One prisoner and two members of the Prison Service were in the vehicle at the time of the accident.
The driver lost control of the van, it went out of control and overturned close to the Carrabane overpass between Junctions 16 and 17 of the M6 (Loughrea to Athenry) yesterday afternoon.
The vehicle may have hit the median dividing the east-west traffic flow and travelled for some distance on its side before coming to a halt.
Two ambulances, two units of Loughrea fire brigade and a number of Garda vehicles were quickly on the scene.
A second prison van, which was parked at Loughrea courthouse also travelled to the aid of those injured in the accident.
All three were removed to Galway University Hospital, but it is understood that none sustained life-threatening injuries.
The prison officers were transporting the prisoner from Dublin to appear at yesterday’s sitting of Galway District Court and the accident caused a major traffic backup for traffic heading west on the motorway.
The Prison Service said that the van was a vehicle typically used to transfer prisoners from one location to another. It contained two separate cells, with staff travelling in the front cabin.