A recent comprehensive analysis has revealed that initiatives designed to encourage sustainable transportation, such as enhanced public transit options and improved cycling facilities, are largely ineffective on their own in significantly curbing national car usage and associated emissions. These so-called 'carrot' policies, while offering valuable social and health benefits, show limited impact on the broader objective of reducing private vehicle reliance. The research underscores the necessity of integrating these supportive measures with more restrictive 'stick' policies, such as increased costs for driving or limitations on car access, to achieve meaningful shifts in travel behavior and environmental outcomes. This insight is crucial for policymakers aiming to develop more effective strategies for urban mobility and climate change mitigation.

The study, featured in Transportation Research, meticulously examined various non-coercive interventions aimed at promoting alternative modes of transport. These interventions, which include making public transportation more affordable and frequent, expanding networks of segregated cycling lanes, redesigning urban spaces to be more pedestrian-friendly, and implementing behavior-change campaigns, have long been championed for their positive contributions. They undeniably lead to more accessible cities, foster healthier lifestyles, and enhance social equity by providing diverse travel options. However, a key finding of the review is that the overall reduction in general traffic volumes resulting from these measures is remarkably small. This limited effect is particularly problematic when viewed through the lens of urgent climate policy, which demands substantial and rapid cuts in carbon emissions.

One of the more counterintuitive discoveries from the research is that upgrading public transport services, whether through reduced fares, increased service frequency, or faster journey times, does not inherently lead to a decrease in car use. Although these improvements successfully attract a larger ridership to buses and trains, the majority of these new passengers are found to be individuals who previously used other sustainable modes of transport, rather than converting from private car ownership. This suggests that while public transport enhancements are beneficial for existing users and encourage some modal shift, they do not sufficiently disrupt ingrained car-driving habits.

Echoing these findings, Professor Ian Walker commented on social media, highlighting the role of habitual behavior. He noted that for many individuals, driving is an unthinking default choice, and simply introducing new bus routes or train services is unlikely to alter this deeply ingrained pattern. Walker's observation reinforces the study's central argument: to truly unlock the potential benefits of alternative transport options, it is essential to introduce measures that create friction or disruption for existing car journeys. Without such interventions, the convenience and habit of car use often prevail, limiting the effectiveness of 'carrot' policies alone.

Similarly, the review observed that while there is ample evidence confirming that better cycling infrastructure encourages more people to cycle, this increase in cycling does not necessarily translate into a reduction in car traffic. The research indicates that a significant proportion of new cycling trips are undertaken by individuals who previously relied on public transport, rather than those who would otherwise have driven. This phenomenon has been repeatedly documented in European cities, where improvements in cycling facilities have often led to a shift from public transport to bicycles, with less impact on private car use. For instance, data from Stockholm showed that a substantial majority of peak-hour cyclists would choose public transport as their secondary option, further illustrating this trend.

A comparative analysis of Stockholm, London, and Copenhagen further supports this conclusion. Despite Copenhagen boasting a considerably higher rate of cycling compared to the other two capitals, its levels of car travel remain broadly similar. This suggests that the widespread adoption of cycling in Copenhagen primarily serves as an alternative to public transport rather than significantly displacing car journeys. Consequently, the study concludes that even substantial increases in cycling participation have a restricted influence on reducing the total kilometers driven by cars.

The overarching implication of this research is that standalone 'carrot' policies, while beneficial in their own right, are insufficient for achieving meaningful reductions in emissions and car dependency. To effect genuine change, these supportive measures must be complemented by 'stick' policies, such as introducing higher costs for driving or implementing restrictions on car access. As Scot Close aptly summarized on BlueSky, "Just as with alternative sources of energy, alternatives to driving are necessary but not sufficient to get people to change. You also need to add more friction to the old way of doing things.” This integrated approach, combining incentives with disincentives, is deemed essential for fostering a significant and sustainable shift towards more environmentally friendly transportation systems.