Report on Highway Guide Sign Fonts

3.0 Research on Clearview

Research related to alternative fonts for signs has been ongoing since the 1990s. The early research led to FHWA's issuance of the Interim Approval for the use of Clearview Font for positive contrast legends on guide signs. Since the issuance of the interim approval, various organizations have continued to research highway sign fonts.

3.1 Early research to develop Clearview

The Clearview font was developed through research starting in the late-1990s. The stated goal of the Clearview font was to increase legibility and reduce halation of highway sign legends in comparison to that of the FHWA Standard Alphabets (to which the developers refer as "Highway Gothic font," even though "Gothic" historically has referred to letter forms of very intricate design, such as those used on newspaper mastheads, by contrast with the simple, non-stylized letter forms of the Standard Alphabets). Specifically, the first studies on Clearview stated that the intent was to replace the Standard Alphabets rather than also explore improvements thereto. This research development effort resulted in final design of Clearview font letters in 2003. The legibility of positive-contrast Clearview legends for guide signs was researched by the Pennsylvania Transportation Institute (PTI) and the Texas Transportation Institute (TTI).

The initial research on Clearview was conducted at PTI. In two PTI studies intended for conventional road guide signs, use of an early version of Clearview, called "Clearview-Bold," is reported to have improved nighttime sign reading distance by up to 16 percent when compared with Standard Alphabet Series E(modified). For drivers traveling at 45 mph, that legibility enhancement could translate into an additional 80 feet of reading distance, or 1.2 seconds of additional reading time. With Clearview-Bold, the desired destination legend is reported as being recognized 1.3 seconds earlier (84 feet) and with greater accuracy, giving the driver significantly more time to react to the information displayed.

By allowing a viewer to read the unique footprint of the word when displayed in upper- and lower-case letters, there is an increase in accuracy, viewing distance, and reaction time. The research reported that when the upper- and lower-case version of Clearview, called "Clearview-Condensed," is compared to the all-capital-letter Standard Alphabet Series D, there was a 14-percent increase in recognition when viewed by older drivers at night, with no loss of legibility. When the size of Clearview-Condensed was increased by 12 percent to equal the overall footprint of the upper-case display, the recognition gain is reported as having doubled to 29 percent with little change in overall sign size. The research did not include evaluation of upper- and lower-case letters using the Standard Alphabets. Because this study did not compare mixed-case (i.e., upper- and lower-case) lettering for both fonts, the result demonstrates only that a recognition (not pure legibility) task is aided by the use of mixed-case lettering rather than all upper-case lettering. It does not demonstrate that one font is superior to the other, nor is it appropriate for such a conclusion to be extrapolated. As a result of this finding, which actually confirmed known performance of lettering, the MUTCD was amended in 2009 to require that place and street names—those on which an observer most commonly uses a recognition task—be displayed using upper- and lower-case lettering, eliminating the option to use all upper-case lettering for these legends.

The first TTI research study compared full-scale freeway guide signs using the "Clearview-Bold" and Standard Alphabet Series E(modified) letter styles. Pilot testing at TTI indicated that there were significant differences in the legibility of full-scale signs as compared to the smaller signs tested in the previous PTI study, when viewed at design legibility distances (at that time legibility distance was considered 40 feet from sign per inch of letter height). The first upgrade to Clearview involved refinement of the font prior to the testing at TTI. The testing of Clearview by TTI compared the revised typeface to Standard Alphabet Series E(modified), again with no refinements or modifications to the Standard Alphabets.

The researchers evaluated shoulder- and overhead-mounted highway guide signs on Type III retroreflective sheeting. In this study, the revised version of Clearview was reported to have performed "no worse than, and in some cases outperformed, Series E(modified)." TTI then performed a second study of the two fonts, this time using microprismatic retroreflective sheeting, the type now predominantly used on highway signs. The results reported an 11- to 12-percent increase in the legibility distance for guide signs using Clearview.

This study also demonstrated that there was an improvement to Series E(modified) when using microprismatic retroreflective sheeting. However, because of the very specific and narrowly focused research hypothesis, this finding was not reported in the conclusion or in the abstract of the study report. Rather, it was found only within the body of the report itself. In the recommendations, the researchers note, "[b]esides, TxDOT already owns approximately 100 licensed versions of Clearview…" and "TxDOT has provided a sign manufacturer one licensed version of Clearview (to be used for TxDOT signs, exclusively)."

3.2 Additional research to expand Clearview following issuance of the Interim Approval

A number of additional research studies on Clearview continued following the issuance of Interim Approval IA-5 in 2004. These efforts, consistent with the developer's originally stated goal of creating a complete replacement for the Standard Alphabets, focused on expansion of the font to guide signing for conventional (non-freeway) roadways and negative-contrast color orientations that would be intended for standard signs, such as regulatory and warning signs. In all, thirteen recent studies were available to inform FHWA's decision to rescind IA-5 allowing provisional use of the Clearview font. Ten of these studies specifically evaluated the Clearview letter style. Only one of these studies considered like modifications to the Standard Alphabets when evaluating against Clearview. Three additional studies, all evaluating the Clearview letter style, became available following the termination of Interim Approval IA‑5. The results and analyses of the major research evaluations related to Clearview are summarized in Table 3.1.

3.3 Implementation of Clearview Font under Interim Approval IA-5

Although the research upon which the Interim Approval for the use of the Clearview font was based on only one series of this lettering style, the Interim Approval was written in a way that would authorize narrower letter forms to correspond to the system of the FHWA Standard Alphabets. The FHWA did this in anticipation of successful future research evaluations. However, subsequent evaluations showed no benefit to the narrower letter forms and degraded sign legibility when compared to the corresponding FHWA Standard Alphabet series.¹³ In addition, tests of alternative lettering in negative‑contrast color orientations (darker legend on lighter background, such as for regulatory and warning signs) showed no improvement and significantly degraded legibility of the sign.¹⁴ Ultimately, the consistent finding among all the research evaluations was that the brightness of the retroreflective sheeting is the primary factor in nighttime legibility.

The presence and availability of two separate letter styles with differing criteria have resulted in significant confusion and inconsistency in highway sign design, fabrication processes, and application. Although the terms of FHWA's 2004 Interim Approval are explicit, there have been misunderstandings and misapplications of the provisional letter style. Inconsistent sign design practices have become more common and appear to have coincided with the provisional allowance of an alternative lettering style due to a lack of consistent implementation and inaccurate presumptions that lesser sign design criteria, such as reduced interline and edge spacing, are broadly acceptable. In addition, many agencies believed that the alternative lettering style should be used in all applications and that all lettering should be displayed in upper and lowercase lettering, regardless of the type of message. There was also considerable confusion that the requirement of the MUTCD to display destination and street names in upper and lowercase lettering equates to the use of the provisional lettering style rather than the Standard Alphabets. In actuality, there is no interdependency between letter style and case. The lack of uniformity associated with the use of Clearview font led FHWA to post a Design and Use Policy for the Clearview alphabet¹⁵ on the MUTCD Web site in 2011.

3.4 Research reports brought forth after IA Termination

In addition to the ten research reports that were previously available, there were three additional reports and papers that were brought to the attention of FHWA as part of the RFI process following the termination. The FHWA reviewed each of the three documents for both research approach and results validity. A summary of FHWA's review of each follows:

The Legibility of the Clearview Typeface System versus Standard Highway Alphabets on Negative- and Positive-Contrast Signs.¹⁶ The purpose of this research report was to compare legibility distances of both negative- and positive-contrast signs under both daytime and nighttime conditions with both older and younger motorists. Reported as the first part of a three-step research effort, the goal was to "identify the relative legibility of the Clearview negative-contrast typeface compared to Standard Highway Series Alphabets and to evaluate the effect of using mixed-case versus all-upper-case words (the current standard) on signs that require a legibility task." Presumably, the ultimate goal of this research would result in completely redesigning the nearly 2,100 standard sign designs in the MUTCD that are currently used on the nation's streets and highways. The report did not describe the study procedure in enough detail to understand how many signs were viewed, the font and word combinations that were used, or the order of presentation, all of which could influence the participants in the research and change the research outcome. While some of the reported results seem to indicate that Clearview outperformed the Standard Alphabets, data provided in the report revealed that the Standard Alphabet upper-case letters, the present standard, had longer legibility distances for older drivers than either Clearview mixed-case or Standard Alphabets mixed-case, the only other letters used for comparison. One of the conclusions of the report indicated that the Clearview typeface in mixed-case is as legible as Standard Highway in all upper-case but takes up less sign space, possibly implying that the reduction in sign space alone is worth considering. The researchers did not state how much less space is occupied. FHWA's analysis reveals that the difference would be negligible and would not affect overall sign size, as sign blanks are sized in 6-inch increments for standardization and economies of scale. The researchers also did not consider that adjusting the intercharacter spacing for Standard Alphabet letters might have resulted in similar legibility distances for both fonts, thereby negating any advantage. Similarly, expanded spacing of the Standard Alphabet lettering in mixed-case was not considered. Ultimately, a review of the actual mean legibility distances provided in tabular form in the report showed that in 5 out of 6 comparisons, sign legends using the Standard Alphabet upper-case letters only, the present standard, had longer legibility distances for older drivers than both Clearview mixed-case and Standard Alphabet mixed-case legends.

Empirical Assessment of the Legibility of the Highway Gothic and Clearview Signage Fonts.¹⁷ This report assessed the differences in legibility of Clearview versus Standard Alphabets in positive- and negative-contrast applications. FHWA found the research testing to be well-designed, the concepts well-described, and reasoning for use of the selected methodology well-explained. However, FHWA also found limitations of the research itself in that it did not compare the commonly used letter series (both for Clearview and Standard Alphabets) and letter forms, upper- and lower-cases, during the testing. The testing included Clearview series 5-W and 5-B, however some States use 5-W-R for their guide signs, a much narrower intercharacter spaced form of 5-W that results in smaller signs, but negates any of the reported legibility benefits of the letter style. When looking at signs with negative-contrast legends (darker legend on a lighter background used on regulatory and warning signs) it compared Clearview against the Standard Alphabet Series E(modified), but Series D is what is predominantly used for these signs. Therefore, the benefits of one letter series versus another could be overstated or understated. Without a more detailed field investigation in which consistent variations in letter design are tested against each other to determine the specific elements leading to legibility improvements, it is impossible to ascertain any improvement from the use of an alternative letter style. Moreover, this study used the same procedure that was used in a previous study by the same research team. This procedure was determined to be flawed under a subsequent study¹⁸ that found the reported measured legibility distance was exaggerated due to the subjects having learned the test words in early trials and confounding recognition distance as part of legibility distance.

Evaluation of Michigan's Engineering Improvements for Older Drivers.¹⁹ This project aimed at evaluating safety benefits of a number of countermeasures used by Michigan Department of Transportation (MDOT) as part of a program to address needs of older drivers. The countermeasures included use of the Clearview font on guide signs, installation of box span signals, installation of pedestrian countdown signals, use of fluorescent yellow sheeting on warning signs, and use of arrow-per-lane signs for guide signs. The evaluation included a perception survey of Michigan drivers, development of Safety Performance Functions, and development of Crash Modification Factors (CMFs). As stated in the research report, MDOT implemented the use of fluorescent yellow sheeting just prior to adoption of the Clearview fonts, so the two countermeasures have been installed together. As a result, it was impossible to collect individual data and conduct an independent evaluation of Clearview font on guide signs. While the researchers tried to compensate for dual countermeasures by calculating CMFs based on looking at areas where only fluorescent yellow sheeting was used and other sites where both Clearview and fluorescent yellow sheeting was used, replacing old sheeting in diminished conditions with new sheeting likely provided a large portion of the difference in legibility, as has been indicated in previous studies. Further, in an investigation of one of the routes examined, other improvements, including resurfacing, restriping, installation of rumble strips, and new installations of guard rail occurred with the installation of the new signs using Clearview. Therefore, the change in crash rates can be attributed to any number of these other improvements rather than the font used on the signs. The FHWA believes that while preference surveys can be useful in determining opinions about various topics, their usefulness in objectively evaluating or quantifying benefits of improvements is unfounded and generally not accepted as definitive in research. In this particular research, the participants were asked to provide opinions on photographic examples that varied in not only letter style, but also in color of sign sheeting, underlining of text, and destination names used on the signs. Photographs cannot simulate the driving task and performance under headlamp illumination. As a result, it is neither possible nor appropriate to attribute the findings to Clearview specifically.

None of this research, nor other research reviewed by FHWA, indicates that Clearview font performs better than Standard Alphabets when using similar design elements, such as case, ratio of upper- to lower-case letters, intercharacter spacing, and age and type of sign sheeting.