Timeline – The Standard Alphabet

A Research Timeline

Typography, Lettering & the Standard Alphabets

The letter forms on American highway signs — known today as the FHWA Standard Alphabets or informally as Highway Gothic — evolved over roughly four decades, from early automobile-club hand-lettered posts in the 1900s to the formally codified Series A through F published in 1945 and 1948. The typefaces are inseparable from the science of legibility research, and T.W. Forbes stands at the center of that science. His 1939 legibility studies established the measurement framework; his 1942 work with Mitchell defined letter-size specifications; and his landmark 1951 Highway Research Board paper — comparing Series E capitals against a newly developed lowercase — set the terms of debate that ultimately produced the mixed-case freeway sign standard still on U.S. roads today.

This timeline tracks three parallel threads: (1) the institutional development of sign lettering standards (Joint Board → MUTCD → FHWA); (2) the scientific research record on letter legibility, particularly Forbes’s contributions; and (3) California’s independent development of Series E Modified and lowercase for freeway overhead signs, which preceded and shaped the national standard.

Sources: TW Forbes archive PDFs · FHWA MUTCD History · Transportation Research Board Library

Era 1

Era I — Before Standardization (1899–1926)

Sign lettering before national standards was ad hoc: automobile clubs hand-painted posts, and state highway departments improvised their own letter forms. No scientific legibility research yet existed for road signs.

1899

First organized highway sign effort

Horseback automobile club owners meet at the Waldorf-Astoria to form what becomes the American Automobile Association. Purpose: place and maintain signs on principal local highways. Letter forms are informal and unstandardized.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1905

Buffalo Automobile Club sign network

Buffalo Automobile Club installs an extensive signpost network in New York State — among the first systematic sign programs in the country.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1909

California Automobile Club

Automobile Club of California signs principal highways within a 250-mile radius of San Francisco. Letter forms unspecified in existing records.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1915

First STOP sign

The first STOP sign appears in Detroit. Black letters on white background — no formal letter specification exists yet.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

c. 1920s

Angular "block letter" style

State highway departments and the Bureau of Public Roads use an angular, condensed block letter style — essentially a simplified geometric gothic. Straight strokes only; rounded forms not yet adopted. This is the precursor style that the 1945 Standard Alphabets will replace.

Source: Standard Alphabets 1961 preface: "The rounded style was created to replace an earlier more angular design, for better legibility and a more pleasing appearance."
Live URL: 1961 Standard Alphabets PDF

1924

NCSHS / AASHO color standards

First National Conference on Street and Highway Safety standardizes colors. AASHO recognizes superior visibility of yellow; advises yellow for all danger and caution signs. No formal letter-form specifications yet — shape and color addressed, not typeface.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1926–27

Joint Board standards & U.S. Shield

AASHO issues Manual and Specifications for the Manufacture, Display, and Erection of U.S. Standard Road Markers and Signs (1927 — rural) and Manual on Street Traffic Signs, Signals, and Markings (1927 — urban). These establish sign shapes and the U.S. Route Shield. Letter-form specifications are rudimentary — angular block style implied. Series B through F in the 1927 guides are precursors, using straight-stroke letters similar in width to their modern equivalents but with unrounded glyphs.

Source: FHWA MUTCD History; trafficsign.us — Standard Highway Signs and Markings: "Series B through Series F evolved from identically named alphabet series which were introduced in 1927."
Live URLs: FHWA MUTCD History • Standard Highway Signs and Markings

Era 2

Era II — First MUTCD & Early Research (1931–1941)

Forbes establishes the scientific framework for measuring sign letter legibility — entirely independently from the standards bodies. His Ohio State doctoral thesis (1931) lays the perceptual psychology groundwork. His 1939 HRB and Journal of Applied Psychology papers are the first rigorous legibility measurements applied specifically to highway signs. Meanwhile the first MUTCD (1935) adopts letter forms by committee consensus without legibility data.

1931

Forbes Doctoral Thesis — Ohio State

T.W. Forbes completes "Visual Estimation of Velocity in Connection with Highway Safety" at Ohio State. Establishes the perceptual psychology framework — reaction time, visual angle, recognition distance — that he will apply to sign letters for the next four decades. First significant scientific approach to the driver’s visual experience.

Source: Forbes Doctoral Thesis, Ohio State University Archive.
Archive PDF: Download PDF

1931

Holmes legibility baseline

R.W. Holmes conducts early legibility distance measurements for black-and-white Series D letters — the first measured baseline data on highway letter visibility. Forbes will cite this work in every subsequent paper as his comparison standard.

Source: Referenced within Forbes’s 1951 HRB paper, which cites "Forbes and Holmes" consistently for Series D baseline data — no standalone Holmes document has been located separately.
Archive PDF (referencing document): Download PDF

1932

Joint Committee formed

AASHO and NCSHS form the Joint Committee on Uniform Traffic Control Devices (JCUTCD) to resolve conflicting rural/urban manuals. Letter-form standardization is part of the mandate.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1935

First MUTCD — angular letters

First edition of MUTCD published (mimeographed; printed version 1937, 166 pages). Promotes symbols on signs; allows rounded versions of some letters as an option — but angular block letters remain the dominant style. No scientific legibility research informs the letter specifications.

Source: FHWA MUTCD History. Per trafficsign.us: "Rounded versions of some letters (with widths loosely appropriate for Series C or D) were specified as an option in the 1935 MUTCD."
Live URLs: FHWA MUTCD History • Historic MUTCD editions

1939

Forbes — First rigorous legibility study

Forbes publishes two landmark papers: "Legibility of Highway Signs" in the Journal of Applied Psychology (Vol. 23, pp. 669–684) and in HRB Proceedings (Vol. 19, pp. 321–335). First application of controlled experimental psychology to highway sign letter measurement. Establishes legibility distance as a function of letter height, stroke width, and spacing — the framework all subsequent studies use.

Source: 1939 Forbes / HRB Sign Legibility paper. (Journal of Applied Psychology and HRB Proceedings Vol. 19 printings have not been located online; no live URL available for those journal volumes.)
Archive PDF: Download PDF

1939

Forbes — Method for Analysis

Forbes publishes "A Method for Analysis of Signs" in the Journal of Applied Psychology. Defines the measurement methodology: scrambled vs. familiar-name conditions, controlled observation distances, statistical analysis of recognition distance. This becomes the standard protocol for all subsequent sign legibility experiments.

Source: 1939 Method for Analysis (Forbes).
Archive PDF: Download PDF

1940

Forbes & Butterfield — arrow legibility

Forbes and Butterfield publish "A Study of the Legibility of Destination Sign Arrows" in Traffic Engineering (Vol. 11, No. 233, July 1940, pp. 39–41). Extends legibility science to sign graphic elements beyond letter forms.

Source: Forbes Bibliography. (Traffic Engineering, 1940, has not been located online; no live URL available for that journal issue.)
Archive PDF: Download PDF

1941

Forbes in Traffic Engineering Handbook

Forbes contributes three chapters to the 1st Edition of the Traffic Engineering Handbook (Institute of Traffic Engineers): "Driver Reaction Time, Perception Time, and Judgment Time"; "The Driver’s Visual Field"; and "Factors of Adequate Sign Design." The sign design chapter codifies the legibility principles for practicing engineers — the first handbook entry to do so.

Source: Forbes Bibliography.
Archive PDF: Download PDF

Era 3

Era III — War, Pentagon & the Rounded Letter (1942–1945)

World War II disrupts civilian research but, paradoxically, accelerates sign standardization. Pentagon construction requires a complete sign system in 1942 — the first real-world test of the new rounded alphabets at scale. Legibility research at the Pentagon directly informs what becomes the 1945 Standard Alphabets publication.

1942

Mitchell & Forbes — ASCE letter size paper

A. Mitchell and T.W. Forbes publish "Design of Sign Letter Sizes" in Proceedings of the American Society of Civil Engineers (Vol. 68, pp. 95–104; also Transactions, ASCE, 1943, Vol. 108, pp. 233–242). First paper to formally specify the relationship between letter height, stroke width, and legibility distance in engineering terms — the mathematical foundation for the Series specifications.

Source: 1942 ASCE — Design of Letter Sizes.
Archive PDF: Download PDF

1942

Lauer — Pentagon road signs, Series D

A.R. Lauer’s legibility study for the Pentagon road network uses Series D alphabets — the most frequently used standard alphabet at the time. Lauer tests letter width-height ratios, stroke widths, and spacing systematically. The study’s findings feed directly into the design of the rounded Series E and the 1945 Standard Alphabets.

Source: 1942 Lauer Pentagon study.
Archive PDF: Download PDF

1942

MUTCD War Emergency Edition

Second MUTCD edition, the "War Emergency Edition," addresses blackout traffic control. Pavement markings introduced in lieu of illuminated signs — the origin of word messages on road surfaces. Angular block letters persist but the rounded transition is underway within the standards committees.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1942–45

Forbes wartime classified research

Forbes serves on National Defense Research Committee work (classified). The Forbes Bibliography lists "various reports (classified) on phases of sound control, 1942–45, NDRC 17.3" and "various manuals on gunnery training procedures, NDRC on Training, Stevens Inst., 1942–43." He is out of highway sign research during this period.

Source: Forbes Bibliography; Penn State archive — Forbes security clearance correspondence, 1954 (folder scan not individually titled; the closest matching file on the drive is flagged below and should be confirmed by visual inspection).
Archive PDF (bibliography): Download PDF
Archive PDF (candidate Penn State letter — unconfirmed match): Download PDF

1944

Work begins on peacetime MUTCD

Joint Committee on Uniform Traffic Control Devices begins meeting in 1944 to prepare the postwar MUTCD. The rounded letter alphabet is the central signing improvement on the agenda.

Source: FHWA MUTCD History; MUTCD history paper hosted on CiteSeerX.
Live URLs: FHWA MUTCD History • MUTCD history paper

1945

Standard Alphabets for Highway Signs — first publication

Bureau of Public Roads publishes Standard Alphabets for Highway Signs — the founding document of the FHWA Series. Defines upper-case Series A through F in full geometric specification. The "rounded" style replaces the earlier angular design. All six series share the same base letter shape; each is progressively wider. Approved by the Joint Committee on Uniform Traffic Control Devices. The 1961 reprinting states explicitly: "first published in 1945."

Source: Standard Alphabets for Highway Signs, 1961 edition preface; H.E. Hilts, 1947 MUTCD paper.
Live URL (1961 reprint): 1961 Standard Alphabets PDF
Archive PDF (Hilts 1947 MUTCD paper): Download PDF

Era 4

Era IV — National Adoption & California’s Divergence (1948–1951)

The 1948 MUTCD formally adopts the rounded Series A–F as the national standard for all signs. Within months, California begins developing something the national standard does not have: a thicker Series E Modified for button-reflectorized freeway signs, and — critically — a lowercase alphabet to pair with it on overhead destination signs. Forbes is the research lead.

1948

MUTCD 3rd Edition — rounded letter standard

Third MUTCD edition (August 1948) formally adopts the rounded-letter alphabet — Standard Alphabets Series A through F — as standard for all signs nationwide. Major format reorganization; guide signs added. This is the moment the angular letter is officially retired at the federal level.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1948

California develops Series E Modified

California Division of Highways begins developing a modified Series E with thicker stroke width — Series E Modified — for use with button reflectors on ground-mounted freeway signs. The heavier stroke accommodates the optics of retroreflective button inserts. Forbes is at UC Berkeley’s Institute of Transportation and Traffic Engineering; the Division is his primary research partner.

Source: Wikipedia — Highway Gothic; ClearviewHWY historical reference; Forbes 1951 HRB paper (Berkeley copy).
Live URLs: Highway Gothic • Clearview historical reference
Archive PDF: Download PDF

1948–50

California lowercase alphabet developed

California Division of Highways develops a lowercase alphabet for mixed-case destination legends on externally illuminated overhead freeway signs. Initially paired with Series D capitals (not Series E Modified). The driving hypothesis: word-shape recognition advantage of lowercase — established in print typography research — should transfer to highway signs. Forbes’s institute runs the research.

Source: Wikipedia — Highway Gothic; Forbes 1951 HRB paper synopsis.
Live URL: Highway Gothic
Archive PDF: Download PDF

1949

Forbes — "Psychotechnology in Traffic Research"

Forbes publishes in Traffic Quarterly, Vol. III, April 1949, pp. 158–165. Articulates the human-factors framework for traffic sign design — applying perceptual psychology systematically to the engineering problem.

Source: Forbes Bibliography. (Traffic Quarterly, 1949, has not been located online; no live URL available for that journal volume.)
Archive PDF: Download PDF

Jan. 9, 1951

California inter-departmental memo — Forbes paper transmitted to Governor

Division of Highways transmits Forbes, Moskowitz & Morgan paper to Director of Public Works C.H. Purcell, who forwards two copies to Governor Earl Warren on January 12. The cover memo identifies Forbes as "a nationally recognized authority on sign legibility" and cites his 1939 Journal of Applied Psychology, 1939 HRB, and 1943 ASCE papers as his credentials. The paper is to be presented at the 30th HRB Annual Meeting later in January.

Source: 1951 Forbes ORIGINAL comparison paper (includes the transmittal memo).
Archive PDF: Download PDF

Jan. 1951

Forbes — HRB 30th Annual Meeting paper

Forbes, Moskowitz & Morgan present "A Comparison of Lower Case and Capital Letters for Highway Signs" at the Highway Research Board 30th Annual Meeting, Washington. Key findings: lowercase letters show approximately 10% greater legibility distance than Series E capitals when compared on loop height — but Forbes’s own Closure to Loutzenheiser’s discussion notes the comparison is complicated by sign-board area and initial-cap issues. The paper establishes the research basis for the eventual mixed-case freeway standard.

Source: HRB Proceedings, Vol. 30, 1951, pp. 355–373. No standalone online scan of this specific volume was located; the TRB Library (which holds the complete digitized HRB Proceedings run) is the authoritative access point, and the paper itself is preserved on the TW Forbes drive.
Live URL (TRB Library, holding institution): Transportation Research Board Library
Archive PDF (archive copy of the paper): Download PDF

Jan.–Feb. 1951

California Highways & Public Works — public publication

The Forbes, Moskowitz & Morgan paper is published in California Highways and Public Works Magazine, pp. 6–9, 61. First public dissemination to the practicing engineering community in California. The magazine reaches every state highway department in the country.

Source: Forbes Bibliography; Forbes 1951 HRB paper. This issue of California Highways & Public Works was previously flagged as a research gap — it has since been located on the drive (see the updated Gaps note at the end of this document).
Archive PDF (bibliography): Download PDF
Archive PDF (CHPW Jan.–Feb. 1951 issue, located): Download PDF

1951

Loutzenheiser discussion — Bureau of Public Roads response

D.W. Loutzenheiser, Chairman of the BPR Committee on Geometric Highway Design, publishes a formal discussion of Forbes et al. in the same HRB volume (pp. 371–373). Loutzenheiser challenges whether the 10% advantage survives when sign board area and initial-capital height are accounted for. Forbes’s Closure: the advantage does hold for same-area comparisons. This exchange sets the terms for the national policy debate over the next seven years.

Source: 1951 Forbes HRB in Book Paper (Berkeley copy) — Discussion section.
Archive PDF: Download PDF

Era 5

Era V — Interstate System & the Mixed-Case Standard (1952–1961)

The 1956 Federal-Aid Highway Act creates the Interstate System — and immediately exposes the inadequacy of existing sign standards for high-speed limited-access roads. BPR research in the mid-1950s evaluates freeway guide sign design. California’s lowercase alphabet, developed by Forbes and the Division of Highways, becomes the de facto model. The 1958 AASHO Interstate Manual adopts it nationally.

1952

Standard Alphabets reprinted

Bureau of Public Roads issues first reprint of Standard Alphabets for Highway Signs (originally 1945). Contains geometric layouts for Series A through F. This is the working document highway departments and sign manufacturers use throughout the 1950s.

Source: MUTCD Wiki; Fontipedia — Highway Gothic.
Live URLs: MUTCD Wiki • Highway Gothic reference

1954

MUTCD revision — Series A and B restricted

The 1954 15-page supplement to the 1948 MUTCD includes 47 revisions. Recommends generally limiting Series A and B to street name and parking signs only — acknowledging that the narrowest, most condensed forms are inadequate at highway speeds.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

1956

Federal-Aid Highway Act — Interstate System created

President Eisenhower signs the Federal-Aid Highway Act of 1956, creating the Interstate System and the Highway Trust Fund. The need for a new generation of guide signs — for high-speed, limited-access roads with advance destination information — immediately drives BPR sign research. California’s mixed-case freeway sign system is the most developed existing model.

Source: FHWA Interstate System History.
Live URL: FHWA Interstate System History

mid-1950s

BPR research on freeway guide sign design

Bureau of Public Roads conducts research evaluating freeway guide sign design: black, blue, and green backgrounds; lowercase letters; other new sign types. The research draws directly on Forbes’s legibility framework and California’s operational experience with Series E Modified and lowercase.

Source: MUTCD history paper hosted on CiteSeerX (see caveat below).
Live URL: MUTCD history paper
Note: this CiteSeerX paper covers the same mid-1950s black/blue/green background and lowercase-letter research described in this entry, but attributes it to AASHO’s Interstate Manual work rather than using the exact phrase "BPR research" — flagged here for transparency rather than presented as a verbatim quote match.

1958

AASHO Interstate Manual — mixed-case adopted nationally

AASHO publishes Manual for Signing and Pavement Marking of the National System of Interstate and Defense Highways (February 1958). Introduces white on green guide signs and mixed-case (upper- and lower-case) letters for destination names — the combination developed by California. Series E Modified paired with the California lowercase alphabet becomes the national standard for freeway destination legend. This is the direct institutional product of Forbes’s 1951 research.

Source: FHWA MUTCD History; Wikipedia — Highway Gothic.
Live URLs: FHWA MUTCD History • Highway Gothic

1961

MUTCD 4th Edition — Series A discontinued; Interstate chapter added

The 1961 MUTCD (333 pages) adds a new chapter for the Interstate Highway System, formally adopting white on green and mixed-case letters. Series A — the narrowest and least legible — is expressly discontinued. Full Standard Highway Signs book published separately by BPR.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History

Era 6

Era VI — Codification & Late Forbes Research (1962–1976)

Forbes continues active research through the 1960s and 1970s. The sign system is increasingly mature but remains contested — letter contrast, retroreflectivity, and sign conspicuity become the new research frontiers. Forbes’s late work shifts from letter form comparison to the perceptual conditions of nighttime reading.

1962

Forbes — Traffic Sign Requirements

Forbes publishes on traffic sign requirements — documenting the engineering specification framework as the Interstate System builds out.

Source: 1962 Traffic Sign Requirements (Forbes).
Archive PDF: Download PDF

1964

Government Index of Type Legibility Studies

National Bureau of Standards (D.Y. Cornog, F.C. Rose, J.L. Walkowicz) publishes Legibility of Alphanumeric Characters and Other Symbols: A Permuted Title Index and Bibliography (NBS Miscellaneous Publication 262-1, December 15, 1964). 325 references. Forbes (1939) and Forbes (1951) are indexed. Establishes the full research lineage of legibility science as it relates to highway signs.

Source: 1964 Government Index of Type Legibility Studies. (NBS Miscellaneous Publication 262-1 has not been located online; no live URL available.)
Archive PDF: Download PDF

1966

Standard Alphabets — 1966 FHWA edition

FHWA reprints Standard Alphabets in a new edition containing upper-case Series B, C, D, E, and F only. Series A formally omitted as "no longer acceptable for use in highway signs." This is the first edition to remove Series A entirely from the publication.

Source: The Beauty of Transport — "Type in the Fast Lane: FHWA Series Typeface, USA."
Live URL: Type in the Fast Lane

1968

Forbes — Letter and Sign Contrast; Congressional Hearing

Forbes publishes on letter and sign contrast specifications as they relate to traffic sign standards. Testifies at Congressional Signing and Design Hearing — the 1968 hearing transcript (802K characters) is the largest single document in the Forbes archive and the most comprehensive public record of the state of sign research at that moment.

Source: 1968 Letter and Sign Contrast (Forbes); 1968 Signing and Design Hearing transcript.
Archive PDF (Letter and Sign Contrast): Download PDF
Archive PDF (Signing and Design Hearing): Download PDF

1971

HRR Letter Size Formula

Highway Research Record paper on letter size formula — translating legibility research into engineering specifications for sign letter height requirements.

Source: 1971 HRR Letter Size Formula.
Archive PDF: Download PDF

1976

Forbes — Practical Aspects of Conspicuity Principles

Forbes’s final major publication in the series: "Practical Aspects of Conspicuity Principles in Sign Design." Shifts focus from legibility distance (whether a letter can be read) to conspicuity (whether a sign attracts attention in the first place). A synthesis of four decades of visual research applied to highway signing.

Source: 1976 Forbes — Practical Aspects of Conspicuity.
Archive PDF: Download PDF

1977

Standard Alphabets — 1977 FHWA edition

FHWA publishes updated Standard Alphabets containing upper-case Series B, C, D, E, E Modified, lower-case E Modified, and F. First official FHWA publication to include lower-case E Modified as a named, specified alphabet series.

Source: FHWA Standard Alphabets, 1977 edition (PDF).
Live URL: FHWA Standard Alphabets PDF

Era 7

Era VII — Digital Era, Clearview, and Restoration (2000–Present)

2000

FHWA Standard Alphabets — lowercase added for all series

The 2000 edition of Standard Alphabets for Traffic Control Devices adds lowercase letters to all alphabet series — completing what Forbes’s 1951 research had set in motion. Also modifies the shapes of some letters. First edition available on the FHWA website.

Source: Fontipedia — Highway Gothic; FHWA MUTCD site.
Live URLs: Highway Gothic reference • FHWA MUTCD History

2004

Clearview font — Interim Approval

FHWA issues Interim Approval No. 5 for the use of Clearview font on positive-contrast guide signs. Clearview, designed by Donald Meeker and James Montalbano, is intended to improve legibility for older drivers. Initial studies show modest improvement.

Source: FHWA Federal Register notice (Delaware DOT-hosted copy of the IA-5 termination document, which recounts the original 2004 approval).
Live URL: Clearview IA-5 termination PDF

2016

Clearview terminated — Standard Alphabets restored

FHWA terminates Clearview Interim Approval on January 25, 2016. Subsequent research found "no practical improvement" and "degraded sign legibility" in some conditions compared to FHWA Standard Alphabet Series E Modified. The FHWA Standard Alphabets — descended directly from Forbes’s 1945–1951 work — are restored as the sole approved lettering for traffic control devices.

Source: Federal Register, January 25, 2016 (Docket No. 2016-01383, 81 FR 4083); Delaware DOT-hosted copy of the termination notice.
Live URLs: 2016 Federal Register notice • Clearview IA-5 termination PDF

2023

MUTCD 11th Edition

The 11th edition of the MUTCD (December 19, 2023) is the current standard. FHWA Standard Alphabets Series B through F and E Modified remain the specified letter forms. Series A remains discontinued.

Source: FHWA MUTCD History.
Live URL: FHWA MUTCD History