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A rare comprehensive analysis of travel reveals the jumbo-sized emissions impact of longer trips

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A rare detailed analysis of travel reveals the jumbo-sized emissions impact of longer trips

Researchers also devised a new metric to assess which travel shifts offer the biggest climate gain for the behavioral-change pain
July 9, 2024

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Less than 3% of one-way trips are longer than 50 miles, according to a new analysis of travel behavior among people living in England. But these long-distance trips account for more than 60% of total miles and nearly 70% of greenhouse gas emissions from passenger travel.

The findings suggest that initiatives to reduce emissions from transportation should target long trips rather than just focusing on everyday commutes and errands as is more commonly the case. Changing long-distance travel behavior “offers an order of magnitude larger ‘efficiency’ compared to urban travel” in terms of emissions saved per trips altered, says study team member Zia Wadud, a transport researcher at the University of Leeds in the UK.

Long-distance travel has received relatively little attention in studies of transport-related emissions. In the new study, Wadud and his collaborators mined data from two existing sources, the National Travel Survey and the International Passenger Survey, to characterize passenger travel behavior and the associated greenhouse gas emissions for people living in England.

The average English resident made 785.6 one-way trips (excluding only the shortest walks of less than 1 kilometer) by all transport modes in 2017, covering 11,877 miles and causing the equivalent of 2,785 kg of carbon dioxide emissions, the researchers report in the journal Nature Energy.

Residents of England made an average of 21.5 long-distance trips per year, covering 7,278 miles and generating 1,929 kg of carbon emissions – a whopping 69.3% of the total emissions.

 

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“We were expecting long distance travel’s contribution to be quite big, but nearly 70% (and even higher if we consider the higher radiative forcing for aviation emissions) was a tad surprising,” says Wadud.

People made just 3.1 international trips per year on average (0.4% of the total), but these trips accounted for 45.5% of the total passenger miles and 59.1% of carbon emissions because many of them were made by plane, an especially carbon-intensive mode of travel.

Like most countries, the UK excludes emissions from international flights from its carbon accounting under international climate agreements. The more common practice of calculating national carbon emissions from passenger travel based on sources such as national travel surveys and fuel sales is likely to result in a serious underestimate, the researchers point out. In essence the findings reveal a major loophole in international carbon accounting.

The researchers also developed a new metric to help compare different strategies to reduce transport-related emissions, called “emissions reduction sensitivity with respect to trips altered,” or ERSTA. ERSTA is the percentage of emissions saved from making a given change to a subset of trips divided by the percentage of total trips that would be altered.

“The metric identifies where the maximum amount of emissions savings can be secured from the smallest number of trip alterations,” the researchers explain. And generally, long-distance trips are the most efficient way to score big emissions savings.

For example, replacing all car trips under 8 miles with walking and cycling could reduce transport emissions by 9.3%, but would affect 55.1% of all trips and 75% of car trips currently taken. If all car trips over 50 miles were made by train instead, this would save 5.2% of overall transport emissions, but would disrupt only 1.8% of all trips, a much more efficient strategy. If people took road trips within Great Britian rather than flying abroad for vacation, this would reduce total transport emissions by 27.6% while affecting only 0.22% of all trips.

“We should focus on decarbonizing long distance travel, given their large share of emissions and the potentially higher efficiency in terms to least changes required in trip making,” Wadud says. This won’t always be easy, he acknowledges – people might actually find it more painful to give up one long-distance holiday a year than to regularly choose a low-carbon travel mode for their commute.

Still, this new way of thinking about travel behavior could at least open up a conversation about the tradeoffs involved in different policy and habit shifts. And the basic idea of emissions reduction sensitivity could likely be applied to many areas of consumption, the researchers say.

Source: Wadud Z. et al.Understanding the large role of long-distance travel in carbon emissions from passenger travel.” Nature Energy 2024

Image: tripletrouble via Flickr.

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