Road Management & Engineering Journal
Copyright © 1999 by TranSafety, Inc.
Fax: (360) 335-6402
George Kochanowski, President of ALL SIGN Products, Inc., has manufactured a polycarbonate stop sign that has the potential to make stop signs significantly more conspicuous to drivers.
The Highway Innovative Technology Evaluation Center (HITEC), a Service Center of the Civil Engineering Research Foundation (CERF), recently evaluated the ALL SIGN Products' Stop Sign. The results were published in their Technical Evaluation Report entitled "Evaluation Findings of the ALL SIGN Products, Inc. Polycarbonate Stop Sign" (copyright 1998 by the American Society of Civil Engineers). This article summarizes HITEC's evaluation process and their conclusions.
To meet their objective to test the ALL SIGN Products' Stop Sign's "retroreflectivity, color and appearance under normal conditions, and the effects of weathering and graffiti," HITEC performed five evaluations:
Evaluations compared the ALL SIGN polycarbonate stop sign to stop signs using retroreflective sheeting materials that were introduced in the 1930s and have been in popular use since the 1950s. Retroreflective sheeting materials now include six types and five classes recognized by the American Society of Testing and Materials (ASTM). These evaluations compared the polycarbonate stop sign to three of the six types:
HITEC emphasized that the ALL SIGN Products' Stop Sign "is clearly not retroreflective sheeting," but it is a retroreflective product. Made completely of plastic, the ALL SIGN Products' Stop Sign "has no sheeting, no aluminum or wood substrate, and no surface paint or ink." Instead the patented sign is formed with a proprietary injection molded process using UV-stabilized polycarbonate resin. The polycarbonate material is the same as that used in some vehicle taillight lenses. This plastic is reflective, resists fading, and is recyclable.
An alloy of DuPont's Tedlar and polycarbonate protects the multicolored sign surface. DuPont's literature indicates that the Tedlar film provides protection from ultraviolet rays, chemicals, and graffiti. Moreover, "Tedlar stands up well to pollutants, resists acid rain attack and mildew, and . . . most airborne dirt does not adhere to Tedlar."
The ALL SIGN Products' Stop Sign incorporates transparent spaces in the red portion of the polycarbonate, and a gap between the front and back of the sign allows ambient light to enter and illuminate the sign.
On the solid translucent back of the sign is a threaded insert used to attach the sign to conventional posts. This design effectively distributes the load over the back of the sign and eliminates the need for hardware protruding from the front of the sign.
HITEC tested ALL SIGN Products' Stop Sign material to determine its retroreflectivity under new, weathered, and vandalized conditions. Researchers performed test procedures on 4-inch x 6-inch samples of both the red and the white material used in the signs. Before undergoing retroreflectivity testing, four of the red and four of the white samples were subjected to accelerated weathering conditions for 2,200 hours using an Atlas Carbon-Arc Weatherometer. In addition, two red and two white samples were covered with black RustoleumTM spray paint that was then cleaned off using nail polish remover.
To measure the retroreflective qualities of the new, weathered, and vandalized materials, researchers took 140 measurements of each sample. Tests on new material showed that "[t]he minimum specification for ALL SIGN Products' Stop Sign often exceeds the ASTM specification for all other types of sheeting." Moreover, "[t]he retroreflectivity of the ALL SIGN Products' material remained very high after weathering." Finally, after spray paint was "easily removed" from the graffiti-damaged samples, the retroreflectivity measurement of those samples was actually higher than the measurements for new samples. Report authors observed, "This suggests that there may have been some residue on the new samples, which was removed when the graffiti was removed. In any event, the removal of graffiti had no measurable effect on the [retroreflectivity] of these materials."
In summary comments on the retroreflective qualities of the ALL SIGN Products' Stop Sign material, the HITEC report offered:
| The optical testing of the ALL SIGN Products' material suggests that this is a
high performance material comparable with the most highly reflective sheeting
available. The retroreflectivity of both white and red products, even after
weathering, exceeds the ASTM specifications for all types of materials. . . .
Given the results of the tests for the weathering and graffiti, the claims of DuPont for their Tedlar material do not seem exaggerated. In fact, since the point of failure does not appear to have been reached, it would appear that only further testing and exposure in a real environment will establish all of the benefits of the polycarbonate with Tedlar combination.
SPECTRAL COLOR PERFORMANCE
With the objective of comparing results from the ALL SIGN Products' red and white materials to Federal Highway Administration (FHWA) requirements, HITEC measured the color coordinates of the ALL SIGN new, weathered, and graffiti-damaged materials.
The white material showed some variance in color values among the new, weathered, and graffiti-damaged samples. The authors felt this separation of values was "not enough to code and discuss the differences." The color values for the red samples were "well within the boundaries for red material, with the new, weathered and graffiti material falling directly on top of each other."
Describing the purpose and scope of this portion of the evaluation, the authors stated:
|The user evaluation was intended to determine the nighttime visibility of the ALL SIGN Products' Stop Sign relative to other conventional stop signs made with different grades of sheeting. A subjective evaluation was also ascertained. Sign recognition was measured as the distance at which each sign was correctly identified. Legibility was measured as the distance that the letters were clearly seen. Subjective evaluation was determined by asking subjects to compare the ALL SIGN Products' Stop Sign with other stop signs.|
The evaluations used 36 subjects--11 from ages 16 to 36 and 25 age 65 or older. ALL SIGN Product's Stop Signs were compared to seven other signs, including five stop signs using various retroreflective sheetings. One of the five stop signs was displayed upside down and one was degraded. The evaluation also included a wrong-way sign and a yield sign. The ALL SIGN Products' Stop Sign was presented twice to each subject.
The researcher drove the test vehicle, with the subject in the passenger seat. Each evaluation began at a distance of 1,350 feet from the sign. As the vehicle slowly approached the sign, subjects gave the name of the sign as soon as they could recognize it (recognition threshold). The subjects next called out when they could read the words on the sign (legibility threshold).
To obtain subjective evaluations of the ALL SIGN Products' Stop Sign, the subjects were asked the following question after both presentations of that sign.
Based on your total driving experience over the past few years (and not just
tonight), how would you compare this stop sign to other stop signs you have
After the second presentation of the ALL SIGN Products' Stop Sign, the subjects were also asked:
Does this last sign seem at all unusual to you?
When the response was yes, the subject was asked, "In what way does it seem unusual?"
Subjective comparisons of the ALL SIGN Products' Stop Sign to signs covered by retroreflective sheeting were obtained by repositioning the test vehicle at 350 feet from three signs and asking subjects if the signs were equally noticeable. If the subjects found the signs not equally noticeable, they were asked to rank the signs from most noticeable to least noticeable. Two evaluations (involving first a group of 21 subjects and then a group of 17 subjects) compared the plastic sign with a total of four different sheeting-covered signs. Finally, at a distance of 250 feet the subjects responded to the question: "Looking again at the three signs, do they look the same or different." If the response was different, subjects told which sign was worst and which best.
Results of the user evaluations for recognition distance showed that "the ALL SIGN Products' Stop Sign was seen as a stop sign at distances as great as any other material tested." These evaluations did not test the hypothesis that the polycarbonate stop sign would be noticed in a visually complex environment from a greater distance than other signs. However, the authors felt this improved recognition "certainly could be inferred from the retroreflectivity measurements . . . ."
Evaluation of the legibility distance of the stop signs included five retroreflective- sheeting signs: three displayed normally, one displayed upside down, and one degraded. The ALL SIGN Products' Stop Sign was displayed twice. The subjects reported being able to read the correctly displayed retroreflective-sheeting stop sign from a greater distance than they reported reading its upside-down equivalent. The authors commented, "This confirms the subjectivity of the test and suggests that the true legibility of the Type I, III, and IV signs is less than the data would indicate." The ALL SIGN Products' Stop Sign's legibility was comparable to the upside-down sign and the degraded sign. All three normally displayed retroreflective-sheeting stop signs were reported to be legible from greater distances than the ALL SIGN Products' Stop Sign.
Responding to the question about how the ALL SIGN Products' Stop Sign compared to other stop signs, the subjects "revealed no preference for plastic or conventional signs." However, when subjects compared the ALL SIGN Products' Stop Sign with other signs at 750 feet, the results showed the ALL SIGN Products' Sign was most noticeable. Of 21 respondents, 20 selected the polycarbonate sign as most noticeable while only one found it least noticeable. From 250 feet, however, only three of 32 subjects said they liked the polycarbonate sign best while 13 said they liked it least.
In summarizing the findings of these user evaluations of sign recognition and legibility, the authors pointed out that "the ALL SIGN Products' Stop Sign will be recognized at the same distance as any other new sign made from modern sheeting materials." The polycarbonate stop sign will be "noticed and recognized" as well as any other sign. The authors noted that although researchers anticipated that the honeycomb pattern of the plastic sign might be perceived as a problem, the evaluation subjects did not mention the pattern.
Regarding the negative subject evaluations of the ALL SIGN Products' sign compared to others at 250 feet, the authors offered:
|The fact that the ALL SIGN Products' Stop Sign was judged worst when compared with other signs at 250 feet is likely due to the fact that some think it is too bright or glaring at this distance and some had problems with legibility. Since drivers do not typically stop and stare at stop signs on a dark road, this response may not indicate what happens in a real driving situation.|
LUMINANCE UNDER AMBIENT DAYLIGHT
Given the increased luminance of the ALL SIGN Products' Stop Sign gained by light passing through the back and sides, this portion of the evaluation "was designed to characterize the plastic sign's translucent effect using controlled front and back lighting." Researchers took luminance measurements from five viewing angles at a distance of nine feet from the sign.
Results indicated that the translucent effect of the sign did not result when backlighting levels were low. The authors concluded, "This aspect of the plastic sign indicates that the sign luminance is determined by the front lighting at low lighting ratios and driven by the back lighting at higher ratios."
In summary, the researchers found that "the plastic sign with the translucent effect does create sign luminance values higher than those of a metal sign." The authors pointed out, "The plastic sign achieved red luminance values two to 23 times brighter and white luminance values one to 12 times brighter than that of the metal sign." When sheeting signs are backlit, they may present drivers with only a silhouette. The plastic sign is less likely to have this problem.
Two reinforced mounting areas on the back of the ALL SIGNS Products' Stop Sign facilitate installation using a 5/16-inch stainless steel nut. This configuration will work for almost any signpost, and the report described installation methods for channel posts, wood posts, square posts, and round posts.
One of two mounting areas with
5/16" stainless steel nut
Standard hex bolt attachment to
Square metal post installation
Round post installation
Round post installation
An additional benefit of this method of mounting the sign to the post is that there are no holes in the face of the sign. As a result, no hardware protrudes from the front of the sign to cause distraction or create a point of potential corrosion.
The authors listed two especially significant findings resulting from the evaluation of the ALL SIGN Products' Stop Sign:
| . . . the ALL SIGN Products' Stop Sign complies with the requirements of the
MUTCD [Manual of Uniform Traffic Control Devices] in all respects
including size, color and appearance and
. . . drivers recognize it as a stop sign at very long distances comparable to the distances achieved with other high performance materials.
Recognizing that the plastic stop sign seems to have less internal contrast and lower legibility ratings than sheeting stop signs, the authors observed that these problems may be trade-offs for the sign's greater conspicuity. Given the importance of conspicuity in the design criteria for stop signs, the authors felt "user preference, internal contrast and legibility may not have much importance." They continued, "Although its potential for high nighttime conspicuity is achieved at the sacrifice of some legibility, this trade-off may be a benefit to safety when the sign is installed in areas with bright lights and visual distractions."
This evaluation's principal findings were that the ALL SIGN Products' Stop Sign:
Copyright © 1999 by TranSafety, Inc.