Legibility research of highway signage typefaces a critical review and a potential design centred approach

Documented legibility studies were found only for transport typefaces used in the United Kingdom Lund 1999 and Highway Standard font series and the Clearview typefaces used in the United

Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=rfdj20

An International Journal for All Aspects of Design

ISSN: (Print) (Online) Journal homepage: www.tandfonline.com/journals/rfdj20

Legibility research of highway signage typefaces:

A critical review and a potential design-centred approach

Shaima Elbardawil

To cite this article: Shaima Elbardawil (2022) Legibility research of highway signage typefaces:

A critical review and a potential design-centred approach, The Design Journal, 25:1, 86-103, DOI: 10.1080/14606925.2021.2004716

To link to this article: https://doi.org/10.1080/14606925.2021.2004716

Published online: 02 Feb 2022.

Submit your article to this journal

Article views: 536

View related articles

View Crossmark data

Legibility research of highway signage typefaces: A critical review and a potential design-centred approach Shaima Elbardawil

University of Sharjah, Sharjah, United Arab Emirates

ABSTRACT

With the increasing prevalence of the automobile, the

transmission of information through the visual means of

signage became critical owing to the safety problems that

followed the growth of the highway system and the

con-tinuous increase in traffic This paper presents a review of

research on the legibility of highway signs and discusses

the key studies of the legibility of typefaces used on them.

It examines in particular the legibility of the Latin typefaces

in English language used on US highway signs, focussing

on the most significant findings on the characteristics of

typefaces and the features that most affect legibility The

paper also discusses the methodological approaches used

to examine legibility in conditions of driving and suggests

that future research should pursue the application of

find-ings in the field of reading research and be informed by

design knowledge.

KEYWORDS

legibility, highway signage, intrinsic factors, typefaces design, research review, design research

Introduction

As highway infrastructure developed and the need for safety increased, prob-lems of visibility and legibility came to be of critical importance The con-stant increase in traffic led to the recognition of the need for effective visual transmission of information to drivers Foster (1973, 20) argued that‘legibility research is concerned with studying the effects of visual information format

on the responses made to it by the reader’ The formats of visual information influencing legibility include typography, design of signage, illustrations, maps, symbols and colours and a combination of them integrates to aid wayfinding on a highway

In practice, legibility primarily depends on the effect of typographical design on individuals’ reading performance under various conditions, at vari-able distances and with various exposure times The typography used for traffic signs should allow distant visibility and rapid recognition at a variety

CONTACT Shaima Elbardawil selbardawil@sharjah.ac.ae College of Fine Arts and Design, University of Sharjah, PO Box 27272, Sharjah, United Arab Emirates.

ß 2022 Informa UK Limited, trading as Taylor & Francis Group

https://doi.org/10.1080/14606925.2021.2004716

of speeds so that highway information can be perceived effectively to achieve traffic safety and operations

This paper reviews legibility studies on highway signs and highlights the key research findings of the typographic factors that affect the legi-bility of information This subject is of interest for a variety of reasons First, highway signs are read under special reading conditions in glance-based environments, where drivers have little exposure to information that is surrounded with different visual stimuli demanding drivers’ atten-tion Second, legibility research is usually investigated within a context of transport engineering and traffic safety and operations, with limited ref-erence to reading sciences and design knowledge The goal of this paper

is to examine the research approach and methods used in existing legi-bility studies of highway signs To achieve this, the study illustrates the impact of extrinsic and intrinsic typographic factors on legibility of signs, explains the research methods used in these legibility studies and com-pares them to a potential design-based legibility research approach Conclusions drawn aim to further guide future design-informed legibility investigations

Legibility studies on highway signage: a review

Highway signage design evolved with the development of urban plan-ning and increased driving population Various Latin typefaces were designed for use in highway signage and wayfinding systems Examples

of these typefaces include the following: the American Association of State Highway Officials (AASHO), which standardized six uppercase type-faces (1929), DIN 1451 (1931), Highway Gothic (Series E-Modified) (1948), Eurostile (1962), Transport (1963) and New Transport (2009), Interstate (1993–1995) and Clearview (2002) Documented legibility studies were found only for transport typefaces used in the United Kingdom (Lund

1999) and Highway Standard font series and the Clearview typefaces used in the United States (US) The published research studies are those that examined the US highway signs typefaces, Clearview and Standard Highway font series These were prepared by the Transportation Research Board and various university transportation research centres, such as the T.D Larson Transportation Institute at Pennsylvania State University and the Texas A&M Transportation Institute, a member of the Texas A&M University System The discussion established here is based on these legi-bility research studies

Both intrinsic and extrinsic visual factors influence the legibility of signs Intrinsic factors include the visual appearance and characteristics of the type-faces used on highway signs, such as letter casing, letter height,

height–width ratio, letter-spacing or tracking and vertical spacing between baselines or leading Extrinsic factors include psychophysical considerations, such as illumination, polarity and colour combination and contrast (Reimer

et al.2014)

Most published works study intrinsic factors in relation to extrinsic fac-tors affecting the visibility and legibility of signs’ typefaces The first work

is found in two major studies In the first, Forbes and Holmes (1939) explore legibility distances of highway destination signs in relation to let-ter height, width and reflectorisation The second was by Forbes, Moskowitz, and Morgan (1951), and it compares the legibility of lower-case and upperlower-case letters for highway signs Both studies determine the distances at which the typefaces under study, the Federal Highway Administration (FHWA) series, can be read for a given letter height Forbes (1969, 12–13) reports on additional early studies describing factors affecting the visibility and legibility of highway signs, such as retroreflect-ive materials and illumination, contrast and irradiation, day or night, driver age, sign design and layout and characteristics of typeface design These studies include Lauer (1932), who investigated sign colour and type characteristics, Mills (1933), who studied sign colour combinations and letter contrast

Further studies explored the impact of one or a combination of visual fac-tors on legibility in highway signs, such as Woods and Rowan (1976), Sivak, Olson, and Pastalan (1981), McNees and Jones (1987), Shepard (1987) and Mace (1988) who studied the impacts of retroreflective materials and illumin-ation Contrast and irradiation were investigated by Forbes et al (1976) and Sivak, Olson, and Pastalan (1981) who focussed on the impact of contrast on legibility in relation to luminance in signs Finley and Wilkinson (1984) and Sturgis and Osgood (1982) investigated the relationship between contrast sensitivity and glare Forbes (1972) and Mace, Garvey, and Heckard (1994) explored the impacts of signage layout design to promote improvements to the legibility of highway signage Nighttime versus daytime and driver age are found to impact signage legibility

Recent studies on the development of legibility in highway signs began in the late 1990s and aimed to improve legibility of highway sign-age typefaces in comparison to that of Clearview The developed research studies resulted in the design of Clearview typeface in 2003 and replaced the old Standard Highway font with Clearview in several

US states

The exploration of improvements to legibility in both typefaces relates to three main factors: night visibility, high-brightness materials and elderly driv-ers A number of studies examined the legibility of Clearview and the Standard Highway font series Research studies published from 1997 to 2002

were done in parallel with development of the Clearview font design This resulted in the interim approval by FHWA for using it in positive contrast applications Research studies that proceeded after 2002 used the final Clearview design and included the complete system of six weights in both negative and positive contrast formats These studies were requested by the FHWA in the Interim Approval process for further legibility studies regarding other applications

Garvey, Pietrucha, and Meeker (1997) studied word pattern recognition and legibility in mixed cases versus upper cases during daytime and night-time for older drivers for Clearview to that of the Standard Highway font Series E and D Although there were no deficiencies evidenced with the Standard Highway fonts, the goal was to use new typefaces with improved legibility The results of the study showed that mixed-case names were recog-nized quicker than all uppercase ones A comparison test was not performed

to examine the legibility of Standard Highway font series and determine whether some refinements would have resulted in a similar improvement in the legibility of the Standard Highway Series Instead, exclusive modification was made to the shapes of letterforms and stroke width for Clearview

Hawkins et al (1999), Carlson (2001), Chrysler, Carlson, and Hawkins (2002), Holick and Carlson (2003), Holick et al (2006), and Miles et al (2014), showed that the Standard Highway font Series E (Modified) has longer legi-bility distances from a distance relative to Clearview in conventional and mounted road signs (shoulder and overhead) in daytime conditions In 2014, the FHWA stopped issuing new approvals for the use of Clearview due to a lack of rigorous evidence for its superiority to Standard Alphabets in terms

of legibility Furthermore, no research indicates that Clearview consistently performs better than Highway Standards Series E (Modified) if similar design elements are used, as measured by letter case, ratio of upper to lowercase letters, inter-character spacing and sign sheeting material

Following the termination of Clearview, three research studies were pub-lished on the legibility of highway signage typefaces, that is, Clearview and Highway Standards Garvey et al (2015) compared the legibility distances of Clearview and Standard Highway in positive and negative contrast signs dur-ing daytime and nighttime conditions for older as well as younger drivers They compared case Clearview (2-B, 3-B and 4-B) with both mixed-case and uppermixed-case Highway Standard (Series C, D and E); and compared mixed-case Clearview typefaces 2-W, 3-W and 4-W with Highway Standard Font Series C, D and E Additionally, they examined the effects of letter height on the legibility distance of mixed-case Clearview The results indi-cated that Standard Highway in all uppercase letters had longer legibility dis-tances than either Clearview mixed-case or Standard Highway in mixed-case letters for older drivers It also showed that the Clearview font in mixed case

might occupy less signage space, thereby increasing the margin size of the current signage layout However, it did not identify the amount of difference

in signage margins nor explored the impact of adjusting tracking on legibil-ity This study required detailed explanation of research procedures, such as font and word combination, as the number of examined signs that can affect the results of the research

Kwigizile et al (2015) evaluated safety benefits of a number of counter-measures used by Michigan Department of Transportation, such as the use

of Clearview on guide signs as part of a programme to address the needs of older drivers The study used preference surveys to compare preferences of identified engineering improvements from drivers who are 65 and above The survey was conducted on the basis of photographs showing the imple-mented countermeasures as a first option and the standard installation as a second option, and the drivers selected their preferences in different situa-tions The photographed examples provided in the survey vary in the fonts used, underlining text, destination names and colour of sign sheeting Survey findings could not be applied because photographs cannot simulate the driving task nor sign illumination

Dobres et al (2017) assessed the legibility of Highway Gothic and Clearview fonts concerning in-vehicle digital displays In line with previous studies, it concluded that similar refinements on Highway Standard fonts can improve legibility, and there is no need to replace it with a new typeface However, the study did not employ simulating conditions under which a driver may read a signage (e.g nighttime and retroreflective materials) and it could not be applied to highway signage

Findings on the impact of typographic factors on signage legibility

Based on their intended purpose, typefaces vary in visual style, structure and proportions

Typeface designs show varied structures, requiring them to be measured

in various ways to indicate the differences in the visual appearance of the letterforms between various typefaces Figure 1 shows a basic type grid, referencing main vertical measurements of a typeface, including x-height, ascent, descent, cap height and leading

Typographical features sizes and proportions are crucial factors determin-ing the legibility of text Different sizes and proportions may affect signage design and layout by influencing the visual arrangement of text and other elements in the display space Research findings on the impact of letter height, letter spacing, ratio of height to stroke width and letter case on the legibility of highway signages are discussed below

Letter height

Letter height or capital height is ‘the distance from the baseline to the cap-ital line’ (Legge and Bigelow2011, 2) It is the key characteristic affecting the legibility of large format displays (Garvey and Mace 1996) Letter height is the key measure by which a legibility distance of a sign is measured in a legibility index Design standards and manuals published by governmental transport authorities (e.g the FWHA Standards Highway Signs) specify a given letter height for a given speed and a sign type in relation to best viewing distance

Most studies that examine the legibility of typefaces used on highway signs under various conditions, conclude that increased letter size improves legibility Forbes and Holmes (1939) show a nonlinear relationship between letter size and legibility distance In practical terms, this means that legibility distance may vary based on the effects of other intrinsic and extrinsic factors, which may also vary in different display sizes

Typographers usually use x-height as the physical size for text This value measures the height of the non-ascending lowercase letters which is the dis-tance from baseline to the x-line The larger the x-height of a typeface, the larger its counters, and the more legible it is Dobres et al (2017, 2) explain that typefaces with more varied shapes and open spacing have been shown

to be more legible than typefaces with more uniform shapes and closed

Figure 1 Framework of Type Cullen (2012, 38)

spacing This finding is especially relevant to typography meant for use on road signage

Observations by typographers and type designers indicate that‘x-height is

a more salient determinant of perceived type size than is body size’ (Legge and Bigelow 2011, 4) The visible size of typefaces arose from the different values of x-height intrinsic to the design of each typeface Typefaces with larger x-height appear to be bigger than those with smaller x-height In con-trast, typefaces with the same x-height but different body size appear to be approximately the same size Figure 2 shows the differences in x-height in various signs’ fonts

Typefaces with a large x-height usually have wider counter parts and higher contrast in letterforms This improves typeface legibility because, first, the shape of individual letterforms became clearer and easily recognizable from a distance Second, in case of halation, the blurry effect in typefaces with large x-height is less harmful as large counters prevent letter strokes from blending causing distortion in the shapes of letterforms (Figure 3) Although Clearview Series 5-W has larger x-height than Highway Standard Series E (Modified), none of the published studies could prove its super-ior legibility

None of the published studies on Clearview examined the impact of x-height as a key measurement affecting legibility

Letter spacing

Letter spacing, or tracking, can be decreased or increased subtly to improve the visual appearance and readability of text The perception of letters may

be impaired when inter-letters spacing is limited, resulting in the crowding effect (Perea et al 2012) Considerate increase of inter-letter spacing relative

to the default settings may aid in the process of word recognition In larger text, as is the case in highway signs, the space between letters expands pro-portionally, which requires adjustment to allow character-sequence patterns

to be easily recognized The effects of cautious letter spacing can be seen in reducing the impact of halation on the readability of signage Applying the right increments of letter spacing prohibit type details to blend with stroke

or completely disappear Examples of the impact of letter spacing in reduc-ing the impact of halation are demonstrated inFigure 4

Figure 2 The difference in x-height in various sign typefaces Author (2020)

For highway signs, the recommendations in the literature regarding opti-mization of inter-letter spacing are limited to daytime situations Case et al (1952, 25) conduct a study of the effects of letter spacing on signage legibil-ity The results showed that the wide spacing gave much better readabillegibil-ity The study offered the following explanation for the greater readability of widely spaced letters:

Due to head movements, eye movements, and instability in the visual mechanism, the image of an object shifts about slightly on the retina, even though the observer may try to keep his head and eyes still When there is wide spacing between two objects, the only effect of this shifting is a slight blurring of the edges of the objects If the spacing between them becomes sufficiently small, the net result of the shifting is a superposition of adjacent letter parts which could decrease letter legibility.

Solomon (1956) supports the findings of Case et al (1952) that indicate that increased space between letters can increase legibility of signs Solomon (1956) concludes that if letter height is restricted, increased inter-letter spac-ing can improve legibility Mace, Garvey, and Heckard (1994) examine the effects of increasing inter-letter spacing on night legibility They study the impact of letter spacing on legibility in the context of different retroreflective materials and letter heights in the Highway Standard font series Although all studies concluded that highway signs’ legibility improves with increased letter spacing, letter spacing that is too open can reduce legibility (Hawkins

et al 1999) This is because, first, it breaks usual character patterns, and second, it may affect word spacing, impeding the recognition of individ-ual words

Ratio of letter height to stroke width

A letter’s stroke width is the thickness of its principal strokes, which indicate the typeface weight (Figure 6) The ratio of letter height to stroke width determines relative letter width, which is an additional factor impacting legi-bility Stroke width varies and can increase and decrease in a single typeface, proportionally with the change of a typeface letter height or between

Figure 3 Different impacts of halation on various sign typefaces with various x-height val-ues Author (2020)

different typefaces, which affects text optimal size and appearance This effect is larger on road signs, where letters are illuminated in different ways and appear on different materials Figure 5 shows a different ratio of letter height to stroke width in different signs’ fonts

Several studies investigate the impact of the ratio of height to stroke width on legibility, in combination with other factors, for example, Uhlaner (1941) and Kuntz and Sleight (1950) studied the impact of the ratios of stroke width to letter height and stroke width to letter width on legibility Research shows that halation increases perceived stroke width of high-con-trast letters on lower-conhigh-con-trast backgrounds (Hawkins et al 1999) The legibil-ity distance of typefaces with wide larger spaces, such as Clearview, is not affected by halation or the differences in lighting in daytime and nighttime Other studies that examine the ratio of height to stroke width show a range

of results describing the differences between daytime and nighttime in eld-erly drivers in relation to sign retroflectivity (Mace, Garvey, and Heckard

1994) Stroke width receives a great deal of attention in the literature, lead-ing to guidelines for optimal stroke width and improved legibility (Tinker

1966, Holick and Carlson 2002) The impact of stroke width on legibility may vary in different contrast polarity, lighting conditions and drivers’ visual acu-ity as well as age (Bullough 2017)

Letter case

In examining the effect of letter case on legibility, the word recognition model provided an explanation of lowercase superiority over upper case This means that readers recognize words as a graphic pattern of ascending, descending and neutral characters, which are compiled in the reader’s mind

to form a word envelop (Figure 6) This increases the speed and distance of

Figure 4 The impacts of character tracking in reducing halation (Transport font) Author (2020)