The incident happened on the A429 between Crudwell and Kemble at around 9.15pm on Friday.
A man and a woman have been arrested after a crash on the A429 left an 18-year-old man fighting for his life.
Police said a 35-year-old woman and a 56-year-old man from Kemble were arrested on suspicion of driving a motor vehicle with excess alcohol, perverting the course of justice and causing injury by dangerous driving.
They have been released under investigation.
The incident happened on the A429 between Crudwell and Kemble at around 9.15pm on Friday night.
Anyone who may have been driving on the A429 at that time should contact police on 101. Police especially want to hear from anyone with dashcam footage.
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