Decarbonizing the Transportation Sector: A Review on the Role of Electric Vehicles Towards the European Green Deal for the New Emission Standards

Abstract

The transportation sector has a significant impact on climate change, as it is responsible for 20% of the global greenhouse gas (GHG) emissions. This paper evaluates the role of electric vehicles (EVs) in achieving Europe’s ambitious target of carbon neutrality by 2050. The limitations of internal combustion engines (ICEs) along with the recent advancements, such as Euro 6 standards, are examined with a pseudo–lifecycle analysis (pseudo-LCA). While ICEs remain cost-effective initially, their higher long-term cost and environmental impact make them unsustainable. The benefits of EVs, including high energy efficiency, minimal maintenance, and reduced GHG emissions, are stated. However, challenges such as range limitations, charging infrastructure, and the environmental cost of battery production persist. Hybrid electric vehicles (HEVs) are highlighted as transitional technologies, offering improved thermal efficiency and reduced emissions, enhancing air quality in both urban and rural areas. The analysis extends to the use of alternative fuels, such as bioethanol, biodiesel, and hydrogen. These provide interim solutions but face scalability and sustainability issues. Policy interventions, including subsidies, tax incentives, and investments in renewable energy, are crucial factors for EV adoption. As EVs are pivotal to decarbonization, integrating renewable energy and addressing systemic challenges are essential for a sustainable transition.

1. Introduction

The transportation sector is considered one of the most energy-demanding areas, currently responsible for approximately 20% of the global greenhouse gas (GHG) emissions [1]. Last year, transport faced the largest increase in GHG emissions, with over 301 megatons of carbon dioxide (CO_2eq), a relative increase of 3.7% (shown in Figure 1), as stated in the EU report [2].

The need for green energy has led to applications serving several policies, including the 2019 European Green Deal. This pact aims for a net-zero emissions outcome by 2050 as a requirement to minimize the amount of existing pollution [2]. Regarding the transportation sector, a 90% emission reduction is imminent; thus a fundamental overhaul is required via a transition to cleaner means [3]. For this reason, automakers are obliged to reduce their fleets’ average carbon emissions by 37.5% by 2030, in commitment to global policies for lessening the effects of climate change. To reach the goal of zero GHG emissions by 2050, the electrification of passenger cars, buses, and heavy-duty trucks is required.

Internal combustion engines have evolved throughout the years in Europe, with innovative standards such as Euro 2 up to Euro 6 [4]. Direct injection, more versatile lubricants, and advanced spark ignition have increased the thermal efficiency (TE) of the Otto 4-stroke engine to 25–35%, resulting in reduced pollution emissions. Diesel engines can deliver up to 45% TE, although these values can be obtained under optimal load. A mean value of 30% and 40%, respectively, is sufficient [5]. However, emissions are still high, especially in urban areas. Conditions such as idling in traffic lead to increased fuel consumption and a significant decline in air quality, contributing to over 60% of moving-state emissions [6].

The utilization of ICE-powered vehicles presents additional drawbacks, including the need for annual maintenance and increased failure rates due to the exploitation of several complex parts, including the catalytic system that filters dangerous gases during combustion, plus the plethora of sensors and actuators [7]. Regarding the pseudo-lifecycle analysis (LCA) method, even though the purchase value is lower than that of hybrid or electric vehicles, the increasing fuel price and spare parts costs add over 10% to the end value. Hence, using a conventional vehicle becomes more expensive, especially in the long term.

The switch from conventional to electric vehicles is a critical step for carbon neutrality and enhancing air quality, as they introduce great advantages, including:

• simpler infrastructure and low maintenance requirements;
• low to zero energy cost, as renewable sources can be used for charging;
• a three times more efficient powertrain compared to ICEs;
• comfortable driving with minimized noise and GHG emissions [8].

EVs utilize an electric motor as the propulsion system, powered by a high-voltage lithium battery pack, while a 12 V auxiliary battery is responsible for secondary loads such as lights and the multimedia system [9]. The climate control (CC) module, which is highly efficient, is directly driven by the high-voltage battery and consumes over 15% of the total load, even though the driving range is compromised with extended CC use. It is expected that EVs will account for 50% of the global automobile market by 2050, and the literature shows a very promising future in the context of minimizing GHG emissions [10]. However, for massive adoption, such limitations as range, limited battery lifespan, high toxicity levels from mining, and the availability of public chargers in central spots should be addressed [11,12]. A direct comparison between the two technologies is depicted in Figure 2.

The shift to massive fleet electrification has been massively studied, and the results show that even if EV sales increase rapidly, the impact on the overall economy and the supply chain will be minor [13]. This is affected by the following factors:

• the increasing cost of such metals as lithium, cobalt, and aluminum;
• massive diesel utilization required by trucks at the mining sites;
• the increased mass of an EV requires more power to ensure high performance compared to an ICEV (internal combustion engine vehicle).

To fill this gap, hybrid electric vehicles (HEV) have stepped up as a transition point. HEVs have a similar operation to a typical ICEV, with the addition of an electric motor, a low-capacity lithium battery, and an automated transmission. In urban areas where low speed is needed, the electric motor can sufficiently provide the energy required to move the vehicle, while under high loads, it acts as an auxiliary power source to assist the ICE, reducing emissions by 25% [14]. Therefore, thermal efficiency is enhanced (over 40%), with the median fuel consumption between 4 to 5 L per 100 km and a small price increase over the ICE variant. This characteristic can also relate to health issues as increased air pollution causes problems such as headaches, cancer, and potential lethal damage to the brain and other organs, summarized in Figure 3 below [14,15].

It is becoming evident that even though internal combustion engines have greatly evolved over the last century, they still represent a key factor in escalated global warming [16]. Hybrid vehicles reduce the impact of gasoline and diesel engines, but they are not adequate to fulfill the zero-carbon target set for 2050. Electric vehicles can reduce emissions and provide cleaner and eco-friendly transport means, but the issues mentioned above must be addressed and will be discussed further in this work.

The manuscript is structured into four main sections. Section 2 describes the technology of internal combustion engines along with the different fuels applied. In the Section 3, electric vehicle configurations and advantages are summarized. The next section focuses on the comparison of these two technologies. In the Section 4, a summary of the findings of this study is presented. In the Section 5, conclusions about the impact of electric vehicles and the necessary steps for the transition to complete fleet electrification are stated.

2. Internal Combustion Engines

2.1. Evolution of ICEs

Internal combustion engines have played a key role in technological growth through the years, powering conventional vehicles, trucks, and aviation by exploiting different thermodynamic cycles for each case [5]. The ICE is a heat engine where the combustion of a fuel and air mixture is engaged through self-ignition (diesel) or spark ignition (gasoline) via a 4-stroke cycle; intake, compression, combustion, and exhaust [16]. The combustion, or the power stroke, is where high-pressure gases expand to move the rotor and, finally, the wheels. Gasoline engines have a typical efficiency of 25–35% while diesel engines can achieve up to 45% total efficiency [17].

Typically, every day, over 50 million barrels of fuel—petrol and diesel—are required to run ICEs across the globe [17]. To reduce the pollution associated with combustion, technological advancements such as modern injectors and lambda sensors are utilized to ensure that the mix is stoichiometric. If the mixture is lean, performance is limited, while the mixture being too rich leads to unburnt fuel and, thus, excess emissions [15]. Accordingly, the use of turbochargers allows engines with minimized displacement (downsized) to provide extra power as they can achieve higher compression ratios, leading to increased fuel economy.

In addition, the introduction of certain subsystems has led to significant gains for fuel economy and eco-friendly transport, including [18,19]:

• an advanced catalyst system with a precatalytic converter to convert 90% of toxic emissions such as carbon monoxide and nitric oxide to CO₂ and NO_X, respectively;
• an exhaust gas recirculation (EGR) valve that returns a portion of the exhaust gases into the engine cylinder for feedback, thus reducing NO_X and enhancing power as pumping losses are reduced;
• gasoline and diesel particulate filters (GPF/DPF) that capture excess soot and other toxic gases diverted by combustion;
• the use of urea, injected into the exhaust to minimize nitrogen oxides in diesel engines.

The main parts of a gasoline exhaust system are presented in Figure 4 [17,18,19].

By exploiting these techniques, the carbon monoxide and nitrogen oxides produced are reduced by 85% and 90%, respectively [18,19,20]. Carbon dioxide emission savings are negligible, as modern catalytic converters are not designed for that purpose. Lately, low-viscosity oils such as 0w16 and electrically driven water pumps have contributed to reduced engine wear and temperature, allowing the employment of a leaner mixture, which further enhances fuel economy and efficiency [20]. It is worth mentioning that there are certain downsides to the use of low-viscosity oils, as they are more volatile, leading to increased oil vapor emissions, while after use, they must be recycled in the same manner as other modern lubricants. These measures make diesel almost irreplaceable for heavy use, especially in trucks, mainly due to the lower cost, maturity, and highly available infrastructure, as refueling is fast and widely accessible [21]. Hence, it is not expected for the European Union and other countries, such as the USA, to ban ICE trucks before at least 2035 [22].

Based on [23], with the current electricity mix, conventional vehicles come very close to their EV counterparts in CO₂ emission. For example, the carbon dioxide coefficient for every kWh produced in certain countries accounts for:

• A high average of 380 g/kWh for Germany.
• A median of 370 g/kWh for the United States.
• Increased emissions for China at 582 g per kWh.
• A very low standard of 30 g CO_2eq per kWh for Norway.

Additional data for the equivalent carbon dioxide emissions for various countries are displayed in Figure 5.

A typical EV with an energy consumption of 20 kWh/100 km will emit from 0.9 to 12 kg of CO₂, while a conventional vehicle with a gasoline engine that requires 6 L/100 km produces 12 kg of carbon dioxide; hence, these values are comparable. However, if the electricity mix is altered by exploiting renewable energy sources at every building, the internal combustion engine falls behind in the goal of green transportation [24]. The surplus electricity can be used for producing hydrogen as a backup energy source.

Using surplus electricity to produce hydrogen as a backup energy storage is a promising solution for managing excess renewable energy and ensuring grid stability [21,25]. This approach, known as Power-to-Hydrogen (P2H), is part of a broader Power-to-X (P2X) strategy. The process begins with electrolysis, where surplus electricity from sources such as solar or wind power is used in electrolyzers to split water into hydrogen and oxygen.

Once produced, hydrogen can be stored in various forms, such as compressed gas, liquid hydrogen, or metal hydrides, allowing for flexible energy management. When renewable energy generation is low, the stored hydrogen can be converted back into electricity using fuel cells or gas turbines, providing a reliable backup power source.

2.2. Alternative and Synthetic Fuels

With the emergence of synthetic fuels, ICEs can become greener and more sustainable for the near future, before the complete adoption of electric vehicles. Such fuels as biodiesel, ethanol, biogas, or common available types such as liquified petrol gas (LPG) and compressed natural gas (CNG) can be used as alternatives to petrol or diesel [26]. Studies [24,27] showed that by increasing the incorporation rate of biofuels such as E85, CO₂ emissions can be reduced thoroughly with small adjustments to the powertrains. Alternative fuels incur a higher cost and have a lower volumetric energy density than diesel or petrol but produce over 35% less particulate matter and carbon emissions [28].

The operation of an ICEV was tested on three different routes, showing that operating in city traffic doubles the emissions compared to highway driving [10]. In addition, the driving style is the most important factor regarding CO₂ emissions as dynamic driving, especially at short distances, stresses the engine and other parts such as brakes, tires, or batteries (in case of an EV) extensively [29]. Aggressive driving behavior leads to extra maintenance costs or possible failures, as well as increased fuel consumption and GHG emissions, which overstep the modern Euro 6b and 6d standards [30].

Biofuels are considered a viable alternative fuel in blends such as B10 with 90% petrol and 10% biofuel or B20 at a ratio of 80% to 20%, respectively. In a study in Malaysia, these 2 blends were tested using widely available palm oil as biofuel in a typical 2000 cc ICEV and a two-wheeler [31]. The results showed that such a transition was not highly effective, as emissions from biodiesel production were close to normal diesel combustion, 2.68 kg CO_2eq/L compared to 3 kg CO_2eq/L, while palm oil production needs to be enhanced, leading to extensive land utilization.

The two most common biofuel types are bioethanol and biodiesel, while other e-fuels including green diesel, obtained by pyrolysis and hydrogenated vegetable oils (HVO), can be employed [32]. Bioethanol is usually found in 5%, 20% and 85% proportions as the E5, E10, and E85 fuels, with only the last two being compatible with modern vehicles. For the hydrotreatment, hydrogen is utilized in the production process, and must be produced by renewables, otherwise the application is not feasible [33]. With the use of these neutral fuels, emissions can be reduced by up to 40%, while HVOs’ high energy density makes them suitable for application in aviation. In 2025, bio-based components will account for 10% of the fuels used in Europe [32]. The need for biofuel utilization with respect to pollution is illustrated in Figure 6 [34].

Another study tested boron-enriched gasoline in anhydrous, acid, and pentahydrate forms, as well as naphthalene and acetone as additives [35]. The results suggested that boric mix utilization increased torque and engine power, while CO₂ and NOx emissions were reduced. However, carbon monoxide and hydrocarbon emissions increased. Naphthalene does not offer any major advantages, whereas acetone induces lower fuel consumption with higher emissions; hence, these fuels are, so far, impractical for use in internal combustion engines.

LPG is currently one of the most renowned alternatives to petrol, used in over 4% of passenger cars and legalized in most European countries since the 1980s [32,36]. It is composed of propane (C₃H₈) and butane (C₄H₁₀) in different ratios. In summer, propane comprises 60% of the mix as it evaporates at lower temperatures, ensuring proper vaporization and, thus, smoother ignition. In winter, butane accounts for 60% of the mixture to avoid excessive evaporation and increase the total energy content per liter due to butane’s higher calorific value [35]. LPG is mainly extracted from natural gas through fractional distillation or from crude oil refining. Since the demand and taxes are lower than for petrol or diesel, LPG pricing is consistent. As its energy density is lower than that of petrol, an additional 10% fuel rate is added to the combustion chamber to meet the stoichiometric ratio standards of modern engines [37].

LPG systems can be implemented to conventional petrol engines without any modifications; hence, many companies provide plug-and-play kits for different car brands. A study [38] showed that mixing LPG with 5% hydrogen further reduces GHG emissions by 25–30% at various ambient temperatures. The only drawback of LPG systems is the expansion of the fuel in the heat, so the auxiliary fuel tank that is installed, usually in the trunk, must be filled maximum to 80% capacity [32]. The complete layout of a typical LPG installation with any common kit includes [39]:

• An auxiliary tank along with the fuel pump and lines.
• A pressure regulator and fuel injectors.
• A control module connected in parallel with the main one via CAN bus.

Figure 7 demonstrates the installation kit from [39]:

Natural gas is another acclaimed fuel that can be integrated into a conventional vehicle with a plethora of benefits [40]. It is found in two forms: liquidized (LNG) and compressed (CNG), with the latter already employed in several internal combustion engines, both by the manufacturer and as an aftermarket layout in dual-fuel mode [41]. It comprises methane in a 96–98% ratio, has a significant octane rating of 130, and as it is extremely vaporizable, a highly homogeneous mixture is formed [42,43]. As the mix burns at a lower temperature, nitrogen oxides are reduced by over 75% and carbon monoxide decreases by 25% with cold starts having an insignificant effect on emissions. This is the reason why CNG is considered an ideal fuel for implementation in conventional vehicles, being the most efficient, economical, highly applicable, and widely available fuel with minimum GHG emissions [44]. The main drawback is that CNG is stored in gaseous form in high-pressure steel tanks, so their storage requires extra space, which natural gas fuel stations cannot provide [45]. The complete layout of a typical indirect CNG system is demonstrated in Figure 8.

Hydrogen is gaining popularity as a fossil fuel alternative due to the lower environmental impact it causes. It is mainly produced from fossil fuels, but it can be extracted from water through electrolysis powered by renewables [46]. It is the most abundant element on planet Earth, with a calorific value of 120 MJ/kg, so it can be used in ICEs at a fuel ratio of 34 to 1, with high diffusivity and 20% more power. In addition, the increased auto-ignition temperature (585 °C) allows for higher compression ratios (CR) and increased efficiency, but with an increase in nitrogen oxides in the exhaust and engine knock [47]. Most studies suggest that hydrogen should be applied as an additive to gasoline or diesel engines through direct injection to offer the characteristics of a dual-fuel layout. Hence, high compression ratios that will let engineers surpass the 50% efficiency mark for ICEs with proper engine design are necessary [48]. The lifecycle of hydrogen for internal combustion engines is presented in Figure 9 as a workflow [49].

3. Electric and Hybrid Vehicles

3.1. Hybrid Electric Vehicles and Fuel Cells

After the 2000s, electric and hybrid electric vehicles have emerged as a replacement to old and highly polluting automobiles and trucks [50]. Hybrid electric vehicles (HEVs) utilize an electric motor as a standalone propulsion unit or along with an internal combustion engine (ICE) through a constant variable transmission (CVT) system. Since the ICE operates within its optimal speed, the system is more efficient (up to 45% total thermal efficiency), with significantly fewer emissions and power losses. In addition, fuel economy is improved by 65% compared to ICE-only vehicles as regenerative braking is employed, retrieving energy by braking and transferring it to the high-voltage battery, with a typical capacity of 740–1000 Wh [51].

There are two additional types of HEVs available, mild hybrid EVs and plug-in EVs (PHEVs) [52]. Mild hybrids incorporate a battery with a lower capacity than a typical HEV and an electrical motor standardized as a “48-Volt” layout with minimal configurations. This system works as an auxiliary source to the ICE to help in high-load situations such as cold starts or heavy traffic, providing a 15–20% improved fuel economy. It requires a complex energy management system with optimized control, and it is considered a small intermediate step toward decarbonization.

PHEVs operate similarly to pure hybrids and consist of a generator, an electric motor, a high-voltage battery, and a CVT [53]. The main difference is the higher battery capacity of 10–15 kWh, providing the ability for external charging. Thus, this configuration can operate purely on electricity for a typical range of 75 km, prioritizing the use of the electric motor over the ICE. When the battery capacity drops below a certain point, PHEVs are still functionable as a pure hybrid, with the renowned fuel efficiency described above. They combine the advantages of both worlds, even though their price is still high—currently, a median price of €40,000, and charging facilities are still inadequate [54].

FCEVs use fuel cells to produce electricity through a chemical reaction to power the electric motor and store excess energy in the battery [55]. They offer many advantages such as zero emissions, fast refueling, and high efficiency, while their only byproducts are water and heat. One study demonstrated that the total efficiency could reach over 96%, while the available range of a typical FCEV is within the range of 430 km [56]. However, still expensive fuel cells due to the high cost of platinum and palladium used as catalysts, the durability of the system, and high hydrogen cost are the reasons of low FCEV adoption, as they currently appear to be an unfeasible option.

As demonstrated, hybrids have a major impact in mitigating emissions with only a small change in driving style, allowing the user to benefit from the lower fuel consumption that HEVs provide. Thus, a unified framework to encourage manufacturers to invest in R&D while offering financial incentives for potential buyers is necessary [57,58].

Layouts of the most common HEV, PHEV, and fuel cell configurations are presented in Figure 10 [51].

3.2. Battery Electric Vehicles

Electric vehicles have emerged as the main technology to reduce GHG emissions leading to the greenhouse effect with increased temperatures and decreased air quality [59]. EVs utilize a high-voltage lithium battery to power the electric motor via an inverter and an auxiliary 12 V accumulator, which is charged from the main system similarly to an HEV to power the vehicle’s accessories. Several features such as higher energy efficiency, low maintenance, and noiseless operation have led to their widespread prevalence in the market despite their high purchase cost, which is estimated to be recovered after 5 years of use [60]. The layout of an electric vehicle is depicted in Figure 11 [51]:

Since no fuel is consumed, there are no GHG emissions; however, emissions from other lifecycle stages, such as production, are still significant, amounting to almost 10 tons more than for a corresponding ICEV. This trend is mainly affected by battery manufacturing, with a carbon footprint of 120 kgCO₂/kWh, although this process is expected to be carbon-free by 2050 [61,62]. Charging via the power grid varies in emissions, as countries with high renewable or nuclear energy use such as Norway and France have almost eliminated power generation emissions [63]. However other countries, such as Poland, India, and China rely heavily on fossil fuels, making EV adoption less impactufl and, in some cases, close to ICEs in terms of pollution [24]. EV adoption must be combined with renewables sources for power generation to achieve the goals established by the EU’s Green Deal. Solar and wind power can also be employed at public charging stations to reduce the carbon footprint by 90%. Thus, EV adoption needs to be combined with green energy production [64].

There are certain drawbacks associated with EV implementation, including:

• limited range;
• low availability of public chargers and long charging time;
• impact on the grid as electricity demand will increase rapidly;
• high operational cost;
• lithium battery limitations due to temperature and rapid charging [65,66].

As the use of electric vehicles is expected to increase rapidly by 2050, the expected impact on the grid will be major, as the capacity is not sufficient to meet the energy demands required by fleet electrification [65]. Expanding the utility grid and the distribution of the network capacity is essential to avoid a potential blackout, while investing in green energy with solar utilization both in public chargers and households is the ultimate step toward sufficiency. In this area, V2G and V2X systems can be applied, where the grid can exchange energy with the EV directly, depending on the power demand curve [66]. When the EV is parked and the power demand is increased, the EV provides energy to the utility grid, whereas when demand is limited, it is recharged by the grid. This pattern proves useful mainly in cities where air pollution and need for electricity are high due to dense population; e.g., in China, particulate matter (PM) emissions are 30% higher than in other urban areas [67,68].

Charger availability is currently an issue. Public chargers are continuously being installed, with a capacity of up to 1 MW by Tesla, while increased subsidies are being applied for users to purchase and install a charger at their households [69]. A second option is applicable mainly to users who live in individual houses or at least own a parking spot to install a private charger. Public ones are still necessary in cases of long trips and in highly crowded areas such as shopping centers and workplaces. That is why additional policies promote this infrastructure with tax reductions and low-interest loans [70]. However, the energy cost is still high, almost up to 4 times the cost of home charging, due to the increased capital cost of the equipment. Hence, this option appears less viable for now [71].

More importantly, the main weakness of an electric vehicle is the battery pack. Even though lithium batteries have evolved rapidly, their limited temperature range requires excessive cooling for charging, while extremely cold conditions result in reduced capacity. In addition, premature aging is an issue, as rapid charging and discharging apply high stress to battery cells [72]. Newer cell technologies such as lithium sulfur (Li–S), lithium air (Li–Air), and solid-state batteries are the current state of the art as they provide higher energy density, increased range and cycle life (>5000) while offering the ability for fast charging to 80% capacity within 10 min [73].

In addition, modern batteries are considered unsuitable for EVs when the maximum available capacity drops below 70% as the range is heavily reduced. In this situation, they can be removed from the vehicle and utilized at renewable energy parks as stationary storage to enhance renewable integration for energy supply during the night. Hence, their useful lifespan exceeds the 20-year limit before being recycled [74].

Downsizing has affected EVs as well. Smaller vehicles require less energy due to their lower mass, so the battery pack is smaller, requiring less materials for manufacturing. In addition, as charging speeds are faster and consume less energy, the stress applied on the grid is also reduced [75]. For example, a Ford Mustang Mach-E has a median of 25% more carbon dioxide emissions than a Tesla Model Y as it has a larger battery and higher energy consumption, so it requires more charging time and power [76]. Hence, the shift from SUVs and trucks to smaller vehicles such as sedans or city cars, in general, can enhance the impact of EVs in the decarbonization of the transport sector, allowing for smart and economical charging [77].

Undeniably, consumer behavior plays a major role in EV adoption. Consumers need to build their social awareness and understand the severity of GHG emissions for global warming. In addition, air quality is greatly affected by pollutants, including particulate matter (PM), nitrogen oxides (NO_X), and sulfur dioxide, which have immediate health effects [78]. The adoption of EVs can eliminate most of these pollutants and is further examined in this work.

Users need a vehicle to be affordable, easy to use, and convenient, without the need for constant charging due to limited battery capacity or searching for an available public charger [79]. Operating cost also plays a key role, as a potential EV owner will purchase an EV with long-term depreciation considering maintenance and charging expenses in mind compared to a conventional car [80]. If EV utilization is combined with a solar panel installation by the household, operation costs regarding daily charging become practically negligible. Meanwhile, in practice, even charging through an individual socket in the garage is less costly for the owner considering domestic tariffs, while slow charging limits battery degradation [66].

Therefore, policies by the authorities are required to provide motivation for users to purchase an EV. There are already certain strategies employed by the EU to promote EV adoption in terms of both tax benefits and incentives, including [81,82,83]:

• VAT and tax deduction.
• Exemption from registration fees and road tolls.
• Purchase cost reduction or cashback.
• Upgrade of the utility grid.
• Free charging at select spots.
• Widely available charging station infrastructure.
• Subsidies for renewable source installation.
• Reduced or no cost for charger installation in-house.

Incentives are also provided for the adoption of light mobility options such as lightweight electric scooters, bicycles, as well as the electrification of public transport, especially in urban areas, to enhance air quality [84]. The measures applied to encounter EV drawbacks are summarized in Figure 12.

4. Results and Discussion

A study [85] in the United States showed that an EV produced 28% fewer emissions than the same vehicle with an ICE. To calculate efficiency in a unified way for this study, the km/kWh metric utilized for EV consumption was selected for simplicity. There are 33.7 kWh in a gallon of petrol, and 1 mile equals to 1.609 km, so the typical fuel consumption in miles per gallon from [85] was converted to kilometers per kWh equivalent value using the following equation [82,83]:

$$\mathrm{k}\mathrm{m}/\mathrm{k}\mathrm{W}\mathrm{h}=\mathrm{}{\displaystyle \frac{MPGe}{3370.5}}\mathrm{}\times \mathrm{}160.9344$$

(1)

For example, a typical ICEV with a fuel consumption of 50 MPGe requires 1 kWh to cover a distance of 2.387 km, or 33.7 kWh for 80.45 km (50 miles), as per the metrics described previously. The comparison of fuel efficiency for ICEVs and EVs is summarized in

Table 1. Comparison of fuel economy in kilometers per kWh for petrol ICEVs and EVs with identical specifications.

Vehicle Model	Class	Highway Economy km/kWh	City Economy km/kWh
Honda CR-V AWD	CUV	1.5	1.2
Audi A4	Compact	1.6	1.3
Dodge Durango	SUV	1.2	0.9
Nissan Titan	Pickup	1	0.7
Tesla Model X	CUV	4.4	4.2
Hyundai Ioniq	Compact	5.8	7.2
Audi e-Tron	SUV	3.5	3.5
Ford F150	Pickup	3.9	3.9

[85,86]. These specific models were selected as they have the same characteristics for each vehicle class.

It is evident from the table above that EV efficiency is superior compared to petrol as identical electric vehicle models can cover more distance. For example, in the SUV class, a Dodge Durango can cover 1.2 km per kWh in highway driving, whereas an equivalent electric SUV can cover 3.5 km/kWh, almost 3 times more. In addition, in urban areas, conventional cars burn excess fuel due to idling in traffic and operation outside of the optimum engine speed range (1500–2500 revolutions per minute), further reducing fuel economy [86].

EVs exploit regenerative braking. The energy produced from this motor is used to charge the battery, leading to improved distance range and efficiency [87]. Thus, EV braking becomes less intense, with limited brake pad wear, reducing emissions and particulate matter production and the impact of transportation’s waste on air quality as shown in Figure 13. However, as the total mass of electric vehicles is higher, mainly due to the increased battery weight, the emissions from road dust wear and tire wear are increased, which is a drawback to their eco-friendly agenda.

Next, we compared the manufacturing, distribution, and operation processes. Raw material processing is higher for EVs as lithium and other rare metals such as cobalt are required for the cells. Manufacturing produces the majority of emissions for the two technologies and is 30% higher for EV as the battery pack manufacturing is complex [88]. Operation cost for electric vehicles is more than 3.5 times lower and can be further reduced to zero considering the use of charging via renewable energy. Decommissioning is identical for both, considering that battery recycling is a separate procedure.

EV manufacturing requires 460 kg of metals such as copper and aluminum, 850 kg of steel, and 500 L of water, while ICEVs require 150 kg of metals, 950 kg of steel, and 510 L of water [89]. The plug-in hybrid is in the middle, with higher material requirements than for ICEVs but lower than for electric vehicles, except steel, the demand for which is 10% higher. Regarding electricity, a conventional vehicle uses 1200 kWh, a PHEV utilizes 1700 kWh, while an EV requires 2100 kWh of energy. Thus, at the production stage, EVs are greatly demanding and generate more industrial waste [90]. The overall impact of EVs depends heavily on the balance within the lifecycle stage, and it requires additional operational time for the outcome to be environmentally positive.

Considering the use of this layout, the final cost per km for an EV is 12% lower than for a vehicle with an ICE, mainly due to taxes and incentives [91]. If these policies are removed, EV cost per km is 25% higher. In that case, EV adoption would not be viable. Details about the emission outputs of the different processes required for conventional and electric vehicles are presented in

Table 2. Carbon dioxide emission equivalent values for conventional and electric vehicles [88,89].

Process	ICEV (gCO2eq/km)	EV (gCO2eq/km)
Raw material processing	92	185
Manufacturing	23	33
Distribution	2.5	3
Operation	351	92
Decommisioning 1	0.7	0.7

¹ Battery pack is excluded.

below.

Incentives also affect manufacturers who invest in their factories in terms of green production for sustainable and less costly EVs. Additionally, research into newer battery technologies is promoted towards the goal of carbon neutrality [92,93]. Volkswagen has already implemented renewable sources to power their factories and reduce their carbon footprint, while planning to deliver 70 electric models by 2030. KIA Motors in Korea is expected to reach net-zero emissions by 2045. BYD built their first zero-carbon park in 2022, with other companies already driving the way towards net-zero emissions and sustainability, so it is a race towards the EV era.

Regarding the lifecycle scenarios, if the battery use in EVs, hybrids, and plug-in hybrids increases steadily, reaching a proportion of 14–25% in total, such as in Thailand with a total of 10 million vehicles, the CO_2eq emissions will be decreasing by 1.7 to 3.6 megatons per year [94]. Towards this goal, incentives which are currently applied, such as decreased taxes, lower purchase cost, and charging prices with renewable utilization, are essential, leading to improved air quality [68].

To further validate the advantages of EVs, a comparison of carbon dioxide equivalent emissions through a 10-year utilization is introduced [95]. As stated before, battery production increases manufacturing emissions by over 3 tons of CO_2eq, while the energy required for a typical use is 33% of the corresponding conventional vehicle fuel cycle, as shown in Figure 14.

Accordingly, these values are expected to change by 2035 if hybrids and plug-ins are included. Two factors are introduced [95]:

• Well-to-Tank (WtT), representing the energy used to produce the fuel or electricity required.
• Tank-to-Wheel (TtW), which is the actual energy that powers the vehicle.

In Figure 15, a comparison of the 4 vehicle technologies is displayed in terms of production, fuel distribution and efficiency, as well as the impact on decarbonizing and mitigating the grid. Thus, battery recycling emissions are also included [96].

Considering alternative fuels, hydrogen can be applied in fuel cell vehicles or directly in internal combustion engines [97]. Research has focused on the applications of green hydrogen production by renewable sources and the need for storage and distribution in high-pressure tanks, which is still expensive and inefficient. Fuel cells are costly due to the use of rare minerals as catalysts, while use in an ICE requires precise injection to avoid knocking. Furthermore, variations in the air–fuel mixture causing heavy nitrogen oxide emissions can be altered by utilizing a selective catalytic converter and particulate filter, so hydrogen may be considered as an alternative. The high flammability of hydrogen is an important factor and has to be studied further.

Biofuels such as biodiesel, bioethanol, or organic oils have great potential for conventional vehicles or hybrids bringing many advantages as they are eco-friendly and can be produced locally [97]. Certain disadvantages, as summarized in

Table 3. Biofuel advantages and disadvantages [97].

Advantages	Drawbacks
Renewable and sustainable	Require pretreatment
Reliable	Expensive development *
Produced locally	Reduced efficiency
Low price	Difficult to scale for commercial use
Reduce oil dependence	Complex network facilities
Increased air quality	Specialized storage
Use of neglected land	Competition with food production

* High budgets are required.

, such as the distribution network, pretreatment before use, and specialized storage, should be confronted for biofuels to be sustainable.

The potential impact of biofuels is presented in Figure 16. Using bioethanol in ICE vehicles, hybrids, and PHEVs can be quite beneficial for the environment as a full hybrid car with biomethane requires 17 km to produce a single kg of CO_2eq, with an ICEV coming second, with almost 14 km/kgCO_2eq [98]. A typical conventional vehicle burning petrol drives just 4 km per kg of carbon dioxide; hence, it is not environmentally sustainable.

Regarding the use of LPG and CNG, which are being exploited as manufacturer or after-market modifications, their advantages over petrol or diesel are evident. LPG systems, which are easy to install, can slightly reduce emissions in modern Euro 6 cars as a transition step towards a green environment, as depicted in Figure 17 [99]. CNG appears to be the ideal gas as it is widely available, cheap, and provides extra benefits to the ICE, reducing the majority of GHG emissions.

With regard to policy concerns, LPG and hydrogen policies are not entirely satisfactory. The technical, economic, and social factors show great potential. The social advantages are the most significant and obvious criterion for CNG, and they also provide the largest contribution to its highest possible value [100]. Similarly, the contributions of technical and economic elements are nearly equal and exhibit favorable features in this manner. Finally, from a technological and sociological perspective, gasoline possesses advantageous properties. LPG, CNG, and biogas are offered more significance because of this trend. Equally significant is the fact that raising the share of policy criteria will make batteries and PHEVs more appealing, especially if driven in the EV mode, and they should be considered as an enabling technology to reach the goal of reversing climate change [101].

EVs appear to be more sustainable after 175,000 km, where the manufacturing and other costs have been offset, but the battery lifespan remains a major concern [102]. There are certain challenges, including range, charger compatibility, and consumer behavior, which must be addressed for massive EV adoption and enhanced sustainability [103]. However, the grid is not yet sufficient to handle the power required for charging, so the exploitation of renewables along with minimizing energy demand of each household are critical for this transition [104,105].

The development of new, low-cost sensors makes it easy to implement affordable air quality monitoring systems [106,107]. Hence, the utilization of these affordable and compact systems allows constant monitoring for environmental conditions over a large urban area [108,109]. The reliability of these sensors can be achieved after evaluation and application of correction factors, as described in different ways in the literature [110,111,112]. For example, Figure 18 shows the 24-h (24 April 2022) variation of particulate matter (PM2.5) in the city center of Athens, Greece, with the monitoring station installed next to a road with heavy traffic [113,114].

From the data in Figure 18, the differentiation can be seen between the low-cost sensor measurements (corrected values) and the reference measurements. The reference data were obtained from iqair.com [115]. The low-cost sensor measurements follow the trendline of the reference measurements (Figure 18a), while the scatter plot shows a satisfactory correlation between the measurements (Figure 18b). The coefficient of determination confirms the above, as its value is close to 84%. Based on the foregoing, low-cost sensors can operate satisfactorily for measurements of environmental conditions, and such systems are easily implemented by people interested in the air quality of the area in which they live and work [116].

The reduction in ambient air pollution, particularly in urban areas with high population densities, leads to decreased incidences of asthma, chronic obstructive pulmonary disease, lung cancer, and other health conditions associated with poor air quality [117]. Furthermore, EVs contribute to a reduction in noise pollution due to their quieter operation, which has been shown to alleviate stress and promote mental well-being. Through the adoption of the EV technology, societies can advance toward cleaner transportation systems, ultimately improving population health and mitigating the detrimental effects of environmental pollution.

The findings of this paper are summarized in

Table 4. Summary of the findings of this paper comparing ICEVs and EVs and different fuel types.

Factor	Context
European Green Deal	Net-zero emissions by 2050
2030 Goal	Fleet carbon emissions reduced by 37.5%
ICE/EV efficiency	EVs are more efficient for both highway and city driving
ICE/EV cost comparison	EVs cost more initially -> less costly in the long run
EV benefits	Low maintenance, energy cost, and noise, comfortable
Fuel independence	EVs can be charged at the household via renewables or via the grid
Main EV drawbacks	High charging time, cost due to minerals such as lithium, low range
ICEV drawbacks	High pollution and maintenance, complex exhaust system
HEVs	Transition point from ICEVs to EVs
HEV benefits	High efficiency and comfort, 25% fewer emissions than from ICEVs
Need for transition	Air pollution effects on human health and GWP
Electricity mix	High impact on EV emissions, range: 1 to 12 kgCO2eq/kwh
Alternative fuels	LPG/CNG, biofuels, hydrogen
LPG, CNG kits	Installed in current ICEs to reduce emissions, mainly NOX (75%)
LPG/CNG drawbacks	Cost of installation, potential failure, reduces trunk space
Hydrogen	Can be used as an additive to ICEs or for storage of surplus electricity
Hydrogen compatibility with ICEs	Increased nitrogen oxides and engine knock, not efficient
PHEVs	EV range ideal for urban areas, low fuel consumption as hybrids
Fuel cells	Highly efficient, but demand rare metals as catalysts
V2G	EVs provide power to the grid at peak hours when parked
Charge availability	Subsidies provided for massive installation
Urban areas	Small EVs with charging at home is the ideal plan
Component wear	EVs offer less brake wear but higher road and tire wear
Production	EVs require more materials, energy, and water
Cost per km	12% lower for EVs than for ICEVs, optimal choice
Lifecycle emissions	EVs tend to reach sustainability at 175,000 km
Biofuels as alternatives	Green, reliable, low priced, and can improve air quality
Biofuel drawbacks	Specialized storage, reduced efficiency, low scaling for commercial use
Km per kg CO2eq	Biogas is the best option for all vehicle types, and HEVs are second
Euro 6 standard	85% reduction in NOX and CO emissions compared to Euro 2
Final aspect	EVs provide eco-friendly transportation but require additional research

below.

5. Conclusions

This study underscores the crucial role of electric vehicles (EVs) in reducing transportation sector emissions and advancing global climate objectives, particularly the European Green Deal aim of net-zero emissions by 2050. The findings highlight that transportation contributes approximately 20% to the global greenhouse gas (GHG) emissions, with the European Union alone reporting over 301 megatons of carbon dioxide equivalent (CO_2eq) emissions annually.

Despite advancements in the internal combustion engine (ICE) technology, including Euro 6 standards with 40% thermal efficiency, these vehicles remain a significant source of emissions. Urban traffic conditions further exacerbate this issue, with idling responsible for up to 60% of city-based vehicular emissions. Over their lifecycle, ICE vehicles emit an average of 12 kg CO_2eq per 100 km, a figure comparable to EV emissions in regions heavily dependent on fossil fuel-based electricity grids.

EVs offer substantial advantages, boasting a threefold increase in powertrain efficiency over ICE vehicles and significant reductions in operational emissions, particularly in regions powered by renewable energy. In Norway, for instance, where the grid’s carbon intensity is just 31 gCO_2eq/kWh, EVs emit as little as 0.62 kg CO_2eq per 100 km. However, challenges remain, including the environmental footprint of battery production—contributing up to 10 tons of CO_2eq per vehicle—and infrastructure limitations such as charging accessibility and range concerns.

Battery production faces such challenges as material scarcity, environmental impact, high energy use, supply chain instability, and limited lifespan. Solutions include developing alternative and abundant materials such as sodium-ion and solid-state batteries to reduce the cost and environmental footprint [118]. In addition, recycling will reduce the need for mining and the exploitation of clean energy in manufacturing, diversifying supply chains, enhancing battery longevity with better chemistries, and AI-driven management will help make battery production more sustainable and efficient.

Hybrid electric vehicles (HEVs) serve as an effective transitional technology, reducing emissions by up to 25% through optimized fuel usage and auxiliary electric motors. Similarly, alternative fuels such as bioethanol and biodiesel can lower emissions by as much as 40%, though scalability and production constraints limit widespread adoption.

Policy measures such as tax incentives, subsidies for renewable energy integration, and investments in charging infrastructure are essential for accelerating EV adoption. The study indicates that with renewable-powered grids, EV lifecycle emissions could drop by over 90%, potentially reducing transportation emissions by 1.7 to 3.6 megatons of CO_2eq annually in high-adoption scenarios.

To fully realize EVs’ potential in decarbonizing transportation, efforts need to focus on mitigating battery production emissions, expanding infrastructure, and increasing renewable energy integration. A multifaceted strategy incorporating technological innovation, policy support, and consumer engagement is crucial to ensuring an equitable and sustainable transition to low-carbon mobility.

Future research should conduct real-world testing of ICEVs, HEVs, and plug-in hybrid electric vehicles (PHEVs) under diverse conditions to refine lifecycle emission assessments. Studies on battery degradation, alternative fuel integration, and the impact of consumer behaviors, such as charging habits and range anxiety, will further define strategies for a sustainable low-emission transportation system.