The decline of the city grid

The crossroad of South Ashland Avenue and West County Line Road, in Will County, Illinois, is a picture of classic midwestern rural America. Ashland Avenue, at that point, is barely wider than a lane. On one side is a vast corn field; on the other, a few ranch houses, each set on at least an acre of land and hidden behind hedges. Farther up the road a bright red combine harvester works its way through the fields. Chevrolet pickup trucks, a few of them seemingly having survived since the 1950s, are the main vehicles rushing along the county line. Yet this junction also represents the very end of the great metropolis of Chicago.

The address of the final home on the corner, listed on the mailbox outside, is “32649”. Divide that figure by 800 and you get 40.8, this is close to the distance in a straight line running south in miles from Madison Street, at the centre of the Chicago loop, its downtown business district. Almost every street address in the city is configured thus. Streets that run east to west are measured from State Street; those that run north to south are measured from Madison. Each standard-sized block measures an eighth of a mile, and the address numbers increase by 100 with each block.

Chicago has the world’s most consistent, orderly grid layout. Passengers on planes landing at night at O’Hare International Airport (address: 10,000 West Balmoral Avenue, putting it 12.5 miles west of downtown) see a city that looks like a giant circuit board, with regimented streets going almost exactly north-south or east-west. At the spring and autumn equinoxes, when Earth is a quarter of the way on its annual orbit around the sun, this means that the sun rises and sets in line with the street grid. On those days, Chicagoans flock downtown to see the streets lit up at sunset as though by a perfectly positioned spotlight—pouring scorn on Manhattan’s equivalent dates, which both come in summer, due to its grid’s off-north alignment.

Thanks to the rise of digital mapping, the relative orderliness of different street systems can now be calculated. Geoff Boeing of the University of Southern California created a measure of city “entropy”, looking at how consistent the direction of streets in over 100 major cities worldwide is, as well as how continuously they run through any given city without interruption. A measure of zero suggests a city with absolutely no consistent street direction. A measure of one implies a perfect grid, with no interruptions or curves. Chicago hits 0.89, higher than any other city on Earth. London, a city stitched together over millennia from villages on the lines of haphazardly placed Roman, medieval and Victorian thoroughfares, gets just 0.015. This can be shown on a polar histogram. Cities like London are circular blobs; those like Chicago, clean crosses.

It will come as no surprise to frequent travellers that of the cities Mr Boeing studied, the 16 most orderly are all in North America. The United States is famous for its grid layouts, and the logical, easy-to-remember addresses they generate. Think of The Velvet Underground’s song, “I’m Waiting for the Man”. Any New Yorker, hearing the lyrics “Up to Lexington, 125”, will know that Lou Reed meant 125th Street, the heart of Harlem. To find streets named in music about London, such as “Abbey Road”, one must consult a map.

Yet street grids far predate the United States. The first grid-planned city known to archeologists is Mohenjo-Daro, built around 2600bc along the Indus river, in what is now south-eastern Pakistan. Like modern Chicago, the ancient city had wide thoroughfares for through traffic (probably then oxen carts, tiny models of which have been excavated from the site), built on a north-south/east-west alignment, binding narrower streets within neighbourhoods on the same grid. The ancient Greeks also liked the design. Since the designers of Mohenjo-Daro’s names are lost to antiquity, the earliest known urban planner is Hippodamus of Miletus, whose plan for that city laid out even square blocks. Hippodamus was also among the first to connect town planning and social order. Aristotle deemed him “the first person not a statesman who made inquiries about the best form of government”.

In Renaissance Europe, many early urban planners favoured radial cities, with roads that spread out from a central plaza, because they were easier to defend. Filarete, who designed one of the first “ideal cities”, planned a city built in the shape of a star, with roads spreading out from a central square featuring a church, and ending at fortress walls. Palmanova, a small fortress town near Venice, is probably the closest example that was actually built.

But the grid kept coming back. In the Spanish colonies, the Law of the Indies decreed that new cities should be planned on grids, though as in Europe, with large squares at the centre for churches. Streets laid out along the squares would then block the wind, which would otherwise “cause much inconvenience” to the religious festivals and the like that were expected to be held in the plaza.

In the United States, a mix of idealism and practicality drove the adoption of the grid. In the late 17th century, William Penn laid out his city of brotherly love, Philadelphia, on a grid, as a sort of enlightenment alternative to the hierarchical European city. Instead of naming streets for what they contained, they were given numbers, or named for the trees lining them. Penn, a Quaker, believed that if all streets were equal, the people would be too.

Yet the reason why most American cities are built on grids is largely to do with money. Thomas Jefferson’s land ordinance of 1785 laid out the as-yet-unconquered land to the west in perfect grids to make it easier to sell plots to farmers, and fund the young government. This logic applied to towns too. Chicago’s grid was first laid out in 1830, when the city was little more than a fort on the Chicago river. Developers of later suburbs simply followed the old pattern, partly because it made it easier for trams to transport people between the new developments and the city. (As a result, as the city spread along the grid without a single numbering system, duplicate addresses proliferated. Chicago’s clever street system was introduced only in the early 20th century, after the postal service threatened to cut the city off.)

What makes the grid pop up again and again? The benefits of building streets in uniform grids are clear to anyone who has ever played SimCity. Roads are expensive to build. Laying them out in grids allows more buildings to sit alongside them, which can more easily be linked to sewage lines, electricity connections and gas pipes. Square lots hold rectangular buildings which are filled with rectangular rooms holding rectangular tables, beds and desks. “All of these rectangles combine and give us this efficiency of geometry,” says Paul Knight, an architect who works for Historical Concepts, a firm based in Atlanta and New York.

And grids are easy to navigate. In London cab drivers have to spend up to four years learning the street network before they can get around without a map. Chicago or New York taxi drivers can achieve much the same thing in a day. Pedestrians can walk in a fairly direct route anywhere they need to go, without worrying about dead ends or impassable barriers between roads.

Grids also allow for what Laurence Aurbach, a historian of urban planning, says is the most consistent rule of city design throughout history: functional traffic separation. That is, the separation of pedestrians from vehicles; fast vehicles from slow ones; and through traffic from local traffic. Grids can have networks of wide main roads and narrow side streets, with pavements and crossings for pedestrians. Faster traffic can be constrained to wider through-streets, where it has to stop less often, leaving narrower residential streets quieter and less polluted. In the Victorian era this meant that a network of trams was easy to interlace through them, providing rapid transport for workers from expanding suburbs back into city cores. On a grid, you can get anywhere you want to go by taking two trams—one travelling north and south and another heading east or west.

And yet in the past century or so, grids have gone out of fashion. Some newish ones exist, such as Milton Keynes, a city first planned out in the 1960s in southern England, and Chandigarh, a city planned by Le Corbusier, a modernist architect, in India in the 1950s. But in the vast majority of new settlements all over the world streets twist and turn and end in cul-de-sacs. This, explains Jeff Speck, an urban planner and author of “Walkable City”, is partly just because cul-de-sacs are cheap: you can fit a larger number of suburban detached houses around a smaller patch of tarmac. But it is also by design. From the 1930s onwards, inspired by thinkers like Ebenezer Howard, a British writer who believed everyone should live in radial “garden cities” of no more than 32,000 residents, governments began to encourage curving streets, as well as zoning to separate industry from residential areas.

The force driving much of this was the arrival of the car. As more of them filled up the streets, regular intersections meant traffic ground to a halt: “gridlock”. Intersections meant more opportunities for crashes. Cul-de-sacs keep out unwanted traffic. The problem with this, as Mr Speck notes, is that it comes at the expense of people not in their own vehicles. If you are walking in a modern suburb, “You’re always going out of your way,” he says. It is not only people walking who have to take less direct routes. Buses are more effective when roads are in grids, allowing passengers to get anywhere with just one change.

Could grids be resurrected? Architects are discovering that cul-de-sacs are a dead end. According to Mr Boeing’s research, neighbourhoods that have been built in America in the past 20 years are more orderly than those of the two decades before. The problem is that these days so few are built they have little impact. And most new housing is grafted on to existing neighbourhoods—with street patterns established long ago.

Should construction one day take off again though, the grid might make a return. The important thing is to get them right. As Jane Jacobs, an influential early critic of the car-centric replanning of cities, argued in “The Death and Life of Great American Cities”, what matters most is that the blocks are short, and the roads not too wide. Short blocks are easy to walk through, and create plenty of space for different businesses. Long blocks, designed to reduce the number of times cars have to stop at traffic lights, “thwart the potential advantages that cities offer”, and turn streets into sewers for vehicles. Bear that in mind, and the oldest form of city planning remains as valuable as ever. ■