The Halifax Regional Municipality has hired an expert to take a hard look at the Armdale Roundabout.

The number of vehicle collisions increased significantly four years ago and has remained high ever since and HRM traffic officials aren't sure why.

After the Armdale Rotary was converted to a roundabout in 2007, there was no change in the collision rate — it stayed the same for a couple of years.

But in 2010 there was nearly a 30 per cent increase in vehicle collisions. That rate has either stayed at that level or jumped even higher in recent years. There were only a few incidents that involved pedestrians or cyclists.

David McCusker, the Halifax Regional Municipality's manager of regional transportation, said the stats are puzzling.

"The volumes have remained steady through that time so it's difficult to attribute to a volume increase," he said.

But McCusker acknowledges that the Armdale Roundabout is unique.

"Armdale has up to three lanes in the circle and that's really not characteristic of a standard roundabout design," he said.

Traffic officials in the city have hired an expert on roundabouts to do a safety audit.

"To see if there is a pattern that can be addressed through minor changes to signage or line painting or the way that the approaches operate," said McCusker.

The cost of the safety audit is expected to be about $10,000.