Questions Swirl After Bus Plows Into Train in Canada Chris Wattie/Reuters Investigators at the scene of a crash involving a bus and a train in Ottawa on Wednesday. The driver was among those killed. OTTAWA - Commuters were shocked and investigators were at a loss to explain why a double-decker transit bus drove past a warning light in Ottawa on Wednesday morning, crashed through safety barriers and plowed into a passenger train, killing six bus passengers and injuring 34 others. No one aboard the Via Rail Canada passenger train, which was derailed, was hurt, the authorities said. The accident took place at the end of the morning rush hour under clear skies. Several passengers aboard the packed OC Transpo bus, which can carry about 90 people, told reporters that while it was clear they were going to crash into the train, the driver seemed to brake only immediately before hitting the train locomotive. "People started screaming "Stop! Stop!" because they could see the train coming down the track," a university student, Tanner Trepanier, told The Canadian Press news agency. An onlooker, Mark Cogan, told reporters the driver "went through the guard rail and just hammered the train and then it was just mayhem." Witnesses said bodies of the dead and some of the injured were thrown from the bus, and a broken barrier from the crossing, not far from the Fallowfield station, could be seen under its wreckage. The bus was traveling on a special road network reserved for transit vehicles. An original plan for the crossing, near the suburban neighborhood of Barr Haven, had called for an underpass rather than a level crossing. But when groundwater problems inflated the plan's costs, the city got permission to use crossing gates that block all traffic lanes. Speculation was widespread that the driver, whom his union identified as Dave Woodard and who was among the dead, had suffered a heart attack or some other medical emergency immediately before the crash or that the accident may have been caused by mechanical failure. Passengers who had boarded just before the crash said Mr. Woodard had seemed to be in good health. The union said he had worked as a bus driver for about 10 years and had a flawless record. Since the double-decker buses were introduced about a year ago, some drivers have complained about the brakes. Jean Laporte, the chief operating officer of the Transportation Safety Board of Canada, which is leading the investigation, said that it may take months to determine a cause. The accident is the second deadly episode involving railways in Canada this summer. On July 6, a runaway freight train carrying crude oil derailed in Lac-Mégantic, Quebec, killing 47 people and destroying its downtown in a series of fiery blasts.