Free, persuasive, and green? Yes, yes, and yes.

What unsustainable behaviour needs to change:

Despite growing awareness, private cars and fossil-fuel-based transport still dominate urban journeys. In the UK, transport is the largest emitting sector, responsible for nearly 25% of total greenhouse gases. And yet, most city trips are under 5km—ideal for walking or short enough for a bike ride, yet still overwhelmingly dictated by cars.

Several behavioural barriers hinder the shift towards more sustainable choices:

• Status quo bias keeps people stuck in their routines—driving simply because it’s what they’ve always done.
• Skepticism toward “free” or shared services, often leads people to view them as lower-quality or unreliable.
• Lack of perceived individual impact, makes e people feel that their choices won’t make a meaningful environmental difference.

These psychological factors create real friction, even when sustainable alternatives are readily accessible.

The Green Nudge:

Enter the bike company forest’s London campaign–a smart example of how behavioural science can drive sustainable action. Rather than relying on a single technique, the ad campaign layers multiple interventions to encourage behaviour change:

• The Power of Free: “10 minutes free daily” taps into our natural preference for zero cost. Free offers dramatically increase participation, with one study showing a 69% spike in purchase intent (Ariely, 2008).
• Costly Signalling: forest states it would be £11 million richer without this offer, signaling commitment and credibility– increasing the perceived value of the service.
• Specific Number Bias: “51,899,782 free minutes” seems more believable than a rounded figure. Specific numbers feel more accurate and persuasive. In one experiment, panhandlers who asked for an exact amount—like 17 cents—instead of “spare change” saw a 60% increase in donations (Hey Buddy, Can You Spare Seventeen Cents? Mindful Persuasion and the Pique Technique, Santos & Leve, 1994). 
• Noble Edge Effect: forest presents itself as a purpose-driven brand, aiming to make zero-emission transport affordable. Research shows that when companies act with genuine social responsibility, customers respond with greater trust and loyalty.
• Variable Rewards: A bike placed beneath the ad offers “100 free minutes” via a QR code—but the bike itself isn’t usable. This small surprise creates a moment of novelty, increasing engagement. One study found that people were more likely to complete a task when the reward was uncertain rather than guaranteed (The Motivating-Uncertainty Effect, Shen, Fishbach & Hsee, 2015).

These interventions don’t just promote a service—they help change habits. forest’s campaign is a strong reminder that behavioural science deserves a central place in sustainable marketing. If we want green options to become the default, we need fewer well-intended awareness campaigns and more insight-driven strategies that create real change.

Know any clever ways to make sustainable travel the easy, obvious choice? Share your ideas or get in touch: hello@green-nudges.com

From Phill Agnew, host of the UK’s top marketing podcast “Nudge.” With senior marketing experience at Brandwatch, Hotjar, and Buffer, Phill brings behavioural science to life for marketers and sustainability changemakers alike.