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Public-transit signs, directing us as subtly as a touch on the elbow, are among the most distinctive voices of cities. Edward Johnston's Railway Sans, the alphabet he created for the London Underground in 1916, is as emblematic of that city as Big Ben, and Hector Guimard's Art Nouveau signs for the "Métropolitain" are as Parisian as the Eiffel Tower. New York City's subway lettering may seem blunt and functional by comparison, yet it inspires its own share of passion, as Paul Shaw demonstrates in "Helvetica and the New York City Subway System." This typographic detective story manages to be a history of the New York subway, a survey of global transportation graphics and an authoritative over view of 20th-century design in action.

Mr. Shaw is irritated with the widespread belief that the modern New York subway system has always been associated with the Swiss typeface Helvetica. This misperception was fueled by the attention the typeface received in 2007 on the 50th anniversary of its introduction, especially in Gary Hust wit's "Helvetica," a documentary survey of the astonishing ubiquity of a lettering style that appears over the entrances of American Apparel and Staples, on Lufthansa airplanes and New York City garbage trucks, on Comme des Garçons bags, and, yes, on New York subway signs. But the last, as Mr. Shaw shows, was not always so.

The New York subway as we know it today was born of the 1940 merger of three separate train lines: the Interborough Rapid Transit, which began in 1904; the Brooklyn-Manhattan Transit lines, dating from 1908; and the Independent lines, which opened in 1932. Each had its own signs, though none were internally consistent. The oldest signs were the lovely mosaics that are still visible in many stations. But black-and-white placards, mostly hand-painted and without any governing standards, had accrued like barnacles.

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By the 1960s, using the New York subway meant navigating what a John Lindsay-era task force called "the most squalid public environment of the United States: dank, dingily lit, fetid, raucous with screeching clatter, one of the world's meanest transit facilities." The ugly and baffling signs underlined the city government's loss of control.

Seeking to bring order out of chaos, the Transit Authority in 1966 turned to the new design firm Unimark International. Two of its leaders, Massimo Vignelli and Bob Noorda, hailed from Milan, where Noorda (who died last year at age 82) had just designed the graphics for the Metropolitana Milanese. The heart of Mr. Shaw's book is the story of what happened when these champions of High Modernism collided with the union labor at the Transit Authority's Bergen Street sign shop.

Helvetica and the New York City Subway System

By Paul Shaw
MIT, 131 pages, $39.95

Mr. Vignelli and Noorda conducted an analysis of the foot-traffic patterns at several of the subway system's most convoluted stations and devised a sequence of coordinated directional signs. By placing information only at the point of decision, never before or after, the designers aimed to eliminate redundancy and contradictions, establishing a system that New Yorkers could navigate with confidence.

Their original plan was to make these signs in Helvetica, Unimark's typeface of choice, as splendidly neutral as its Swiss birthplace. Noorda had used Helvetica for the Milan transit system, and Mr. Vignelli would soon deploy it for everyone from Knoll Furniture to J.C. Penney. The Transit Authority's sign-makers, however, didn't have the then-exotic Helvetica at hand. They countered with the prosaically named Standard Medium—like Helvetica, a sans-serif font, but less refined, based as it was on older 19th-century models.

The loss of Helvetica, though, was the least of the designers' problems. Expecting to implement their recommendations, they were simply thanked for their advice while Bergen Street went to work. As a result, the introduction of the new sign system at the first stations in late 1967 was, in Mr. Vignelli's words, "the biggest mess in the world."

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New signs were installed, but the old ones were left up. Then the Transit Authority added still more signs, hastily made by hand in an attempt to address the resulting chaos. Typical of the confusion was the fact that the sign-makers misread the blueprints. Not understanding that a black horizontal bracket was meant to secure the signs from above, they painted a black stripe along the top of each sign. In the face of public criticism of what the Daily News called the "Flubway," Unimark was brought back to plan a system-wide implementation.

The clash between modernist idealism and "New Yawk"-style practicality re-emerged with Mr. Vignelli's new subway map in 1972. Inspired by Henry Beck's revered 1931 map for the London subway, Mr. Vignelli distilled the labyrinthine tangle of lines to a colorful, simplified geometry—with Helvetica this time. Striking as it was, the Vignelli map design proved too simple for many and was replaced within seven years by a more conventional map that resembles the one in use today.

Yet the sign system took hold. Unlike the map, there was no debate about its functionality. As it was rolled out in more stations, commuters became familiar with the sans-serif lettering and color-coded disks that identified the different subway lines. By 1989, no-longer-exotic Helvetica was so easy to obtain that it was finally designated as the typeface for the whole of the transit system.

Assiduous font-spotters might glimpse an occasional bit of Standard Medium in some subway stations, but, as Mr. Shaw makes clear in one of the best-researched books on modern design to date, this most New York of places is today a realm dominated by a Swiss typeface specified by a pair of Italian designers. There isn't better testimony to the city as a melting pot or to the strange turns that any major design project inevitably takes.

—Mr. Bierut is a partner in the design firm Pentagram. He began his career in 1980 as an assistant to Massimo Vignelli.