Multimodality and CO2 emissions: a relationship moderated by distance

Encouraging multimodality as a tool to reduce exclusive car use is seen as a key ingredient of transport policies aimed at reducing greenhouse gases emissions, such as CO2. These policies are based on the assumption that increasing multimodality will contribute to a reduction in emissions. Yet, hardly any scientific attention has been paid to the empirical relationship between multimodality and CO2 emissions. This article addresses this unexplored question at both the individual and trip level using the English National Travel Survey. We find that the level of multimodality is only weakly associated with CO2 emissions. It is only when controlling for levels of travel activity (trip frequency, total distance travelled) that a moderate association in the expected direction is observed (i.e. that higher levels of multimodality correspond with lower CO2 emissions). This suggests that greater levels of travel activity among multimodals tend to offset the benefits derived from their more diverse modal choices. Similar patterns emerge from the trip-level analyses: higher emissions are found for (the typically longer) multimodal trips compared to unimodal trips, even when the only mode used is the car. However, for trips over similar distances, multimodal trips do have lower emissions. While there is merit in encouraging greater multimodality, this can hardly be the only or primary goal of climate mitigation policies in the transport sector. More attention needs to be paid to the key role of high levels of travel activity, and how these could be reduced.