Colombia ha avanzado significativamente en la incorporación de autobuses eléctricos (BEBs) en su sistema de transporte público, y ahora es uno de los países líderes en movilidad sostenible en América Latina. Bogotá cuenta con 1.486 autobuses eléctricos de las 1.590 unidades que tiene el país.   

Colombia ha impulsado la descarbonización del transporte urbano a través de la Ley 1964 de 2019, la cual exige la incorporación progresiva de autobuses de cero emisiones en los sistemas de transporte público, con el objetivo de alcanzar el 100% de la flota para el año 2035, con metas intermedias del 60% hacia el año 2031. Adicionalmente, la Ley 2294 de 2023, en su artículo 172, establece un mecanismo de cofinanciación por parte del gobierno central, que permite “la financiación entre un 40 y 70% de proyectos de sistemas de transporte público de pasajeros.” Debido a este mecanismo, otras ciudades del país—Medellín, Ibagué, Santa Marta, Montería, Sincelejo y Armenia—han realizado pilotos con buses eléctricos liderados por la Alianza ZEBRA. 

Este blog tiene como objetivo cuantificar los beneficios climáticos de la transición hacia autobuses eléctricos. Compara las emisiones de gases de efecto invernadero (GEI), expresadas en dióxido de carbono equivalente (CO₂e), a lo largo del ciclo de vida de autobuses eléctricos a batería, a gas natural vehicular (GNV) y diésel, para calcular las emisiones de GEI que pueden evitarse mediante la electrificación de la flota.   

El Consejo Internacional de Transporte Limpio (ICCT, por sus siglas en inglés), colíder de la Alianza ZEBRA junto con C40, ha desarrollado una metodología simplificada de análisis de ciclo de vida. Esta metodología considera las emisiones de GEI producidas durante la vida operativa de un autobús, incluyendo tanto las emisiones asociadas a la fabricación y el mantenimiento (ciclo vehicular), como las derivadas de la producción y el uso de combustible y electricidad (ciclo energético). Más detalles sobre el alcance de este análisis se encuentran en un documento de trabajo publicado en 2024.  

En la Tabla 1 se resumen los datos sobre las características operativas de los autobuses, presentando los promedios de América Latina. La tabla enumera los valores medios de las distancias recorridas anualmente, la capacidad de la batería, el consumo de energía de los BEBs, así como el consumo de energía equivalente para autobuses a diésel y GNV. Estos datos se presentan para los cuatro tipos y tamaños de autobús considerados en este análisis.  

Tabla 1. Características operativas medias de vehículos estándares

En cuanto al chasis y los sistemas de propulsión, tanto de autobuses eléctricos a batería como de combustión interna, se aplicó un factor fijo de emisión de 6,6 kg CO₂e/kg. Se supone que todos los vehículos utilizan baterías de litio-ferrofosfato con ánodo de grafito, con emisiones equivalentes a 58 kg CO₂e/kWh y una densidad de batería de 0,14 kWh/kg.  

La metodología considera una vida útil fija de proyecto de 15 años para BEBs, con un recambio de batería previsto tras siete u ocho años de funcionamiento. Por lo tanto, el cálculo tiene en cuenta las emisiones equivalentes a la fabricación de un BEB y dos baterías. Para mantener un periodo de análisis comparable en los autobuses con motor de combustión interna, que normalmente operan durante 10 años, la herramienta considera las emisiones equivalentes a la fabricación de 1,5 autobuses con motor de combustión interna. 

Las emisiones de mantenimiento se basan en los factores de emisión de autobuses urbanos de 12 m de longitud. Estos factores son de 52,4 g CO₂e por kilómetro recorrido por vehículo (vkm, por sus siglas en inglés) para autobuses con motor diésel, de 70,1 g CO₂e/vkm para autobuses a GNV y de 67,5 g CO₂e/vkm para autobuses eléctricos. 

Las emisiones del ciclo de combustible y electricidad incluyen aquellas generadas por la producción y el consumo de energía utilizada por el vehículo, ya sea combustible fósil, biocombustible o electricidad. Estas emisiones se clasifican en dos fases: del pozo al tanque, que corresponden a las emisiones generadas durante la producción de combustible y electricidad, y del tanque a la rueda, que son emitidas por el tubo de escape durante la combustión del combustible. En Colombia, la red eléctrica es mayoritariamente hidroeléctrica; el país cuenta con una de las intensidades de carbono en generación de electricidad más bajas de la región, según la Agencia Internacional de la Energía.  

La Figura 1 muestra las emisiones de GEI de autobuses eléctricos y con motor de combustión interna durante su vida útil en Colombia. Las barras muestran la composición total de emisiones de GEI por fuente: fabricación del chasis y del sistema de propulsión, fabricación de la batería, mantenimiento, producción de combustible, consumo de combustible, y generación de energía eléctrica. 

Figura 1. Comparación de emisiones de GEI de autobuses de un solo cuerpo (entre 8 y 27 m) para autobuses eléctricos a batería, a gas natural y diésel durante sus vidas útiles en Colombia

Para autobuses entre 8 y 11 m, el BEB emite un 78% menos de GEI que el autobús a GNV y un 76% menos que el autobús diésel. Resultados similares se observan para los otros tamaños de autobús considerados en este análisis, con reducciones de emisiones estimadas para el BEB de 80% al 81%. En todas las categorías, los autobuses a GNV emiten más emisiones que los autobuses diésel, y las diferencias se amplían a medida que los autobuses se hacen más grandes: las emisiones del autobús a GNV son 9% superiores a las del autobús diésel en la categoría de 8–11 m, 21% en la de 12–15 m, 28% en la de 18 m y 31% en la de 27 m. 

Colombia se ha comprometido a reducir sus emisiones de GEI en un 51% para el 2030, como parte de su camino hacia la carbono neutralidad en el año 2050. Para alcanzar estos objetivos, será necesario realizar esfuerzos constantes para reducir las emisiones del sector transporte. Los análisis de emisiones del ciclo de vida, como el que se presenta aquí, son herramientas clave para comprender las fuentes actuales de emisiones y evaluar los beneficios de la transición a tecnologías de cero emisiones. Con esta información, las autoridades pueden diseñar políticas específicas y efectivas para reducir las emisiones del transporte por carretera y contribuir al cumplimiento de las metas climáticas del país. 

Este blog forma parte del trabajo que realizamos en el marco de la Iniciativa ZEBRA.  

The UK Department for Transport (DfT) published the outcome of the consultation on its zero-emission vehicle (ZEV) regulation last month and it generally signals more flexibility and some relaxation of the policy. Let’s take a look at a few reasons to celebrate, a few areas of concern, and a few key points where the yet-to-be-determined details will make a big difference. 

I’ll start with some good news: There are no changes to the regulation’s annual targets for 2025–2030. Regardless of flexibilities, the annual targets set the pace for reductions in emissions, and the targets are staying at 80% ZEVs for cars and 70% ZEVs for vans in 2030. (Here ZEVs include battery electric vehicles and hydrogen fuel-cell electric vehicles, but not plug-in hybrids or vehicles using e-fuels.) This remains a world-leading regulation. The United Kingdom also remains committed to 100% ZEV sales for cars and vans in 2035, as DfT reiterated that there are no exceptions to that target. 

Now, about the newly proposed flexibilities. The regulation includes two “big” ones: (1) transfer of credits for sales of non-ZEVs with lower carbon dioxide (CO₂) emissions and (2) borrowing. Both were extended through 2029, rather than expiring after 2026, as originally planned. In terms of the borrowing flexibility, the limits for cars in the extended years are relatively low—20% in 2027, 15% in 2028, and 10% in 2029 (roughly aligned with the ICCT’s suggestions). All borrowed allowances must be repaid by 2030 and there’s no mention of lowering or removing the 3.5% “interest rate” applied when these are used. Maintaining that interest for the duration of the policy would be critical for encouraging timely compliance and sticking to the United Kingdom’s legally binding carbon budgets. 

A large opening for PHEVs 

The much bigger change is to the ability to earn credit in the ZEV scheme by reducing the average CO₂ emissions of non-ZEVs. This flexibility was originally strictly limited: It was only available in 2024, 2025, and 2026, and these sales could only account for a declining fraction of a manufacturer’s overall ZEV mandate compliance. This reflected the reality that automakers had already invested in hybrids and plug-in hybrid electric vehicles (PHEVs) and couldn’t change their product mixes dramatically in the near term. It allowed them to get credit for the reduced emissions from those vehicles while still requiring a focus on ZEVs in the medium term. Table 1 shows both the original (current) limits and the newly proposed limits on how much manufacturers can use this flexibility for cars as a percentage of their annual ZEV credit requirement.  

As you can see, the consultation outcome allows for a relatively high portion of transfers through 2029. The changes to compliance with the ZEV sales requirement make the overall regulation function more like a technology-neutral CO₂ standard, at least for the next 3 years or so. This is bad news for any certainty regarding future ZEV sales (and hurts the case for investing in charging infrastructure and ZEV supply chains), but the impact on total CO₂ savings from the regulation is difficult to forecast. That’s in part because of the way PHEVs are treated in the consultation outcome.  

Although the United Kingdom is adopting new PHEV utility factors in line with the Euro 6e emission standard, it will allow manufacturers to submit the “old” PHEV CO₂ scores, which are known to be artificially low, for the purposes of complying with the non-ZEV CO₂ score. And it’s not clear how long this will last. When combined with the relaxed limits on non-ZEV CO₂ transfer, this has the effect of making PHEVs a very compelling option for compliance. PHEVs would effectively provide more than 0.5 ZEV credits per vehicle, especially as more longer-range PHEVs are coming on the market. So, while PHEVs don’t count as ZEVs, the regulation now rewards their sale much more than before, particularly in the early years. 

How could this look in practice? The figure below illustrates a scenario in which manufacturers maximize the credit transfers and sell more PHEVs. Here all PHEVs match the specifications of the Volkswagen Tiguan eHybrid, which was the best-selling PHEV in the United Kingdom in the first quarter of 2025, and we assume that manufacturers do not use any borrowing. Manufacturers may also sell PHEVs to comply with the non-ZEV CO₂ standard (which does not require any reductions from 2021–2030), but these cannot be double-counted in the ZEV standard and are not shown in the figure. The new changes to the UK regulation mean that in 2025, hardly any ZEV sales would be required at all, and through 2029, manufacturers could comply by selling more PHEVs than ZEVs. 

Figure 1. Maximum contribution of PHEVs to ZEV mandate compliance before and after proposed changes

Important decisions are still to come

Of course, the ZEV mandate isn’t the only policy influencing the market. If PHEVs don’t receive fiscal incentives or tax benefits, most manufacturers are unlikely to pursue a PHEV-heavy compliance pathway. Thus, whether the flexibilities create a sort of PHEV “lock-in” in the United Kingdom is probably going to depend on when DfT switches to using the new utility factors and how PHEVs are taxed.

Because the consultation remains “subject to further engagement with industry on detailed legislation,” switching to the Euro 6e PHEV utility factors as soon as possible, and no later than January 1, 2028, is an important opportunity to strengthen the policy. It’s also worth exploring whether the limits on flexibilities could be tightened more quickly, and it’s important to maintain the interest rate on borrowing.

Taken as a whole, this regulation keeps the United Kingdom among the global leaders. When thinking in terms of long-term climate goals, the most important opportunity is to lock in the 100% ZEVs by 2035 ambition by finalizing the regulation for 2031–2035. This would provide a solid signal of the medium- and long-term trajectory of the market and ensure that all stakeholders—including vehicle manufacturers, fleets, charging providers, and electricity grid operators—are ready to invest and make the United Kingdom’s ZEV transition a success.

In seeking to advance sustainability in the aviation industry, robust estimates of emissions are essential because they support informed decision-making. Previous ICCT research found that travelers on U.S. routes can reduce carbon dioxide (CO₂) emissions attributable to their ticket by 22% on average, and up to 63%, by choosing the least-emitting flight available.  

Consumers can access emissions estimates for future flights around the world from Google’s Travel Impact Model (TIM), and since 2023, the ICCT has worked with global experts to refine the model through an Advisory Committee that we lead. This partnership established seven core principles and a roadmap to ensure continuous improvement of the TIM for rigorous, transparent, and consistent emissions reporting.  

As the TIM continues to evolve, it holds promise to become the global standard in low-carbon travel search. Here I’ll highlight some of the work behind its development, including the model validation and model selection approaches that enhance its reliability for travelers, airlines, and policymakers.  

Estimating fuel burn is the first step in assessing emissions, and this is challenging due to the variability in flight operations. Emissions will differ based on aircraft technology, weather, and operational practices, and even for the same aircraft and route, fuel burn can vary significantly. The TIM uses the European Environment Agency (EEA) model, which bases estimates on aircraft type and route distance and creates simplified linear relationships. Using the operations of Brazilian airlines in 2019 and the four most commonly used aircraft types, Figure 1 compares the TIM (version 1.8.0) estimates (dashed lines) with real-world fuel burn at the flight level (dots). The large variability reflects the complexity and uncertainty of flight operations, where fuel burn depends on a range of interdependent and sometimes unpredictable factors such as weather and operational practices.
 

Figure 1. Fuel burn versus distance for each individual flight by the four most common aircraft types in the ANAC data in 2019

Model validation

Validation is a quantitative assessment of how well model prediction represents real-world data. For validating the TIM, we needed data from past flights, including fuel burn, ideally at the flight level or at least aggregated by route and aircraft type. The only public dataset identified that met the requirements was the Brazilian Civil Aviation Agency (ANAC) microdata, which provides historical flight data for Brazil since the year 2000 at the flight level. As it’s limited to Brazilian airlines, Google combined ANAC’s public data with private operational data shared by partner airlines worldwide. The aircraft types covered by this sample represent approximately 76% of global flights in 2019 and the validation sample now contains more than 3 million flights. The Google engineering team is continuously working with airlines to expand it to enhance model representativeness and reliability. There is a three-step process to promote reliability: 

1. Data cleaning: We remove irrelevant or incomplete data. 
2. Data aggregation: We group fuel burn data by route, aircraft type, and airline. This is necessary because some private airline data was shared in aggregated form; it contained fuel burn averages by route and aircraft type rather than at the flight level. By aligning our analysis with the level of granularity available in the shared data, we ensure consistency. 
3. Error analysis: We compare the TIM’s estimates with real-world fuel burn using metrics such as median absolute error and error distribution. “Error” is defined as the difference between actual and estimated fuel burn, expressed as a percentage. The actual fuel burn refers to the values in the validation dataset, and estimated fuel burn refers to the TIM estimates. Positive errors indicate overestimation and negative errors indicate underestimation. 

The TIM validation framework uses four key metrics for evaluation: median absolute error (the central tendency of errors), error threshold analysis (the percentage of estimates within different error bounds), distance-based metrics (error trends by route length), and the distance and aircraft error metric (error trends by route length and aircraft type). Details of the metrics are in this technical brief, and Figure 2 illustrates the error distribution curve for the TIM (version 1.8.0) estimates. As shown, the fuel burn is more often underestimated than overestimated by the model. The TIM underestimates the fuel burn for nearly 75% of the airline-aircraft type-route combinations in the validation sample.

Figure 2. Frequency (left) and cumulative (right) distributions of the error in the TIM’s fuel burn estimates when compared with the real-world fuel burn from the combination of ANAC 2019 and private airlines data

Model selection 

The TIM fuel burn estimation was originally based on the EEA 2019 model, which allows users to define only aircraft type and stage length; other significant factors like flight trajectory and payload are not included. Recognizing these limitations, the TIM Advisory Committee explored alternative fuel burn models. 

Nine models were assessed qualitatively (details in the technical brief), and five were shortlisted for detailed evaluation using the validation methodology: EEA 2023, OpenAP, Poll-Schumann, Piano 5, and ICAO ICEC. Because these models vary in structure and require different operational assumptions such as trajectory and payload, we standardized assumptions where possible to be able to compare them. The tested scenarios, based on real-world operations and described in the technical memo, reflect these simplifications. Figure 3 illustrates how the error distributions of these models compare with EEA 2019.  

Both EEA 2019 and EEA 2023 showed narrow error distributions, reflecting good accuracy. However, EEA 2023 consistently outperformed EEA 2019 across key metrics. In contrast, OpenAP demonstrated a wider error spread, indicating lower predictive accuracy for the data used. Intermediate performers, such as ICAO ICEC, Poll-Schumann, and Piano 5, showed moderate error variability. These evaluations showed EEA 2023 to be the most suitable model, and it was adopted in mid-2024. 

Figure 3. Comparison of the error distribution across alternative models

In January 2024, the Advisory Committee incorporated validation into the TIM workflow to evaluate fuel burn model updates. Then, in June 2024, in addition to adopting EEA 2023, they applied a distance correction factor that enhanced the TIM’s accuracy and alignment with real-world operations. The distance correction factor refines stage length inputs by replacing Great Circle Distance with an average route distance based on real-world flight paths. This adjustment reduced the median absolute error from 7.80% to 6.30%. Future Advisory Committee work on second-order fuel burn effects like payload, engine variants, and aircraft age is expected to further improve the accuracy of the TIM and thus further improve its value for a wide range of stakeholders, including the flying public.

Special thanks to Ana Beatriz Reboucas and Jayant Mukhopadhaya for their significant contributions to the research on the TIM website.

There has been a remarkable rise in new battery electric vehicle (BEV) registrations in Belgium over the last few years, with nearly 128,000 units registered in 2024, a 37% increase over the previous year. The growth between 2022 and 2023 was even more impressive, as new registrations grew by 148% (Figure 1). This case highlights how progressive, targeted government policies can help grow the BEV market. Let’s dive into it.

Figure 1. Total new registrations of battery electric cars by year in Belgium

Sources: ACEA and the European Alternative Fuels Observatory  

In 2024, more than one in four new passenger cars registered in Belgium was a BEV (28%). This percentage was significantly higher than in other key European markets, including the United Kingdom (20%), France (17%), and Germany (14%), as shown in Table 1. From 2023 to 2024, Belgium recorded the largest growth in BEV shares among these markets, with an increase of almost 9 percentage points.

Table 1. Shares of battery electric cars in new registrations in key markets  

Source: ACEA  

Companies are vital to these changes. In 2024, company cars accounted for 62% of the over 448,000 new passenger car registrations in Belgium; that’s about 276,000 cars, 40% of them BEVs. In comparison, private individuals registered around 172,000 passenger cars, just 10% of them BEVs. Of the almost 128,000 new BEVs registered in 2024, 87% were by companies. Additionally, by the fourth quarter of 2024, there were nearly 74,000 charging points accessible to the public in Belgium, a 66% jump over the same quarter the previous year.

This isn’t surprising when you consider that a key piece of legislation implemented in Belgium in December 2021 encouraged the uptake of zero-emission vehicles in company fleets. One part of the story in Belgium involves tax deductions for company cars. This approach is gradually discouraging the acquisition of traditional internal combustion engine vehicles (ICEVs) and plug-in-hybrid vehicles (PHEVs) while offering benefits for BEVs and fuel-cell electric vehicles (FCEVs). For ICEVs purchased, leased, or rented by companies between July 2023 and December 2025, the tax deduction will drop from a maximum of 100% until end 2024 to 0% by January 2028 (Table 2). On the other hand, BEVs and FCEVs bought or leased until December 2026 will still benefit from a full 100% tax deduction; starting January 2027, deductible rates on these will also decrease to a maximum of 67.5% by 2031.

The second part of the story is the private use of a company car by an employee. If an employee has the permission by his employer to use a company car for personal purposes, this is a taxable benefit. Consequently, it will be treated as part of an employee’s income and taxed accordingly. The private use of a company car by an employee is a common practice in Europe. In Belgium, the benefit in kind (BIK) is calculated based on factors like car catalogue value, fuel type, carbon dioxide (CO₂) emissions, and registration date. The rates for BEVs and FCEVs have remained stable, while CO₂ emission rates and minimum benefit amounts for ICEVs have become stricter over the past decade. The solidarity contribution, also known as the CO₂ contribution, is the employer’s obligation; this is a monthly charge based on the vehicle’s CO₂ emissions, fuel type, and an indexation coefficient. Since July 2023, an “increase coefficient multiplier” has been added for ICEVs. For example, in 2024, the yearly solidarity contribution for a diesel car with CO₂ emissions of 129 g/km exceeded €1,900, whereas for a BEV it was less than €400.

Figure 2 shows selected policies and monthly shares of new BEV registrations beginning in January 2022. While there are fluctuations among the months, the policies aimed at companies appear to have contributed to a rise in BEV adoption when considering the yearly averages.

Figure 2. Monthly BEV shares in new passenger car registrations in Belgium and selected policy measures