Planning hierarchical urban transit systems for reductions in greenhouse gas emissions

Abstract

Public transit systems with high occupancy can save greenhouse gas (GHG) emissions. However, current transit systems had not been designed to reduce environmental impacts. This motivates the study of the benefits of optimal design and operational approaches to reducing the environmental impacts of transit systems. Transit agencies could resort to level-of-service (LOS) changes, for example, reductions in vehicle kilometers traveled. In previous work, we explored the unintended consequences of lowering transit LOS on emissions from a single-technology transit systems. Herein we extend the analysis to account for a more realistic case: a transit system with hierarchical structure (trunk and the feeder lines) providing service subject to demand elasticity. By considering the interactions between the trunk and the feeder systems, we provide a quantitative basis for designing and operating integrated urban transit systems that can reduce GHG emissions and societal costs. We find that large cities may achieve societal cost as well as emission savings by employing a hierarchical structure, while the non-hierarchical structure may be better for small cities. Highly elastic transit demand may cancel emission reduction potentials, yet for mass transit modes these potentials are still significant. Transit networks with buses, bus rapid transit or light rail as trunk transit modes should be designed and operated near the cost-optimal point when the demand is highly elastic, while this is not required for metro.

Evaluating the Efficacy of Zero-Emission Vehicle Deployment Strategies: The Maryland Case

“…The estimated results showed that the high-ZEV ownership scenarios could reduce the CO 2 Eq emissions per VMT (shown in Table 5) among all counties and the gaps in CO 2 Eq emissions per mile among six road types (shown in Figure 8). In recent years, public transportation's role in reducing GHG emissions has gained renewed attention [34], so convenient and competitive public transport options should be provided to attract more car users to transit, especially in dense metropolitan areas. In counties with high emissions per VMT values, which are rural and where typically more low-income households reside, subsidies can be provided to incentivize ZEV purchasing.…”

Coordination Investigation of the Economic, Social and Environmental Benefits of Urban Public Transport Infrastructure in 13 Cities, Jiangsu Province, China

“…Extensive research on the environmental benefits of PT infrastructure has been conducted to analyse environmental impact and particularly the sustainable development of cities [31]. The use of the PT infrastructure is also related to CO 2 emissions [32], the long-term use of infrastructure construction can shorten the recovery time of greenhouse gases [33], and proper planning of a PT system helps to reduce greenhouse gas emissions [34]. Because the transportation sector is one of the main drivers of carbon emissions [35], it is important to determine the factors that affect carbon dioxide emissions in the transportation sector for the construction of low-carbon cities [36].…”

Heterogeneous Design for Feeder Services of Trunk Transit System

“…Most recently, their network was enhanced by ref. [6] with the consideration of feeder buses' emission cost (as a constraint into the optimization). These two works both assumed a uniform demand over the study domain to simplify the modelling, and all the design variables (i.e., the line spacing and station spacing, service headways) of rail and bus systems are reduced to scalar variables.…”