Bosses running what is believed to be the most expensive rail line in the UK have defended the new shuttle service, insisting its value is "huge".
A one-way fare for the 1.3-mile trip on the Dart system between Luton Airport and its nearest mainline station - Luton Airport Parkway - will cost £4.90 and the journey takes under four minutes.
That works out at £3.77 per mile, which means it is more costly that the Heathrow Express that runs between Heathrow Airport and Paddington station.
Since last week, a limited number of passengers have been invited to use the £290m Dart (direct air-rail transit) scheme at no cost.
But by the end of this month, a full commercial operation is set to begin.
And the current bus service between the airport and railway station - which costs £2.40 one-way and £3.80 for a return - will then be withdrawn.
The "innovative" Dart service, which the King tried out during a visit to the Bedfordshire town last December, was funded by Luton Rising, the body which runs and owns the airport on behalf of Luton Council.
It includes a new station built next to Luton Airport Parkway.
Construction delays, the impact of the COVID pandemic and inflation have been blamed for the scheme opening two years behind schedule and around one-third over budget.
Luton Rising said on its website: "The Luton DART is an innovative passenger transit system, connecting Luton Airport Parkway station to London Luton Airport in under four minutes.
"The new link replaces the original bus shuttle, delivering a significantly better passenger experience to the airport."
Chief executive Graham Olver claimed the Dart is "like the Suez Canal". He said: "It connects two important parts. Its value is in the connectivity. There's a station here that's future-proofed.
"We have a bridge. We have tunnelling. We have a station at the airport. Per mile of course it looks expensive, but its value is huge."
Mr Olver admitted the Dart is more expensive than the bus "but it's all really about value and convenience".
"Everyone that we've spoken to who's travelled on it has been delighted that the quality of service is so much better.
"If you're a savvy purchaser, coming from London a family of four can get a return ticket for less than £50."