Retroreflectivity Measurements Research Articles

Modeling retroreflectivity degradation of pavement markings across the US with advanced machine learning algorithms

Retroreflectivity is the primary metric that controls the visibility of pavement markings during nighttime and in adverse weather conditions. Maintaining the minimum level of retroreflectivity as specified by Federal Highway Administration (FHWA) is crucial to ensure safety for motorists. The key objective of this study was to develop robust retroreflectivity prediction models that can be used by transportation agencies to reliably predict the retroreflectivity of their pavement markings utilizing the initially measured retroreflectivity and other key project conditions. A total of 49,632 transverse skip retroreflectivity measurements of seven types of marking materials were retrieved from the eight most recent test decks covered under the National Transportation Product Evaluation Program (NTPEP). Decision Tree (DT) and Artificial Neural Network (ANN) algorithms were considered for developing performance prediction models to estimate retroreflectivity at different prediction horizons for up to three years. The models were trained with randomly selected 80% data points and tested with the remaining 20% data points. Sequential ANN models exhibited better performance with the testing data than the sequential DT models. The training and testing R2 ranges of the sequential ANN models were from 0.76 to 0.96 and 0.55 to 0.94, respectively, which were significantly higher than the R2 range (0.14 to 0.75) from the regression models proposed in past studies. Initial or predicted retroreflectivity, snowfall, and traffic were found to be the most important inputs to model predictions.

Modeling of Restriping of Waterborne Paints Using Transverse Test Deck Data in Hot and Humid Climate

The National Transportation Product Evaluation Program (NTPEP) database is a promising tool for U.S. state agencies to evaluate the performance of waterborne paint pavement markings. Out of the total 50 U.S. states, 29 states (57%) utilize the NTPEP data to assess the performance of waterborne paints to be included in the approved materials list. Yet, this dataset is based on transverse retroreflectivity (RL) measurements, which are significantly different from the longitudinal RL measurements in real-world conditions. As such, the key objective of this study was to develop a methodology that converts the transverse RL measurements of waterborne paints to the corresponding longitudinal measurements in hot and humid climate. This approach could be used by transportation agencies to predict the service life of their waterborne paints and make reliable restriping decisions. To achieve this objective, three road sections were selected in Louisiana, U.S., and four different waterborne paints were installed in the transverse and longitudinal directions. These road sections consisted of seven subsections with varying traffic levels and pavement surface types. The data collected included durability readings and longitudinal and transverse RL measurements at five time periods between October 2020 and April 2022. Based on the collected data, two non-linear regression models (for asphalt and concrete surfaces) were developed, with reasonable accuracy, to predict the longitudinal RL of waterborne paints based on the corresponding transverse RL. The predicted longitudinal RL could then be used to determine the expected service life of waterborne paints and make reliable restriping decisions.

Road Marking Glass Microspheres Fabricated from Rice Husk Ash

In this work, it is reported a comparison between solid microspheres produced from glass having conventional industrial sand (IS) and glasses made with rice husk ashes (RHA) as a source of silica. The same composition was used to fabricate both glasses. The focused was the production of glass microspheres for road horizontal marking, which would attend the type classification called Premix. The microspheres were obtained by the horizontal flame method. The results showed that characteristics such as production yield, morphology, granulometry and, mainly, retroreflectivity measurements are not altered when rice husk ash is present in the glass composition, showing that this can be a sustainable alternative material for this important application.

Establishment of a metric to characterize retroreflector properties using a consumer-grade colour camera

Abstract The coefficients of retroreflection and chromaticity coordinates are critical metrics for determining the quality of a retroreflector. However, conventional retroreflection measurement techniques rely heavily on the night-time colour, size and characteristics of the sample being measured. This complicates the measurement process and leads to deviations in the test results. In addition, chromaticity cannot be determined using this approach. Therefore, it is necessary to improve the measurement accuracy, simplify the measurement process and achieve the measurement of the traffic sign RA and chromaticity coordinates simultaneously. In this study, an improved method for retroreflector characterization using imaging was proposed. This allowed for the measurement of the coefficients of retroreflection and the chromaticity coordinates simultaneously, and only a white standard sample was required for calibration. The primary components of the proposed system included a lighting projector, a receiver, two motorized rotational stages, a retroreflective sample holder and customized software that using scaling factors to convert a digital signal into sample retroreflection coefficients and retroreflective chromaticity coordinates. The experimental results indicated that the raw data output from the camera exhibited a positive correlation relationship with the luminous flux from the surface of the retroreflector. The maximum measurement errors for the retroreflection and chromaticity were −12.2 cd/(lx·m2) and −2.09%, respectively. This method was inexpensive and convenient, used a commercially available digital camera, could help to identify defects in retroreflection and chromaticity for retroreflective sheeting and led to increased accessibility for the quality control of retroreflective sheeting.

Raised Pavement Marker Assessments Using Mobile Retroreflectivity Unit Technology

Currently, the Florida Department of Transportation (FDOT) State Materials Office collects 25,000 lane miles of line-stripe pavement marking (PM) retroreflectivity data each year using RoadVista Laserlux G7 (LLG7) mobile retroreflectivity units (MRUs). The focus of this study was to configure an LLG7 MRU to accurately and repeatably detect and measure the retroreflectivity of in-service Class B raised pavement markers (RPMs) while simultaneously collecting PM retroreflectivity data. At this time, FDOT assesses the quality of in-service RPMs as part of a visual inspection. Currently, there are no standards or devices for mobile RPM retroreflectivity measurements. As these LLG7 MRUs were designed to measure PMs in units of RL (mcd/m2/lux), an additional objective was to derive regression equations that correlate the industry-standard units for RPMs (RI [mcd/lux]) and the RL values collected by the MRU. Through research-based experiments and with coordination from RoadVista, modifications were made to the LLG7 MRU to detect and measure RPM retroreflectivity in relation to RL. Regression equations were derived pertaining to retroreflectivity measurements between a handheld RPM retroreflectometer (RI) and an LLG7 MRU (RL) on in-service RPMs. The results indicate that the modified MRU can be used to effectively assess RPM retroreflectivity in tenth-mile intervals in a highly repeatable manner with an average error in estimated RI of ±13.5% without affecting PM data. Overall, utilizing the modified MRU for statewide RPM assessments is a significant improvement from the current process of visual assessments and allows the FDOT to quantify RPM quality on a network level.

Research on the law of reflection coefficient of reflective film of traffic sign based on Angle

In this paper, a large number of digital printing reflective film retroreflectivity measurement. Based on the multi-angle test of the reflective film of the mainstream manufacturers in the market, the reverse reflection coefficient of the digital printing reflective film was obtained. Through the curve fitting of the measured values of the backreflection coefficient under different measuring angles by using the scatter plot, the variation law of the luminosity of the digital printing reflective film with incident Angle and observation Angle was obtained. The variation law of backreflection coefficient explored in this paper has certain significance to the application guidance of digital printing reflective film for traffic signs.

Study on National Technical Specification of the Standard Retroreflectivity Measurement Device

Start your abstract here…The study aims to explore the technical specifications of the standard retroreflectivity measurement devices. Based on the measurement principle of retroreflection coefficient, the metrological characteristics of standard retroreflectivity measurement devices were proposed and the three main metrological indices of light source (color temperature, illuminance and positioning error of incident angle) were experimentally explored. The allowable error range of the retroreflection coefficient measurements was determined to calculate the corresponding ranges of metrological indices. With the entropy weight method, the weight of the influence of each index on retroreflection coefficient measurements was analyzed. The analysis results showed that the illuminance had the most significant influence on the retroreflection coefficient and accounted for 41.30%, followed by color temperature (34.43%) and angle change (24.26%). The study provides the important technical support for the development of technical specifications of standard retroreflectivity measurement devices.

Predicting the Retroreflectivity Degradation of Waterborne Paint Pavement Markings using Advanced Machine Learning Techniques

Waterborne paint is the most common marking material used throughout the United States. Because of budget constraints, most transportation agencies repaint their markings based on a fixed schedule, which is questionable in relation to efficiency and economy. To overcome this problem, state agencies could evaluate the marking performance by utilizing measured retroreflectivity of waterborne paints applied in the National Transportation Product Evaluation Program (NTPEP) or by using retroreflectivity degradation models developed in previous studies. Generally, both options lack accuracy because of the high dimensionality and multi-collinearity of retroreflectivity data. Therefore, the objective of this study was to employ an advanced machine learning algorithm to develop performance prediction models for waterborne paints considering the variables that are believed to affect their performance. To achieve this objective, a total of 17,952 skip and wheel retroreflectivity measurements were collected from 10 test decks included in the NTPEP. Based on these data, two CatBoost models were developed with an acceptable level of accuracy which can predict the skip and wheel retroreflectivity of waterborne paints for up to 3 years using only the initial measured retroreflectivity and the anticipated project conditions over the intended prediction horizon, such as line color, traffic, air temperature, and so forth. These models could be used by transportation agencies throughout the United States to 1) compare between different products and select the best product for a specific project, and 2) determine the expected service life of a specific product based on a specified threshold retroreflectivity to plan for future restriping activities.

Calibration Scheme for Portable Retroreflectometers of Road Traffic Signs

Portable retroreflectometers are widely used for engineering measurements and are equipped with a set of work plates that are used to fit fitting curves and switch the working curve in the intrinsic software (self-calibration). The measuring principle employed is the substitution method. Therefore, the accuracy of the work plate values and curve-fitting ability of the internal software are important factors related to the accuracy of the instrument’s measurement results. A calibration scheme for portable retroreflectometers is proposed in this paper. This scheme not only considers calibration in the laboratory, but also on-site measurements. The work plate values can be obtained by a standard retroreflection measurement system, or by a matching portable retroreflectometer. When the work plate values are obtained through the matching instrument, a set of reference plate values must be obtained first. The reference plates, the color and coefficients of retroreflection of which are similar to those of the work plates, were calibrated by the standard retroreflection measurement system using the direct illuminance method. The reference plates were used to adjust the fitting curve in the internal software of the instrument. The work plates were then measured by the matching instrument to obtain a set of work plate values. The reference plates were measured by a self-calibration portable retroreflectometer, and the relative error between the instrument’s results and reference values was calculated.

Effect of Glass Bead Refractive Index on Pavement Marking Retroreflectivity Considering Passenger Vehicle and Airplane Geometries

Pavement marking retroreflectivity depends on several factors including but not limited to the type of retroreflective optics, binder, installation quality, marking condition, and measurement type/geometry. Texas A&M Transportation Institute (TTI) evaluated the retroreflectivity of 19 pavement marking panels, prepared with different types of glass bead at standard 30-m and non-standard measurement geometries. The non-standard geometries represented typical commercial airplane configurations. The primary purpose of the research was to evaluate the effects of the glass bead refractive index (RI) (1.5 versus 1.9) and the measurement geometry on pavement marking retroreflectivity. Results showed a decrease in retroreflectivity with an increase in observation and entrance angles for both 1.5 and 1.9 RI. The study showed higher retroreflectivity levels for high RI beads at all the geometries evaluated. The result showed that 1.9 RI beads exhibit an average of 171% (862 mcd/m2/lx) higher retroreflectivity at standard 30-m car geometry as well as 102% (193 mcd/m2/lx) higher retroreflectivity at airplane geometry compared with 1.5 RI beads. The study found that an increase in bead RI had a larger effect on retroreflectivity than did an increase in bead size. The effect of the measurement geometry on the retroreflectivity level of the markings highlights a limitation of using the 30-m car geometry to represent the visibility of markings from a pilot’s perspective. Additional work should be conducted to better assess the visibility of markings from various vehicle platforms and how to best represent the visibility through retroreflectivity measurement.

Measurement of raised pavement marker’s photometric performance

Large error exists in the photometric performance test of raised pavement marker. This paper reports a set of retroreflective measurement standard devices built to measure raised pavement markers based on the principle of direct measurement, and the photometric performance of the raised pavement markers was tested. The study also involved calibration of a portable meter using the standard device. According to the experimental comparison, the method proposed in this paper provides a new direction for the development of retroreflection measurement technology. The results measured by the proposed method showed high accuracy. This method can solve the large measurement error problems with indication errors of 2% at most.

PAVEMENT MARKING REFLECTIVITY EVALUATION THROUGH RADIOMETRIC CALIBRATION OF THE LEICA P40 TERRESTRIAL LASER SCANNER

Abstract. Pavement markings serve as important traffic control devices, delineating traffic lanes and conveying regulations, guidance or warnings to roadway users. To ensure that pavement markings are clearly visible, especially at night, transportation agencies periodically assess the retroreflectivity of various categories of markings through manual approaches at discrete location. Because the radiometric information such as intensity in the lidar data cannot inherently be considered as a retroreflectivity measurement without additional processing, this study rigorously assesses the ability to determine pavement marking retroreflectivity from the Leica ScanStation P40 through radiometric calibration. For the evaluation, data were collected at a study site in Philomath, Oregon using the Leica P40, Leica Pegasus: Two mobile lidar system, and a handheld retroreflectometer as a reference. The results show that, with appropriate calibration, the lidar data can adequately assess the retroreflectivity of pavement markings. Additionally, while corrections have been proposed for range and angle of incidence, these corrections are not straightforward to apply for retroreflective materials, as will be discussed herein. While mobile lidar technology is ideal for a system-wide asset management framework, terrestrial laser scanning can be utilized for detailed investigations at sites such as intersections with highly variable wear where both can enable significant cost savings and applied for a variety of purposes simultaneously including asset management and project development.

The effects of damage on sign visibility: An assist in traffic sign replacement

Abstract Traffic signs often convey critical information to drivers. To ensure visibility in nighttime or low light conditions, traffic signs must be in compliance with the minimum retroreflectivity standards outlined by the manual on uniform traffic control devices (MUTCD). Among all of the assessment methods (visual nighttime inspection, retroreflectivity measurement) and management methods (expected life, blanket replacement, and control signs) outlined in the MUTCD, expected sign life has been the most selected by agencies for maintaining compliance. In current literature, little research exists with regard to schedule sign replacement, focusing rather on the current favorite predictor, sign age. However, after collecting data on 1683 in-service traffic signs across the state of Utah, this study primarily concluded that not only sign age, but other contributing factors affect sign retroreflective performance. Aiming to determine the effects of various damage forms on sign retroreflectivity, statistical methods, including regression models, chi-square test, t -test, and odds ratio were employed to analyze traffic sign data. At the conclusion, the strong association between damage and retroreflectivity compliance of traffic signs was evident. In addition, to identify more critical damage forms, the effects of various forms on traffic sign retroreflectivity were compared. These conclusions provide insight to inform transportation agencies in the development of sign management plans and schedule sign replacement.

Image-based retro-reflectivity measurement of traffic signs in day time

The visibility of a traffic sign at night depends on its retro-reflectivity, a property that needs to be frequently monitored to ensure transportation safety. In the U.S., Federal Highway Administration (FHWA) maintains regulations to ensure minimum retro-reflectivity levels. Current measurement techniques either (a) use vehicle mounted device during the night, or (b) use manual handheld devices during the day. The former is expensive due to nighttime labor cost. The latter is time-consuming and unsafe. To address these limitations, this paper presents a computer vision-based technique to measure retro-reflectivity during daytime using a vehicle mounted device. The presented algorithms simulate nighttime visibility of traffic signs from images taken during daytime and measure their retro-reflectivity. The technique is faster, cheaper, and safer as it neither requires nighttime operation nor requires manual sign inspection. It also satisfies FHWA measurement guidelines both in terms of granularity and accuracy. The performance of the presented technique is evaluated under various testing conditions. The results are promising and demonstrate a strong potential in lowering inspection cost and improving safety in practical applications on retro-reflectivity measurement.

Can daytime digital imaging be used for traffic sign retroreflectivity compliance?

To ensure traffic sign visibility for the information transfer between traffic signs and drivers, transportation agencies are required to achieve and maintain traffic signs to at least minimum retroreflectivity levels. To do this, the Manual on Uniform Traffic Control Devices (MUTCD) outlined two assessment methods – visual nighttime inspection and retroreflectivity measurement – and three management methods – expected life, blanket replacement, and control signs. This study aimed to examine whether or not visual condition derived from daytime digital imaging can be used to achieve sign retroreflectivity compliance. To accomplish this goal, we used two data sets. A sample data of over 1700 signs was manually collected in the field, and the background retroreflectivity of each sign was measured using a handheld retroreflectometer. In addition, sign data of over 97,000 traffic signs was digitally collected by driving an equipped vehicle. Sign visual condition ratings (good, fair, and poor) data was obtained from inspection of daytime digital images taken of each individual sign. By focusing on the overlaps in the two data sets including almost 1500 signs, we obtained a range of retroreflectivity measurements for each sign condition. Also, we employed the basic definition of conditional probability to assess the probability of traffic sign retroreflective pass or failure, depending on whether the sign was recorded in good, fair, or poor conditions. At its completion, the study found that though daytime digital imaging cannot be considered a reliable alternative for sign retroreflectivity measurements, nighttime digital imaging may have potential for use, and both allow transportation agencies to know which signs should be investigated manually.

Investigation of Longitudinal Pavement Marking Retroreflectivity and Safety

This research was initiated to determine whether a correlation between pavement marking retroreflectivity and safety could be established. Previous research on this topic provided mixed results and sometimes counterintuitive findings. Using data from Michigan, the researchers evaluated relationships between crashes and longitudinal pavement marking retroreflectivity. The retroreflectivity data consisted of pavement marking measurements representing white edge lines, white lane lines, yellow edge lines, and yellow centerlines. The data included crashes and retroreflectivity measurements from 2002 to 2008. Only nighttime crashes that occurred at nonintersection and noninterchange segments during the nonwinter months (between April and October) were considered (wet crashes were also excluded). The following specific types of crashes were initially identified as target crashes for this study: nighttime, single vehicle nighttime, fatal plus injury nighttime, and single vehicle nighttime fatal plus injury. The findings lend support to the positive safety effects of maintaining retroreflectivity of pavement markings.

The Impact of Pavement Type and Roughness on Paint Marking Retroreflectivity

This article addresses the impact of asphalt type and roughness on paint pavement marking retroreflectivity. Marking retroreflectivity and pavement roughness data were collected on two-lane highways in North Carolina. A t test was used to analyze the data. It was found that the mean values of the retroreflectivity measurements for the plant mixed pavements are significantly higher than those for the bituminous surface treatment (BST; chip seal) pavements. The mean left-wheel international roughness index (IRI) values and right-wheel IRI values for plant mixed pavements are lower than for the BST pavement. The conclusion is that marking crews should consider applying higher-quality paint markings (thicker paint and more glass beads) on BST pavements to achieve the same service life as the markings on plant mixed pavements. This would provide drivers with a more consistent and uniform marking retroreflectivity and the agency or municipality with a more consistent marking schedule.

Assessment of Sign Retroreflectivity Compliance for Development of a Management Plan

The Manual on Uniform Traffic Control Devices (MUTCD) specifies minimum retroreflectivity requirements that include an obligation for agencies to develop a strategy for maintaining compliance. States were given a deadline of January 1, 2012, for the implementation of an assessment or management plan, which led to an increased emphasis on sign asset management. However, a new rule was submitted to the Federal Register to extend and modify the deadlines. With budget considerations, it is important that a transportation agency implement an assessment or management plan that is efficient and provides compliance with the standards required by the MUTCD. The development of an efficient plan requires knowledge of the overall condition of an agency's assets as well as unique considerations regarding its performance. Through a review of previous data collection efforts, this paper details the development of a data collection strategy for assessing the performance of traffic signs maintained by the Utah Department of Transportation (DOT). Agency operations, site selection, and attribute collection were all considered during the development of a collection plan for an agency where limited inventory and installation data were available. Retroreflectivity measurements were taken for 1,433 Utah DOT signs. This sample provided a snapshot of current compliance and assisted in the selection of an asset management plan for maintaining sign retroreflectivity. Results from the study showed that the Utah DOT's signs were well over 90% compliant with the MUTCD standards and preliminary management strategies were presented to address vandalism and other damage.

Refinement of Drivers' Visibility Needs during Wet Night Conditions

The purpose of this project was to develop a specification for the minimum retroreflectivity of pavement markings in wet nighttime conditions. For this specification to be established, the performance of four retroreflective pavement marking materials in wet night conditions was evaluated. The performance of the pavement markings was evaluated by driver participants under simulated rain conditions with a protocol similar to that of studies that had already been performed at the Virginia Tech Transportation Institute, Virginia Polytechnic Institute and State University. The performance of the markings was verified on the basis of the participants' ability to detect the end points of the markings in both rainy and clear conditions. This investigation reached the following conclusions: (a) The materials developed over recent years showed an improved performance over those tested previously. (b) The log-linear relationship found previously was functional for the data provided. Two models were developed. The model with no intercept provided a more constrictive boundary at low levels of retroreflectivity. (c) A retroreflectivity value above 250 millicandelas per square meter per lux (mcd/m2/lx) provided limited return in terms of detection distance. (d) A specification limit of 150 mcd/m2/lx provided adequate visibility for 55 mph in dry conditions and 40 mph in wet conditions with standard dry retroreflectivity measurements and 1 in./h measurements for wet conditions. This value should be the minimum maintained over the life of the marking. (e) The retroreflectivity specifications for a white and a yellow material should be equal. (f) The rumble stripe showed a significant recovery time improvement over the other tested materials. A minimum retroreflectivity of 150 mcd/m2/lx for white and yellow pavement markings in both dry and wet nighttime conditions is recommended.

Laboratory Comparison of Retroreflection Measurement System

As the wide application of retroreflective materials, following problems such as safety warning effect, quality, manufacturing technology, test method become more and more important. Many national test centers or big manufactures build retroreflection measurement systems. In order to identify these laboratories’ ability, we organize this laboratory comparison. After 6 months experiments, this comparison successfully finishes. And all the test data are dealt with statistical analysis.