It happened on April 25 this year and the teenager committed the offence while on an undertaking to appear at Ayr Sheriff Court on May 13.
It was one of five offences the girl, who cannot be named for legal reasons, committed.
On the same day, she assaulted two police officers in the execution of their duty by repeatedly spitting at them.
Five days prior to the carriageway incident and the one with the police officers, at the A&E department of Ayr Hospital in Dalmellington Road, the girl behaved in a threatening or abusive manner, likely to cause a reasonable person to suffer fear and alarm and she did behave in an aggressive manner, repeatedly shouting, swearing and uttering abusive remarks.
On the same date the girl punched a cubicle wall in the hospital, causing damage.
The accused, from Ayr, appeared at the town’s sheriff court on Tuesday, August 20, and admitted the offences.
She also pleaded guilty to failing to comply with bail curfew conditions which had been imposed by the court.
The accused’s solicitor said: “She was 16 at the time of the offences. She has now turned 17.
“The offences involved a substantial amount of alcohol. She has been on a curfew since April.”
Sheriff Scott Pattison sentenced the teenager to an 18-month community payback order and 220 hours of unpaid work in the community to be completed within the next nine months.
The girl will also be placed under supervision.
