By Tom Symonds BBC transport correspondent

You may not believe it, but Britain's railways have improved.

The popularity of trains is partly due to improved service

Trains are more punctual than they've been for seven years partly as a result of improvements in the standard of the track, which reduces breakdowns.

Train companies have also got better at drawing up slightly slacker timetables, which they can actually keep to.

In fact many of the hold-ups for passengers these days are to do with planned engineering work, which should at least improve services in future, even if they do disrupt journeys today.

With Network Rail now boasting of a profit, to be ploughed back in the railways, can this much-maligned industry now relax?

No. Because success has brought a new problem.

Passenger numbers are now at a 50 year high and they're expected to grow by at least 10% a year in future.

'Grand projects'

The popularity of trains is partly due to the improved service, but also the steady growth in the economy, and the gradual snarl-up that is now enveloping Britain's roads.

Next week, the government will publish its biggest warning yet that how we get around in this country will be vital for our future economic success.

Any government wanting to build lots of new railway would have Britain's unwieldy planning laws to deal with First profit for Network Rail

The former British Airways Boss Rod Eddington has written a report that argues whether its rail, road or air travel, we need more of it.

On the railways that could mean pouring millions into a new high speed rail line to link up some of the major cities. Network Rail believes it could even be self-financing.

Eddington isn't keen. He's said to be worried about spending time, money and effort on French-style 'grand projects'.

Longer trains

Any government wanting to build lots of new railway would have Britain's unwieldy planning laws to deal with, to say nothing about the inherent lack of space in most of the country.

Instead his blueprint is expected to involve making better use of what we've already got.

New signalling would allow trains to run closer to each other

This is something Network Rail's already trying to do of course. It carries out line-by-line studies to work out how to squeeze extra services into the existing timetable.

Beyond that, train companies, Virgin in particular, are examining the possibility of running longer trains. This can mean extending station platforms, so its not necessarily an easy option.

Introducing double-decker trains is a daunting task as well, because of the need to raise the heights of bridges and tunnels across the network. Often suggested, it seems unlikely ever to happen.

Another long-term idea is to introduce computerised signalling systems which would allow trains to run closer to each other, every two minutes rather than every four.

It is technology that is already used on French high speed lines and therefore proven. But it would be expensive and disruptive to fit on our main rail routes. A trial is due to start next year.

So the big squeeze on Britain's railways has no simple solution.

The main problem is that it requires us to think now about the transport systems we will need in future.