Q. How does high-speed rail impact on plans to improve the existing network?

We suggest that what is needed is a joined-up strategy, with a long-term investment plan for the development of high-speed rail and the existing network. In some cases, it would be possible to save money on schemes that will become unnecessary. In general these are as yet unidentified and unfunded, but they would become necessary in due course, especially along the north-south main lines.

Q. What capacity benefits does high-speed rail offer?

Running over its own tracks into city centres, it provides, on the high-speed line for frequent long distance high speed trains and regional/commuter expresses, offering together up to (say) 15,000 seats/hour in each direction. By removing the need to operate classic intercity trains on the existing network it frees up paths for freight, for limited stop and local/regional passenger services. The latter group of train types operate together much more efficiently in terms of route capacity utilisation, with much less spread of journey times.

The very wide spread of benefit, for freight as well as passenger service expansion, means that it would be wrong to think of high-speed rail as tackling just the one capacity problem that arises on north-south routes. It offers much more than this, and also adds capacity for:

• London commuting
• Regional/local services into the main cities of the midlands and the north
• Freight

Having created a new infrastructure, it would be possible to adopt, in some future year, a duplex (double deck) vehicle design to achieve a further step change in passenger capacity without expensive infrastructure modification.

Q. How can you operate ‘regional/commuter express’ services over a high-speed line without compromising line capacity?

By reducing the speeds of the longer distance high speed trains over the common section approaching major cities. The time penalty, over say 60 km, of reducing speeds from 300km/h to 225km/h is 4 minutes. The prize is the ability to operate as many as (say) 18 trains/hour over the common section, compared with 11 trains/hour over the true high-speed section (the latter being the maximum achievable currently at 300km/h+). This is most likely to be relevant in the case of London. It means that 2 x (18 – 11) = 14 additional commuter trains per hour can be operated on the new high speed lines themselves on the north/west approaches to London, which is where demand growth is likely to be greatest.