Skip Ribbon Commands
Skip to main content

Project title

Investigating the economics of the 3rd rail DC system compared to other electrification systems (T950)

  • Project number:

  • Topic:

  • Status:


Project Summary

This research project carried out a high-level assessment of whether it would be prudent to convert from the existing 750V DC system to 25kV AC system, from an economic and technical perspective.

Project Abstract

Project Briefs are hosted on
This research, carried out on behalf of the Future Electrification Group (a sub-group of Vehicle/Train Energy System Interface Committee (V/TE SIC)), has considered the long-term options for modification or replacement of the 750V DC third rail electrification system. This is used over a significant part of the UK main line network and this work was to determine whether there is a prima facie case on economic grounds for conversion to 25kV AC overhead electrification; and if so, over what approximate period this conversion could practicably be carried out.

The research considered appropriate options for future power source(s) on DC routes where renewal dates for these routes are in the short- to medium-term. The options considered were:
• Modification of existing DC system
• Conversion to an alternative DC system
• Replacement with an AC system
As part of this research a desk top study was undertaken for two example routes, looking into infrastructure issues, rolling stock conversion, signalling compatibility, and energy efficiency.

The main deliverable for this research is a report that provides a (national) generic high-level business case for conversion from 750V DC to a 25kV AC electrification system. This research has concluded that the potential benefits of changing to a 25kV OLE system are:
• Cost reductions in the capital investment of installing an AC system when compared with a DC system.
• Reduced energy losses and carbon footprint for 'like for like' service (comparing the same 4-car EMU service with AC and DC). Results also indicate that an equivalent AC service consumes at least 20% less energy.
• Increased power, enabling higher average speeds, increasing capacity and as a result, reducing journey time by 3–5% (on average).
• Reduction in safety risk to unintended trespassers from possible electrocution.

This research has provided valuable information about the economics of the third rail 750V DC system compared with the 25kV AC electrification system. The results of this research will inform Network Rail plans for the next and subsequent Control Periods (CP5 and beyond) and inform the industry decision on what the most appropriate future strategy for the 750V DC third rail system should be. Any possible future work is likely to start during CP5, taking around 15 years to complete. The findings have been communicated to various rail industry groups including the Technical Strategy Leadership Group, V/TE SIC and Planning Oversight Group. The GB rail industry is considering the research findings in the context of its longer-term strategy and planning.

Read Project Brief

Project Reports

Project Reports are hosted on SPARK

This project has no reports available

This document is hosted on SPARK


You are now being redirected to SPARK, RSSB's knowledge sharing hub, to access the requested information.

Your RSSB user name and password can be used to access SPARK.