## How Much Power Is Needed To Run A Train At 125 Or 100 mph?

In an article in the October 2017 Edition of Modern Railways, which is entitled **Celling England By The Pound**, Ian Walmsley says this in relation to trains running on the Uckfield Branch, which is not very challenging.

A modern EMU needs between 3 and 5 kWh per vehicle mile for this sort of service.

Can I get any other figures for running at 125 mph, that agree or disagree with these figures?

**Class 801 Train**

I have found this on this page on the RailUKForums web site.

A 130m Electric IEP Unit on a journey from Kings Cross to Newcastle under the conditions defined in Annex B shall consume no more than 4600kWh.

This is a Class 801 train.

- It has five cars.
- Kings Cross to Newcastle is 268.6 miles.
- Most of this journey will be at 125 mph.
- The trains have regenerative braking.
- I don’t know how many stops are included

This gives a usage figure of 3.42 kWh per vehicle mile.

**InterCity 125**

Note that the Class 43 power cars of the InterCity 125 (HST) put 1,300 kW to the rail and have a 1,700 kW engine. Two of these powerful beasts giving out a total of 3,400 kW,, can sustain a ten-car train (two power cars and eight passenger cars) at 125 mph.

In the roughly thirty seconds, it would take to cover a mile, an HST could use 3400/120 kWh or 28.3 kWh.

Counting the locomotives as a car and dividing by ten gives 2.83 kWh per vehicle mile.

This is actually a maximum figure, as the driver could throttle-back if required.

This figure is not out of line with the 3.42 kWh per vehicle mile for a Class 801 train, that I stated earlier.

The force was with Terry Miller and his team.

**Class 222 Train**

The Class 222 trains have one 580 kW engine in each car.

In the thirty seconds, it would take to cover a mile, a Class 222 train would use 580/120 or 4.83 kWh per vehicle mile.

Again this must be a maximum figure.

**Class 170 Train**

The Class 170 train is a 100 mph train with a 315 kW engine in each car.

In the thirty-six seconds, it would take to cover a mile at 100 mph, a Class 170 train would use 315/100 or 3.15 kWh per vehicle mile.

Again this must be a maximum figure.

Conversion Of 125 mph Figures to 100 mph Figures.

The resistance of any vehicle goes up with the square of the speed.

100*100/125/125 is 0.64.

My crude calculations give.

- Class 801 train – 125 mph 3.42 kWh per vehicle mile
- Class 801 train – 100 mph 2.19 kWh per vehicle mile
- InterCity 125 – 125 mph 2.83 kWh per vehicle mile
- InterCity 125 – 100 mph 1.81 kWh per vehicle mile
- Class 222 train – 125 mph 4.83 kWh per vehicle mile
- Class 222 train – 100 mph 3.09 kWh per vehicle mile

I’d love to know the real values.

**Conclusions**

I know this was a rather rough and ready calculation, but I can draw two conclusions.

- Trains running at 125 mph seem to need between three and five kWh per vehicle mile.
- The forty year old InterCity 125 has an efficient energy use, even if the engines are working flat out to maintain full speed.

The only explanation for the latter is that Terry Miller and his team, got the aerodynamics, dynamics and structures of the InterCity 125 almost perfect. And this was all before computer-aided-design became commonplace.

In future for the energy use of a train running at 125 mph, I shall use a figure of three kWh per vehicle mile.

It is also probably a good starting point for a 100 mph train.

After all, if a forty-year-old diesel-electric train built from steel can achieve that figure, surely a modern electric train built from aluminium can do better!

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