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previous studies in that the evaluation focuses on the most recent period. Since
the massive construction and expansions of transportation infrastructure in the
US is mostly complete, it is reasonable to believe that the general impacts of the
matured US transportation infrastructures are no longer as significant as they
used to be during their evolving stages. Second, general equilibrium analysis
may find a smaller effects than partial equilibrium analysis because of its
consideration of the whole economy.
Second, the study identifies the relative importance of spatial impacts of
different transportation modes in the US from a multimodal and comparative
perspective. Under the same percentage of increase of public transportation
capital, contribution from highways and streets takes about 49 % of total impacts
of transportation, while the modes of air, water and transit only take 33, 13 and
5 %, respectively (see Fig. 10.4 ). The assessment confirms that the US highway
and streets plays a dominant role among all transportation infrastructure systems
in economic development while public transit and passenger transportation play
the least important role among the systems.
Third, the study develops a SECGE model for transportation impact analysis.
The method integrates spatial econometric estimation with general equilibrium
analysis, which enables researchers to control for the issue of spatial dependence
under equilibrium. This integration is important as spatial dependence has been
observed among some economic sectors through these spatial autocorrelation
tests. Without considering this issue, the elasticity of factor substitution will be
biased in traditional OLS estimation, which then may impair validity of CGE
assessments. This has been confirmed in our comparative analysis using both
OLS estimation and spatial econometric estimation.
However, the differences are only found to exist among the sectoral
productions especially among those sectors where spatial dependence is expli-
citly identified, but not among the aggregate economic outputs. The impacts of
domestic production of different sectors become relative high when the substi-
tution elasticities estimated from spatial econometric models. In particular, a
higher percentage increase of outputs is observed among transportation sectors
including truck, air, transit and water when a 10 % increase of overall transport-
ation capital is implemented. The increase of output could possibly be explained
by the inclusion of spillover effects of transportation infrastructure under
SECGE, which could not be measured in traditional CGE models.
Given the fact that the study focuses on the national level, the spatial impacts
do not vary significantly as spatial dependence may not be a serious issue at such
a highly aggregate level of analysis. Although the differences are relatively
small in this aggregate case study, implications for more sensitive disaggregated
regional models are clear, and will be investigated in the future.
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