Intersection density is a fundamental element of walkability. The more intersection density there is in a street network, the more walkable the streets are. The predominance of cul-de-sacs in the expansion of cities or in the creation of new cities has been extensively documented in various studies in Europe, North America and Oceania. In the United
States, for instance, the predominance of cul-de-sacs is the result of decisions made by individuals, real estate developers or the government. However, cul-de-sacs have a negative impact on street connectivity. More traffic congestion has been associated with the predominance of cul-de-sacs in new settlements that make people from the same neighbourhood use the same arterial streets to connect to a highway. The same has been observed in Europe and Oceania.
FIGURE 3.3 RATIO OF LAND ALLOCATED STREETS TO STREET DENSITY IN CITY CORE CITIES OF EUROPE, NORTH AMERICA AND OCENIA
Ratio of LAS to SD 0.0
0.5 1.0 1.5
Auckland
Barcelona
New York
Brussels
Saint Petersburg
Toronto
London
Montreal
Sydney
Melbourne
Copenhagen
Washington, D.C.
Los Angeles
Calgary
Phoenix
Moscow
Paris
Athens
Amsterdam
Helsinki
STREETS AS PUBLIC SPACES AND DRIVERS OF URBAN PROSPERITY 56
The predominance of cul-de-sacs not only reduces intersection density but also reduces street density. Fewer streets are built and fewer intersections are allocated on those that have been built. The length of the street network per square km expressed in terms of street density is much lower in suburban areas than in city centres. Indeed, by opting for street networks that are predominantly cul-de-sacs, the intention of real estate developers is to build more houses on fewer streets. As shown in Figure 3.3, the street density in the city core is more than two times higher than the street density in the suburban areas of most cities. Except for Auckland and Saint Petersburg, where the street density is below 15 km per square km, street density is 20 km per square km or more in the city centre while the street density is below 15 km per square km in suburban areas of most cities. This trend is similar to what has been observed in relation to the proportion of land allocated to streets. In fact, the reduction of land allocated to streets in suburban areas could be associated with the fact that a large proportion of land in suburbs is allocated to residential plots, not to streets.
Figure 3.4 shows that in suburban areas of cities analyzed here the intersection density is low compared to city centres.
Since most suburban areas were built in cul-de-sacs, some even as gated communities, they have fewer intersections compared to city cores. Except for the suburban areas of Helsinki (120.6 intersections per square km), in all suburban areas analyzed here the intersection density is less than 100 intersections per square km. This is clearly an indication of unconnected street networks that do not promote multiple options for the inhabitants to access services, such as work places, health centres and schools. Inhabitants of gated communities are obliged to use the same arterial streets that link them either to the centre of their neighbourhood or to highways that lead to main city centres. In addition, there may be congestion on most arterials serving as connectors.
FIGURE 3.4 INTERSECTION DENSITY IN CITIES EUROPE, NORTH AMERICA, OCEANIA
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0
Number of intersections per square km
Cities
City core Sub-urban areas
Auckland Moscow Saint Petersburg Copenhagen Phoenix Brussels Calgary Los Angeles New York Sydney Washington, D.C. Barcelona Melbourne Montreal London Paris Toronto Athens Helsinki Amsterdam
57 CHAPTER 3: THE STATE OF STREETS IN EUROPE,
NORTH AMERICA AND OCEANIA
The city of Auckland presents a very specific case, with its city core planned as a suburb with very low connectivity.
Its intersection density is below 70, indicating a city where movement within the city centre is as complex as it is in suburban areas. As illustrated in Fig. 3.4, the city core of Auckland is within the group of suburban areas at the bottom of the graph. In other terms, it has same intersection density as suburban areas. Lack of connectivity in the city centre of
Auckland is well illustrated in map 3.1. Although some of the houses in the northeastern parts of the city may be located only 400 metres from the train stations, residents have to walk for more than 1 kilometre to reach it, due to poor street connectivity. Arterial streets are mainly for cars, with lack of pedestrian lanes and bicycle paths. However, with “complete streets” or “livable streets” projects, some arterial streets have been re-designed to accommodate all users.
Lengthy street networks also promote high intersection density, i.e. high connectivity. The city core of Amsterdam, with a street density of 30.7 km per square km, also has the highest intersection density in the city core (314 intersections per square km), compared to the city core of Auckland, which has an intersection density below 100 (72.9), corresponding to a street density of 12.7 km per square km. This means that despite the narrowness of its streets, streets in Amsterdam are well- connected; they promote walkability and are better able to connect people to services, such as workplaces, health centres, schools, etc. In all European and North American cities covered in this study, the intersection density in the city core is higher than 100, indicating sufficient level of street connectivity.
Lengthy street networks with sufficient street width are preferable to wide streets within short networks since they cover more neighbourhoods. Lengthy street networks can promote spatial and social inclusion. In fact, many social inequalities observed in cities are the result of the way cities are planned. Some areas have many and wide streets while other areas have few and narrow ones. This is the main criticism of urban plans of new cities or expanding cities that are based on master plans that divide the city according to the social or economic status of residents. Street networks thus have an impact of the wellbeing of people, as discussed later in this chapter.
Train Station RailwayLine Distance to Train Station
Most Direct Route Normal Route
Sturges Road Train Station
Poor connectivity doubles distance travelled to train station.
Source: Image © 2013 Google and 2013 Whereis® Sensis Pty Ltd
MAP 3.1: POOR STREET CONNECTIVITY IN AUCKLAND, NEW ZEALAND
STREETS AS PUBLIC SPACES AND DRIVERS OF URBAN PROSPERITY 58
FIGURE 3.5 RELATIONSHIP BETWEEN STREET DENSITY AND INTERSECTION DENSITY CITIES OF EUROPE, NORTH AMERICA AND OCENIA
Sources: Ximaion re porionse volorestiunt.
y = 10.51x - 46.633 R² = 0.9449
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0
5.0 10.0 15.0 20.0 25.0 30.0 35.0
Intersection Density (number of intersections per km2)
Street Density (length of street network per km2)