Simon Choi

Balancing mobility and CO 2 reduction by a mode share scheme: a comparison of Los Angeles and Seoul metropolitan areas

Planning approaches towards the promotion of public transit are widely discussed among planners and policy-makers to reduce the greenhouse gas (GHG) emissions from automobiles and light-duty trucks. However, one of significant side effects created by these approaches is decreased mobility. Since mobility is the critical foundation for the economic development of cities, it is important to balance the level of regional mobility and GHG reduction achieved by a mode share scheme. Using the Cobb–Douglas functions, this paper attempts to identify the best mode share scheme for an urban passenger transportation system to achieve the maximum reduction of GHG emissions, while maintaining the current carrying capacity of the public transit system and regional mobility in the Los Angeles Metropolitan Area (LAMA) and the Seoul Metropolitan Area (SMA). This paper identifies that both metropolitan areas can reduce CO2 emissions by the best public transit mode share. However, it suggests that the CO2 reductions achieved by the mode share adjustment of the areas are noticeably different, indicating that LAMA and SMA can reduce 3.5% and 20.6% of their current CO2 emissions through the adjustment of mode share, respectively. This paper concludes that a sprawled, automobile-oriented city like Los Angeles can achieve limited CO2 emission reductions by adjusting public transit mode share, compared to Seoul, which is a dense, compact city.

Comparative evaluation of temporal correlation treatment in crash frequency modelling

ABSTRACT There is relatively little research dedicated to the evaluation of different temporal treatments on modelling performance. This study proposed two new methods which combined the strengths of linear trend and time-varying coefficients with the autoregressive process and compared their performance with seven other temporal models used in the past. All models generated a similar number of statistically significant variables and close variable coefficients, but different modelling performance. For prediction accuracy, the model which accounts only for autoregressive effect illustrated superior performance in terms of cross-validation and typical assessment, which was based on same data used to develop models. Nonetheless, if the penalized criterion was used, both proposed models outperformed other competing models, indicating their capability to yield similar prediction accuracy with relatively smaller effective number of parameters. This suggests further exploration of models that combine various temporal treatments. Finally, the correlations were also observed among the various modelling assessment criteria.

Effects of urban spatial structure on level of excess commutes: A comparison between Seoul and Los Angeles

This study investigates the effects of the urban spatial structure on the excess commuting rate (ECR) by comparing commuting patterns in two cities having distinctive urban forms, Seoul, Korea and Los Angeles, California, USA. A major difference was found in that commuters working closer to employment centres, or living in single-family detached housing in LA, are likely to have lower ECR, but not in Seoul. Employment suburbanisation, strict zoning separating residence and workplace and single-family housing-dominant low-density suburbs in LA are regarded as the reasons for their lower ECRs, which, by definition, imply relatively shorter actual commute duration and/or longer minimum time. Seoul can learn a lesson from LA for employment decentralisation in order to reduce actual commute time, while land use patterns in Seoul such as high level of mixed land use and compact development can provide policy implications for LA for improving commuters’ accessibility and reducing minimum time.

Environmental Justice for Minority and Low-Income Populations Next to Goods Movement Corridors in Southern California

Southern California is the largest international trade gateway in the United States. The region generates enormous activity involving the movement of local and domestic goods. Given the expected growth in international trade and movement of domestic goods, significant growth in truck volumes and rail traffic to facilitate the reliable movement of goods and to support economic growth is anticipated in the region. As the movement of goods is a major contributor to local and regional environmental issues such as air pollution and health risk, a regional priority is not only to mitigate the environmental impacts of the system involving the movement of goods but also to ensure that, pursuant to Title VI of the Civil Rights Act, equity exists in the distribution of environmental benefits and burdens from federally funded programs involving the movement of goods and projects. Therefore, to prevent disproportionately high and adverse environmental effects and health risks from affecting minority and low-income populations as a result of the movement of goods, the Southern California Association of Governments analyzed the environmental justice implications of the system involving the movement of goods included in the regional transportation plan. The objective of this paper is to identify the minority and low-income populations affected, to analyze their spatial distributions along major truck corridors and freight rail corridors, and to address the environmental justice implications of the system involving the movement of goods in Southern California.