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Publication Number: FHWA-HRT-04-133
Date: December 2005

Enhanced Night Visibility, Volume II: Overview of Phase I and Development of Phase II

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CHAPTER 3—ACTIVITY 2. EVALUATION OF FLUORESCENT INFRASTRUCTURE MATERIALS

Past research on UV–A headlamps and fluorescent TCDs found that they increased nighttime driving visibility distance. Further, pedestrian visibility increased by as much as 117 percent.(1) Based on the results of this previous research, this technology might increase visibility in adverse weather such as fog, rain, and snow.

Much of the past research took no photometric measurements of the fluorescent TCDs to compare the effects of the UV–A and fluorescent technology with those of the halogen headlamps and marking systems currently in place. Much of the research had also been conducted in ideal nighttime conditions, and the true potential of the system during adverse weather conditions had yet to be quantified.

Therefore, there was a need to objectively measure the increased visibility that can be achieved with UV–A headlamps and fluorescent TCDs. These measurements needed to be performed not only during darkness but also during fog, rain, and snow. These measurements were necessary to enable the research team to quantify differences, if any, from the halogen headlamps and TCDs currently in use. The results would provide the data necessary for the subsequent economic analysis.

The project was to be conducted in two phases. The initial testing was to be conducted on the Smart Road with a variety of prototype UV–A headlamps and fluorescent TCDs. This was intended to allow researchers to identify the combinations of headlamps and TCD materials that held the most promise for wide-scale deployment. After the design parameters had been determined, the headlamps and fluorescent TCDs were to be readied for deployment and testing on up to 160 km (99 mi) of Virginia’s roadways.

To meet the objectives of this study, several questions had to be answered by the Infrastructure Team. Those questions are addressed in the tasks described on the following pages.

TASK 2.1: COMPARE FLUORESCENT TCDS AND UV–A HEADLAMPS WITH CONVENTIONAL TCDS AND HEADLAMPS

In task 2.1, the researchers were asked to specify photometric characteristics of fluorescent TCDs illuminated with UV–A headlamps as compared to conventional TCDs illuminated with standard headlamps. To address this question, a three-phase approach was planned: an analytical evaluation, preliminary field testing on the Smart Road, and onroad testing. In Phase I, the analytical evaluation was intended to predict the visibility of prototype fluorescent and conventional materials to be tested on the Smart Road. This evaluation would allow researchers to determine and model the characteristics of the fluorescent materials in the illumination of various headlamps (e.g., UV of varying wavelengths and HID headlamps). This evaluation would help identify critical design parameters of the headlamps and TCDs requiring further development and refinement. The results were expected to provide TCD action spectra that closely matched those of headlamps. The vehicle team, with input from fluorescent TCD manufacturers, was to coordinate this portion of the research.

Phase II, the preliminary Smart Road field testing, was envisioned to consist of several combinations of the various TCDs and headlamps to quantitatively determine the increased visibility of fluorescent TCDs when illuminated with UV–A headlamps over conventional TCDs with tungsten-halogen and HID headlamps. This portion of the research was to allow experimentation with various combinations of headlamp sources and fluorescent and nonfluorescent TCDs in varying visibility conditions in a controlled, real-world setting. The most promising combinations of UV–A headlamps and fluorescent TCDs were to be selected for onroad testing in Phase III.

Phase III, critical to the overall success of the project, was to be designed with significant input from the driver/pedestrian team, vehicle team, and manufacturers. This phase was to provide researchers with a keen insight into how the UV–A headlamps and fluorescent TCDs perform in real-world traffic conditions using private citizens as the driving participants. It was thought that the participants would drive their own personal automobiles retrofitted with the prototype UV–A headlamps. In this phase, up to 160 km (99 mi) of roadways were to be marked with fluorescent TCDs.

Experimental Design

The design of the experiment for each phase would depend on the number of headlamp sources and the number and types of fluorescent and nonfluorescent TCDs to be evaluated.

Apparatus

Following is a list of the apparatus needed for the Phase I analytic evaluation tasks:

  • Goniometer: apparatus to manipulate the TCDs to measure retroreflectivity.

  • UV–A light source.

  • Light tunnel (VDOT, TFHRC, or 3M).

Following is a list of the apparatus needed for the Phase II and Phase III preliminary field testing on the Smart Road and onroad testing:

  • Portable UV–A irradiance meter to measure the amount of UV–A radiation reaching the same region of the TCD where the luminance is being measured.

  • Portable telephotometer to capture the luminance values for each TCD evaluated.

  • Portable retroreflectometer to obtain retroreflectivity measurements for each type of TCD tested. The retroreflectometer for the pavement marking measurements uses 30-m geometry.

  • Vehicles outfitted with standard tungsten-halogen, HID, and prototype UV–A headlamps.

  • Segments of roadway installed with conventional and fluorescent TCDs.

  • Smart Road’s all-weather testing equipment.

Procedures

Phase I

Following is a list of procedures that were to be used in Phase I:

  • Pavement markings: Samples of pavement markings were to be applied to metal plates and placed on the goniometer. These samples were to be illuminated by halogen low beams and then by the UV–A headlamps. The luminance values for both conditions were to be summed to represent the luminance when both sources are used together. The corresponding illuminances or irradiances were to be measured. A ratio of luminance in UV–A to irradiance from UV–A was to be computed to yield the fluorescent efficiency of the material. Also to be determined were the action spectra of materials.

  • Sign sheeting: This testing was contingent on obtaining UV–A-activated retroreflective sheeting samples. Two series of sign luminance measurements were to be made at a set of predetermined entrance and observation angles, one series in halogen low beams and one series in UV–A headlamps. These two luminances were to be summed to represent the luminance when both sources are used together. The corresponding illuminances or irradiances were to be measured. A ratio of luminance in UV–A to irradiance from UV–A was to be computed to yield the fluorescent efficiency of the material.

Phases II and III

Preliminary combinations of materials and headlamps that were to be used in Phases II and III are listed in table 2. Luminance measurements of both conventional and fluorescent TCDs were to be made using halogen low beams, halogen high beams, HID, and halogen low beams supplemented with prototype UV–A headlamps. The luminance measurements were to be taken using a portable telephotometer at select distances from the light source (see figure 1). It was envisioned that the distance between intervals would be determined during the initial testing on the Smart Road and in conjunction with computer modeling of visibility.

Diagram. TCD evaluation intervals. Click here for more detail.

Figure 1. Diagram. TCD evaluation intervals.

Photometric measurements of TCDs were to be made in ideal daytime and nighttime conditions as well as during rain, fog, and snow. These measurements were to include luminance, luminance contrast, retroreflectivity, fluorescent efficiency, color, and daytime reflectivity. (See List of Key Performance Measures for detailed definitions and their respective measures.) These measures were to enable researchers to quantify the added visibility of this technology in all conditions. The actual methods were to be tested and likely refined on the Smart Road. In addition, the TCDs were to be measured at the initial installation and subsequently once every 2 months for 2 years (years 2 and 3 of the project) in similar types of environmental conditions (weather permitting). This would allow researchers to better understand the effects that the environment has on these devices when compared to conventional, nonfluorescent devices.

Table 2 depicts the combinations of pavement marking type and headlamp type to be analyzed. The pavement markings listed were to be tested as the right edgeline (white), white lane line (or yellow centerline where applicable), and yellow edgelines. Other types of pavement markings (e.g., stop bars) might have been tested on the Smart Road to determine whether deployment was recommended. Photometric measurements were to be made of each type of pavement marking using the appropriate instrument. Durability of the markings was to be tested using applicable American Society of Testing and Materials (ASTM) standards D713-90 and D913-88.(2,3)

Table 2. Pavement marking and headlamp combinations for testing.
Pavement Marking Type Halogen Low Beam Halogen High Beam HID Low Beam with
UV–A
Conventional paint w/nonfluorescent beads X X X  
Conventional paint w/fluorescent beads X X X X
Fluorescent paint w/nonfluorescent beads X X X X
Fluorescent paint w/fluorescent beads X X X X
Conventional thermoplastic w/nonfluorescent beads X X X  
Conventional thermoplastic w/fluorescent beads X X X X
Fluorescent thermoplastic w/nonfluorescent beads X X X X
Fluorescent thermoplastic w/fluorescent beads X X X X
Conventional preformed tape X X X  

Fluorescent and nonfluorescent ground-mounted post delineators were to be tested using the applicable measures previously discussed. The delineators were to be installed on both sides of the road. The nonfluorescent delineators were to be compared to fluorescent delineators using halogen low beams, HID, and halogen low beams supplemented with the prototype UV–A headlamps.

Testing of signs was contingent on obtaining UV–A-activated retroreflective sheeting samples. The number of potential sign types and colors to be studied was quite large. It was envisioned that only right shoulder-mounted signs would be evaluated. As for sign colors, the research team decided to limit the possible number of sign colors to be studied. Initial colors to be considered were white (regulatory), red (stop and yield), yellow (warning), and green (guidance). All of these signs were to be mounted as permanent signs. Construction zone signs (fluorescent orange) were also considered for study. These could have been temporary signs (rigid signs placed in sign stands) or permanent sign installations (rigid signs on wood posts). The actual type and color of signs to be tested would be determined after the applicable sheeting manufacturers had been identified and the sign sheeting colors had been made available.

As with the pavement markings and the delineators, the fluorescent signs (if available) were to be compared to their nonfluorescent counterparts using halogen low beams, halogen high beams, HID, and halogen low beams supplemented with UV–A headlamps.

It was envisioned that the results of the individual comparisons of the pavement markings, delineators, and signs (if available) tested on the Smart Road could be combined to convey the magnitude of driving environment visibility enhancement achievable with supplemental UV–A headlamps.

Testing Facility

As noted previously, Phase I of the testing was to take place in the laboratory and light tunnel using equipment from VDOT, TFHRC, and 3M. Phase II was to take place on the Smart Road.

Phase III was to take place on various, yet-to-be determined sections of Virginia's roadways, including Afton Mountain. These sections of roadway, to be selected during the initial testing on the Smart Road, were to use fluorescent TCDs. After the proposed test sites were selected, their characteristics were to be forwarded to FHWA for review and approval. The selected sites were to depend on the test participants, who would have been using their personal vehicles. This was to ensure that a large population of drivers outfitted with the prototype UV–A headlamps would traverse sections of roadway that had been marked with the fluorescent TCDs and with conventional TCDs. The testing scenarios developed in Phase II were to be refined and used in this phase.

Several criteria were to be used in the site selection process to ensure that this research examined a cross section of roadways:

  • Type of roadway: two-lane rural roads, two-lane suburban roads, two-lane urban roads, four-lane divided roadways, and four-lane urban roads.

  • Traffic density.

  • Operating speeds: less than 72 km/h (45 mi/h) and above 72 km/h (45 mi/h).

  • High accident rates resulting from adverse weather or nighttime conditions.

  • Frequent occurrences of fog and smoke.

  • Locations with limited visibility.

  • Pedestrian activity.

Stratification of test roadways was to afford researchers the opportunity to determine which installations garner the highest returns on the investment. The findings were intended to provide guidelines for future installations of fluorescent TCDs.

The existing conventional markings on Afton Mountain were not to be eradicated. Instead, the new fluorescent markings were to be installed alongside the existing markings, allowing for a direct comparison between them in daytime, nighttime, and adverse weather conditions including rain, snow, and especially fog.

List of Key Performance Measures

During the planning stage, the research team agreed to the following minimum key performance measures, but the team also anticipated that additional measures would develop as the study progressed:

  • Luminous (cd/m²): Luminous flux in a beam emanating from a surface in a given direction, per unit of projected area of the surface as viewed from that direction, per unit solid area. This may be thought of as a measure of how bright the object appears to the driver.

  • Luminance contrast: The degree of dissimilarity of the luminance of two areas, expressed as a number (see figure 2). Contrast tells how clearly a target stands out from its background.

    Figure 2. Equation. Luminance contrast. Luminance contrast equals the difference of maximum luminance minus minimum luminance, that difference divided by maximum luminance.

    Figure 2. Equation. Luminous contrast.

    Where

                Lmax = maximum luminance

                Lmin = minimum luminanc

  • Coefficient of retroreflection, RA (cd/lux/m²): The ratio of the coefficient of luminous intensity of a plane’s retroreflecting surface to its area. Essentially, this coefficient is a measure of the device’s ability to return light back to its source.

  • Coefficient of retroreflected luminance, RL (cd/m²/lux): The ratio of the luminance of a projected surface to the illuminance at the surface on a plane normal to the incident light.

  • Fluorescent efficiency (cd/W): A measure of a material’s ability to convert a given amount of UV–A radiation to visible light. It will vary depending on the spectral composition of the incident UV–A.

TASK 2.2: DETERMINE DURABILITY OF FLUORESCENT TCDS COMPARED TO CONVENTIONAL TCDS

Durability of TCDs is of concern to people responsible for installing and maintaining the infrastructure. Departments of transportation currently have a good understanding of the durability of various types of conventional, nonfluorescent TCDs. The addition of fluorescent pigments is of concern; they have a potentially short useful life because of their daily exposure to natural UV–A light. In this project, these effects were to be examined by placing both fluorescent and nonfluorescent pavement markings, as shown in table 2, on the Smart Road and assessing their changes over time.

Apparatus

Following is a list of the apparatus needed in this task:

  • Visual inspection.

  • Retroreflectometer (pavement markings were to be measured using a 30-m geometry device).

  • Telephotometer.

  • Vehicle outfitted with UV–A headlamps.

  • Daytime color measurement device.

Procedure

Pavement marking durability was to be conducted according to ASTM D713-90 and D913 88.(2,3) Both fluorescent and conventional pavement markings (including those markings with fluorescent glass beads) were to be analyzed. Background data on conventional, nonfluorescent pavement marking information were also to be reviewed.

Luminance measurements were to be made using the low beams of the vehicle supplemented by the UV–A headlamp.

List of Key Performance Measures

During the planning stage, the research team agreed to the following minimum key performance measures, but the team also anticipated that additional measures would develop as the study progressed:

  • Durability: A material’s resistance to wear and loss of adhesion to the pavement’s surface over time. A material’s durability might vary depending on the type of pavement where it has been installed.

  • Glass bead retention: The ability of fluorescent pavement markings to ensure proper bonding of the binder with the glass beads and to maintain long-term glass bead retention.

  • Color retention: The ability of a marking to retain its color in normal wear and under a variety of environmental conditions. The color of the material was to be measured to determine if the material undergoes any color shift when activated by UV–A light. (This measurement could be performed in the laboratory.) This performance measure was also to be used to determine if the material discolors over time.

DETERMIND ANY SPECIAL FLUORESCENT TCD INSTALLATION AND/OR REMOVAL PROCEDURES

Task 2.3 asked the researchers to determine if fluorescent TCDs require any special installation and/or removal procedures when compared to their nonfluorescent counterparts. The infrastructure team was to rely on the applicable vendor or manufacturer to supply the installation and removal specifications. (It was envisioned that this task would be aimed at the pavement marking more so than any of the other TCDs.) The manufacturer was also to provide a list of VDOT-approved companies for the installation of their respective TCDs. Notes regarding any deviation from standard installations or removals were to be taken. A cost associated with these deviations was to be generated and used in subsequent economic analyses. These deviations were to be discussed in detail, as were their implications to departments of transportation. Members of the infrastructure team were to carry out this task with close coordination from the manufacturers, vendors, and installers.

Apparatus

Following is a list of the apparatus needed in this task:

  • Pavement marking vehicles.

  • Visual inspections.

  • Written specifications.

  • Smart Road.

  • Video recorder and 35-mm camera.

Procedure

The installation and removal requirements of the fluorescent pavement markings were to be compared to those of the nonfluorescent markings. Staff from VTRC and VDOT were to inspect the installation of the markings on the Smart Road (Phase II), as well as the installation during the deployment phase (Phase III). Notes regarding the installation process were to be taken, and any deviation from existing practices was to be highlighted and further discussed. Special attention was to be given to the surface preparation required for proper adhesion to the pavement. Again, instances where the procedure deviated from standard practice were to be noted.

In addition to installation requirements, the requirements of removing the pavement markings were to be evaluated, project duration permitting. As with the installation requirements, instances where the procedure deviated from standard practice were to be noted.

The handling, fabrication, and installation requirements for delineators and signs (if available) likely would be identical to those of their nonfluorescent counterparts. VDOT likely would have fabricated the signs in its sign shops, provided the shops had the necessary equipment. Staff from VTRC and VDOT were to be onsite during the installation of these devices to monitor and record the installation practices.

TASK 2.4: DETERMINE ANY FLUORESCENT TCD ENVIRONMENTAL CONCERNS

The infrastructure team was to rely on the manufacturers of the TCDs to supply the Material Safety Data Sheets and comply with existing Environmental Protection Agency regulations relating to pavement markings during installation, disposal, and eradication.

 

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