Greenhouse Gas and Climate Change Assessment

Problem: Mitigating the production of greenhouse gas (GHG) emissions and developing strategies to prepare for changes in climate is an important challenge to the transportation planning profession. Purpose: This article identifies the research needed to inform planning practice on the relationship between transportation and climate change. Methods: I chaired the panel that prepared a recent Transportation Research Board special report on research needs related to reducing GHG emissions from the transportation sector and adapting transportation systems to climate change. The report considered needs both for short-term policy guidance and for longer-term research into fundamental relationships between GHG emissions, climate change, and transportation. Here, I review those findings and highlight the questions of greatest importance to planning. Results and conclusions: Additional research is needed on: the range of GHG impacts; how and whether to consider indirect GHG impacts; the sensitivity of GHG emission estimates to variations in critical assumptions; the range of GHG reduction strategies that should normally be analyzed; the level of GHG analysis appropriate for small-scale planning studies; whether to use lifecycle or operational GHG; how to define a preferred scenario; the extent to which reducing GHG emissions affects other goals and priorities; and the costs and tradeoffs associated with options for mitigating GHG emissions. This research should yield policy direction for planning practice on: how to rank GHG reduction compared to other transportation goals; what state or federal requirements for GHG planning will be and how they will relate to regional and local policy goals and constraints; what new information analysis and evaluation should produce; what changes will be needed in data collection, models, and methodologies to yield this; and whether changes will be needed in interagency consultation and public involvement. Takeaway for practice: I recommend a comprehensive research program that addresses these questions, reduces uncertainty about relationships between transportation and GHG emissions, and informs planners and others about the consequences of potential transportation strategies. Research support: None.