Design of energy efficient rolling stock is of paramount importance for sustainability over design life. Low axle load and low power/seat are indications of an energy efficient design of a high-speed rolling stock.  Table-1 shows the comparative features of leading high-speed rolling stocks of the world1,4.   As can be seen from the table power/seat is lowest in Japan; and in Taiwan, where also Japanese Shinkansen technology is used in rolling stock. This is due to low axle load and wider body to accommodate more seats.

Table-1: Comparative features of High-Speed Rolling Stocks across the world (NA: Information Not Available)

HSR efficiency is normally used to indicate actual energy efficiency in operation of high-speed rolling stock.  Various studies have been undertaken to estimate the efficiencies of the HSR operating across the world. A comparative set of figures for different HSR across the world is shown in Exihibit-12,3. The Shinkansen comes out as one of the most energy efficient HSR rolling stock in the world with HSR efficiency as 0.029 kWh/seat-km.

While the efficiency range of HSR rolling stocks is in the range of 0.029 kwh/seat-km to 0.041 kwh/seat-km, the energy efficiencies vary across different HSR lines based on a various parameter, such as route distances, number of stops, rolling stocks, seat capacities, speeds, etc.

Efficient regenerative braking system along with intelligent brake blending and smart operation of high-speed rolling stock play a crucial role in enhancing HSR efficiency.

A study of the effect of coasting over constant speed running on energy efficiency has been done by carrying out simulations of high-speed rolling stock running considering a standard rolling stock of around 10 MW power with maximum operating speed of 320 km/h over a typical HSR line of 500 km. The study shows how smart time tabling and resorting to coasting between stations can result in much improved energy efficiency.

10 stoppages have been considered in a 500 km line with average station spacing of around 50 km. The minimum inter station distance is considered as 35 km and maximum 75 km for the study.

Exhibit-2 and 3 show running of the rolling stock in a 50 km section in constant speed mode and coasting mode. As can be seen, the journey time increases by 7% whereas net energy consumption reduces by 3% in coasting mode over constant speed mode.

Exhibit-4 shows effect on energy efficiency and travel time when for different inter station distances, coasting is resorted in place of constant speed running.

*Note:

(i)    Calculations are considering level section
(ii)    The waiting time at starting & destination station is considered as 5 minutes
(iii)    The stopping time at intermediate stations are considered as 1 minutes at small stations and 2 minutes at big stations.
(iv)    No speed restrictions because of curves have been considered
(v)    100% auxiliary energy consumption has been considered for complete run
(vi)    Regenerative braking has been considered from 320 km/h to 120 km/h
(vii)    Efficiency from wheel to line is considered as 82%

For inter station distance up to around 40 km constant speed working is advantageous as energy efficiency increases when coasting is done in place of constant speed running. Whereas for distances more than 45 km, coasting is advantageous as energy efficiency decreases although run time increases.

Thus, by resorting to constant speed running on shorter inter station distances and coasting on longer inter station distances, over all energy efficiency improvement of around 8% can be achieved with around 14% increase in journey time over a typical 500 km HSR line. Time tables usually include a recovery time added to the minimal running time to allow for short delays. This recovery time is normally between 5% to 12% of the minimal running time. So, this 14% increase in time can be adjusted in recovery time. It will be interesting to verify this study once HSR is operational in India.

1. Joint Feasibility Study Report for MAHSR project

2. Supplementary EIA Report of Sep 2018 for MAHSR project

3. Journal of Modern Transportation: March 2016, Volume 24, Issue 1, pp 1–21 / A multidimensional examination of performances of HSR (High-Speed Rail) systems

4. UIC