Two council workers were injured when the gritter they were in left the road in slushy and wet conditions.
The vehicle left the A970 at the Lang Kames about four miles south of Voe and rolled down an embankment. The two workers were able to get out of the cab but are receiving medical treatment for minor injuries.
Police and other council staff were called to the scene and an internal SIC investigation will be carried out to establish the cause.
In a statement the SIC said: “Road conditions at the time were slushy and wet, between prolonged spells of sleet and hail showers. No other vehicles or third parties were involved.”
The gritter will be recovered from the roadside in the next few days, when the weather allows it.