Editing Grid plan (section)

== Benefits and criticisms ==

===Financial cost===
[[File:Block Sizes and Street Length.svg|thumb|right|Block sizes and street length]]
[[File:13½ Street.jpg|thumb|right|In a numbered grid system, adding an extra street can cause confusion]]

''Street width'', or right of way (ROW), influences the amount of land that is devoted to streets, which becomes unavailable for development and therefore represents an [[opportunity cost]]. The wider the street, the higher the opportunity cost. Street width is determined by circulation and aesthetic considerations and is not dependent on the pattern configuration. Any configuration can have wide or narrow streets.

''Street length'' influences proportionately the number of street components that have to be constructed such as pavement, curbs and sidewalks, storm sewers and drains, light poles, and trees. The street length of a given area of development depends on the frequency at which streets occur which in turn depends on the length and width of a block. The higher the frequency of streets the longer is their total length. The smaller the block dimensions the higher the frequency of the streets. As the frequency of street increases so does the number of intersections. Intersections normally cost more than straight street length because they are labour-intensive and require street and traffic signage.

''Pavement width'' influences the cost by affecting the amount of materials and labour required to provide a finished road surface. Pavement width is generally based on traffic engineering considerations and is not dependent on pattern configuration. As with the street width, any pattern can have wide or narrow pavements.
Of all three factors that affect cost, street width, street length and pavement width, only street length is pattern dependent. An objective cost comparison would, therefore, rely on this variable with the full understanding that the other variables, though optional, can play a role.

Not only do these street dimension factors increase infrastructure costs and inhibit land utilization and by turn, affordability, but they also impact a city's economic productivity. "Street width plays a crucial role in shaping our perception of scale, influencing how distant or accessible destinations appear".<ref name=":2">{{Cite web |date=2020-01-06 |title=Some Thoughts on Narrow Streets |url=https://www.strongtowns.org/journal/2015/3/17/some-thoughts-on-narrow-streets |access-date=2025-04-03 |website=Strong Towns |language=en-US}}</ref> Wider streets have less developable land within a square mile generating tax revenue (tax revenue falls) while having greater area of streets to maintain (expenses go up).<ref name=":2" /> 

Traditional orthogonal grid patterns generally have greater street frequencies than discontinuous patterns. For example, Portland's block is 200 feet × 200 feet while Miletus' is half that size and Timgad's half again (see diagram). Houston, Sacramento and Barcelona are progressively bigger reaching up to four times the area of Portland's block. New York's 1811 plan (see above) has blocks of {{convert|200|ft}}. in width and variable lengths ranging from about {{convert|500|ft}} to {{convert|900|ft}} feet. The corresponding frequency of streets for each of these block sizes affects the street length.

A simple example of a grid street pattern (see diagram) illustrates the progressive reduction in ''total'' street length (the sum of all individual street lengths) and the corresponding increase in block length. For a corresponding reduction of one, two, three and four streets within this {{convert|40|acre|ha|adj=on}} parcel, the street length is reduced from an original total of {{convert|12600|ft}} to {{convert|7800|ft}} linear feet, a 39% reduction. Simultaneously, block lengths increase from 200 × 200 feet to 1240 × 200 feet. When all five blocks have reached the ultimate size of {{convert|1240|feet}} four street lengths out of total eight have been eliminated. Block lengths of {{convert|1000|ft}} or larger rarely appear in grid plans and are not recommended as they hinder pedestrian movement (Pedestrianism, below). From the pedestrian perspective, the smaller the block is, the easier the navigation and the more direct the route. Consequently, the finer grids are preferred.

Patterns that incorporate discontinuous street types such as crescents and [[cul-de-sac|culs-de-sac]] have not, in general, regarded pedestrian movement as a priority and, consequently, have produced blocks that are usually in the {{convert|1000|ft}}  range and often exceed it. As a result, street frequency drops and so does the ''total'' street length and, therefore, the cost. In general, it is not the street pattern per se that affects costs but the frequency of streets that it either necessitates or purposely incorporates.

An inherent advantage of the orthogonal geometry of a proper grid is its tendency to yield regular lots in well-packed sequences. This maximizes the use of the land of the block; it does not, however, affect street frequency. Any frequency of orthogonal streets produces the same [[packing problems|packing]] effect. Orthogonal geometry also minimizes disputes over lot boundaries and maximizes the number of lots that could front a given street. [[John Randal]] said Manhattan's grid plan facilitated "buying, selling and improving real estate".<ref name="crabgrass" />

Another important aspect of street grids and the use of rectilinear blocks is that traffic flows of either pedestrians, cars, or both, only cross at right angles. This is an important traffic safety feature, since no one entering the intersection needs to look over their shoulder to see oncoming traffic. Any time traffic flows meet at an acute angle, someone cannot see traffic approaching them. The grid is thus a geometric response to our human physiology. It is very likely the original purpose of grid layouts comes from the Athenian Agora. Before the grid organization, markets were laid out randomly in a field with traffic approaches at odd angles. This caused carts and wagons to turn over due to frequent collisions. Laying out the market stalls into regularized rows at right angles solved this problem and was later built into the Athenian Agora and copied ever since.

===Ecological features, rainwater absorption, and pollutant generation===
[[File:Platslc.jpg|thumb|right|Surveyor's plan of Salt Lake City, circa 1870s – an example of a typical, uniform, square-grid street network]]
Typical uniform grids are unresponsive to [[topography]]. [[Priene]]'s plan, for example, is set on a hill side and most of its north–south streets are stepped, a feature that would have made them inaccessible to carts, chariots and loaded animals. Many modern cities, such as [[San Francisco]], [[Vancouver]], and [[Saint John, New Brunswick]], follow Priene's example. In a modern context, steep grades limit accessibility by car, and more so by bicycle, on foot, or wheelchair, particularly in cold climates.

The same inflexibility of the grid leads to disregarding [[Natural environment|environment]]ally sensitive areas such as small streams and [[creek (stream)|creeks]] or mature woodlots in preference for the application of the immutable geometry. It is said{{By whom|date=July 2023}} of the New York City grid plan that it flattened all obstacles in its way. By contrast, recent discontinuous street patterns follow the configuration of natural features without disrupting them. The grid represents a rationalist, [[reductionist]] solution to a multifaceted issue.

The grid's inherent high street and intersection frequencies produce large areas of [[impermeable surface]]s in the street pavement and the [[sidewalk]]s. In comparison with recent networks with discontinuous street types, grids can be up to 30% higher in impermeable surfaces attributable to roads. The emerging environmental priority of retaining as much as 90% of [[rain|rain water]] on site becomes problematic with high percentages of impermeable surfaces. And since roads constitute the largest share of the total impermeable surfaces of a development, the difficulty is compounded by the grid type of layout. For these reasons modern planners have attempted to modify the rigid, uniform, classic grid.

Some cities, notably [[Seattle]], have devised means to improve a street's retention capacity. However, frequent intersections as they occur in a regular grid would pose an obstacle to their effective application.

A street network pattern can affect the production of pollutants by the amount of car travel that it necessitates and the speed at which cars can travel. The grid plan with its frequent intersections may displace a portion of the local car trips with walking or biking due to the directness of route that it offers to [[pedestrian]]s. But, as long as cars are also allowed on those streets, it makes the same routes more direct for cars, which could be an enticement for driving. The potential car trip displacement would result in a reduction of [[pollutant]] [[exhaust gas|emissions]]. The advantage of the intersection density for pedestrians, however, can have a contrary effect for cars due to its potential for reducing speeds. Low speeds below {{cvt|20|mph|km/h}} have a significantly higher coefficient of pollutant production than above {{cvt|30|mph|km/h}}, though the coefficient after leveling off tends to increase gradually after {{cvt|50|mph|km/h}}.<ref>Final Facility Specific Speed Correction Factors:M6.SPD.002 David Brzezinski, Constance Hart, Phil Enns Assessment and Standards Division, Office of Transportation and Air Quality, U.S. Environmental Protection Agency</ref> This effect is accentuated with high traffic density in areas with commercial uses where speeds come to a crawl. Since the grid plan is non-hierarchical and intersections are frequent, all streets can be subject to this potential reduction of average speeds, leading to a high production of pollutants. Greenhouse and noxious gases can be detrimental to the environment and to resident health.

===Social environment and security===

In his seminal 1982 study on livable streets that was conducted in neighbourhoods with a grid, Donald Appleyard showed that social networking and street playing degraded as traffic increased on a street. His research provided the groundwork for [[traffic calming]] and for several initiatives such as [[living street]]s and [[Home Zone]]s, all of which are aimed at improving a street's social milieu. The amount of traffic on a street depends on variables such as the population density of the neighbourhood, car ownership and its proximity to commercial, institutional or recreational edifices. Most importantly, however, it depends on whether a street is or could become a through road to a destination. As a through road, it could sustain unpredictable levels of traffic that may fluctuate during the day and increase over time.

A key characteristic of the grid pattern is that any and all streets are equally accessible to traffic (non-hierarchical) and could be chosen at will as alternative routes to a destination. Cut-through driving, or shortcutting, has been resisted by residents.<ref>Philip Langdon, 2006: Seaside Stews Over Street Connections. ''New Urban News'', September 2006</ref> Cities responded by making modifications to prevent it. Current recommended design practice suggests the use of 3-way intersections to alleviate it.<ref>{{cite web |url=http://www.cues.fau.edu/cnu/docs/Traditional_Neighborhood_Development_Street_Design_Guidelines-ITE.pdf |title=Traditional Neighborhood Development Street Design Guidelines |publisher=[[Institute of Transportation Engineers]] |date=October 1999 |location=Washington, DC |archive-url=https://web.archive.org/web/20110220174833/http://www.cues.fau.edu/cnu/docs/Traditional_Neighborhood_Development_Street_Design_Guidelines-ITE.pdf |archive-date=February 20, 2011 |access-date=May 23, 2017 }}</ref>

The geometry of the normal, open grid is evidently unsuitable for protecting or enhancing the social environment of a street from the negative influence of traffic. The scale of the block, as argued by [[Jane Jacobs]]—writer and activist, in her landmark ''The Death and Life of Great American Cities'' (1961), is "one of the four most important factors in generating diversity".<ref name=":3">{{Cite web |title=small blocks |url=http://npl.wiki/view/small-blocks |access-date=2025-04-03 |website=npl.wiki}}</ref>  Blocks longer than 400 feet (about 120 meters) disrupt the “intricate pools of fluid street use” that are necessary to support diverse economic and cultural interactions, and to maintain a “fabric of intimate economic cross-use”.<ref name=":3" /> Another key aspect is the overall street connectivity pattern, where smaller block sizes are crucial for enhancing accessibility, in addition to irregular block dimensions that emulate pedestrian movement. [https://www.ucl.ac.uk/bartlett/news/2019/nov/tribute-bill-hillier Bill Hillier], a professor of Architectural and Urban Morphology and his colleagues developed a “space syntax” model for street design, demonstrating that natural pedestrian movement—including trips to commercial areas—relies on the broader structure of the street grid. This supports Jacobs’ observation that block sizes directly influence economic activity and social interactions.<ref name=":3" /> Similarly, a 1972 ground-breaking study by [[Oscar Newman (architect)|Oscar Newman]] on a [[Defensible Space Theory]] described ways to improve the social environment and security of neighbourhoods and streets. In a practical application of his theory at Five Oaks, the neighbourhood's grid pattern was modified to prevent through traffic and create identifiable smaller enclaves while maintaining complete pedestrian freedom of movement. The positive outcome of these changes reinforces Appleyard's findings and the need to reduce or prevent through traffic on neighbourhood streets; a need that cannot be met with a typical, uniform, open grid. 

The question of neighbourhood security has been a constant focus of research since Oscar Newman's work. New research has expanded the discussion on this disputed issue. A recent study<ref>Hillier, Bill and Sahbaz, Ozlem (March 2008) "An evidence based approach to crime and urban design Or, can we have vitality, sustainability and security all at once?" Bartlett School of Graduate Studies, [[University College London]]</ref> did extensive spatial analysis and correlated several building, site plan and social factors with crime frequencies and identified subtle nuances to the contrasting positions. The study looked at, among others, dwelling types, unit density (site density) movement on the street, culs–de-sac or grids and the permeability of a residential area. Among its conclusions are, respectively, that flats are always safer than houses and the wealth of inhabitants matters, density is generally beneficial but more so at ground level, local movement is beneficial, but not larger scale movement, relative affluence and the number of neighbours have a greater effect than either being on a cul-de-sac or being on a through street. It also re-established that simple, linear cul-de-sac with good numbers of dwellings that are joined to through streets tend to be safe. As for permeability, it suggests that residential areas should be permeable enough to allow movement in all directions but no more. The overprovision of poorly used permeability is a crime hazard. The open, uniform grid could be seen as an example of undifferentiated permeability.

A recent study in California<ref>Handy, Susan; Sommer, Samantha; Ogilvie, Julie; Cao, Xinyu; and [[Patricia Mokhtarian|Mokhtarian, Patricia]] (2007) "Cul-de-Sacs and Children's Outdoor Play: Quantitative and Qualitative Evidence" [[University of California, Davis]]</ref> examined the amount of child play that occurred on the streets of neighbourhoods with different characteristics; grid pattern and culs-de-sac. The findings indicate that the open grid streets showed substantially lower play activity than the cul-de-sac street type. Culs-de-sac reduce [[Perceived risk|perceived danger]] from traffic, and thereby encourage more outdoor play.  It pointed the way toward the development of hybrid street network patterns that improve pedestrian movement but restrict cut-through driving. Similar studies in Europe<ref>Huttenmoser, Marco and [[Marie Meierhofer]] (1995) "Children and Their Living Surroundings for the Everyday Life and Development of Children." Children's Environments 12(4): 1-17</ref> and most recently in Australia<ref>{{cite journal | last1 = Veitch | first1 = Jenny | last2 = Salmon | first2 = Jo | last3 = Ball | first3 = Kylie | name-list-style= amp | year = 2010 | title = Individual, social and physical environmental correlates of children's active free-play: a cross-sectional study | journal = International Journal of Behavioral Nutrition and Physical Activity | volume = 7 | page = 11 | doi = 10.1186/1479-5868-7-11 | pmid = 20181061 | pmc = 2841089 | doi-access = free }}</ref> found that children's outdoor play is significantly reduced on through roads where traffic is, or perceived by parents to be, a risk.  As a result of this misperception of risk, children living in cul-de-sac communities are more likely to be killed by vehicles.  This increased risk of death is due to multiple factors, including the families driving longer distances to reach their destinations, parents spending less time teaching their children to be as wary of traffic, and an increased risk of the parents accidentally driving over the children in their "safe" driveways and cul-de-sac streets.<ref>[https://www.npr.org/templates/story/story.php?storyId=5455743 Cul-de-Sacs: Suburban Dream or Dead End?], Morning Edition on NPR</ref><ref>{{Cite web|url=http://bettercities.net/article/tomorrow%E2%80%99s-cities-tomorrow%E2%80%99s-suburbs|title=Tomorrow's Cities, Tomorrow's Suburbs &#124; Better! Cities & Towns Online|archive-url=https://web.archive.org/web/20170118041952/http://bettercities.net/article/tomorrow%E2%80%99s-cities-tomorrow%E2%80%99s-suburbs|archive-date=2017-01-18|url-status=dead|access-date=2019-07-20}}</ref><ref>{{cite web|url=https://usa.streetsblog.org/2011/06/07/cul-de-sacs-are-killing-us-public-safety-lessons-from-suburbia/|title=Cul-de-Sacs Are Killing Us: Public Safety Lessons From Suburbia|date=7 June 2011}}</ref>

Traditional street functions such as kids' play, strolling and socializing are incompatible with traffic flow, which the open, uniform grid geometry encourages. For these reasons, cities such as [[Berkeley, California]], and [[Vancouver, British Columbia]], among many others, transformed existing residential streets part of a grid plan into permeable, linked culs-de-sac. This transformation retains the [[Permeability (spatial and transport planning)|permeability]] and connectivity of the grid for the active modes of transport but filters and restricts car traffic on the cul-de-sac street to residents only.

===Pedestrian and bicycle movement===
[[File:Paris Street Network Segment.jpg|thumb|upright=0.9|right|A 2×2 km square segment of the street network of [[Paris]] that often, and erroneously, is characterized as a grid. It shows the highly irregular city blocks and the range of street orientations, both common attributes of many historic cities]]
Street networks of old cities that grew organically, though admired for being picturesque, can be confusing for visitors but rarely for the original inhabitants (see plan). Similarly confusing to visitors are the plans of modern subdivisions with discontinuous and curvilinear streets. Change of street orientation, particularly when gradual or arbitrary, cannot be "mapped" in the mind. Impasses, crescents or [[cul-de-sacs]] frustrate the traveler especially when they are long, forcing an arduous retracing of steps.

Frequency of intersections, however, becomes also a disadvantage for pedestrians and bicycles. It disrupts the relaxed canter of walking and forces pedestrians repeatedly onto the road, a hostile, anxiety-generating territory. People with physical limitations or frailties, children and seniors for example, can find a regular walk challenging. For bicycles this disadvantage is accentuated as their normal speed is at least double that of pedestrians. Frequent stops negate the speed advantage and the physical benefit of bicycling and add to frustration. {{citation needed|date=February 2015}} Intersections are not only unpleasant but also dangerous. Most [[traffic collision]]s and injuries occur at intersections and the majority of the injuries to pedestrians crossing ''with'' the right of way.

A dilemma arises from trying to meet important planning objectives when using the grid: pedestrianism, cost efficiency and environmental responsiveness. To serve pedestrians well, a rectangular configuration and high frequency of streets and intersections is the preferred route, which the orthogonal grid geometry provides. To reduce development costs and environmental impact, lower frequency of streets is the logical path. Since these two design objectives are contradictory a balance needs to be struck. Such balance has been achieved in leading modern projects such as [[Vauban, Freiburg]] and [[Village Homes]], Davis. Both score high in pedestrian and bike mode share and, at the same time, in reducing negative development externalities. Their layout configurations represent a fusion of the classic grid plan with recent street network patterns.

Examining the issue of [[walkability]], a recent comparison of seven neighbourhood layouts found a 43 and 32 percent increase in walking with respect to a grid plan and conventional suburban layout in a [[fused grid]] layout, which has greater permeability for pedestrians than for cars due to its inclusion of dedicated pedestrian paths. It also showed a 7 to 10 percent range of reduction in driving with respect to the remainder six neighbourhood layouts in the set, an environmental benefit.<ref>Xiongbing Jin (2010) "Modeling the Influence of Neighbourhood Design on Daily Trip Patterns in Urban Neighbourhoods", [[Memorial University of Newfoundland]]</ref>

===Safety===
Perceived and actual safety play a role in the use of the street. Perceived safety, though perhaps an inaccurate reflection of the number of injuries or fatalities, influences parents' decision to allow their children to play, walk or bike on the street. Actual levels of safety as measured by the total number of collisions and the number and severity of injuries are a matter of public concern. Both should inform the layout, if the street network is to achieve its optimum use.

Recent studies have found higher traffic fatality rates in outlying suburban areas than in central cities and inner suburbs with smaller blocks and more-connected street patterns.<ref>{{cite journal | pmc=1448007 | pmid=12948977 | volume=93 | issue=9 | title=Urban sprawl as a risk factor in motor vehicle occupant and pedestrian fatalities | year=2003 | journal=Am J Public Health | pages=1541–5 | last1 = Ewing | first1 = R | last2 = Schieber | first2 = RA | last3 = Zegeer | first3 = CV | doi=10.2105/ajph.93.9.1541}}</ref><ref>{{cite web |url=http://www.virginia.edu/topnews/releases2002/lucy-april-30-2002.html |title=Danger in Exurbia {{!}} U.Va. Study Reveals Outer Suburbs More Dangerous Than Cities |access-date=2006-09-03 |url-status=dead |archive-url=https://web.archive.org/web/20060903234004/http://www.virginia.edu/topnews/releases2002/lucy-april-30-2002.html |archive-date=2006-09-03 }}</ref>

An earlier study<ref>Eran Ben-Joseph, Livability and Safety of Suburban Street Patterns: A Comparative Study (Berkeley, CA: Institute of Urban and Regional Development, University of California, Working Paper 641, 1995)</ref> found significant differences in recorded accidents between residential neighborhoods that were laid out on a grid and those that included culs-de-sac and crescents. The frequency of accidents was significantly higher in the grid neighborhoods.

Two newer studies examined the frequency of collisions in two regional districts using the latest analytical tools. They investigated the potential correlation between street network patterns and frequency of collisions. In one study,<ref>Using Macrolevel Collision Prediction Models in Road SafetyPlanning Applications Gordon R. Lovegrove and Tarek Sayed Transportation Research Record: Journal of the Transportation Research Board, No. 1950, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 73–82</ref> cul-de-sac networks appeared to be much safer than grid networks, by nearly three to one.
A second study<ref>Sun, J. & Lovegrove, G. (2009). Research Study on Evaluating the Level of Safety of the Fused Grid Road Pattern, External Research Project for CMHC, Ottawa, Ontario</ref> found the grid plan to be the least safe by a significant margin with respect to all other street patterns.

A 2009 study<ref>{{cite journal | last1 = Dumbaugh | first1 = Eric | last2 = Rae | first2 = Robert | year = 2009 | title = Safe Urban Form: Revisiting the Relationship Between Community Design and Traffic Safety | journal = Journal of the American Planning Association | volume = 75 | issue = 3| pages = 309–329 | doi = 10.1080/01944360902950349 | s2cid = 153379995 }}</ref> suggests that land use patterns play a significant role in traffic safety and should be considered in conjunction with the network pattern. While all intersection types in general reduce the incidence of fatal crashes, four-way intersections, which occur regularly in a grid, increase '''total and injurious crashes''' significantly. The study recommends hybrid street networks with dense concentrations of T-intersections and concludes that a return to the 19th century gridiron is undesirable.

Stringent adherence to the grid plan can cause steep inclines since the topology of the land is not taken into account. This may be unsafe for drivers, pedestrians and bicycles since it is more difficult to control speed and braking, particularly in winter conditions.

===Reconstruction and development===
One of the greatest difficulties with grid plans is their lack of specialization, most of the important amenities being concentrated along the city's main arteries. Often grid plans are found in [[Ribbon development|linear settlements]], with a main street connecting between the perpendicular roads. However, this can be mitigated by allowing mixed use development so that destinations become closer to home. Many cities, especially in Latin America, still successfully retain their grid plans. Recently, planners in the United States and Canada have revisited the idea of reintroducing grid patterns to many cities and towns.