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What is the carbon emission reduction potential of active travel?

man and child on bike

Connect2 delivered 84 new walking and cycling routes which have transformed everyday travel for local people across the UK

woman with children and pushchair crossing bridge

The Pont-y-Werin bridge linking Penarth to Cardiff was completed as part of the Connect2 project

5 November 2018

This blog was co-written by Dr Andre Neves, Delivery Planner - Active Travel, Transport for London, Dr Christian Brand, Associate Professor and Acting Director, Transport Studies Unit, University of Oxford and Dr Andy Cope, Director of Insight, Sustrans.

New research shows that, taking into account individual travel patterns and constraints, walking or cycling can realistically substitute for 41% of short car trips, saving nearly 5% of CO2e emissions from car travel. This is on top of 5% of ‘avoided’ emissions from cars due to existing walking and cycling.

We are all aware of the need to reduce carbon emissions. The transport sector is a particularly challenging area for carbon emissions. Transport is the only sector in the UK where carbon emissions continue to increase.

The most obvious solution to reducing carbon emissions is to encourage people to replace the trips that they currently make by car with walking and cycling trips. New research from the University of Oxford presents realistic, empirically derived evidence on the potential of walking and cycling to displace motorized travel and thus reduce GHG emissions.

Conducted by the iConnect research group, the study estimates the potential impact on carbon emissions of a shift from driving to walking and cycling in Cardiff.

Sustrans, supported by a grant from the Big Lottery Fund, completed more than 80 new, high-quality walking and cycling routes between 2009 and 2013. These schemes were part of the Connect2 programme

The routes were delivered with a range of partners and extended the National Cycle Network in communities UK-wide. Working closely with Sustrans, the iConnect study group used the Connect2 scheme in Cardiff as a case study area for their research.

We selected Cardiff as the natural experimental setting for this in-depth study, as the site was one of the larger Connect2 projects set in an urban area.

The Cardiff Connect2 Scheme consisted of five elements, including a new traffic-free bridge over the river Ely, opened in 2010, and improved link routes for pedestrians and cyclists (completed between 2011 and 2013) that increased connectivity between Penarth, Cardiff Bay Area facilities and Cardiff City Centre.

The aim of the scheme was to enable commuters to walk or cycle from Penarth into Cardiff (or the opposite way) and local residents to access the leisure and commercial facilities in the Bay and in Penarth without the need to travel by car.

The new paper reflects the lack of evidence at the micro level on the realistic, empirically derived potential of walking and cycling to displace motorized travel and thus reduce greenhouse gas emissions. The aim of this study was to investigate the potential for carbon 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 carbon emissions from motorised travel.

In principle, short car trips are amenable to walking or cycling for most people. However, it is acknowledged that trip characteristics (mainly trip purpose and the complexities of daily travel) influence mode choice to a great extent (alongside built environment, personal and household characteristics). The study assessed the mode shift potential of short car trips by taking into account trip purpose and their complexity; for example, whether a short car trip was part of a tour/home-based trip chain, where a study participant was not the driver, trips that involved escorting to and from a place or shopping trips to large retail areas. Car trips exhibiting these characteristics are not considered to be easily switchable to walking or cycling.

In sum, 59% of journeys recorded by the study were less than 3 miles, and 49% of all car trips were less than 3 miles. The main reasons to drive a car over short distances included time constraints, convenience, need to carry heavy goods, giving a lift to passengers, escorting children or lack of feasible alternatives. Taking into account constraints around trip chains and trip purpose, the study found that walking or cycling could realistically substitute for 41% of short car trips, which is equivalent to 4.5% of all car trips.

How realistic are these figures?​

Firstly, the 41% potential for mode shift can be considered a realistic, if conservative, estimate for typical car drivers. Different assumptions about what trips could be moved from cars to active modes lead to different outcomes. The study excludes the possibility of shifting any trips that are escorting (i.e. taking people to places they need to go to), being a passenger in a car and shopping to large retail outlets. If those were not excluded, the mode shift potential would increase to 69% of short car trips.

Furthermore, by taking a relatively conservative approach to the definition of short car trips (under 3 miles) the study may underestimate both potential and avoided CO2e emissions. For instance, if the analysis increased the threshold to 5 miles (which was well within the range of the study participants who cycled) the share of short car trips that could potentially be replaced would increase by 11.2%. So, on both counts, the estimates are conservative, and much greater savings are possible.

Is this enough to make a difference?​

Climate change is a global problem. A change in travel patterns in Cardiff alone is not going to impact much in a global sense. But the research from Cardiff reflects changes that are possible in cities and towns throughout the UK, and in many cities and towns globally. As the only sector where emissions are increasing, if we could achieve a 5% reduction in levels of carbon emissions from transport, and achieve that fairly quickly, this would be a very positive step forward.

And as well as the considerable potential carbon emission reduction from these trips, when the wider environmental impacts of active travel, including ‘co-benefits’ of improved air quality, increased levels of physical activity, reduced noise and reduced fossil fuel use, the case for supporting walking and cycling is very compelling.

The source paper was written on behalf of the iConnect consortium: Christian Brand, Fiona Bull, Ashley Cooper, Andy Day, Nanette Mutrie, David Ogilvie, Jane Powell, John Preston and Harry Rutter. The iConnect consortium was funded by the Engineering and Physical Sciences Research Council (grant reference EP/G00059X/1). Christian Brand undertook this research also as part of the research programme of the UK Energy Research Centre, supported by the UK Research Councils under EPSRC award EP/L024756/1.

Neves, A., Brand, C. (2018) Assessing the potential for carbon emissions savings from replacing short car trips with walking and cycling using a mixed GPS-travel diary approach. Transp. Res.: Part A: Pol. Practice. DOI: https://doi.org/10.1016/j.tra.2018.08.022.

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