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Federal Highway Administration
Manual on Uniform Traffic Control Devices for Streets and Highways: Termination of Interim Approval No. 5, Clearview Font for Positive Contrast Legends on Guide Signs
Introduction: On January 25, 2016, the FHWA published a notice in the Federal Register1 terminating the use of an alternative letter style, Clearview™, on traffic control devices. The use of this alternative letter style was authorized under the provisions of the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) for Interim Approval. Agencies wishing to use the alternative letter style were required to request approval from FHWA. The alternative letter style has not been adopted in the MUTCD.
Research History and Implementation: Initial studies evaluated only one letter form type of the provisional letter style with two different intercharacter spacing criteria. These are now known as 5-W and 5-W-R, the latter of which has a compressed intercharacter spacing so that the length of a word would approximate that of the same word composed of the FHWA Standard Alphabet Series E(modified). This compressed version was found to provide no improvement over Series E(modified). These studies did not evaluate numerals for legibility or recognition. The narrower letter forms of the provisional letter style (designated as 1-W, 2-W, 3-W, and 4-W) were also not evaluated for legibility in these studies.
The study2 on which the Interim Approval was primarily based found that changing the type of retroreflective sheeting alone resulted in a 6% improvement in legibility to the FHWA Standard Alphabet Series E(modified). However, this quantitative result was not otherwise reported as a major finding. The practical difference attributed to the letter style was characterized as "modest" and the apparent improvement of the provisional letter style could be "partly attributed to [its] increased size." Because of the narrowly focused research statement, which examined the cumulative effect of a change to two variables, the study recommended that the sponsoring agency adopt a new standard to change both the retroreflective sheeting to microprismatic and the letter style to 5-W 3. The fact that the sponsoring agency already owned 100 licenses of the design and fabrication software for the provisional letter style and had furnished one licensed copy to a sign fabricator was also noted in the recommendation.
Legibility and recognition deficiencies with numerals of the provisional style were reported in a field experiment as early as 2009. A formal evaluation6 later confirmed that the numerals of the Standard Alphabets exhibited superior performance when compared with those of the provisional lettering style.
A 2014 study7 found that there is no practical difference between Series E(modified) of the Standard Alphabets and 5-W of the provisional letter style when tested in positive-contrast color orientations.
Explorations of the provisional letter style in negative-contrast color orientations8 revealed that the provisional letter style actually reduced the nighttime legibility when compared with the Standard Alphabets.
Recognition vs. Pure Legibility
Research has focused primarily on the legibility of one letter style compared to another. One of the studies acknowledged the fact that the excessively long legibility distances reported in some of the earlier work were actually the result of recognition, rather than legibility, due to learning effects by the participants among the set of test words. These research evaluations did not necessarily simulate the actual process of reading a sign: detection, recognition, and reaction via multiple glances. While legibility alone might be considered a valid surrogate measure for the entire process of interpreting a highway sign, marginally differing results do not necessarily indicate a practical significance that can justify an institutional or systematic change.
Degradation of Consistency in Signing Layouts
The presence and availability of two separate letter styles with differing criteria have resulted in significant confusion and inconsistency in the highway sign design and fabrication processes. Although the terms of the FHWA’s 2004 Interim Approval are explicit, misunderstandings and misapplications of the provisional letter style have resulted. In 2011, the FHWA issued a Design and Use Policy9 on this topic that included explicit criteria in question-answer format with photographic examples to illustrate acceptable and unacceptable practices. This additional guidance has failed to allay these practices. The following are representative examples of ways in which these concerns have manifested themselves:
Conclusions of Research Evaluations
A significant number of research studies have been performed in pursuit of an alternative letter style. However, inconsistent or counterintuitive conclusions have been drawn from the results as reported to support or promote use and/or further study of an alternative letter style. The following examples illustrate this concern:
The recommendation of this study was to continue using Clearview for positive-contrast signs based on the fact that it had been implemented and there was no difference or negative reaction reported. Though, there appeared to be no consideration of the need to continue to use the Standard Alphabets in the majority of signing applications. This evaluation concluded that retroreflective sheeting materials might affect legibility, regardless of the letter style, corroborating past evidence. Additionally, it was reported in this evaluation that the intercharacter spacing of Clearview was often "manually adjusted" to avoid increasing the size of signs.
Interestingly, a number of agencies are now using 20-inch leading upper-case letters with either 5-W or 5-W-R of the provisional lettering style. However, there is not necessarily a proportional increase in legibility or recognition with increases in letter height15, 16. The basic premise of the development of an alternative letter style was to address a generalized hypothesis17 that letter heights of 20 inches would be needed to address the needs of older drivers, partly due to irradiation that can occur with different combinations of high-brightness retroreflective materials. This conclusion was extrapolated from a laboratory simulation and came during the infancy of higher-brightness retroreflective background sheeting on highway guide signs. It was intended to address a more practical visual acuity that would represent a broader cross-section of drivers and was at best, an approximation, as the actual Standard Alphabets were not used in this simulation. The research on an alternative lettering style was promoted largely as a means to avoid unnecessarily enlarging signs to meet this recommendation (cited in various articles as anywhere between a 20% increase to as much as a 33% increase), thereby sparing transportation agencies those additional costs while gaining the benefit of improved effectiveness. The presumption was that letter forms completely different from those of the Standard Alphabets would be the solution and did not examine modification to or optimization of the established Standard Alphabet letter forms. In fact, even the early research18 had determined that it was the relative contrast of the level of retroreflectivity used for the legend and background that was the critical factor in the legibility and that high-contrast brightness combinations should be avoided.
2 Carlson, P. J. Evaluation of Clearview Alphabet with Microprismatic Retroreflective Sheetings, Report No. FHWA/TX-02/4049-1. Texas Transportation Institute, August 2001, resubmitted October 2001. [Return to Note 2]
4 Chrysler, S. T., P. J. Carlson, and H. G. Hawkins. Nighttime Legibility of Ground-Mounted Traffic Signs as a Function of Font, Color, and Retroreflective Sheeting Type, Report No. FHWA/TX-03/1796-2. Texas Transportation Institute, September 2002. [Return to Note 4]
5 Holick, A. and P. J. Carlson. Nighttime Sign Legibility as a Function of Various Combinations of Retroreflective Sheeting and Font, Report No. FHWA/TX-04/1796-4. Texas Transportation Institute, September 2003. [Return to Note 5]
8 Holick, A., S. T. Chrysler, E. Park, and P. J. Carlson. Evaluation of the Clearview™ Font for Negative Contrast Traffic Signs, Report No. FHWA/TX-06/0-4984-1. Texas Transportation Institute, January 2006, resubmitted April 2006. [Return to Note 8]
12 Smiley, A., C. Courage, T. Smahel, G. Fitch, and M. Currie. Required Letter Height for Street Name Signs: An On-Road Study, Paper No. 01-2225. Human Factors North and Toronto Transportation, 2001. [Return to Note 12]
13 Mahmassani, H. S., C. W. Frei, and M. Saberi. Clearview™ Font in Illinois: Assessing IDOT Experiences and Needs, Report No. FHWA-ICT-13-003. Northwestern University Transportation Center, January 2013. [Return to Note 13]
15 Mace, D. J., P. M. Garvey, and R. F. Heckard. Relative Visibility of Increased Legend Size vs. Brighter Materials for Traffic Signs, Report No. FHWA-RD-94-035. Federal Highway Administration, 1994. [Return to Note 15]
17 Staplin, L. K., K. Lococo, and J. Sim. Traffic Control Design Elements for Accommodating Drivers with Diminished Capacity, Report No. FHWA-RD-90-055. Federal Highway Administration, 1990. [Return to Note 17]
United States Department of Transportation - Federal Highway Administration