On any given day, hospitals divert ambulances as much as 40 per cent of the time due to overcrowding in their emergency departments – but reducing the volume of walk-in patients with minor illnesses will not alleviate the problem, says a new study by U of T researchers. “There is much speculation about the causes of overcrowding and ambulance diversion, but little research has actually been done on this issue,” says Dr. Michael Schull, assistant professor in emergency medicine at U of T and emergency department physician at Sunnybrook and Women’s College Health Sciences Centre. “We felt it was important to examine the problem in a more systematic way, so we looked at the experience of Sunnybrook and Women’s emergency department over a one-year period.”