It begins, as these things tend to, with a child who is bored and stuck.

New York, 1867. A boy of nine is out with his mother and they cannot cross the street. There are no automobiles; there will be none for another generation. What has happened is simply that about a dozen horses and carriages have arrived at the same place with no agreement as to who goes first, and so nobody goes at all. Drivers shout. Horses shift and object. The policeman, if there is one, watches with the expression of a man who has not been told what his job is.

Most children forget such an afternoon by supper. This one did not. Decades later he set it down with a restraint that is somehow more striking than outrage would have been: there were only about a dozen horses and carriages involved, and all that was needed was a little order to keep things moving. Nobody knew what to do. Neither the drivers nor the police knew anything about the control of traffic.

Read that again with the date attached. In 1867 there was no such thing as the control of traffic. There was no profession, no manual, no theory, no word for the problem. A nine-year-old had noticed a gap in the furniture of civilisation, and the gap would stay open for another thirty-two years, waiting for him to be ready.

He could afford to wait, which is the least romantic and most decisive fact about him.

His father was Amos Eno, a Connecticut boy who had come down to New York with nothing much and ended up one of its great landlords, the man behind the Fifth Avenue Hotel. The son went to Yale, took his degree in 1882, was tapped for Skull and Bones, and joined the family firm, where he spent seventeen years in the property business and was very comfortably rich. Nothing in that sentence predicts anything.

Then, in 1899, at the age of forty, he left. Not for politics, not for philanthropy of the usual kind, not for a yacht. He left in order to devote the rest of his life to street traffic, a subject in which no man on earth could then claim expertise, because the subject did not exist. There was no department to join, no journal to publish in, no chair, no client, no salary. He would have to invent the discipline before he could practise it.

This is where the inherited money stops being a footnote and becomes the engine. Reform in that century was almost always financed by somebody who did not need to be paid — the abolitionists, the sanitary commissions, the temperance ladies. Eno’s peculiarity was not his independence but his choice of cause. Offered the whole menu of nineteenth-century good works, he ordered the intersection.

In 1900 he published his opening move, an article with no literary ambition at all: Reform in Our Street Traffic Urgently Needed. The venue tells you more than the title does. It ran in Rider and Driver, a magazine for people who kept horses, because in 1900 those were the people who owned the street, and it was them he had to persuade. Somewhere in it he suggested that it might be useful to put signs at intersections instructing vehicles to stop. Nobody did anything about it for fourteen years.

Three years later he produced the thing itself.

In 1903 the City of New York adopted his Rules for Driving and the Regulation of Street Traffic, by common consent the first set of official traffic laws ever adopted anywhere. Other American cities copied it, in no small part because Eno went to see them about it. Europe took it up. By 1909 an expanded version was operating in New York as the world’s first comprehensive city traffic plan, and London and Paris followed.

What is charming about the Rules, if you ever have the chance to read them, is that they are not written like legislation. They are written like a book of manners. Here is how one overtakes. Here is how one turns. Here is who yields to whom, and how close one may follow, and what is to be done when reversing, which was evidently an adventure. The grammar of the road, composed from nothing, by one man, with a pen and a private income, in the tone of a person explaining to a houseguest where the coats go.

He had a taxonomist’s streak that is frankly delightful. Parked vehicles he divided into the live and the dead. A live vehicle could move off at once; a dead one could not, being horseless or driverless or merely abandoned by a man who had gone to lunch. The dead, he ruled, had no business at the kerb and could go and sit in a vacant lot. Thus, in a single stroke and without anybody noticing, the off-street car park.

And then, in the middle of all this good sense, there is one sentence which is almost never quoted, and which quietly changed who the street belonged to.

In 1903 that was not a description. It was a proposal, and a fairly outlandish one. The street of 1903 was where children played and vendors stood and everybody walked when the pavement was crowded, which it always was. To announce that the roadway was primarily intended for vehicles was rather like announcing that the village green was primarily intended for cricket and everyone else should kindly stand at the edge.

He was not being sinister. He was being an engineer, and engineers optimise for flow. But the flow he optimised for belonged to vehicles, and from that afternoon onward the person on foot was, technically and then eventually morally, in the way.

It would be unfair to hand him the bill for everything that followed. The campaign that actually drove pedestrians off the roadway came two decades later and belonged to other men: as the historian Peter Norton showed in Fighting Traffic, the jaywalker was largely a public-relations invention of the motor industry in the 1920s, complete with parade floats and schoolroom lectures and a word chosen to make the offender sound like a yokel fresh off the turnip cart. Eno never argued for any of that, and would probably have found it vulgar.

But they built it on his sentence. He wrote the premise down first, in an official document, in 1903, when it was still an eccentric opinion — and an eccentric opinion, once it is printed in a municipal code, has a way of becoming the weather.

He disliked the traffic light on what can only be called aesthetic grounds. A signal, in his view, manages traffic by stopping it, which struck him as an admission that the design has failed. He preferred the circle: a junction at which nothing ever halts, because everything is going the same way round. It is a fundamentally optimistic device, and it is his signature across three capitals.

New York first. In 1905 his rotary scheme was built at the point where Broadway meets the bottom of Central Park, and Columbus Circle became the reason Americans spent the next century calling these things circles while the English called them roundabouts. Paris in 1907, the Étoile, which we have already watched revolve. London in 1926, Piccadilly Circus, reorganised on the same principle twenty-one years after New York. Paris again in 1927, the Rond-Point on the Champs-Élysées — the last of the great set pieces, laid out when its author was sixty-nine years old.

France, which understands the value of a man who makes its capital work, put him in the Legion of Honour. Britain listened. Italy listened. Between the wars, an American amateur with no engineering degree and no driving licence advised the governments of Europe on how their cities ought to move, and the governments of Europe took the advice.

Which brings us to the small rectangle of card that makes the whole thing irresistible.

In 1912 the Préfecture de Police at Nancy issued William Phelps Eno a driver’s licence. It survives, signed by one A. Bertillon, and it is described in the record with beautiful French tact as an honorary driver’s licence.

Honorary. Meaning: we are aware, monsieur, that you cannot do this. We are issuing it regardless, because the alternative — that the author of our traffic regulations holds no standing whatever upon our roads — offends the French sense of order considerably more than the fiction does.

He never used it. He rode instead, all his life, and he distrusted automobiles — not as a pose, but as the settled opinion of a man who had spent thirty years studying what they did to a city and had reached his own conclusions about the species.

There is a serious idea sitting inside the joke. The participant optimises for himself; the observer optimises for the system. Ask a driver to design an intersection and you will get the intersection that flatters his own route to work. Eno had no route. He had a view from the saddle, an income that arrived whether he was right or wrong, and not one penny of interest in the outcome — which is, when you set it out like that, a rather exact description of a good judge.

The internet has him down as the man who invented the stop sign, the roundabout, the crosswalk, the one-way street and the taxi rank, which is the sort of tidy list that ought to make anyone suspicious. Only the last part of the legend — that he never drove — survives contact with the record intact. The rest wants sorting, and the sorting is more flattering to him than the legend is.

The stop sign he proposed in 1900 and did not build. The first one went up in Detroit, in 1914 or 1915 depending on which account you trust, a white square two feet across with black letters on it, generally credited to a police sergeant named Harry Jackson. The octagon arrived in 1923, from the highway departments of the Mississippi Valley, on the wonderfully literal theory that the more corners a sign has, the more dangerous the thing it warns about. Red came only in 1954, nine years after Eno was dead.

The circle was not his invention either. The Frenchman Eugène Hénard was drawing circular junctions before him and Letchworth built Britain’s first in 1909; what Eno supplied was the campaign, and the specific junctions listed above. One-way streets are older than the United States. The honest ledger says he popularised much and originated less than the captions claim.

And then it says this. He wrote the first traffic code in the world, and the first police manual for enforcing one. He gave us the safety island, the taxi stand, the regulated crossing, the parking lot and the idea that a street is a system with rules rather than a place where things simply happen to happen. Signposts can be attributed to a sergeant in Detroit. The framework cannot be attributed to anyone but him, and the framework is what changed the world.

It is the usual injustice of popular history, in reverse. We hand people credit for objects because objects photograph well, and in doing so we quietly rob them of the larger thing, which photographs not at all.

In 1921 he did the thing that separates a serious man from a hobbyist, and endowed an institution to outlive him. The Eno Foundation for Highway Traffic Control — today the Eno Center for Transportation in Washington — was built to keep studying the subject after its founder had stopped breathing, and it is still there, a hundred and five years later. He had by then drawn up a subway plan for New York before anyone took the idea seriously, supported the railways, and commissioned research into what aviation was likely to do to everything else, which in the 1920s was a question most people had the sense not to ask.

He died on 3 December 1945, aged eighty-seven, at the hospital in Norwalk, Connecticut, and was buried at Simsbury. The papers of the man who had ordered the streets of three capital cities went, as he wished, to a small-town public library. The war was ending; America was about to build the interstates and do things with the automobile that he would almost certainly have deplored. He left at the right moment, as men of taste generally contrive to do.

Tomorrow morning you will stop at a white line you never agreed to, proceed on a right of way you cannot remember being granted, and go round a circle in the direction everybody else is going, and none of it will cost you a single conscious thought. That is not an accident of civilisation. It is a document, drafted in 1903 by a gentleman who did not drive, which has been obeyed so completely and for so long that it has stopped looking like a document at all.

The most powerful rules are always the ones nobody remembers being written. Somebody wrote them. Usually somebody with time, money and a view of the business from outside — in this case, from about sixteen hands above the ground.

Twelve carriages, one bored child, and all that was needed was a little order. He was quite right about that. He simply never got around to mentioning whose order it would turn out to be.