Assessing the potential for carbon emissions savings from replacing short car trips with walking and cycling using a mixed GPS-travel diary approach

Andre Neves,Christian Brand

doi:10.1016/j.tra.2018.08.022

Andre Neves, Christian Brand

Open Access

https://doi.org/10.1016/j.tra.2018.08.022

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Abstract

There is a growing recognition of the role that walking and cycling can make in reducing greenhouse gas (GHG) emissions by substituting motorized travel, particularly on short trips. However, there is a lack of evidence at the micro level on the realistic, empirically derived potential of walking and cycling to displace motorized travel and thus reduce GHG emissions. The aim of this study was to investigate the potential for GHG emissions savings from replacing short car trips with walking and cycling and the extent to which high quality infrastructure for walking and cycling may influence day-to-day travel decisions, change the spatial and temporal nature of local journeys and impact on overall GHG emissions from motorised travel.To achieve this aim this study conducted an in-depth observational study of a purposively selected cohort of 50 residents in Cardiff, Wales. Using a mixed-method approach detailed quantitative and qualitative data were collected for each participant using personal Global Position System (GPS) devices, 7-day travel diaries and contextual interviews over two seasonally matching 7-day time periods in 2011 and 2012. GHG emissions for motorized travel modes were derived using journey distance, vehicle technology details and average speeds obtained from the GPS data. The spatial and contextual data provided new insights into the complexities of walking behaviour and factors influencing cycling for everyday travel or recreation, including route choice decisions, activity destinations and the role of the new infrastructure to enable change.We found significant potential of active travel to substitute short car trips, with sizeable impacts on carbon emissions from personal travel. Half of all car trips were less than 3 miles long. Taking into account individual travel patterns and constraints, walking or cycling could realistically substitute for 41% of short car trips, saving nearly 5% of CO2e emissions from car travel. This was on top of 5% of ‘avoided’ emissions from cars due to existing walking and cycling. The evolving high quality walking and cycling infrastructure in the case study area was unlikely to promote a significant reduction in carbon emissions from (displaced) car journeys on its own.The study contributes to the debate on how to achieve stringent low carbon targets in urban transport. The combination of methods for data collection developed and employed in this study also helps to inform future research on the wider environmental impacts of active travel, including ‘co-benefits’ of improved air quality, reduced noise and reduced fossil fuel use.

Highlights

Policies and strategies focused on reducing greenhouse gas emissions from transport have primarily focused on techno-economic, regulatory and pricing measures such as improving vehicle efficiency through technological innovation and standards, fuel switching to low carbon fuels, and CO2e-graded vehicle road taxation and fuel duties (Brand et al, 2013a; Santos et al, 2010)
The purpose of this paper is to explore in detail the potential for CO2e emissions reductions from substituting short car trips by walking and cycling in a real life setting
We examine the CO2e emissions impacts of short car trips based on observed travel activity data, followed by an assessment of the CO2e emissions mitigation potential of walking and cycling

Summary

Introduction

Policies and strategies focused on reducing greenhouse gas (or carbon dioxide equivalent, CO2e) emissions from transport have primarily focused on techno-economic, regulatory and pricing measures such as improving vehicle efficiency through technological innovation and standards, fuel switching to low carbon fuels (electric vehicles, biofuels), and CO2e-graded vehicle road taxation and fuel duties (Brand et al, 2013a; Santos et al, 2010). Due to so called ‘cold start’ excess emissions during the start phase of trips, short car trips have a higher impact per mile on air pollution and CO2e emissions than longer journeys, especially in the winter (Beckx et al, 2010; Brand et al, 2013b; de Nazelle et al, 2010; Vagane, 2007) For these reasons, promoting active travel is increasingly recognised as a key element of low carbon strategies (de Nazelle et al, 2010; Kahn Ribeiro et al, 2007; Lindfeldt et al, 2010; Lovelace et al, 2011; Maibach et al, 2009; Pucher et al, 2011; Rabl and de Nazelle, 2012) with potential climate change, energy, air quality and health ‘co-benefits’ (Haines et al, 2009; Rabl and de Nazelle, 2012; Woodcock et al, 2009)

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