Police are investigating reports of careless driving and vandalism.
The motoring offence is reported to have happened shortly before 9am on Wednesday.
A white Renault is said to have overtaken carelessly while driving north between the South Nesting junction and the Kergord junction, forcing other cars to take evasive action.
Police are particularly keen to speak with the driver of the oncoming vehicle and a further vehicle, which was described as a Black Mitsubishi.
Police are also looking to speak to any potential witnesses after reports of vandalism to a red Volkswagen Golf in Lerwick.
That incident is said to have happened on Monday or Tuesday in the car park between 182 and 192 Sandveien.
The Golf’s rear wiper was said to have been damaged.
Anyone with additional information on either incident is being asked to contact 101, or the independent charity Crimestoppers anonymously on 0800 555 111.