Freight transport decarbonization is challenging due to the slow implementation of policies to meet climate goals. This paper analyzes the dynamics of the implementation of freight decarbonization measures. A System Dynamics model was developed and applied to the Brazilian freight system to simulate the use of more sustainable modes and means of transport, including electrification, increased use of biofuels, acceleration of fleet renewal, and modal shift. Significant emission reductions are found in the scenarios combining a shift to alternative modes and a rapid phase-out of diesel vehicles. Even so, the Brazilian freight sector's emission budgets towards limiting global warming to 1.5 °C and 2 °C will be depleted during the current and next decade, respectively. An absolute reduction of carbon emissions before 2050 seems unlikely. Besides confirming the need to study the dynamics of the freight system, the findings corroborate the urgency for stronger actions on freight decarbonization.

As part of the global efforts to mitigate climate change, policymakers are designing measures to reduce the carbon emissions of the freight transport system. As global agreements for decarbonisation specify strict time windows, it is important to understand the speed at which the transport system is capable of changing. Our paper proposes a causal loop diagram based on System Dynamics that qualitatively maps the system’s causal and dynamic responses to five key decarbonisation strategies. As the main contribution, this conceptual model provided a broad overview of the freight system, formed by subsystems that interact with each other through feedback loops, forming its dynamic behaviour. Through this conceptual modelling effort, we can identify the rebound effects of policies over the whole system, which could defeat the desired decarbonisation results. The model pointed out policies and feedback loops as the dynamic levers to promote freight decarbonisation and influence the system’s dynamic responses.