TRAFFIC ACROSS THE BRIDGE - Bridges - page 109

opening of a new car-manufacturing plant escalates population growth far
beyond our expectations. Alternatively, whole industries can die in a region,
as steel industries did a few decades ago in parts of the US, causing huge
out-migrations. These uncertainties are the very reasons we call this process
“forecasting” rather than “prediction.”
As model makers, we should also grapple with changing distributions
of land uses. The growing immigrant neighborhood, the new food-distribu-
tion warehouse, and the office buildings and shopping malls all exert new
demands on roads. We can try to anticipate by tracking new building per-
mits, real estate prices (increased prices indicate more pressure to build or
rehabilitate), and major real estate announcements, such as the decision to
build a new airport or 50-story hotel complex. If we follow good forecast-
ing practice, we will recognize the uncertainties and provide low, moderate,
and high forecasts (say for population change) and let the decision makers
decide which they most believe.
The Need for Scenarios
Not the least of the challenges when it comes to forecasting urban futures
is a subtle paradox. The local officials, business people, and leading citi-
zens who now want the forecast (say on the future growth in density of
a residential neighborhood) are themselves in part responsible for helping
bring about the outcome in question. That is, the people who want future
land use information are in part now responsible for making the decisions
that generate the future. For example, public officials may be responsible
for changes in ordinances to permit denser housing; land developers may
be ones to invest in the building of new housing; and activists may oppose
growth that cuts down trees and increases local traffic.
This is why public participation in the process called scenario build-
ing has become so important to land use planning. Representatives and
stakeholders from the region are asked to attend meetings and take part
in exercises with urban planners to foresee the kind of city they would
like to have. Ideally, their preferences get worked into regulations guiding
future growth. The regulations may, for example, determine where tall office
complexes or dense residential projects will be permitted. What is important
in such scenario efforts is not to get random public guesses and opinions
about what the future will hold (an aggregation of uninformed opinions
won't do much good) but to get citizens' involvement in present decisions
on the locations of future land uses. These present decisions lend a measure
of stability to future trends and improve forecasting.
Then again, economic conditions change and opinions shift. The
mayor and council members may now commit to a land use plan, but next