A street is a public thoroughfare in the built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable surface such as concrete, cobblestone or brick. Portions may also be smoothed with asphalt, embedded with rails, or otherwise prepared to accommodate non-pedestrian traffic.
Originally the word "street" simply meant a paved road (Latin: "via strata"). The word "street" is still sometimes used colloquially as a synonym for "road", for example in connection with the ancient Watling Street, but city residents and urban planners draw a crucial modern distinction: a road's main function is transportation, while streets facilitate public interaction. Examples of streets include pedestrian streets, alleys, and city-centre streets too crowded for road vehicles to pass. Conversely, highways and motorways are types of roads, but few would refer to them as streets.
Streets can be loosely categorized as main streets and side streets. Main streets are usually broad with a relatively high level of activity. Commerce and public interaction are more visible on main streets, and vehicles may use them for longer-distance travel. Side streets are quieter, often residential in use and character, and may be used for vehicular parking.
In the interest of order and efficiency, an effort may be made to segregate different types of traffic. This is usually done by carving a road through the middle for motorists, reserving sidewalks on either side for pedestrians; other arrangements allow for streetcars, trolleys, and even wastewater and rainfall runoff ditches (common in Japan and India). In the mid-20th century, as the automobile threatened to overwhelm city streets with pollution and ghastly accidents, many urban theorists came to see this segregation as not only helpful but necessary in order to maintain mobility. Le Corbusier, for one, perceived an ever-stricter segregation of traffic as an essential affirmation of social order — a desirable, and ultimately inevitable, expression of modernity. To this end, proposals were advanced to build "vertical streets" where road vehicles, pedestrians, and trains would each occupy their own levels. Such an arrangement, it was said, would allow for even denser development in the future.
These plans were never implemented comprehensively, a fact which today's urban theorists regard as fortunate for vitality and diversity. Rather, vertical segregation is applied on a piecemeal basis, as in sewers, utility poles, depressed highways, elevated railways, common utility ducts, the extensive complex of underground malls surrounding Tokyo Station and the Ōtemachi subway station, the elevated pedestrian skyway networks of Minneapolis and Calgary, the underground cities of Atlanta and Montreal, and the multilevel streets in Chicago.
Transportation is often misunderstood to be the defining characteristic, or even the sole purpose, of a street. This has not been the case since the word "street" came to be limited to urban situations, and even in the automobile age, is still demonstrably false. A street may be temporarily blocked to all through traffic in order to secure the space for other uses, such as a street fair, a flea market, children at play, filming a movie, or construction work. Many streets are bracketed by bollards or Jersey barriers so as to keep out vehicles. These measures are often taken in a city's busiest areas, the "destination" districts, when the volume of activity outgrows the capacity of private passenger vehicles to support it. A feature universal to all streets is a human-scale design that gives its users the space and security to feel engaged in their surroundings, whatever through traffic may pass.
Despite this, the operator of a motor vehicle may (incompletely) regard a street as merely a thoroughfare for vehicular travel or parking. As far as concerns the driver, a street can be one-way or two-way: vehicles on one-way streets may travel in only one direction, while those on two-way streets may travel both ways. One way streets typically have signs reading "ONE WAY" and an arrow showing the direction of allowed travel. Most two-way streets are wide enough for at least two lanes of traffic.
Which lane is for which direction of traffic depends on what country the street is located in. On broader two-way streets, there is often a center line marked down the middle of the street separating those lanes on which vehicular traffic goes in one direction from other lanes in which traffic goes in the opposite direction. Occasionally, there may be a median strip separating lanes of opposing traffic. If there is more than one lane going in one direction on a main street, these lanes may be separated by intermittent lane lines marked on the street pavement. Side streets often do not have center lines or lane lines.
Practically all public streets in Western countries and the majority elsewhere (though not in Japan; see Japanese addressing system) are given a street name or at least a number to identify them and any addresses located along the streets. Alleys typically do not have names. The length of a lot of land along a street is referred to as the frontage of the lot.
Streets also tend to aggregate establishments of similar nature and character. East 9th Street in Manhattan, for example, offers a cluster of Japanese restaurants, clothing stores, and cultural venues. In Washington, D.C., 17th Street and P Street are well-known as epicenters of the city's (relatively small) gay culture. Many cities have a Radio Row or Restaurant Row. This phenomenon is the subject of urban location theory in economics.
A road, like a street, is often paved and used for travel. However, a street is characterized by the degree and quality of street life it facilitates, whereas a road serves primarily as a through passage for road vehicles or (less frequently) pedestrians. Buskers, beggars, boulevardiers, patrons of sidewalk cafés, peoplewatchers, streetwalkers, and a diversity of other characters are habitual users of a street; the same people would not typically be found on a road.
In rural and suburban environments where street life is rare, the terms "street" and "road" are frequently considered interchangeable. Still, even here, what is called a "street" is usually a smaller thoroughfare, such as a road within a housing development feeding directly into individual driveways. In the last half of the 20th century these streets often abandoned the tradition of a rigid, rectangular grid, and instead were designed to discourage through traffic. This and other traffic calming methods provided quiet for families and play space for children. Adolescent suburbanites find, in attenuated form, the amenities of street life in shopping malls where vehicles are forbidden.
If a road connects places, then a street connects people. One may "hit the road" to see the wonders of the world—Jack Kerouac famously chronicled one such journey—but the latest bling will "hit the streets" before it ever appears on a road. It is "on the street" where one hears an interesting rumor, where one bumps into an old acquaintance, where one acquires smarts. One seldom sees a "road" vendor except of fresh produce, or a "road" performer. You'll never find yourself on a long "street" to nowhere or under assault by a violent "road" gang, hence politicians seldom view with alarm the prevalence of "crime in the roads". The street, not the road is home to the homeless unless they are hoboes, and even Kerouac's hero finally returned to find his friends on a New York street.
In the United Kingdom many towns will refer to their main thoroughfare as the High Street (in the United States it would be called the Main Street — however, occasionally "Main Street" in a city or town is a street other than the de facto main thoroughfare), and many of the ways leading off it will be named "Road" despite the urban setting. Thus the town's so-called "Roads" will actually be more street like than a road.
Some streets may even be seen as highways. Hurontario Street in Mississauga, Ontario, Canada, is commonly referred to as "Highway 10" — even though such a highway designation no longer officially exists. This is probably due to the fact that the street is a modern suburban arterial that was urbanized after decades of having the status and function a true highway, so people continued to use the number because of force of habit.
In some other English-speaking countries, such as New Zealand and Australia, cities are often divided by a main "Road," with "Streets" leading from this "Road", or are divided by thoroughfares known as "Streets" or "Roads" with no apparent differentiation between the two. In Auckland, for example, the main shopping precinct is around Queen Street and Karangahape Road.
Streets have existed for as long as humans have lived in permanent settlements (see civilization). However, modern civilization in much of the New World developed around transportation provided by motor vehicles. In some parts of the English-speaking world, such as North America, many think of the street as a thoroughfare for vehicular traffic first and foremost. In this view, pedestrian traffic is incidental to the street's purpose; a street consists of a thoroughfare running through the middle (in essence, a road), and may or may not have sidewalks along the sides.
In an even narrower sense, some may think of a street as only the vehicle-driven and parking part of the thoroughfare. Thus, sidewalks and tree lawns would not be thought of as part of the street. A mother may tell her toddlers "Don't go out into the street, so you don't get hit by a car."
Among urban residents of the English-speaking world, the word appears to carry its original connotations (i.e. the facilitation of traffic as a prime purpose, and "street life" as an incidental benefit). For instance, a New York Times writer lets casually slip the observation that automobile-laden Houston Street is "a street that can hardly be called 'street' anymore, transformed years ago into an eight-lane raceway that alternately resembles a Nascar event and a parking lot." Published in the paper's Metro section, the article evidently presumes an audience with an innate grasp of the modern urban role of the street. To the readers of the Metro section, vehicular traffic does not reinforce, but rather detracts from, the essential "street-ness" of a street.
At least one map has been made to illustrate the geography of naming conventions for thoroughfares; street, avenue, boulevard, circle, and other suffixes are contrasted against one another.