22 Regions and land mosaics
rows, shrub strips, lines of balcony plants, or even a sequence of green roofs
(Hienet al.2007).Roadnetworks
The form and usage of road networks vary widely, from a regular grid
with similar roads and traffic levels to a highly irregular net with a strong hierar-
chyofroads and traffic flows (Formanet al.2003,Forman 2004b). The latter case
has major highways with large traffic flows and tiny lightly used roads. It also
has high-road-density portions and low-road-density portions, and intermixed
straight and winding roads. Furthermore, community planners often discuss
thepros and cons of including cul-de-sac or dead-end roads in the network. All
these options overlie a mosaic of land uses in the urban region, and provide
to-and-from access for residents and business.
Meeting traffic demandis traditionally the watchword for transportation plan-
ners. Sometimes, in response to economic investment or other interests, govern-
ment builds a road to open up a little-used area for development. Perhaps more
frequently, when development and traffic build up, and then demand increases,
government builds or widens a road. Thus road building may stimulate devel-
opment, and development may stimulate road construction. In the former case,
thequestion is whether the value to society of the little-used area, e.g., for pro-
tecting an aquifer or recreational opportunities or biodiversity, is greater or less
than the value resulting from road building. In the case of development stim-
ulating roadbuilding, the question is whether a viable alternative for moving
people or goods exists rather than road construction. Providing alternate modes
(types) of transportation, as well astraffic calming,theslowing and channeling of
traffic by creative road designs and modifications, are widely known planning
approaches.
Topromote a sense of community in neighborhoods, designing the road net-
works ‘‘for 7-year-olds and 70-year-olds” is sometimes advocated. In other words,
provide for attractive, safe walking, playing, bicycling, and meeting places. In
addition, this can be combined with road-network design, at least at a limited
scale, to provide attractive, safe accessibility for visitors.
Road networks are also of major ecological importance (Formanet al.2003,
Forman 2006). The road infrastructure and the traffic on it in an urban region
have effects reverberating widely through the natural systems present. A busy
highway may degrade the avian communities in natural vegetation for hundreds
of meters on both sides, presumably due to traffic noise (Reijnenet al.1995, 1996,
Formanet al.2002).
Probably most roads alter the groundwater levels and surface-flowing waters
locally, but because the network is so dense around metro areas, hydrology is