Bicyclists gather in front of the Vancouver Art Gallery in preparation for another Critical Mass protest ride. (CBC)

An estimated 1,000 bicycle-riding members of Critical Mass again disrupted Friday's rush hour traffic in Vancouver in the latest of the group's planned monthly protests to promote urban bike use.

They gathered in front of the Vancouver Art Galley at West Georgia Street and Howe Street at 6 p.m. to begin their latest group ride.

The huge pack snaked through a number of areas downtown and on Vancouver's east side, crossing the Cambie Street Bridge and the Burrard Street Bridge as part of a spontaneous three-hour circuit.

There were no early reports of the kind of angry confrontations between bicyclists and car drivers that have marked previous Critical Mass protests. Still, drivers did express frustration with the traffic disruption.

"I'm just trying to get to an engagement party for somebody, so we'll see. I hope I'm on time," one driver told CBC News as her car idled on a downtown street.

"It's a bad thing. Bad for us. It's bad for them, too," another driver said, nodding in the direction of the bike riders.

Vancouver police said they'd met with participants of the ride, who declined to indicate the route the cyclists plan to take.

Mayor critical of chaos

Earlier this week, Vancouver Mayor Gregor Robertson made a public plea for co-operation. He said the traffic chaos associated with the monthly protest ride needs to stop.

"We need to move from what has been more of a protest in the past, to just having a great celebration ride, having a predictable route and being able to manage the conflict right out of the picture," Robertson said Thursday.

But the Critical Mass bike ride has evolved without leaders or planning, and the route is determined on the whim of whoever happens to be at the front, causing traffic tie-ups and leaving pedestrians stranded on sidewalks during the Friday afternoon commute.

'We saw an increase in the violence that has occasionally marred the ride.'—Vancouver Police Insp. Rick McKenna

Vancouver police say the protests swell to thousands of riders in the summer, covering more than eight city blocks and lasting for hours, and police are worried about angry clashes with the public.

"Last month we saw an increase in the violence that has occasionally marred the ride. The violence has come from both sides. This time a driver was arrested for assault and a bicyclist was injured. Riders are often guilty of mischief and tactics that exacerbate the conflict," Insp. Rick McKenna said in a statement issued Tuesday.

Police are also concerned about alcohol and drugs consumed on the ride.

Vancouver's Critical Mass ride is part of a worldwide phenomenon that takes place on the last Friday of the month in about 300 cities. The riders aim to take over major roads to promote the use of bicycles as a primary mode of transporation and to push for more bike lanes.