**1. Introduction**

On a global scale, the world transport sector generates the second largest share of GHG emissions. In 2014, this sector contributed 21% of global GHG emissions generated by energy use [1]. The rapid growth of the global transport sector's GHG emissions has been driven by road transport, which increased by 71% between 1990 and 2016, and represented 75% of the sector's global emissions in 2016 [2]. If this trend continues, this sector will generate 10,317 million tons of CO2e (MtCO2e) by the year 2040, which would represent a growth of 38% compared to transport GHG emissions in 2014 [3].

To know which substantive measures are being implemented currently for mitigating GHG emissions from transport sector that can help us to construct the LCS scenario, a survey of literature from national and international cases was carried out, specially selecting China, Germany, India and USA. Our search process and criteria to define the selection of these countries were the following: first, they are among the eight top world transport sector GHG emitters (see Table 1); second, their road transport sector represented more than 60% of their transport sector GHG emissions according to data available for 2010, third they have prospective studies with grea<sup>t</sup> ambition to reduce GHG reductions above 40% in their transport sector by year 2035 in relation to a baseline scenario or a reference year and finally, they present at least two future scenarios and five transport sector mitigation measures. Table 1 shows the four countries and the studies that were selected after applying this search process and mentioned criteria.


**Table 1.** Countries with the highest proportion of global greenhouse gas (GHG) emissions in the world transport sector and the high ambition GHG reduction prospective country studies in this sector.

> \* [8]; \*\* [9]. Source: Based on [4–9].

Consequently, this review considered the following four country studies with ambitious mitigation scenarios in the transport sector: USA [4], China [5], India [6] and Germany [7]. The proposed mitigation measures of these four studies are diverse and have high potential for reducing GHG emissions. They include tra ffic optimization; bus rapid transit; light urban train; railways and waterways; subways; increase of public and non-motorized transport, such as the bicycle; vehicle sales' restriction; mode shift; e fficient vehicles and trucks; plug-in electric vehicles; plug-in hybrid electric vehicles; battery electric vehicles; fuel cell electric vehicles; electric trains; hybrid buses; diesel hybrid cars; hydrogen hybrid cars; and use of ethanol and biodiesel to substitute fossil fuels.

In relation to GHG emissions from fuel combustion, in 2014 Mexico was ranked eleventh in the world, generating 1.6% of the global volume, equivalent to 422 MtCO2e, of which 78% came from two sectors: transport and energy (electricity and fossil fuels) [10]. Transport sector contributed with 31.6% followed by electricity generation with 23.1%.

In year 2013, due to concerns about the growth of criteria air pollutants generated by automobiles in Mexican big cities, which have negative e ffects on public health, an O fficial Mexican Standard (NOM in Spanish) was published NOM-163-SEMARNAT-ENER-SCFI-2013 [11], with the purpose of obliging automotive manufacturers to increase the fuel e fficiency of light vehicles, thereby reducing the unit consumption of energy and, consequently, the emissions of SOx, NOx, particles, and CO2e. Public concern about the problem of the growing emissions of the Mexican transport sector has also led to various studies that include GHG emissions' reduction in the transport sector, [12–15]. These studies consider mitigation measures, such as hybrid and electric cars; biofuels such as ethanol and biodiesel; and managemen<sup>t</sup> measures and practices for the e fficient use of energy, such as the implementation of efficiency standards, increased use of rail for freight transport, and a public bus rapid transport system. Together, these measures from these studies [12–15] have the potential to reduce CO2 emissions by the year 2030 by between 16% to 38%, which is equivalent to 48 and 131 MtCO2e of avoided emissions.

In year 2015, Mexico signed the Paris agreement, a non-mandatory commitment to comply with its national determined contributions (NDC) [16] where Mexico obliges itself to reduce its national GHG emissions by 22% in its unconditioned goal, and 36% GHG reduction in its conditioned goal (that implies greater foreign investment and technology transfer), in relation to an o fficial baseline GHG emissions, which in year 2030 would have emissions of 762 MtCO2e; in addition to achieving a maximum emission peak in 2026. In the Mexican NDCs, the transport sector is compelled to achieve 18% reduction in GHG emissions by 2030 as an unconditioned goal, according to its o fficial baseline GHG emissions, which represents a reduction of 48 MtCO2e.

According to the literature review on Mexican studies, the National Institute of Ecology and Climate Change (INECC by its acronym in Spanish), carried out a study in 2018 [15] analyzing 8 measures that will reduce emissions by 48 MtCO2e by 2030, to comply with the Mexican NDC commitments; nevertheless, this constitutes the least ambitious scenario among the mentioned authors. Other, more specific studies, cover only one type of measure at a national level, such as focusing on CO2 mitigation through mixing liquid biofuels as additives to fossil fuels in di fferent proportions, either ethanol with gasoline or biodiesel with diesel [17–20]. For studies at cities level with some mitigation measures see [21–23].

This paper describes the construction of a very ambitious but feasible scenario to establish a low carbon transport sector in Mexico through the integration of 21 GHG mitigation measures. To shape the range of measures, both international and domestic experiences that might contribute to increasing mitigation ambition in the proposed new NDC to be reviewed in 2020 were considered. The main objective of this article was developed through the following structure: in the introduction section an overview of world transport sector was displayed, then the literature review findings and the followed steps to determine the selected transport sector prospective studies were described along with the current situation of Mexican transport sector. Then, the general methodology is described: starting from explaining how the original model was implemented using Excel spreadsheets and LEAP software, as well as a clarification of the scope of this article. Subsequently, once defined the reference year, the baseline scenario (BLS) and the alternative low carbon scenario (LCS) were constructed including input data, assumptions for both scenarios and a description of the 21 mitigation measures to the LCS were added. Next, the evolution of the vehicle fleet and the energy consumption calculation model as well as the cost benefit analysis model are described. Finally, results and conclusions are presented.

### **2. Mexican Transport Sector Current Situation**

The energy consumption of the Mexican transport sector increased at an average annual growth rate of 4.4% between 1965–2014, consuming 2246 PJ in 2014, that represented a share of 45.9% of the country´s final energy consumption. Road transport energy consumption was 91.3% of the whole sector, air transport contributed 6% of total consumption, maritime contributed 1.3%, rail contributed 1.2%, and electric transport contributed 0.2%. In terms of fuel type, gasoline was the most consumed fuel, contributing 65% of the total transport energy, followed by diesel, at 27%, kerosene, at 6%, liquefied petroleum gas (LPG), at 1.76%, electricity, at 0.18%, and dry gas and fuel oil together at 0.06% [24]. The number of vehicles increased at an average annual growth rate (AAGR) of 5.9% between 1995–2014, totaling 38 million by the end of that period. Private vehicles accounted for 67.2% of the total, followed by cargo trucks, at 25.9%, motorcycles, at 6.0%, and passenger buses, at 0.9% according to [25]. Carbon dioxide (CO2) emissions due to road transport increased at an AAGR of 2.4% between 1990–2014, reaching 153.5 MtCO2e by the end of the period, with 71.7% of the total due to gasoline burning, 25.5% to diesel, and 2.5% to LPG. Therefore, gasoline road transport is responsible for 67% of the GHG emissions of the transport sector, with passenger vehicles contributing 38% and cargo trucks contributing 29% [10].
