Unlimited travel possibilities become a lot more limited from the end of this month. Up to now, the best bargain for anyone wanting to see plenty of the United States was the unlimited travel air pass issued by Delta or Northwest. For dollars 499 (pounds 335), you could fly anywhere you wanted to in the US; Northwest would even take you to several Canadian cities.

Both airlines' unlimited travel schemes expire at the end of the month, and there are no plans for them to continue. The logic of this decision is hard to understand, since the cost to the airline was tiny. Travel was entirely on a standby basis - for any flight, you could be denied boarding, or even turfed off before take-off, if a fare-paying passenger turned up. But with careful planning, avoiding Fridays and Sundays, and the connivance of reservations agents ('the non-stop to Chicago is overbooked, but I can get you there through Cincinnati'), it was an impulse traveller's dream.

You could sit at the terminal at Minneapolis and study the weather charts before deciding between Disneyland in California and Walt Disney World in Florida. Then if, on your stroll to the right gate, you passed a departure to somewhere exotic-sounding such as Sarasota or San Antonio, it was difficult to avoid the temptation to ask if there was a spare seat. And because you were not booked on a flight, you never had to worry about getting to the airport on time.

If you were running short of cash, you could eliminate expenditure on food and accommodation by shuttling back and forth across the continent. But the greatest fun was to be had aboard the tiny commuter planes. I spent a joyful day bouncing from Boston to Martha's Vineyard to Nantucket, and have become irritatingly accustomed to flying across Los Angeles rather than driving - Delta operates a handy 50-mile hop over the deformed, congested freeways between Los Angeles and Ontario airports.

The Northwest pass even extended to bus services, as I found when I checked in at Portland for a 'flight' to Salem, Oregon. We were led out on to the apron, but instead of the expected Boeing found ourselves herded into a Ford minibus. The in-bus service was terrible.

There were other drawbacks, such as the tendency to see rather too much of the airlines' hub airports: I am on nodding terms with rather too many gate staff at Detroit, Atlanta and Salt Lake City. Some of them seemed to enjoy the stress they could generate while you waited, uncertain about getting a seat on the last flight out of Cleveland, but most were conspiratorially co-operative. Since the airline stood to gain not a single extra cent if I boarded a particular flight, I was continually impressed by the pains taken to get me on board.

These next few days offer your last chance to see huge chunks of the US on the cheap. If you're tempted, use one of the implausibly low fares across the Atlantic (eg, pounds 169 return to New York on Icelandair, through Benz Travel, 071-439 4181), and combine it with the 30-day pass through Delta (0800 414767) or Northwest (0293 561000). You must start your 30 days before the end of March.

One new possibility has arisen for seeing the North-eastern US for only pounds 99 for a week's unlimited flying. You can travel between New York, Hartford, Cleveland, Baltimore/Washington and Windsor (just across the bridge from Detroit). The catch is that you keep having to change planes in Toronto: the pass is for travel on the Air Canada subsidiary, Air Ontario (0737 832525).

Next week, Bargain Breakdown: how Virgin Atlantic spends the pounds 195 you pay for its new London-LA, New York-London fare.

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