County transport chiefs have ruled out extending a popular free travel scheme for young children to those aged 16 to 18.

The Freedom Pass, which is run by Kent County Council, currently allows 11 to 16-year-olds free bus travel across the county.

It has proved hugely successful since its introduction in 2007 and about 100,000 journeys are made using the pass each month. From September, it will be available across the whole county.

Backbench councillors on KCC's policy scrutiny committee pressed the authority to consider extending it to older children, saying it would further reduce congestion in busy town centres. They also urged the council to change the rules so about 1,400 youngsters who live in Kent but go to schools outside the county are able to apply for the £50 pass.

However, Cllr Keith Ferrin (Con), KCC cabinet member for highways, said the costs of extending the scheme would be prohibitive even though he would be "delighted" if he could find the money.

He said: "The budget implications would be major and would involve [spending] the same amount of money again. The take-up would be very high, probably much higher than it is in the lower age group. We have to set boundaries and extending the scheme to 16-to-18-year-olds would be beyond the scope of what we could do," he said.

He also resisted demands to amend the existing rules that prevent pupils who live in Kent but go to school elsewhere from having a pass.

"Of course we would prefer it if everyone was able to have a pass. We have looked at the numbers and there are between 1,300 and 1,400 who are in this position. I am not comfortable about that."

Opposition Labour spokesman Cllr Roger Truelove said: "The numbers are not huge and I do not believe the costs would be prohibitive."

Tonbridge councillor Godfrey Horne (Con) said extending the scheme would ease congestion even more. "This is the age they [16-to-18-year-olds] are beginning to look at cars and we should be able to stop it."

KCC believes that the scheme has already helped ease the impact of the "school run" on traffic congestion around the county.