5.1.7. Introduction of Hybrid Buses

This article states that the hybrid buses measure is more important than the electric public transport systems (subway and trams -see the following measure 5.1.8), although the electric option has a greater mitigation potential, especially when the GHG emission factor of the power grid is high, and for this reason it is considered as the most important and aggressive low-carbon scenario to achieve in public transport systems. However, in this article, it is considered that hybrid buses have a much greater development than the electric option because the hybrid option avoids the high investments of the development of the rail infrastructure and the acquisition of trains, so from the economic and financial point of view it has a greater viability for a country like Mexico. Hybrid buses are presented in our article as a transition option that has an important development while lowering the costs of electric trains and developing the rail infrastructure to use them.

The introduction of hybrid buses, with the goal of constituting 15% of the total vehicle fleet of passenger buses in medium and large cities by 2035 has been considered. It is assumed that 30% of new buses by the year 2035 will be hybrid [36] and that their fuel economy will be 30% higher than that of conventional engines [47]. It is assumed that this measure applies only to 46% of the national bus fleet for urban use (HDV-P) and that the hybrid bus fleet increases from 41 vehicles in 2012 to 7694 in the year 2035, which implies an average annual growth rate of 25.6%. This measure implies an average di fferential cost of 282,491 USD for each hybrid bus relative to conventional buses. Finally, M cost for hybrid buses represents 10.7% of the incremental investment cost according to [36].

## 5.1.8. Electric Public Transport Systems

This measure promotes electric public transport systems (subway and trams) to reduce emissions and noise. According to [36], subway trains are promoted in the largest and most polluted cities in Mexico: Guadalajara, Monterrey, and the Metropolitan Area of Mexico City, and in the rest of the country, extension of the tram network is promoted. It is considered that from the second year, a total of 2.6 km of subway per year would be built in the three mentioned cities. This data is estimated observing the increase in the length of the metro in Mexico City between 1969–2012, during which it extended 226 km over a period of 43 years, according to [48], that is 5.2 km per year. It is assumed that half the extension per year is considered for the mentioned three cities. In the case of trams, 89 wagons were considered in 2012 reaching 960 in 2035 [36]. According to this author, it is assumed that 95% of transport users demand comes from public transport users and 5% from private car users. Also, for subway trains and trams investment costs of 0.371 and 1.297 USD per kilometer travelled per year, respectively, were considered. Finally, a subway and tram systems are assumed to expand to an average of 0.36 and 4.2 million kilometers travelled per year, respectively.
