The font on American road signs is called Highway Gothic. Formally it is the FHWA Standard Alphabets, drawn by Theodore W. Forbes and published in 1948, and you have read more of it than of any book you own. It is also the subject of the only typeface dispute in history to be settled, unsettled, and then re-settled by an act of the United States Congress.
A wartime alphabet
The FHWA series came out of the Public Roads Administration during the Second World War, and arrived as six widths rather than one design: Series A through F, narrow to wide. The width you use depends on how much room the sign has. Series A is so condensed it was eventually abandoned as illegible; Series F is the generous one you get when the sign is big enough not to argue.
Then California changed it. Between 1949 and 1950, Caltrans engineers working on freeway signing took Series E and thickened its strokes to twenty percent of the letter height. The result — Series E-Modified — is the one you actually picture when you picture a road sign: wide, chunky, white on green.
The reason for the thickening is a detail almost nobody knows. Early guide signs weren't printed in reflective material. They were studded with button copy: dozens of small glass reflectors embedded along the spine of every letter, so headlights would light up the letterform as a constellation of dots. A stroke too thin couldn't hold enough buttons. The most recognisable letterform in American public life owes its proportions to the width of a piece of hardware.
The other decision that shaped modern signs came in 1958, when the AASHTO manual for Interstate signing made mixed case the standard for freeway place names. ALL CAPS had been normal. Mixed case won because word shape — the ascenders and descenders that give Baltimore a silhouette BALTIMORE doesn't have — is something the eye can catch at distance and at speed.
Then the signs got too bright
Highway Gothic was drawn for a world of dim reflectors. Retroreflective sheeting kept improving through the following decades, and eventually it improved past the typeface.
The problem has a name: halation, also called irradiation or overglow. When a letter is bright enough, it appears to bleed outward. The glow spills into the enclosed spaces — the counters — of the letters that depend on them. A lowercase e fills in and becomes a luminous blob. An a stops being an a. And because Series E-Modified had those deliberately thick strokes, it had comparatively little counter space to lose.
This lands hardest on older drivers, whose contrast sensitivity declines with age, and on anyone driving tired in rain. It was, in other words, a public safety problem produced by an improvement.
The challenger
Clearview was the answer. It was developed by Don Meeker and Christopher O'Hara of Meeker & Associates with James Montalbano of Terminal Design, working alongside Martin Pietrucha and Philip Garvey at the Pennsylvania Transportation Institute, with supporting research from Gene Hawkins and Paul Carlson.
The design strategy followed directly from the diagnosis. If halation eats counters, give it more counter to eat. Clearview opened up the problem letters — a, e and s — and raised the height of the lowercase relative to the capitals, so the letters carrying the word's shape are simply bigger. Committed to mixed case throughout. The claim from the research was roughly a twenty percent improvement in legibility and recognition at the same sign size, which in highway terms is enormous: it means reading your exit meaningfully earlier at seventy miles an hour.
On 2 September 2004, the FHWA granted Clearview Interim Approval IA-5. Note the wording, because everything later turns on it: positive contrast, guide signs. Light letters on a dark background — white on green, blue, brown. Nothing else was approved. Not black-on-white speed limit signs. Not yellow warning signs.
What went wrong
Two things, and neither is really the typeface's fault.
The first is that an interim approval covering one narrow case met a country of state highway departments who liked the new letters. Clearview started appearing where it had never been approved — in negative contrast, on regulatory and warning signs — and in the narrower widths. Subsequent evaluation found that in exactly those uses it performed worse than the Highway Gothic series it replaced. Dark letters on a bright ground have the opposite problem to halation: the background blooms inward and eats the letter, and generous open counters stop helping.
The second is subtler and more uncomfortable. When you replace an old sign with a new one, you don't only change the typeface — you change the sheeting, the sign, and often the size. Some portion of the measured gain was very plausibly the new sign, not the new letters.
On 25 January 2016, the FHWA terminated the interim approval. Existing signs could stay; new ones would go back to Highway Gothic.
And then Congress got involved
The termination did not hold. States that had re-signed entire networks in Clearview now faced re-signing them again. Congress required the FHWA to review the prior research along with the safety and cost implications of its own decision, and on 28 March 2018 the agency reinstated the interim approval on the terms that existed before 2016.
It did so while stating that it made no recommendation or endorsement of the font.
Approved, terminated, reinstated, unendorsed. Fourteen years, and the official position is that you may use it and they would rather not say.
So both typefaces are on the road today. Highway Gothic is the standard and the default. Clearview is permitted, on some signs, in some contrasts, at the discretion of the state. The next sign you pass is a vote in an argument nobody officially won.
What about street name signs?
Different problem, same alphabet. The green blades on residential corners generally use the same FHWA series in a narrower width, because a street name has to fit a sign a fraction the size of a freeway gantry. This is where Series C and D earn their keep, and where you occasionally find a city that has commissioned something of its own and is quietly pleased about it.
The MUTCD requirement people notice most is the mixed-case one: street name signs moved away from ALL CAPS for the same reason freeway signs did in 1958. Word shape is information, and capitals throw it away.
What a type designer takes from this
The lesson of the Clearview affair is not that Clearview was bad. It is a careful, well-researched typeface built by serious people to solve a real problem, and in the case it was designed for it appears to do so.
The lesson is that legibility is a property of a system, not of a font. The same letterforms that win in white-on-green lose in black-on-white. The same design that helps at a hundred feet of glowing sheeting does nothing on a printed page. Change the contrast, the size, the material or the distance, and the ranking changes with it. A typeface is not legible; a typeface is legible at something, for someone, on something.
Which is the argument for testing type in the conditions it will actually live in, rather than in a specimen. A face chosen because it looked convincing at 200 pixels on a designer's monitor is a face chosen under laboratory conditions that no reader will ever reproduce.
It is also, if I'm honest, the reason I started drawing letters at all. I grew up reading highway signs, and the thing that stuck was that letters which have to work outdoors, at speed, for strangers are the honest ones. Nothing on a road sign is there to be admired. Every decision in it is load-bearing.
A footnote from Britain
Britain ran the same experiment and got a cleaner result. In the late 1950s and early 1960s, Jock Kinneir and Margaret Calvert designed the Transport typeface for British road signs, arriving independently at mixed case and at generous, open letterforms — and paired it with a matched system of pictograms and colour rules rather than treating the letters as a separate problem.
It was adopted, and it stayed adopted. Sixty years on it is still there, essentially unrevised. Designing the whole system at once, it turns out, is more durable than swapping the typeface inside a system built for a different one.
Can you download either of them?
Not straightforwardly. The FHWA Standard Alphabets exist as federal engineering drawings rather than as a font you install, and the digital versions floating around vary a great deal in quality and fidelity. Clearview is a commercial typeface and is licensed as one.
If you want the highway idiom under an open license, Overpass — drawn by Delve Fonts and available through Google Fonts — is an interpretation of the Highway Gothic letterforms and is free to use.
Vigil is not a highway typeface and I am not going to pretend otherwise. It is a geometric sans built for text, with the same large lowercase and open counters that the road-sign research keeps arriving at, for the same underlying reason: the counters are where legibility lives.