William Phelps Eno

Traffic Regulations first drafted by Eno, as issued by New York City on February 8, 1909

Though automobiles were rare until Eno was an older man, horse-drawn carriages were already causing significant traffic problems in urban areas like Eno's home town of New York City. In 1867, at the age of 9, he and his mother were caught in a traffic jam. He later wrote, "That very first traffic jam (many years before the motor car came into use) will always remain in my memory. There were only about a dozen horses and carriages involved, and all that was needed was a little order to keep the traffic moving. Yet nobody knew exactly what to do; neither the drivers nor the police knew anything about the control of traffic." As reported in 1909:[3]

The regulation of street traffic was unknown in New York up to the year 1900, and although the number of carriages, automobiles, delivery wagons, trucks and other vehicles was much smaller than it is to-day, blockades were frequent throughout the city. Often the greater part of a day was consumed in transporting merchandise from one point to another, especially in the downtown shopping districts, while charges were proportionate to the time consumed. Quarrels between police, truckmen and cab-men were common, and it was only by resort to the "night stick" that in many instances blockades could be cleared away. There was no bureau of street traffic, no traffic squad and not one officer employed on the street to keep vehicles moving.

These conditions provoked much complaint and criticism in private and in public, but nothing was done to correct them until William Phelps Eno, a public-spirited citizen who spends his winters in Washington, undertook to secure a change. He asserted that to accomplish anything worthwhile three things were necessary:

1. We must have concise, simple and just rules, easily understood, obeyed and enforced under legal enactment.

2. These rules must be so placed and circulated that there can be no excuse for not knowing them.

3. The police must be empowered and ordered to enforce them, and men should be trained for that purpose.

In 1900, Eno wrote a piece on traffic safety entitled Reform in Our Street Traffic Urgently Needed. In 1903, he wrote a city traffic code for New York, the first such code in the world, and subsequently designed traffic plans for New York, London, and Paris.

Columbus Circle rotary plan in Eno's Street Traffic Regulation, 1909

During that same year, Eno proposed the first version of today's roundabouts or traffic circles, which he termed "the rotary or gyratory traffic system". In his 1920 book, Eno recalled that "in 1903, the New York Police Department asked that a plan be suggested for Columbus Circle, where accidents were occurring almost daily. It was advised that vehicles should keep to the right, going around the circle in one direction instead of two. In 1905, the plan was put in operation.... In 1907, the system was put in operation at the Arc de Triomphe in Paris, but whether due to the suggestion sent them from New York or not is not clear." His 1909 book, Street Traffic Regulation, contains a diagram of the Columbus Circle rotary.

Eno also appears to have introduced one-way streets, as recalled in The Science of Highway Traffic Regulation 1899-1920, page 39: "On the author's advice, One-Way Traffic was put in force in a few streets in New York in the spring of 1908; in Boston in the autumn of the same year; in Paris in 1909, where it has since been greatly extended, and in Buenos Aires in 1910. It is now used in many cities throughout the world."