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 CO 2 emissions by the best public transit mode share. However, it suggests that the CO 2 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 CO 2 emissions through the adjustment of mode share, respectively. This paper concludes that a sprawled, automobile-oriented city like Los Angeles can achieve limited CO 2 emission reductions by adjusting public transit mode share, compared to Seoul, which is a dense, compact city.