(13) The Code of Federal Regulations (CFR) at 23 CFR 655 defines pavement marking colors. The MUTCD web page http://mutcd.fhwa.dot.gov/kno-colorspec.htm also references pavement marking colors. The importance of pavement marking retroreflectivity has been recognized in the current MUTCD, which states, “Markings that must be visible at night shall be retroreflective unless ambient illumination assures that the markings are adequately visible. All markings on Interstate highways shall be retroreflective.”(13)

Maintaining Pavement Marking Retroreflectivity Performance

The most common way to specify retroreflectivity for markings is to use the international standard of 30-meter geometry, expressed in units of millicandelas per square meter per lux

(mcd/m2/lx). As the name indicates, this geometry represents the viewing scenario of a pavement marking 30 meters in front of a vehicle (specifically, a passenger sedan although vehicle size is not a critically sensitive parameter in nighttime pavement marking performance). Agencies often specify pavement marking retroreflectivity criteria for newly installed markings and less often for in-service pavement marking performance.

Generally, maintaining the daytime performance of pavement markings (i.e., presence and color) is less of an issue for agencies than maintaining nighttime performance (retroreflectivity). The nighttime performance of pavement markings can be more difficult to maintain for a variety of reasons, including wear due to traffic, roadway debris, and especially snowplowing activities.

http://mutcd.fhwa.dot.gov/ http://mutcd.fhwa.dot.gov/kno-colorspec.htm http://mutcd.fhwa.dot.gov/kno-colorspec.htm

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Pavement markings generally use small glass beads to retroreflect light back toward the vehicle.

The glass beads are applied to a variety of binder materials (e.g., water-based paints, solvent-based paints, thermoplastic, and epoxy) so that they are partially embedded but also exposed. If the beads get damaged or knocked out of the binder material, the retroreflectivity will degrade even though the marking may still be present. Generally, the retroreflectivity of pavement markings will fade faster than the presence of the marking, making the nighttime performance more difficult to maintain than the daytime performance. Another factor that comes into play with markings is that they are installed in varying field conditions (e.g., different contractors using different equipment applying the markings at different speeds during a variety of weather conditions), making their initial performance variable. Studies have also shown that it is difficult to accurately predict pavement marking retroreflectivity degradation, even if the initial retroreflectivity level is known.

As pavement markings degrade and become less retroreflective, their effectiveness for communicating the intended travel path and roadway alignment to nighttime road users diminishes. If left unattended, pavement marking retroreflectivity can diminish to the point that the markings cannot be seen in time for nighttime drivers to properly react. Thus, to maintain nighttime effectiveness, pavement markings must be replaced before they reach the end of their useful retroreflective life.

This report focuses on those methods that are most appropriate for monitoring pavement marking retroreflectivity to determine when they need to be replaced. Other techniques briefly described in chapter 2 may be appropriate for other purposes but were considered inadequate for the purposes of maintaining pavement marking retroreflectivity in accordance with the standard in the MUTCD.

Report Organization

This report outlines maintenance methods intended to provide agencies with a flexible means of maintaining conformance with the MUTCD standard for minimum retroreflectivity of pavement markings. Although mainly descriptive of the evaluation and monitoring processes, all methods described in chapters 3 through 7 are helpful in the decision process for replacing or restriping longitudinal markings.

Chapter 2 covers the objectives of the pavement marking retroreflectivity maintenance methods.

The maintenance methods are introduced and defined. In addition, other inspection techniques that are not recommended to be used as maintenance methods are discussed.

Chapter 3 includes a description of the measured retroreflectivity method. This chapter includes information related to sampling and averaging pavement marking retroreflectivity with handheld and mobile equipment. This chapter identifies the link between the measurements and the

MUTCD retroreflectivity levels. This chapter also identifies the advantages and potential concerns of this method.

Chapter 4 describes the consistent parameters nighttime visual inspection method. Background information on this method, instructions for conducting this inspection method, and how this

July 2022 5 method links to specific retroreflectivity levels are described. Advantages and potential concerns are also included.

Chapter 5 describes the calibrated pavement markings nighttime visual inspection method.

Background information, a description of the general procedures, details of applying this inspection method, and how this links to specific retroreflectivity levels are included. This chapter also identifies the advantages and potential concerns of this method.

Chapter 6 describes the service life based on historical data method. Procedures for conducting this method, current practices, and linking the service life to the MUTCD retroreflectivity levels are included. Advantages and potential concerns are also included.

Chapter 7 describes the service life based on monitored markings method. Procedures for conducting this method and linking the service life to the MUTCD retroreflectivity levels are included. This chapter also identifies the advantages and potential concerns of this method.

Chapter 8 includes a list of questions and answers to support the pavement marking retroreflectivity methods.

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CHAPTER 2. OVERVIEW OF THE METHODS

Introduction

Traditionally, agencies have implemented different methods to ensure their pavement markings are maintained to meet drivers’ needs in relation to local conditions, needs, and priorities. These maintenance methods are understood to incorporate both the process to determine when to re-mark roadways and a schedule to replace the markings. The methods in this report do not, however, cover the actual installation process, which varies significantly depending on the materials, specifications, and equipment used. This chapter introduces the objectives in implementing a retroreflectivity maintenance method and then briefly describes a number of potential methods that FHWA recommends would achieve the objectives. Each method is then described in detail in chapters 3 through 7. This chapter also describes other techniques that were considered and determined not appropriate to achieve the objectives.

The maintenance management process begins with agency policies and practices regarding the use of pavement marking materials. Agency policies have often been driven by the costs of the various marking materials and weighed against their durability. Agencies in the north that have consistent snow removal needs experience considerably different marking durability from agencies in the south that do not have these needs.

Once new pavement markings have been installed, there is a need to determine when the markings will reach the end of their useful life so they are replaced before they no longer provide the intended delineation in both daytime and nighttime conditions. By and large, the most common method used to trigger the replacement of pavement markings has been visual inspection. However, other retroreflectivity maintenance methods have also been tested and implemented, including measuring retroreflectivity and re-applying markings based on anticipated service life.

The MUTCD recommends agencies to use a method, which may include a single method or combination of methods described in this report, designed to maintain retroreflectivity at or above the minimum levels specified.

Objectives of the Methods

The intent of these maintenance methods is to provide a systematic means for agencies to ensure their longitudinal pavement marking retroreflectivity is continually at or above minimum maintained retroreflectivity requirements as established in the MUTCD. Use of the method implies not only determining when pavement markings need to be refreshed, but also scheduling the replacement of deficient markings in a timely manner. While the use of one or more of these methods will not guarantee that every inch of pavement marking will meet or exceed the

MUTCD minimum levels at every point in time, these methods will help ensure that longitudinal pavement markings are typically replaced before they become inadequate in terms of their nighttime visibility.

Having a method in place to maintain retroreflectivity can help agencies prioritize how to spend limited resources, maximize the life of pavement markings, and ultimately contribute to

July 2022 8 improved safety for the motoring public. While the use of a particular method does not guarantee that all markings will be visible at all times, such as during snow and rain events, the overall safety of the agency’s roadway network will be improved by having such a maintenance method in place.

Regardless of how an agency chooses to ensure that pavement marking retroreflectivity is properly maintained, documentation of the process can be beneficial for many reasons. Written procedures help ensure that agency personnel properly follow the selected method, and maintenance records provide the agency with a systematic process for scheduling replacements and justification for the allocation of limited resources. For example, measurements of pavement marking retroreflectivity might show that certain markings are near or below the MUTCD levels earlier than expected based on service life predictions. The records provide documentation that an appropriate maintenance method was followed, and permit the agency to assess and revise the expected service life for a given type or group of markings, if necessary. If an agency has a method in place to manage or assess its markings and establishes a reasonable schedule for replacing markings as needed, the agency is better able to justify that it has met its performance goals. It is also quite possible that agencies will realize that they can achieve more life from their markings than previously expected. Documentation of the pavement marking retroreflectivity maintenance process can include a variety of information and levels of detail. The form and extent of documentation are up to the discretion of the individual agency. However, some items an agency might consider are described as follows:

• To prioritize and manage their programs, agencies may want to include a feature in their pavement marking retroreflectivity maintenance method that can adapt to changes in roadway volume and speed.

• Similarly, the maintenance management program could be flexible so that changes to pavement marking practices (i.e., binder material selection and retroreflective optics selection) can be easily accommodated.

• Because ambient illumination has an impact on the visibility of pavement markings, agencies may choose to place a lower priority on roadways where ambient illumination assures that the markings are adequately visible. A report from Alaska shows that when continuous lighting is used along stretches of highway with low pavement marking retroreflectivity, the pavement marking visibility can remain adequate.(14) On its lighted sections of roadway, Alaska strives to maintain retroreflectivity, but knowing that presence, combined with lighting, provides adequate nighttime visibility, Alaska is free to allocate its resources to other priorities. This does not apply to intersection or safety lighting, where isolated areas of a roadway are lighted—those areas still need to be included in the agency’s maintenance method.

In the United States, two primary documents describe roadway lighting criteria: the

Recommended Practice: Lighting Roadway and Parking Facilities (ANSI/IES RP-8-21) and the

American Association of State Highway and Transportation Officials (AASHTO) Roadway

Lighting Design Guide, 7th Edition (known as the AASHTO Guide).(15, 16) The Recommended

Practice for Lighting Roadway and Parking Facilities, published by the Illuminating

Engineering Society (IES), is commonly used by public agencies as the basis for establishing the appropriate lighting level design values for roadway lighting. This publication has been approved by the American National Standards Institute (ANSI) and is commonly referred to as RP-8. The

July 2022 9

RP-8 lighting design criteria parallels the lighting criteria found in the AASHTO Guide, except for the general land-use parameter. The RP-8 criteria are based on an assessment of the roadway classification and pedestrian conflict area classification rather than the general land-use classification found in the AASHTO Guide.

A roadway or corridor may be planned for rehabilitation or resurfacing but have existing pavement markings with retroreflectivity approaching minimum levels. In such cases, a decision needs to be made about restriping the roadway, given that it will soon be resurfaced. In these cases, an agency could choose to set a maximum time frame between identification of potential inadequate pavement marking retroreflectivity and resurfacing. If more time than the maximum time frame is expected, an agency could decide to install a low-cost temporary pavement marking (e.g., conventional waterborne paint and AASHTO M247 Type I beads), issue a restriping contract, or include a provision within the resurfacing contract that conveys the maintenance of the markings, according to the MUTCD standard, to the contractor once the project is let for construction.

Resources will change over time, and unexpected events will occur. It will be important to establish documentation and make revisions as necessary. When extraordinary events occur, such as resource shortages or circumstances outside the control of the agency, documentation can be advantageous for justification of not meeting MUTCD levels. Repetitive instances of failure to maintain retroreflectivity may indicate a need to change resources or revise the documented method. Examples to address such occurrences could be:

• Revisions to standard operating procedures to accelerate replacement schedules in high-wear areas.

• Inclusion of new resources in lieu of or in combination with agency resources.

• Characterization of procurement rule changes that impact material deliveries.

Pavement Marking Visibility and Retroreflectivity

The ability to see a pavement marking at night is not solely a function of the retroreflective characteristics of the pavement marking, but is also dependent on several other factors such as:

• The amount and pattern of light produced by a vehicle’s headlights.

• The amount of light reaching the pavement marking.

• The visual complexity of the scene (e.g., rural or urban).

• The weather (e.g., clear, rainy, or foggy).

• The visual capabilities of the observer.

A key factor in determining the visibility of a pavement marking is the contrast between the marking and the adjacent pavement surfaces. During daylight hours, ambient light provides pavement marking visibility by striking the marking surface. The reflected light scatters in all directions, but some of it reaches the driver’s eyes. However, in dark environments (without roadway lighting), vehicle headlamps produce most of the light striking a pavement surface, and therefore the retroreflective properties of the pavement marking govern the amount of light that reaches the driver’s eyes. While optics such as glass beads primarily provide the retroreflective performance of pavement markings, other factors also contribute to retroreflective performance.

July 2022 10

These include the properties of the binder material (e.g., color, pigment type and amount, type, and thickness), pavement surface roughness, and amount of debris and dirt on the marking.

Acceptable Pavement Marking Retroreflectivity Maintenance Methods

The FHWA hosted a series of workshops around the country to solicit city, county, and State transportation agency input regarding issues about implementing a national standard on minimum pavement marking retroreflectivity levels.(17) One of the most consistent comments was that a one-size-fits-all solution would not be practical, and that FHWA needed to provide flexibility in terms of meeting the minimum retroreflectivity levels. Therefore, this report includes several potential methods that agencies can choose from to maintain the retroreflectivity of their markings. Although mainly descriptive of the evaluation and monitoring processes, all methods listed here and described in detail in chapters 3 through 7 are helpful in the decision process of replacing or restriping longitudinal markings. Appendix B provides examples of how an agency might implement each of the maintenance methods.

Measured Retroreflectivity Method (See Chapter 3)

In this method, pavement marking retroreflectivity is measured and directly compared to the

MUTCD minimum levels. The retroreflectivity measurements can be made with either handheld or mobile instruments using the standard 30-meter geometry. Inspectors must follow the instructions provided by the manufacturer to obtain reliable retroreflectivity readings, including periodically calibrating the equipment. Chapter 3 has more information about this method.

Nighttime Visual Inspection Methods

This report describes two types of nighttime visual inspections that can be implemented to maintain pavement marking retroreflectivity. Both methods are meant to be conducted during dry nighttime conditions. These two methods have common elements such as:

• The use of low-beam headlamp illumination.

• Inspections conducted at prevailing nighttime speeds.

• The use of trained inspectors.

• The dependence on subjective evaluations.

Consistent Parameters Nighttime Visual Inspection Method (See Chapter 4)

The consistent parameters inspection method is based on factors similar to those that were used in the research to develop a set of recommended minimum retroreflectivity levels. This method involves a nighttime review at highway speeds with low-beam headlamps by an inspector who is aged 60 years or older. The trained inspector judges the adequacy of the markings to meet his or her nighttime driving needs. Chapter 4 has more information about this method.

Calibrated Pavement Markings Nighttime Visual Inspection Method (See Chapter 5)

This method uses a trained inspector to view calibrated pavement markings at night prior to conducting a nighttime visual inspection. Calibrated pavement markings have known retroreflectivity at or above MUTCD levels. These pavement markings are set up where the

July 2022 11 inspector can view them in a manner similar to the conditions of the nighttime visual inspections.

The markings can be in a maintenance yard, along a service road or other such facility, or on a road open to public travel. The inspector uses the visual appearance of the calibrated pavement markings to establish evaluation thresholds for that night’s inspection activities. Chapter 5 has more information about this method.

Service Life Based on Historical Data Method (See Chapter 6)

Using this method, an agency documents pavement marking installation dates and, using historical data or research results, establishes a schedule for replacing the markings. The schedule to replace the markings is designed to prevent the pavement marking retroreflectivity from falling below the MUTCD minimum levels. Pavement marking replacement schedules can be set for similar markings in similar conditions (considering factors such as pavement marking type, retroreflective optics, pavement type, pavement condition, and traffic volumes). Chapter 6 has more information about this method.

Service Life Based on Monitored Markings Method (See Chapter 7)

Using this method, an agency documents pavement marking installation dates and periodically monitors the retroreflectivity of a subset of the markings as a way to track their durability. The monitored markings represent a larger group of similar markings in similar conditions. When the monitored markings degrade and approach the MUTCD minimum levels, the entire group of markings (both monitored and the larger group they represent) are restriped. This is an alternative method for agencies that want to use a service life type of method but do not have historical data or specific research supporting service life estimates for their region and specific conditions. Chapter 7 has more information about this method.

Other Methods

An effective approach may be to combine one or more of these methods or to develop other methods based on engineering studies. If an agency develops a different method, however, it is important that the method be based on an engineering study and tied to the MUTCD minimum levels. An example of a combined method is performing one of the visual assessment methods to determine the quality of the markings: markings deemed as failing are replaced, markings deemed as adequate are left alone, and markings deemed as marginal are evaluated with a measured retroreflectivity method.

Techniques Not Recommended as Pavement Marking Retroreflectivity Maintenance Methods

FHWA identified several other pavement marking assessment techniques and considered but ultimately did not include these in the recommended methods, either because they could not be tied to a specific retroreflectivity level or due to other concerns. These techniques are described as follows. Future technologies and research may demonstrate that these techniques, or other innovative techniques, can be successfully used to maintain pavement marking retroreflectivity levels above the minimum levels in the MUTCD.

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Sun-over-the-Shoulder Technique (Not a Recommended Method)

The sun-over-the-shoulder check is an evaluation of pavement marking retroreflectivity normally used to assess the general quality of freshly installed pavement markings. This quality control check is conducted during daylight hours. Contractors and agencies use this technique to check bead coverage during installation; it does not ensure specific retroreflectivity levels. The sun-over-the-shoulder technique is not considered a suitable pavement marking maintenance method to determine if and when longitudinal pavement markings have reached the end of their useful service life because it does not have a capability to tie the observation to a level of retroreflectivity at night.

Comparison Panel Technique (Not a Recommended Method)

The comparison panel technique involves placing a comparison panel with a known retroreflectivity level at or above a specific retroreflectivity level next to an in-service pavement marking. An inspector views the combination at a specified distance (e.g., 30 meters). If the comparison panel appears brighter than the pavement marking, the marking needs to be replaced.

This technique needs to be conducted at night and with traffic control (for safety reasons). While this method is acceptable for the airfield markings for which it was developed, workshop participants deemed it unsafe for roadways because it entails too much risk for the inspectors.

Lane Line Count Technique (Not a Recommended Method)

To use this technique, inspectors count the number of lane lines visible from the driver’s seat of a static test vehicle. This count of visible lane lines is multiplied by the lane line length and spacing to calculate visibility distances. While it is possible to tie a retroreflectivity level to a visibility distance, the need to have the inspection vehicle in a static position places the inspectors at risk. It is not feasible to accurately count the lane lines from a moving vehicle. In addition, this technique would not be possible on roadway sections without broken lines (e.g.

two-lane roads with no passing allowed).

Windshield Marking Technique (Not a Recommended Method)

With this technique, a mark (using tape) is placed on the windshield at the line of sight for the inspector. This mark coincides with a visibility distance derived from a preview time of

2.2 seconds and the posted or prevailing nighttime speed of the roadway. The inspector then drives the roads at appropriate speed (the mark would need to be adjusted for speed) and disqualifies any segments where the pavement marking cannot be seen at the appropriate distance. This technique is not directly tied to specific pavement marking retroreflectivity levels.

In addition, there is concern that minor changes in the driver position (e.g., slouching) would affect the accuracy of this system. Future research may determine an effective method using this technique.

Control Markings Technique (Not a Recommended Method)

A maintenance method described in the MUTCD for maintaining traffic sign retroreflectivity is called the control sign method and involves monitoring a subsample of traffic signs to determine their service life based on minimum sign retroreflectivity levels. As the control signs near the

July 2022 13 end of their retroreflective life, they are scheduled for replacement along with the other in-service signs of the same age and materials. The control signs can be signs in a maintenance yard or in-service signs.

For pavement markings, this method is called the service life based on monitored markings method and is different in that the monitored markings must be in-service markings because the degradation of markings is so dependent on the wear they experience from traffic. Chapter 7 has more information about the service life based on monitored markings method.

Comparison Light Box (Not a Recommended Method)

A comparison light box is a handheld device that performs a daytime check of pavement marking retroreflectivity. The device is similar in size to a pavement marking retroreflectometer but is significantly less expensive. The device is composed of a box with a mirror and a light to show the appropriate geometry as the inspector looks directly down into the box. The image that the inspector sees is a side-by-side comparison of the in-service marking and a calibrated marking (placed within the device) that has a specific retroreflectivity level (at or above MUTCD levels). While this device provides a side-by-side comparison, it is not appropriate to use a comparison light box in a similar manner to a handheld pavement marking retroreflectometer.

Both devices are used by placing them on the pavement marking to be inspected, but the retroreflectometer can be operated with a trigger pull and does not need the inspector to glance away from the roadway. With the comparison light box, on the other hand, the inspector needs to look down into the device, focus, and then make a decision, demanding the inspector look away from the roadway for a significant period. The comparison light box technique works, if it is used in a safe location such as with the appropriate traffic control. However, the handheld retroreflectometer provides a more objective measure of retroreflectivity and reduces user risk by allowing the user to scan traffic. The handheld retroreflectometer is more expensive but is preferred over the comparison light box.

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CHAPTER 3. MEASURED RETROREFLECTIVITY METHOD

Introduction

In general, pavement marking retroreflectivity can be measured in the field in two ways: with handheld instruments or with mobile instruments. Handheld instruments must be placed on the pavement marking. Mobile instruments are attached to a vehicle and measure the pavement marking retroreflectivity as the instrumented vehicle is driven at typical roadway speeds. Both types of instruments provide objective retroreflectivity values that can be used in direct comparison to the MUTCD levels. The measurement method as an exclusive process to maintain pavement marking retroreflectivity has not historically appealed to agencies, as will be discussed in this chapter. However, when combined with a visual or service life method, the measured pavement marking retroreflectivity method adds an element of objectivity to the overall maintenance program. This combination of methods may enable agencies to more efficiently use their maintenance budgets.

Background

Pavement marking retroreflectivity levels are specified in the MUTCD at 30-meter geometry.

Essentially, retroreflective measurements made under 30-meter geometry simulate the retroreflective performance of the pavement marking at a distance 30 meters in front of the vehicle (using entrance and observation angles of 88.76 and 1.05 degrees, respectively)

(figure 2).

Figure 2. Diagram. 30-meter geometry.

For handheld retroreflectometer measurements, ASTM International has developed a standardized practice, ASTM D7585/D7585M, Standard Practice for Evaluating Retroreflective

Pavement Markings Using Portable Hand-Operated Instruments.(18) This standardized practice provides guidance on topics such as how many readings are needed. Currently, there is no national standard for mobile retroreflectometer measurements.

Several handheld retroreflectometers that can be used to measure pavement marking retroreflectivity are commercially available. While both the handheld measurement instruments and the mobile measurement instruments provide similar results related to measurement bias, repeatability, and reproducibility,(19) using handheld instruments can be time consuming if many

July 2022 16 roadways with miles of pavement markings are to be sampled. Mobile pavement marking retroreflectivity measurement instruments offer flexibility and efficiency for the measurement process. However, mobile measurement instruments necessitate a relatively high level of capital investment for those agencies interested in purchasing their own. Alternatively, some companies specialize in pavement marking measuring services using both handheld and mobile measurement instruments.

Inspector Training

The company selling the handheld or mobile retroreflectivity measurement instrument is best suited for providing training for proper use of the device. Specific calibration procedures and maintenance schedules for the equipment are important to follow in order to obtain accurate and repeatable measurements.

General Procedures

Measuring retroreflectivity using a handheld instrument is to be performed in safe conditions with appropriate traffic control. Measuring retroreflectivity using a mobile instrument provides relief from the need for traffic control. Using either type of instrument, the measurements must be made under dry conditions (pavement marking retroreflectivity can be measured under wet recovery and wet continuous conditions, but the minimum maintenance levels in the MUTCD pertain only to dry conditions).