Abstract: Road transportation emissions present a substantial threat to societal sustainability, impacting air quality, environmental conservation, climate change, and the overall well-being and public health of communities. In Latin American countries, the challenge of addressing air pollution is heightened by the rapid growth of the vehicle fleet. This challenge is being tackled by promoting a transition to cleaner technology vehicles and adjusting travel patterns. In Colombia, where a significant portion of both freight and passenger transportation heavily relies on road transport, tackling these emissions is a vital challenge. This study aims to assess future emission trends under various scenarios, considering factors such as vehicle fleet growth, the penetration of cleaner vehicle technologies, and changes in passenger travel behavior, examining their impact on climate change goals. Our emphasis was on estimating annual exhaust emissions following a top-down approach for NO2, PM2.5, SO2, CO, CO2, and BC, originating from road transport in Colombia. The base year for our estimation was 2019, and the prospective scenarios focus on the period 2020-2050. Vehicle activity data were collected from automotive sales websites, while emission factors were derived from COPERT 4.5 for different vehicle types, fuels, and EURO emission standards, using vehicle registration data and relevant local variables such as slopes, fuel quality, temperature, and altitude. We projected the national vehicle fleet using population and GDP variables, employing a trend-based projection and a constrained growth model that considers saturation rates and congestion. Travel behavior was captured by the annual vehicle- kilometer traveled in passenger cars. Four scenarios were defined, and corresponding emissions were reported every five years from 2020-2050. The Business As Usual (BAU) scenario reflects the trend of fleet growth. Scenarios A, B, and C correspond to low, moderate, and high clean vehicle technology penetration scenarios, defined based on a previous study for energy transition in Colombia. In the BAU scenario for 2050, emissions are projected to reach 137 tons of black carbon, 166,112 tons of carbon monoxide, 85,668,826 tons of carbon dioxide, 8,975 tons of nitrogen dioxide, 431 tons of PM2.5, and 5,654 tons of sulfur dioxide. Comparative analysis reveals that scenario A results in a 38% reduction, scenario B achieves a 53% reduction, while scenario C, characterized by high technological penetration and limited fleet growth, attains an impressive 80% reduction in emissions compared to BAU. Regarding compliance with national climate change goals, scenarios A and B fall short, while scenario C successfully achieves a 40% reduction in black carbon by 2030 and barely approaches the 2030 and 2050 greenhouse gas reduction goals by 50% and 90%, respectively. A breakeven analysis reveals that travel behavioral changes offer Colombia better chances to comply with climate change goals. Our findings emphasize the crucial role of high technological penetration in achieving significant emission reductions in Colombian road transportation; however, a change in travel behavior is also essential. Therefore, this study underscores the importance of proactive public policies that encourage the growth of clean technologies and parallel strategies to discourage private vehicle use for a sustainable and climate-resilient future.

Keywords: Road transportation emissions, energy transition in transportation, cleaner technology vehicles, climate change goals, Greenhouse gas reduction