An assessment of the CO2 emissions reduction in high speed rail lines: Two case studies from Turkey

Abstract

Transportation sector is one of the major emitters of greenhouse gases due to high consumption of fossil fuels in passenger and freight transportation. In recent years, high speed rail systems (HSR) have become an important policy option for intercity transportation in many countries, including Turkey, as they have relatively low emissions impact. Currently, the total HSR network in Turkey extends to 1213 km and connects 7 cities mostly located along a main HSR corridor. Annual ridership of the first two lines, Ankara-Eskişehir (ANK-ESK) and Ankara-Konya (ANK-KON), have reached almost 2 million passengers each, while total ridership in all four lines was about 3.5 million passengers in 2014. With the upcoming two new HSR lines, total length of HSR network will exceed 3000 km by 2020.Despite the increase in ridership, no effort has been conducted to evaluate HSR from environmental perspective, which was the main motivation, and has been chosen as the scope of this study. As a first step, the CO2 emissions reduction performance of the HSR lines in Turkey was determined based on a proposed line-based methodology. The method included the determination of i) current emissions of HSR lines, ii) estimated emissions from the alternative modes expected to be used in No-HSR situation, as stated in a HSR user survey, and iii) the difference in emissions as the HSR reduction performance. Calculation of an average CO2 emissions reduction value per passenger-km travelled (PKT) enabled determination of emissions reduction potential of the existing and upcoming HSR lines under estimated future demands in the last step. The proposed methodology not only considered CO2 emissions from alternative modes, but also factored in the effect of intercity travel demand induced by HSR observed at this early development stage in Turkey.The results suggested that HSR caused a total reduction of 24.3 ktCO2 currently on two study corridors, and may even result in a reduction of 452.7 ktCO2 in 2023, if estimated ridership is realized in all lines. Line based analyses showed that HSR performance in reducing CO2 emissions was limited as highly demanded HSR lines currently served short routes and mostly caused modal shift from bus services, which were also efficient compared to car. The CO2 emissions reduction potential of future HSR services can be higher if a) new HSR lines can create a network effect along the main corridor and b) supplementary policies can be developed to generate high HSR demand that would be shifted from car, and even air, on the longer routes.