Almost 500 shifts that should have seen two on board ambulances had only a sole employee take charge of the vehicle between April and June this year, according to new figures.
In 2008, Ms Sturgeon announced that £4.7 million would be spent on ensuring that the need for single crews would end "in all but the most exceptional circumstances." It followed concern raised about patient safety due to the frequency with which it was occurring, particularly in rural areas.
Ms Sturgeon, Deputy First Minister, told MSPs that single crewing would be eliminated by January 2009.
Her successor Alex Neil has admitted more than half of the one-person ambulance shifts in the latest three-month period had taken place when there were no exceptional circumstances, usually meaning short-term sickness absence, and that the Scottish Ambulance Service was still "working hard" to achieve the goal.
Conservative Highlands and Islands MSP Mary Scanlon obtained the latest figures through a written parliamentary question after local concern about the number of ambulances that were still being sent out with only one crew member.
She said: "This may not be an issue in urban areas, but it certainly is in rural ones. Nicola Sturgeon categorically said in 2008 that there would be no more single crews, but from this answer that's clearly not happened, despite the investment.
"It's not good for ambulance staff and it's certainly not good for patients. Trained paramedics cannot be expected to tend to a patient and drive an ambulance at 90mph at the same time, it's a completely unacceptable level of service."
The number of double-crewed ambulance rostered to be staffed by one paramedic accounted for 1.1 per cent of all shifts across Scotland in the three-month period. The practice occurred when there were no exceptional circumstances 260 times, or in 0.6 per cent of all shifts nationwide. If the figures were repeated over the whole year, it would mean more than 1000 two-person ambulances would be staffed by only one crew member during shifts.
Where single-crewing occurs, it is often as cover cannot be secured in rural areas at short notice. Many stations in remote areas of Scotland struggle to recruit or retain staff, as paramedics often prefer to practise their skills in busy areas, leading to pressure over staffing and accounting for single crewing when there are not exceptional circumstances.
A spokesman for the Scottish Ambulance Service said it does not routinely roster staff to be on their own on a double-crewed vehicle.
However, he added: "There may be occasions where some shifts are single-crewed, but every effort is be made to bring in cover if rostered staff are unavailable.
"This occurs in less than 1 per cent of shifts, other than for exceptional reasons. In some rural stations, which operate with smaller pools of staff, the challenges of recruitment and retention, as well as short-term absence, can at times have an impact on availability of relief staff. Shift cover is monitored on an ongoing basis."
A government spokesman said: "The numbers of instances of single crewing remains extremely low in comparison with the actual number of shifts across Scotland, taking into account the patterns of greatest demand for the service."
It said it was continuing to work with the service to reduce occasions when single crewing occurs.