A £700,000 scheme to double the size of the Thornhill park-and-ride at Sandhills car park is likely to be completed by May next year.
Planning consent was given earlier this year for 200 new parking spaces.
Further details were revealed at the county council environmental committee, where councillors approved funding for the development.
The car park is just off the A40 and is used by people commuting to London.
The extension, immediately west of the present car park, would use the same access and would incorporate security lighting and cameras.
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