Urban structural and socioeconomic effects on local, national and international travel patterns and greenhouse gas emissions of young adults

The inverse relationship between urban density and greenhouse gas (GHG) emissions caused by driving is well established. However, at the same time the few existing studies have observed higher levels of long-distance travel and particularly air travel in the same densely built parts of urban regions. This may lead to GHG emissions reduction in local travel offset by the concomitant increase in long-distance travel. With this study we aim to identify the main factors involved in differences in local, national and long-distance travel patterns and the resulting GHG emissions, with a special focus on the role of the different urban zones in the Helsinki Metropolitan Area (HMA) in Finland. We used a softGIS survey to collect data on the personal travel of young adults living in HMA. SoftGIS methodology provides the opportunity to obtain detailed spatial data on participants' residential locations, travel destinations, and destination characteristics such as travel modes, frequencies and trip purposes. Special attention was paid to national and international trips, for which data were collected over 12 months, a period long enough to capture actual travel patterns. GHG emissions were assessed with a wide scope life cycle assessment (LCA) approach, including vehicles and infrastructure, and the results were elaborated with a two-part regression model on participation in travel and amount of GHG emissions. The study found that the residential location was associated with travel emissions on all scales, and independently from major socioeconomic characteristics. Residents of centrally located and densely built urban zones have on average lower emissions from local travel but higher emissions from international travel than residents of car-oriented suburban zones, and the association holds true after controlling for income, education level and household type. Differences in emissions from local travel between most central and most suburban zones were almost completely offset by differences in emissions from international travel. International long-distance trips were a dominant source of travel-related GHG emissions in all urban zones, particularly due to plane flights.