The Scottish Government's transport minister has dismissed concerns from MSPs that the introduction of free bus travel for under-22s could see fares increase for other passengers.
Graeme Dey insisted he had been "alive to the risk" of such unintended consequences when developing the scheme.
He spoke out as MSPs on Holyrood's Transport Committee gave their backing to the policy - which builds on existing free bus travel for those aged under 19.
The transport minister told the committee that extending this to all those aged under 22 had "enormous potential" and was a "fantastic opportunity".
That was despite telling MSPs that the Scottish Government currently has only "guesstimates" on how many young people will take advantage of the policy when it comes into effect from January 31, 2022.
Dey said: "We won't initially see the kind of levels of usage that we ultimately are going to see. There will be a soft period where we will undoubtedly see an uptake in usage, and we will have to build upon that.
"So we have estimates, but they are guesstimates, frankly, about levels of usage.
"But we are confident this is going to be a major success as a policy."
While bus operators will be reimbursed for all travellers who benefit from free tickets, the committee heard the payments for this would be less than the full cost of an adult fare.
And Tory MSP Liam Kerr raised concerns that that could mean charges for other passengers would have to rise.
The Conservative told Dey that the money bus operators would receive would be "significantly less" than a full adult fare, demanding to know if there was "any risk that adult fares may have to increase at any point to compensate for lost revenue"
But the minister told him: "We don't believe that to be a risk because we are working very closely with the operators, the bus operators on this scheme.
"The levels of reimbursement have been shaped very much on that dialogue and we are committed to return to these numbers in due course if anything emerges that suggests that the levels of reimbursement are not appropriate.
"So we don't anticipate an issue of the type you are flagging."
Dey told the committee: "Free bus travel for people under 22 will help strengthen our response to the climate emergency, and support our green recovery by embedding sustainable travel habits in young people."
The policy is being brought in as part of a budget deal between the Scottish Government and the Greens.
And Green MSP, Mark Ruskell, said: "This is going to be a brilliant policy. I think it is going to be transformational for young people. So many young people, particularly in rural areas, are excluded by the price of bus travel."
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