Role in the Built Environment
The street is a public environment shared between all sorts of people. As a component of the built environment as ancient as human habitation, the street sustains a range of activities vital to civilization. Its roles are as numerous and diverse as its ever-changing cast of characters.
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.
Circulation
Rue Saint-Jacques, a street in Montreal, 1910
Circulation, or less broadly, transportation, is perhaps a street’s most visible use, and certainly among the most important. The unrestricted movement of people and goods within a city is essential to its commerce and vitality, and streets provide the physical space for this activity.
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 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 on a large scale, a fact which today’s urban theorists regard as fortunate for vitality and diversity.
Transportation is often misunderstood to be the defining characteristic, or even the sole purpose, of a street. This has never been the case, 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, or children at play. Many streets are bracketed by bollards or Jersey barriers so as to prevent passage unless on foot. 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.
Vehicular Traffic
A street full of vehicles in Shanghai
Despite this, the operator of a motor vehicle may 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 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. 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.
Parking for Vehicles
Many streets, especially side streets in residential areas, have an extra lane’s width on either or both sides for parallel parking vehicles. Most minor side streets allowing free parallel parking do not have pavement markings designating the parking lane. A somewhat recent trend has been to start marking off parking lanes on more important streets. Some streets are too busy or not wide enough to allow parking on the side. Sometimes parking on the sides of streets is allowed only at certain times. Signs off to the side of the street often state regulations about parking. On the side of some streets, particularly in business areas, there may be parking meters into which coins must be paid to allow parking in the adjacent space for a limited time. There may be parking lane markings on the pavement effectively designating which meter a parking space corresponds to. Occasionally, a street may have enough width on the side that there is angle parking.