Pavement Marking Retroreflectivity Research Articles

Impact of Bead Density on Paint Pavement Marking Retroreflectivity

This paper addresses the impact of bead density on paint pavement marking retroreflectivity. The writers collected retroreflectivity data and glass bead images on 40 segments of two-lane highways. Bead density is defined as the surface percentage of glass beads exposed above the paint marking material. Numerous methods for determining bead density were considered and studied. A new approach, referred to as a computer-aided counting method, was developed and a bead density analysis program was written. The program was used to analyze 108 images to obtain a bead density value for each image. A correlation study was conducted between pavement marking retroreflectivity and bead density. The findings of the study show that the normal range of glass bead density for older markings is 9–24% of the paint marking surface area. Furthermore, bead density values have a positive correlation with marking retroreflectivity readings; higher bead density leads to higher retroreflectivity. White paint markings have significantly higher retroreflectivity values than do yellow markings when the bead density values are the same.

Use of Pavement Marking Degradation Models to Develop a Pavement Marking Management System

The Pennsylvania Department of Transportation collected periodic pavement marking retroreflectivity data on 88 roadway segments over a 1-year period from May 2007 through May 2008. The purpose of this effort was to use the data collected to develop a series of pavement marking degradation models that could be used to implement a management system. In this study, panel data models were used to estimate the service life of both waterborne and epoxy pavement markings because of the repeated retroreflectivity measurements recorded over time. It was found that pavement marking retroreflectivity decreases as the age of both epoxy and waterborne-paint pavement markings increase. White pavement markings were shown to have higher estimated service lives than yellow pavement markings. Traffic exposure was found to be negatively correlated with pavement marking retroreflectivity in the waterborne-paint analysis, but traffic exposure was not statistically significant in the epoxy pavement marking retroreflectivity model. A life cycle cost analysis showed that waterborne paints are more cost-effective than epoxy pavement markings if applied on a statewide basis.

Pavement Marking Degradation Modeling and Analysis

The objective of this research was to determine the performance characteristics of thermoplastic pavement markings in North Carolina and to create viable degradation models. Additionally, an evaluation of paint pavement-marking materials was conducted and models were created for them as well. The resulting models provide pavement-marking managers with valuable tools that will allow them to focus limited resources where they are most needed and avoid replacing materials with effective life still remaining in them. Consideration was given to the analysis of the relationships between pavement-marking retroreflectivity values and variables such as time, traffic volume, and marking color. Unique to this research is the inclusion of lateral location as a key variable affecting the performance of pavement markings. Another key contribution to pavement-marking management from this research was the development and use of level of service increments for describing the status of a given marking at some point in time. Using the tools reported herein an expected service life for thermoplastic and paint pavement markings in North Carolina can be estimated. A key finding of the research is that the markings have a far greater life expectancy than originally expected. Combining our predictive tool with level of service increments provides a holistic infrastructure management approach to pavement markings.

Analysis of Effects of Pavement Marking Retroreflectivity on Traffic Crash Frequency on Highways in North Carolina

Pavement markings provide useful visual and navigational guidance information to motorists. Current warrants for the application of pavement markings in the United States are based on traffic volume, traveled way width, and number of travel lanes. To be effective, pavement markings must be visible to drivers, particularly at night. The purpose of this paper is to perform an exploratory analysis to determine if a relationship between pavement marking retroreflectivity and crash frequency exists. First, models of pavement marking retroreflectivity degradation were developed from selected highways in North Carolina using artificial neural networks. Monthly estimates of pavement marking retro-reflectivity levels were then appended to roadway inventory and crash frequency data. Generalized estimating equations were used to estimate the monthly target crash frequency. The results indicate that the regression parameter estimates for yellow and white edgeline pavement markings were negative, but neither was statistically significant for the two-lane highway nighttime target crash frequency model. For multilane highways, all of the pavement marking retro-reflectivity parameter estimates were statistically significant. The white pavement marking retroreflectivity parameter estimates were negative, as expected. The yellow pavement marking retroreflectivity parameter estimate was positive.

Exploratory Analysis of Accelerated Wear Testing to Evaluate Performance of Pavement Markings

Wear testing of pavement markings in the United States is commonly performed by AASHTO's National Transportation Product Evaluation Program. The pavement markings evaluated in this program are applied in a transverse manner along existing roadways, and a variety of objective measures are collected over a 2-year period. This paper reports the findings from an exploratory study on using the Model Mobile Load Simulator, third scale (MMLS3), to evaluate pavement marking performance along transverse test sections. Accelerated trafficking on wet and dry pavement surfaces was applied on sections of markings consisting of various waterborne paint products, marking thicknesses, and bead types and densities. Pavement marking retroreflectivity measurements were recorded at various stages of MMLS3 trafficking and compared with measurements of a test deck consisting of the same pavement markings subjected to live traffic. The findings suggest that the MMLS3 can consistently replicate the degradation pattern of the various pavement markings with regard to loss of retroreflectivity as a function of traffic passages. Performance varied among the various types of markings, with higher retroreflectivity observed for thicker markings with higher bead densities. Trafficking on wet pavement surfaces accelerated the degradation of the markings’ retroreflectivity.

The Impact of Directionality on Paint Pavement Marking Retroreflectivity

This article addresses paint centerline pavement marking retroreflectivity. The authors collect yellow centerline retroreflectivity data on two-lane highways, taking measurements in two directions. A paired t test on the data shows that there are differences and they are statistically significant. A field study is initiated to investigate the relationship between the direction the marking is painted and the retroreflectivity direction. The key result of this study is that paint centerline retroreflectivity values measured in the direction of paint striping are significantly higher than values measured in the opposite direction. Findings indicate that it is the lower retroreflectivity values of yellow centerlines (measured in the opposite direction from paint striping) that should be used to compare with the newly proposed Federal Highway Administration minimum standard because the drivers in that direction experience lower marking retroreflectivity at night. The implications for safety, for policy making, and for transportation asset management are significant.

Review and Development of Recommended Minimum Pavement Marking Retroreflectivity Levels

Research was conducted to review and develop minimum levels for pavement marking retroreflectivity to meet nighttime driving needs. A previous study performed in the 1990s using a computer model called the Computer-Aided Road-Marking Visibility Evaluator resulted in a table of minimum levels of pavement marking retroreflectivity values that FHWA used to develop its initial set of minimum pavement marking retroreflectivity levels. Since then, additional research has been completed as well as development of a newer, more feature-intensive computer model called the Target Visibility Predictor (TarVIP). The research presented used TarVIP to study pavement marking retroreflectivity needs while using the most recently available information pertaining to driver, vehicle, and headlamp trends in the United States. In this research, previous pavement marking research efforts that included findings or recommendations related to minimum retroreflectivity are summarized. Next, a comprehensive survey on the factors that affect pavement marking visibility and minimum RL levels was performed, with key factors identified. They included pavement marking configuration, pavement surface type, vehicle speed, vehicle type, and presence of raised reflective pavement markers. From findings of the key factor reviews, the TarVIP model was used to generate preliminary results that could then be analyzed by sensitivity analysis. The research resulted in a set of recommended minimum pavement marking retroreflectivity levels for typical conditions on U.S. roadways. Limitations of the research were listed as well as concepts for future work.

Pavement Marking Retroreflectivity

Previous research has shown that greater longitudinal pavement marking retroreflectivity levels increase drivers’ visibility and detection distance. However, increased visibility may cause drivers to feel too comfortable during nighttime conditions, and drivers may then pay less attention, operate their vehicles at unsafe speeds, or both. Before-and-after studies have been conducted on a pavement marking improvement such as repainting stripes or changing to a more durable marking material. Studies have also used models to estimate the retroreflectivity on the basis of the date of installation and vehicle exposure or have assumed a linear reduction in retroreflectivity over time. Only two studies have related field-measured pavement marking retroreflectivity to safety performance (crash data). One study analyzed the relationship between 3 years of pavement marking retroreflectivity data collected by the Iowa Department of Transportation on all state primary roads and corresponding crash and traffic data. The other study developed a spatial–temporal database by using measured retroreflectivity data to account for the deterioration of pavement markings over time, along with a statewide crash database to attempt to quantify a relationship between crashes and the quality (measured by retroreflectivity) of pavement marking. Three sets of data were analyzed: the complete database, records for two-lane roads, and records with retroreflectivity values less than or equal to 200 mcd/m2/lx only. The distributions and models of the entire database and the two-lane records did not show that poor pavement marking retroreflectivity correlated to a higher crash probability. However, when only records with retroreflectivity values of 200 mcd/m2/lx or less were examined, a statistically significant, albeit weak, relationship was determined.

Pavement Marking Retroreflectivity Inspection Data

Quantifiable life-cycle models of the service life of pavement markings are essential for a cost-efficient pavement marking management system. A study was conducted to develop an analysis procedure for typical pavement marking retroreflectivity inspection data. Retroreflectivity data collected by the National Transportation Product Evaluation Program on water-based paints in 2002 on a Pennsylvania test deck were used. Those data were considered interval-level duration data, and a Weibull analysis was performed. A Weibull analysis is a typical method in reliability engineering in which Weibull scale and shape parameters are estimated from failure data for making objective maintenance decisions. Results of the Weibull analysis indicated that the water-based paints had shape and scale parameters of 1.42 (±0.05), and 601.67 (±17.73) days, respectively, for skip line areas and 2.38 (±0.08) and 227.41 (±4.48) days, respectively, for left wheelpath areas. It was also determined that the probability of 2-year water-based paints lasting above 100 mcd/m2/lx varied from 0% to 27%. The lower limit corresponds to the left wheelpath, and the upper limit corresponds to the skip line area. The left wheelpath markings failed to stay above 100 mcd/m2/lx after approximately a year, while skip line markings could maintain 100 mcd/m2/lx ratings or higher for more than 1,000 days. White markings were found to last longer than yellow markings for the same exposure. This study used data from a single site in Pennsylvania. A multisite analysis accounting for time and space variations is recommended before adopting this method for minimum pavement marking retroreflectivity standard assessment.

Modern Pavement Marking Systems

Road marking systems have retroreflective properties to assure adequate nighttime visibility. Modern systems can also provide night visibility under rain and wet conditions. The FHWA is currently working to establish requirements for minimum maintained retroreflectivity of pavement markings on all U.S. roads. Its task is complicated by the fact that conventional dry retroreflectivity measurements do not tell the entire story about pavement marking visibility at night. To that end, there is ongoing research into the relationship between a pavement marking system's retroreflective properties and the level of on-road visibility the system provides. A pavement marking system is composed of three basic components: the optics, the structure, and the binder. Each component influences the retroreflective efficiency of the marking, its visibility at night, and the reliability of predictive correlations between the two. Such correlations are required to set practicable minimum maintained pavement marking visibility levels. A Comité Européen de Normalisation 30-m coefficient of retroreflected luminance (RL) value is commonly assumed to be a good predictor of the on-road visibility of pavement marking. While useful for quality assurance, this standardized RL value is not a measure of visibility. This paper describes choices for pavement marking components and their impact on night visibility. Data on the fundamental relationship between optics and retroreflective efficiency related to road marking visibility are presented. Dry and wet conditions are considered, as are flat and structured markings. Field measurements of pavement marking luminance are presented to illustrate how the optical design of a pavement marking system controls nighttime visibility.

Statistical Validation of the Effect of Lateral Line Location on Pavement Marking Retroreflectivity Degradation

This article examines the effect of lateral location on the degradation of retroreflectivity in thermoplastic pavement-marking systems. The authors examined data collected on North Carolina roads over a 5-year period and conducted a statistical analysis to determine if there was a significant difference in the rates of retroreflectivity degradation between edge lines and center lines. The study concluded that there was statistical evidence that lateral line location does have an effect on retroreflectivity degradation and that center lines degrade faster than edge lines. Understanding retroreflectivity performance over time facilitates the development and implementation of guidelines and tools that can be used for holistic asset management. Based on their findings, the authors recommend changes in pavement-marking maintenance strategies.

Application of Innovative Time Series Methodology to Relationship between Retroreflectivity of Pavement Markings and Crashes

The innovative time series methodology that is presented was used to examine the relationship between the safety impact of longitudinal pavement markings and their retroreflectivity. The need for the methodology was determined through an examination of the pavement marking safety literature, the desire to build on previous retroreflectivity research, and an understanding of how retroreflectivity is a function of the age of pavement markings and markers. The time series methodology involves solving for multipliers that represent the change in the expected number of crashes as a function of pavement marking retroreflectivity while simultaneously solving for seasonal effect multipliers. The time series methodology is explained in detail; its usefulness has been demonstrated through the analysis of 8 years of pavement marking and marker installation data, traffic volumes, and crash data. Safety effect multipliers were solved for yellow and white pavement markings separately and in combination. The multipliers covered different road types and crash severities by using retroreflectivity models and California's data for more than 118,000 nonintersection, nondaylight (night, dawn, and dusk) recorded crashes. To apply the time series methodology, it was necessary to develop retroreflectivity models as a function of age, color, marking material type or marker type, climate region, and amount of snow removal. The results showed that retroreflectivity levels have no effect to a small effect on the safety performance of those roadways maintained to a reasonable level of pavement marking.

Characterization and Mitigation of Temperature Sensitivity within Mobile Retroreflectometer Unit

Mobile retroreflectometers have demonstrated great potential as a tool to assess the retroreflectivity of pavement markings, on both project and network levels. Such devices can collect and process much more data than their handheld predecessors can. However, studies have shown concerns with repeatability and reproducibility. Successful integration of pavement marking retroreflectivity readings into a pavement management system hinges on the accuracy of the collected data. Previous research has centered on data collection techniques to minimize error (collection frequency, averaging), but little research has focused on the technology and the components making measurement possible. Results were summarized for the characterization and the mitigation of a temperature sensitivity uncovered during the Florida Department of Transportation's evaluation of a mobile retroreflectometer unit. During routine data collection, offsets in the measured retroreflectivity were observed between results from repeat runs on the same section. A strong correlation was observed between the temperature of the device and measured retroreflectivity. More specifically, as the temperature within the device increased from 20°C to 40°C, a 30% increase in measured retroreflectivity resulted. Testing revealed that the optical filters operating outside their manufacturer-specified temperature range were primarily responsible for the temperature sensitivity. The response of the filter set over a broad range of temperatures was characterized, and a compensation algorithm was created to reduce system error. A thermoelectric cooler was incorporated to regulate the internal temperature of the retroreflectometer. With these modifications, a temperature sensitivity of ±3% resulted over a temperature range of 20°C.

Cost- and Longevity-Based Scheduling of Paint and Thermoplastic Striping

Because no national guidelines exist on establishing pavement marking service life, the scheduling of road striping has been inconsistent among maintenance agencies. This study establishes a way to set striping schedules that accounts for factors affecting scheduling, mainly application cost, service lifetime, and user cost relative to crashes during the striping lifetime. Striping useful lifetime is defined as the striping age beyond which pavement markings become ineffective in relaying necessary vehicle positioning information, when deteriorated pavement marking retroreflectivity reaches a minimum acceptable value. An exponential regression model was used to depict the relationship between striping age and average daily traffic (ADT), using a retroreflectivity threshold of 150 mcd/m2/1x. Striping useful lifetime was established for ADT levels using exponential regression analysis. Application costs were based on the latest available unit costs from the Alabama Department of Transportation for white and yellow longitudinal stripes of paint and thermoplastic markings. Using the National Safety Council estimates of crash severities, user costs were based on the dollar equivalency of the damage to vehicles and occupants in retroreflectivity-related crashes. The data were extracted from the crash experience of approximately 1,300 mi (2100 km) of state highways in 32 Alabama counties. For use in scheduling striping, paint and thermoplastic striping costs were compared on an equivalent annual basis, accounting for application and user costs. Although the crash data and retroreflectivity data were collected on Alabama roads, the findings and conclusions are applicable to areas of warmer climate where snowfall is uncommon.

Computer-Based Modeling to Determine the Visibility and Minimum Retroreflectivity of Pavement Markings

The Federal Highway Administration was mandated by the U.S. Congress to establish in-service levels of minimum pavement-marking retroreflectivity and commissioned research to determine the minimum in-service level from a driver’s point of view. Computer Aided Road Marking Visibility Evaluator (CARVE) was developed and refined to systematically investigate drivers’ visual needs in terms of nighttime pavement-marking visibility and to allow the formulation of minimum retroreflectivity recommendations. The components within CARVE and the methods, algorithms, and equations that are used to determine the visibility distance of a given pavement-marking treatment are presented and discussed. CARVE systematically manipulates the pavement-marking efficiency (ηPM) up and down using a bisecting-search algorithm until the desired minimum required preview distance for selected conditions is achieved. Future expansions of CARVE, or the development of models that supersede it, may require additional research to investigate the wet-weather visibility of pavement markings, the effects of combined treatments consisting of pavement markings and raised reflective markers, and the visibility in inclement weather such as fog and blowing snow.

Minimum In-Service Retroreflectivity of Pavement Markings

Minimum in-service retroreflectivity values for pavement markings are presented based on visibility computations performed with the CARVE (Computer-Aided Road-Marking Visibility Evaluator) computer model. CARVE accurately computes all geometric and photometric relationships for each headlamp separately; applies the human visual luminance contrast threshold database from Blackwell (Part III, 1946) adjusted by a field factor function that has been obtained from a number of pavement marking visibility field experiments; and provides retroreflectivity values for the pavement markings for any selected single-point geometry (e.g., ASTM 30-m geometry, observation angle = 1.05°, entrance angle = 88.7°). Based on the CARVE computation results, a set of in-service pavement marking retroreflectivity values are derived for fully marked, dark, straight, and dry roads using paint-and-beads pavement markings. The derived minimum retroreflectivity values for fully marked roads without raised pavement markers (RPMs) are highly speed dependent, because the computations are based on a constant minimum preview time of 3.65 s (3.0 s true preview and 0.65 s for eye-fixation duration). A separate set of minimum retroreflectivity values, based on a constant preview time of 2.0 s, is provided for fully marked roads with RPMs in good working order. It was found that the minimum retroreflectivity requirements for pavement markings could be substantially relaxed if RPMs (in good photometric working condition) were used. The proposed minimum retroreflectivity values are based on a 62-year-old driver (about the 85th percentile of the licensed driver population, about the 95th per-centile of the nighttime driver population based on trip frequency data as a function of the time of day).

Driver Preview Distances at Night Based on Driver Eye Scanning Recordings as a Function of Pavement Marking Retroreflectivities

Pavement marking visibility models and tightly controlled pavement marking field experiments indicate that increased pavement marking retroreflectivity does in fact result in longer pavement marking visibility distances. The authors suggest that drivers should be provided with a pavement marking visibility distance long enough to allow for a preview time of 3.65 s at a given vehicle speed. This minimum required preview distance can be translated into a minimum required pavement marking retroreflectance. Questions were raised that perhaps drivers may not take advantage of brighter pavement markings (increased retroreflectance)—that is, drivers may not be looking as far ahead as possible from a pavement marking visibility point of view. This study was conducted to test whether drivers increase their longitudinal eye fixation distance when pavement marking retroreflectance is increased. Eye scanning data from six subjects were used to establish longitudinal eye fixation distributions on straight and level roads under low-beam illumination at night. In general, drivers appear to adjust their visual information acquisition behavior (longitudinal eye fixation distances and eye fixation preview times) when driving on roads with bright and highly visible pavement markings. Within the range of pavement marking retroreflectances investigated, it appears that, at least for half the drivers tested, brighter markings are indeed better and provide longer preview distances, which is desirable from an information acquisition, information processing, and safety point of view.

Visibility of Road Markings as a Function of Age, Retroreflectivity Under Low-Beam and High-Beam Illumination at Night

A study was conducted to obtain visibility data for old and young subjects performing a pavement marking end detection task on a fully marked road under headlamp illumination conditions. A total of 20 healthy subjects (10 old and 10 young) were used. It was found that observer age had a highly significant effect on pavement marking visibility. The effect of headlamp illumination (high-beam versus lowbeam) was found to be rather weak, probably because of the low-beam headlamp pattern, which favors the right-edge line. Pavement marking retroreflectivity was found to be significant at the levels investigated in the experiment. The new yellow dashed centerlines (tape) with a gapto-stripe ratio of 9.1/3 had a retroreflectivity of RL = 222 mcd/m2/lx and RL = 399 mcd/m2/lx under the medium and high conditions, respectively. The new white edge lines (tape) had a retroreflectivity of RL = 268 mcd/m2/lx and RL = 706 mcd/m2/lx under the medium and high conditions, respectively. The average end detection distances ranging from 124.8 m (average preview time 5.1 s for 88.5 km/h) for the old group under low-beam illumination on the medium retroreflectivity road to 237.3 m (average preview time 9.7 s for 88.5 km/h) for the young group under high-beam illumination on the high retroreflectivity road may appear to be rather long. However, the reader should be aware that markings as bright as the ones used in this research are the exception instead of the rule in real-world driving situations. The aim of this study was to determine the end detection distances obtainable under fairly favorable pavement marking material conditions.

Field Surveys of Pavement-Marking Retroreflectivity

Field surveys of pavement-marking retroreflectivity were conducted throughout the United States. Thirty-two state and local highway agencies participated in the study by identifying pavement-marking sites for measurement. The retroreflectivity of both white and yellow pavement-marking lines of six different marking materials—conventional paint, waterborne paint, epoxy, polyester, thermoplastic, and tape—was measured in the field. Field measurements of pavement-marking retroreflectivity for sites under the jurisdiction of all 32 participating agencies were made in the fall of 1994. Selected sites were remeasured in the spring of 1995 for six of the participating agencies. All field measurements were made with a Retrolux Model 1500 retroreflectometer. A comparison of the fall 1994 and spring 1995 results are presented. Data analyses were conducted to determine the mean, standard deviation, and distribution of the coefficient of retroreflected luminance (retroreflectivity) and the contrast ratio between the retroreflectivity of the pavement markings and that of the adjacent pavement surface by color of line and pavement marking material. However, it was difficult to state any definitive comparisons between material types without knowing the relative ages and manufacturers of the markings, and such data were unavailable. The economic implications of particular threshold values for replacement of pavement markings were also evaluated.

Pavement Marking Retroreflectivity Requirements for Older Drivers

Traffic pavement markings serve to regulate, guide, and channelize traffic and supplement other traffic-control devices. Because of their retroreflective properties pavement markings are critical for guidance at night, when reference objects near the edge of the roadway are difficult to see. Nighttime luminance levels provided by pavement markings that may be adequate for younger drivers may be less than adequate for older drivers. Both subjective evaluations and quantitative measures of in-place roadway markings were made to determine minimum marking retroreflectivity levels required for older drivers. In the field study more than 85 percent of subjects aged 60 years or older rated a marking retroreflectance of 100 mcd/m2/lx as adequate or more than adequate for night conditions. This base value does not include the effects of windshields and headlights that are less than clean or the variability of individual vehicle headlight performance. A comparison between the results for older drivers and the results of a similar 1989 study of younger drivers was also made. It was found that whereas the average subjective ratings were similarly distributed relative to the retroreflectivity of pavement markings, there was a significant difference in the subjective ratings made by older and younger drivers. Older drivers consistently rated the retroreflectivity of markings lower than did younger drivers.