Built systems 171Some metropolitan areas have engulfed ring roads, but most regions have
avoided, or not yet followed, the European approach. Instead, the varied ben-
efits and relatively few shortcomings of a star or spoke design of radial roads
are maintained.
[S3]Excluding Europe and North America, all large cities have ring highways and almost
no small or medium city does(Figure7. 2).
Both city size and geography effects are present for this design, one of the
veryfewsuch cases in the 78 major patterns highlighted in Chapters6 and7.
Ring roads are a response to large metropolitan areas and help stimulate
surrounding urbanization. Or perhaps cities in other geographic areas are copy-
ing Europe and North America where vehicles and traffic first became dense.
Irrespective, large cities (>4 million population) have strong development pres-
sure inward and outward from ring roads, which make rural areas and villages
seem easily accessible to the metro area. In contrast, small and medium cities
are mainly surrounded by nearby connected greenspace. Thus the difference
between large and small/medium cities for average distance of city residents to
connected greenspace is great and growing.
Radial highways, ring highways, and commuter-rail lines
[S4]Large cities tend to have more primary radial roads than do small cities,
and those of large cities are multilane, whereas radial roads of medium and small cities
are about half multilane and half two-lane(Figure7. 3).
Acitysizeeffectisevident. Large cities are directly connected to more satel-
lite cities and distant towns and cities, whereas small cities are more indi-
rectly connected. More radial roads create more strip-development barriers to
regional walking, wildlife movement, and stream/river corridors, and subdivide
the regionintomoreandsmaller sections. Strip development tends to spread
over a wider area. In contrast, with few radials, large segments of greenspace
escape development pressure. Two-lane highways tend to roadkill more wildlife,
but multilane highways cause a greater barrier effect, wider wildlife-avoidance
zones, and more habitat fragmentation, which normally is much more ecologi-
cally serious than roadkills (Formanet al.2003).
[S5]All European and North American cities have at least four primary radial roads, while
cities in Africa and South Asia-Australia average 2--3 radials, many being paved two-lane
(Figure7. 3).
Ageography effect is present. Fewer radial roads mean that larger areas escape
development pressure. Traffic and development are channeled in only two or
three directions from the city.