….let's share our railways knowledge

Specific Energy Consumption of High Speed Rail as compared to Semi-HSR

By on October 20, 2013

There is a general belief that the train resistance (resulting high specific energy consumption) of high-speed train is high as compared to normal speed train. The UIC sponsored study proved it otherwise with following arguments explained in the discussion

  • Curve Resistance: High speed Rail routes had to be straighter, a must for the high-speed route, and therefore, less curve resistance. The curving factor is around 0.08 as compared to 1.424 for conventional semi-HSR line.
  • The factor a in the equation a+bv+cv2 corresponds to the design of the rolling stock. The design of high-speed rolling stock is improved one resulting low value in the range of 0.5 to 0.9 as compared to 1.2 to 2 for semi-HSR
  •  Air resistance consists of drag due to frontal pressure force and another side friction drag.
    • Frontal drag depends on the front and rear of the train mainly on a cross-section surface area and on air density. The factor c for semi-HSR is worked out to be 0.0022 as compared to 0.00096 for HSR assuming a cross-section surface area of about 12 m2 in both the cases.
    • Friction drag due to shear stresses occurs on the train’s wet surface whose surface area is the two sides. Here also c factor for HSR is 0.000021 as compared to 0.00003 for semi-HSR.

High speed Train with Egg shape frontal cross-section

IR 140 Kmph/6000HP WAP7  with similar frontal cross-section as that of 160 Kmph/5000HP WAP5

  • A passenger train consumes considerable energy towards auxiliary services such lighting, air conditioning, heating etc. If we reduce the journey time, energy consumed towards such services will also reduce. With high speed, the journey time reduces considerable, thus making a significant impact in total energy consumption.
  • Better use of gradient of repose (gradient of repose is defined as the gradient for which the train, without braking or applying traction, maintain a speed equal to its maximum speed on the line section) without any need of application of brake.
  • High speed route are straight and therefore the distance between two points is less to the extent of 12% as compared to conventional route. This means reduction in energy consumption but certainly will not account for SEC.
  • The study is in reference to Spain which is operating HSR as well as Semi-HSR trains. The operation of Semi-HSR is on 3000V DC network where as HSR is on 25kV network thus saving on ohmic loss which is significant to the extent of 16%.

There is no experience of Indian Railways in this regard, therefore, difficult to comment. But the above study certainly provides platform towards energy conservation techniques in traction. These are summarized as follows:

  • Use of technology to improve suspension and riding so  to reduce the effect of factor a in the train resistance
  • To monitor the events of mechanical brake application and its analysis for solution to reduce it.
    • In case Indian Railways upgrade its passenger and freight speed to 160 and 100  Kmph respectively, there will be considerable saving in energy which otherwise is wasted for controlling the speed.
  • To calculate gradient of repose for all type of stock so that the stock is operated without any application of brake. This can be achieved by working  on down gradient at minimum speed so as not to exceed maximum permissible speed at the end of the down gradient.

In the figure below, Section AB and BC  is on up and Dn gradient respectively. The down gradient is more than the angle of repose. It means that the vehicle will attain speed more than the permissible speed, therefore application of brakes is but natural. The only way to avoid this is either increase the permissible speed or reduce the speed at B so that permissible speed during the journey on down gradient is never exceeded. Reducing speed at B is possible by coasting on section AB. The time loss shall be small but still be worked out so that it does not exceed the make up time margin available.



  • There will be saving of 200 lts of diesel oil if there is a reduction of journey time of Rajdhani by one hour which otherwise is used to provide air conditioning and lighting amenity in the train.


Post a Comment

Your email address will not be published. Required fields are marked *

There Are 3 Comments

  1. Vikash Anand says:

    sir, the curving factor is not clear. we were taught about curve resistance, it didn’t include curving factor, perhaps

    • Mahesh Jain says:

      Curve resistance is of a particular curve. On a route there may be many curves of different curvature and all combined give a curving a factor per 100 Km(say). This curving factor for HSR is much less as compared to semi-HSR. As a rule, curves are avoided on HSR therefore, the curving factor is low.

  2. Rakesh singhai says:

    But you are not comparing apple to apple. All the features you mention can be used for semi high speed trains too. Rather imagine a high speed train running at half the speed. This will reduce energy consumption greatly.