Does Carpooling Reduce Carbon Emissions? The Effect of Environmental Policies in France

This note summarizes the published research paper by Olave-Cruz et al. (2025)

Motivation

Reducing carbon emissions from road transport is essential to achieving climate goals. According to the French Ministry for the Ecological Transition, road transport is the largest emitting sector in the economy, accounting for 28.7% of total carbon emissions in 2020. Moreover, more than half of these emissions come from individual vehicles, highlighting the urgent need for effective strategies to meet climate objectives.

Carpooling has emerged as a promising innovation to reduce carbon emissions from road transport. These services are offered by private digital platforms that act as intermediaries between drivers and passengers. Car travelers offer seats in their vehicles in exchange for sharing the monetary costs of the trip. Carpooling is often considered an environmentally friendly alternative, as sharing the same mode of transport can potentially reduce carbon emissions. However, by lowering overall travel costs, carpooling might divert travelers from cleaner modes of transport (modal shift effect) or increase the frequency of trips made by existing car travelers (volume effect). Consequently, there remains significant uncertainty regarding the conditions under which carpooling effectively reduces carbon emissions.

The objective of this research is twofold. First, it aims to develop a baseline metric for evaluating carpooling’s potential to mitigate carbon emissions. This metric is based on the principle that carpooling mitigates carbon when the emissions from the trip are lower than the combined emissions of all travelers’ alternative modes of transport in the absence of carpooling. Second, it empirically examines the impact of various public policies and strategies on this baseline metric and, ultimately, on their potential for carbon mitigation.

Methodology

The baseline metric for evaluating carpooling’s potential to mitigate carbon emissions is defined as a threshold in the occupancy rate of carpooling trips. This measure is robust because the occupancy rate reflects travelers’ preferences and, consequently, the emissions of alternative modes of transport. Using publicly available data on car emissions coefficients and travelers' preferences for alternative modes, we calculate the minimum carbon mitigation occupancy rate in France.

Leveraging a unique dataset from the leading carpooling platform in France, this research investigates the impact of various mechanisms on the baseline metric. The study focuses on two primary levers that align closely with common policies aimed at reducing CO2 emissions: fluctuations in the monetary trip costs for cars and incentives for drivers to travel as passengers in carpooling, users that we refer to as switchers.

To measure travelers’ responses to fluctuations in monetary trip costs, we combine geolocated data on fuel stations with the city of origin for each trip. This allows us to assess how the number of seats offered and requested in carpooling changes when fuel prices increase, which is commonly referred to as the elasticity of supply and demand. In the second part of the analysis, we use these responses to fuel prices to study three key mechanisms with the potential to enhance occupancy rates: the implementation of a carbon tax, subsidies targeting new travelers, and the transition of drivers to passengers.

Key results and recommendations

The findings suggest that a 10% increase in diesel prices is associated with approximately a 3.6% rise in seats offered, a 4.8% increase in seats requested, and a 5.2% increase in the total number of seats booked. Our analysis reveals that increases in fuel prices significantly boost the demand for carpooling, leading to higher occupancy rates. Moreover, the evidence shows that novice users exhibit more pronounced effects compared to their more experienced counterparts. This finding has significant policy implications, highlighting the potential effectiveness of strategies aimed at attracting novice users to carpooling services.

The study also evaluates the impact of the French carbon tax on carpooling activity. While the current tax has led to an increase in carpooling participation, the stagnation of the tax rate since 2018 has limited its effectiveness. In other words, the failure to enforce the policy resulted in an average loss of almost 53 thousand additional seats booked between 2019 and 2022. Beyond carbon pricing, strategies that encourage drivers to become passengers show promise for further reducing carbon emissions. Simulations indicate that incorporating new users from solo-driven cars could save more than 60 tons of CO2 every day. Finally, the findings demonstrate that subsidies, such as those provided through the French “Certificat d’Économie d’Énergie” scheme, could be more effectively tailored by focusing on occupancy rates and incentivizing switching behavior.

Policy implications and conclusion

This paper emphasizes the pivotal role of occupancy rates—the number of passengers per trip—as a key metric for evaluating carpooling’s potential to mitigate carbon emissions. Based on these indicators, estimates of the occupancy rate in France suggest that carpooling can serve as a practical and effective strategy for mitigating carbon emissions, given current preferences and travelers’ preferences over alternative modes of transport. However, solo driving remains a predominant condition in carpooling, underscoring the need for fine-tuned policies to further reduce carbon emissions from this mode of transport.

Building on the viability of carpooling as a potential strategy to reduce carbon emissions from road transport, this research examines how policies affecting monetary trip costs and promoting switchers can boost occupancy rates. A key finding highlights the sensitivity of novice users to fluctuations in trip costs, suggesting that policies aimed at attracting new passengers could yield substantial environmental benefits. Moreover, the results on carpooling elasticities reflect users’ decision to choose carpooling over driving alone. Notably, passengers benefit from lower cost shares compared to drivers. Finally, this study demonstrates that policies and strategies designed to encourage drivers to become passengers can lead to significant reductions in carbon emissions.

This study provides crucial evidence that carpooling, when supported by well-designed economic and environmental policies, can serve as an effective tool for reduc¬ing carbon emissions from road transport. By leveraging insights into user behavior, and fine-tuned monetary incentives, policymakers can enhance the environmental benefits of carpooling and move closer to achieving climate objectives. The findings reported here not only inform the current policy debate but also pave the way for innovative strategies to make carpooling a key player in sustainable transport systems.