Scientific research: Sustainable shipping, proven impact
In e-commerce logistics, many claims are made about sustainable shipping. Platforms display green labels, run A/B tests on shipping fees, or publish consumer surveys. But a green label in the checkout is not proof that you actually reduce CO₂. An A/B test that optimises shipping revenue measures commercial impact, not environmental impact. And a survey about what consumers say they want is not a field experiment about what they actually do.
Wuunder takes a different approach. Together with the University of Groningen, we study the impact of sustainable delivery options on consumer behaviour and checkout conversion in live checkout environments with real orders, and calculate CO₂ reduction and fleet impact based on real delivery data. These studies were only possible because Wuunder provided the live checkout environment, e-commerce delivery data and logistics domain expertise. The University of Groningen carried out all analyses and conclusions entirely independently. The results are published in peer-reviewed scientific journals, not in marketing reports.
Why does this difference matter? The EU Green Claims Directive requires that you can substantiate sustainability claims with evidence. Scientific research provides that evidence. An A/B test on pricing does not. Companies that cannot substantiate their claims risk sanctions, from fines to mandatory corrections. Scientific validation significantly reduces that risk.
Research results at a glance
| Category | Metric | Result |
|---|---|---|
| Sustainable impact | CO₂ reduction per shipment | -7.5% |
| Sustainable impact | Fewer delivery vans on the road | ~20% |
| Consumer behaviour impact | Customers choosing GreenChoice (Soxs.co) | 88% |
| Cost and revenue impact | Conversion uplift | +30% |
| Cost and revenue impact | Warehouse peak reduction (Reduced Monday peak) | Up to 30% |
The checkout determines everything
"Decide or Default? How Defaults, Information, and Financial Incentives Influence Sustainable Delivery Choices in a Field Experiment"
Authors: Sanne Wolf, Paul Buijs, Dirk Pieter van Donk
Preprint on SSRN (not yet peer-reviewed), 2026
What is it about?
Can webshops encourage consumers to choose the sustainable delivery option? This field experiment tested three interventions in a real checkout environment at a Dutch e-commerce retailer:
- Default: preselecting the sustainable option in the checkout
- Sustainability information: a label or explanation with the sustainable option
- Financial incentive: €0.50 or €1.00 discount on the sustainable option
What was studied?
A large-scale field experiment over 8 months in a live checkout environment. 14 different conditions were tested, both individually and in combination. This is, to the best of our knowledge, the first field experiment to study consumer behaviour around sustainable delivery options in a live checkout environment.
Key findings:
- Default is by far the most powerful: when the sustainable option is preselected, ~75% choose it (vs. 7% without default)
- Information (labels, explanations) has only a small effect
- Financial incentives (€0.50/€1.00 discount) have a modest effect, considerably less than the default
- Combining all three interventions (default + information + financial incentive) leads to the maximum effect: up to 88% of customers choose the sustainable option. From 7% to 88%, a shift of 81 percentage points
- Consumers are not blind: they do switch to the fast option when it becomes more attractive (urgency, price, delivery time)
Why this matters:
This research proves that checkout design is a powerful tool. Most webshops preselect next-day as default. By simply preselecting the sustainable option, at no extra cost, without complex technology, you achieve the biggest behavioural shift. And that shift translates directly into higher conversion: customers who see a sustainable delivery option that aligns with their values are less likely to abandon the checkout. At Neleman, this led to +30% conversion. GreenChoice in the Wuunder Checkout does exactly this: it automatically preselects the smartest delivery day as default, so customers complete their purchase more often and receive their order more sustainably.
An additional analysis of the 100 largest Dutch webshops found that 62% offer a sustainable delivery option, but only 12% have it set as default. The vast majority let consumers manually opt in, leaving the fastest win on CO₂ reduction and warehouse optimisation on the table.
Sustainable Delivery Choices in the Checkout
Sustainable Delivery Choices in the Checkout
Download the scientific research
From checkout to warehouse to carrier
"From willingness to wait to sustainable impact: Smoothing e-commerce delivery volume peaks"
Authors: Marith J. Zeelenberg, Onur A. Kilic, Paul Buijs
Published in Transportation Research Part D, vol. 156, April 2026 (open access, peer-reviewed)
DOI: 10.1016/j.trd.2026.105349
What is it about?
When customers choose a later delivery day at checkout, flexibility is created. But how do you use it? This study analyses two strategies:
- Concentrating: bundling deliveries to reduce the number of vans needed
- Spreading: distributing deliveries across the week to flatten peaks and minimise fleet size
What was studied?
The research used Wuunder e-commerce delivery data from 2024 (~300 retailers in the Netherlands) to build a mathematical model calculating the impact of order spreading and concentration for urban (Groningen) and rural (Drenthe) regions, scaled to national level.
Key findings:
- Spreading (what GreenChoice does) reduces the required fleet size by ~20%, with only a minimal increase in route distance (<0.1%)
- Concentrating saves at most 3.4% route distance, but requires a 3x larger fleet
- When life-cycle emissions of the fleet are included (production + use), spreading delivers a net CO₂ reduction of 7.5%. Concentrating actually increases total emissions
- The maximum fleet reduction is already achieved at just 25% order spreading
- By spreading peaks (especially the Tuesday peak after weekend orders), carrier delivery quality increases: less overload means a higher percentage of on-time deliveries
Why this matters:
This research scientifically proves that the choice at checkout ripples through the entire chain. The customer picks a delivery day → the warehouse has less Monday peak → the carrier needs fewer vans on Tuesday → 20% fewer delivery vans on the road, 7.5% less CO₂ per shipment. Not by planting trees, but by making the chain smarter.
Smoothing e-commerce delivery volume peaks
From willingness to wait to sustainable impact
Download the scientific research
Customer cases
Neleman: +30% conversion
Neleman, an organic wine brand and Wuunder customer, activated GreenChoice in their checkout. The result: +30% conversion. Sustainability sells, because consumers reward brands that align with their values.
Soxs.co: 88% choose GreenChoice
At Soxs.co, a Dutch socks brand, 88% of customers voluntarily chose the green delivery day when GreenChoice was offered. Not because they had to, but because the choice was there.
Green Claims Directive: substantiate your sustainability claims
From 2026, the European Green Claims Directive imposes stricter requirements on environmental claims. You can no longer simply say "sustainable shipping", you need to prove it.
Wuunder GreenChoice is built on scientific research from the University of Groningen. The studies were conducted with real e-commerce data and in live checkout environments with real consumers. This makes GreenChoice one of the few delivery options on the market whose environmental impact has been independently validated.
This means:
- Scientific evidence helps you substantiate "sustainable shipping" claims to your customers
- You have independent data showing that your delivery options actually reduce CO₂
- You build towards the burden of proof the Green Claims Directive requires
- GreenChoice works via standard carriers like PostNL, DHL and DPD, with no expensive bike couriers or extra shipping costs for the consumer
The research team
The studies are conducted at the Faculty of Economics and Business of the University of Groningen, Department of Operations:
- Marith J. Zeelenberg, PhD candidate, lead author of the order spreading study
- Sanne Wolf, PhD candidate, lead author of the checkout default experiment
- dr. ir. Paul Buijs, assistant professor, supervisor and co-author of both studies
- dr. Onur A. Kilic, assistant professor, co-author of the order spreading study
- prof. dr. Dirk Pieter van Donk, professor, co-author of the checkout experiment
The research was co-funded by the EU Horizon Europe programme (GreenTurn, grant 101147942).
Would you like to know more about a greener shipping process?
We are happy to help you make your checkout and shipping greener!
Frequently asked questions
Q: Is the research independent?
A: Yes. Wuunder provided data; the analyses and conclusions were carried out entirely independently by the University of Groningen.
Q: Is the research peer-reviewed?
A: The order spreading study (Zeelenberg et al.) is published in Transportation Research Part D, a peer-reviewed scientific journal. The checkout experiment (Wolf et al.) is available as a preprint and is still under review.
Q: Can I use the results in my own communications?
A: Yes. The scientific evidence helps you substantiate sustainability claims in line with the EU Green Claims Directive. Reference the source.
Q: Does this apply only to the Netherlands?
A: The studies were conducted with Dutch data. The underlying principles (order spreading, defaults in checkouts) are not country-specific. GreenChoice is currently available in the Netherlands.
Q: How do I activate GreenChoice?
A: GreenChoice is available for Shopware, Magento, Salesforce Commerce Cloud and via the Wuunder API. Contact us at wuunder.com/en/contact.