CO2 mission benefits of shifting car trips towards sustainable modes in Finnish city regions

Abstract Background Shifting from car use to walking, cycling, or public transport increases physical activity and decreases transport-related CO2 emissions. The potential for sustainable travel remains, however, poorly understood. Methods We exploited Finland's National Travel Survey (NTS) 2021 (n = 8815 respondents in city regions, n = 562 in Helsinki) to estimate how many everyday trips chains by car could be replaced with sustainable modes, i.e. active travel or public transport, based on maximal daily time budget for active travel (45 minutes of walking or 20-35 minutes of cycling) and location in walkable or public transport (PT) zones. For the capital region, Helsinki, the assessment was strengthened by combining the NTS data with counterfactual travel times from the Helsinki Region Travel Time Matrix 2023, with a maximum limit of 60-75 minutes of PT/day or a PT travel duration that is at most 20-50% longer compared to car. The direct CO2 emission benefits of reduced car use were then estimated. Results In our scenarios for Finnish city regions, 24-40% of home-based trip chains by car might be replaced with sustainable modes (5.4-12% with active travel). For the Helsinki region, the corresponding result was 51-67% (9.3-16% with active modes). The emission reductions (from reduced car mileage as driver) were 12-21% and 26-44%, respectively. Conclusions According to our assessment, the potential of sustainable modes to replace car travel and the resulting reduction in CO2 emissions in Finnish city regions are high, even when considering realistic travel behaviour (trip chaining) and seasonality (no cycling during winter). This begs the question of why car travel remains so prevalent. While there are many subjective factors linked to car use, our results indicate that a potential for sustainable travel exists and that coordinated efforts to make car use less attractive might bring major emission benefits, in addition to positive impacts on health and liveability in urban areas.