OTTAWA -- City buses in the nation's capital halted Thursday morning in sombre tribute to six people killed when an OC Transpo bus collided with a Via Rail passenger train a year ago.

Bus drivers who could safely do so pulled over and turned off their engines for a moment of silence at 8:47 a.m. EDT -- the exact time that OC Transpo bus 8017 slammed into the Via locomotive last Sept. 18.

Flags on city buildings were lowered to half-mast for the day in remembrance while police and rail officials kept watch over the crash site as people placed flowers and personal mementos nearby.

There are no answers yet for family members and friends of the victims who have struggled with questions about why the crash occurred and whether it could have been prevented.

The Transportation Safety Board has painstakingly pieced together bits of bus wreckage and witness interviews for nearly a year and officials said they are just now in the early report-writing stage of their investigation, promising an update by next week.

Transit, city and union officials say the tragedy took a toll on the entire city.

The bus route number, 76, has since been officially retired. But Craig Watson, president of Amalgamated Transit Union local 279, says the catastrophe is still fresh in the minds of city bus drivers, as it is for the surviving passengers and the friends and loved ones of those who died.

"I don't think a single driver goes by there without remembering what happened and the tragedy of six people's lives cut short," said Watson.

"The whole city, really, took a deep reflection on everything because so many young people were lost in this," he added.

TSB investigators Robert Johnston and Dan Di Tota were scheduled to offer an update on their preliminary findings at a news conference next Wednesday, although board officials say final conclusions could be far off.

Driver Dave Woodard was killed when the train sheared off much of the front of the double-decker bus after it went through a rail crossing gate.

Passengers Connor Boyd, Kyle Nash, Michael Bleakney, Karen Krzyzewski and Rob More were also killed.

Boyd and Nash were students at Carleton University and Krzyzewski was a Carleton graduate. The school also held a memorial.

"Our thoughts go to their families and friends at this time, as well as to all others who lost their lives or were injured in the accident," university president and vice-chancellor Roseann O'Reilly Runte said in a statement Wednesday.

Since the tragedy, the city has removed brush and anything else that might have obstructed the view at the west-end crossing where the accident happened, said John Manconi, OC Transpo's general manager.

Within a month of the crash, the speed limit on the approach road in both directions was reduced and new warning signs have been erected.

Via Rail has personnel at the crossing every day, monitoring traffic and using signs to slow approaching vehicles and guide trains into and out of the nearby station.

A team of peer supporters went to city bus garages to help grieving colleagues as they recalled the events of last year.

Local 279 vice-president Sharon Bow has been in direct contact with Woodard's widow and teenaged daughter since the tragedy and in particular in the days leading up to the anniversary, said Watson.

"We wanted to make sure that the family is OK with what we're doing just to make sure that it wouldn't upset them in any way," he said.

The fatal collision focused attention on the more than 40,000 provincially and federally regulated public and private level railway crossings throughout the country.

After the accident, the Ottawa area was plagued for months by signal and gate malfunctions at a number of crossings, including the fatal site.

However, investigators have said there were no malfunctions there on the day of the crash. They say the crossing gate was fully horizontal and warning lights flashed for 25 seconds before the collision.

Foreign Affairs Minister John Baird and MP Pierre Poilievre, who represent ridings in south Ottawa, said Thursday that emotions remain raw from the incident.

"We can't help but experience these feelings every time we drive past the crossing," the MPs said in a joint statement.

"To allay the fears of our neighbours, we have been steadfast in our determination to ensure all local rail crossings function the way they should."