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186 � Transportation Statistics Annual Report 1996
ate or worse were required to submit plans to
reduce ozone precursors by 15 percent from the
1990 base within six years, and by 3 percent per
year thereafter until standards are met. For
severe or extreme nonattainment areas, these
plans must include transportation control measures.
(These measures are defined and
described in the next section.)
Somewhat different rules apply for areas that
are in nonattainment only for CO. Since CO is
so closely linked with highway vehicles, these
rules call for the adoption of TCMs when
growth in vmt exceeds allowable levels. The
sanctions for nonattainment areas that fail to
comply with these rules include withholding of
federal highway funds. (TRB 1995, 16–17) In
addition, the CAAA requires state and metropolitan
officials to demonstrate that all new
transportation infrastructure projects in nonattainment
and maintenance areas contribute to
reductions in emissions.
ISTEA emphasizes integrated planning of different
transportation modes, consideration of environmental
impacts in plan assessment, and
efficient provision of transportation services.
(Gifford et al 1994, and Lyons 1994) ISTEA
highlights the importance of metropolitan areas
as planning units. It places new responsibilities
on metropolitan planning organizations (MPOs),
which represent local governments and public
agencies within the metropolitan areas. To qualify
for federal funds, each MPO must submit a
long-range plan that includes environmental and
intermodal considerations, and a transportation
improvement program (TIP) with policy instruments
and management tools to accomplish the
plan’s goals.
One objective of EPACT is to reduce U.S.
dependence on imported petroleum by promoting
use of alternative fuel vehicles. While
EPACT is not, strictly speaking, environmental
legislation, the effect of its requirements could
be to reduce emissions in metropolitan areas.
Transportation Control Measures
Measures to reduce travel demand, improve
traffic flow, divert travel away from peak periods,
or mitigate harmful impacts of existing traffic
are known collectively as transportation
control measures. Metropolitan transportation
planners have used TCMs in their efforts to
reduce congestion for many years. The CAAA
and ISTEA identified TCMs as important elements
in an overall strategy to reduce emissions
of pollutants from vehicles, especially in nonattainment
areas. Some TCMs that reduce congestion,
such as shifting trips to off peak, may have
uncertain effects on emissions, however.
TCMs are used to encourage: 1) changes in
mode choice—primarily to shift trips from single-occupancy
vehicles (SOVs) to high-occupancy
vehicles (HOVs) or transit; 2) changes in
work day or work week trip scheduling by commuters;
3) flow improvements to reduce congestion
levels without changing the number of
vehicle trips; and 4) changes in vehicle stock to
improve emissions performance. The first two
address the level and pattern of travel demand,
and are therefore known collectively as travel
demand management (TDMs) measures, while
the second two rely on improved systems management
practices and vehicle technology.
TCMs can be implemented through several
mechanisms. Information and education is used
to publicize TCM programs and to prepare
guidelines. Economic incentives may be used to
promote desirable actions or discourage undesirable
activities (see box 8-3). TCM implementation
also can entail investment in public
facilities, the transportation infrastructure, and
systems management. Finally, regulations may
be used to prohibit undesirable actions or
require desired activities.
Table 8-6 classifies 15 kinds of TCMs according
to the four categories of changes and
implementation mechanisms described above.