During critical mass in Toronto they decided to take to the expressway. While I have seen this in other cities, in Toronto they took over the entire thing.
The cyclists were part of Critical Mass, the huge group cycle that takes place on the last Friday of every month in Toronto and around the world. According to Martin Reis, who was in the pack, the decision to ascend the ramp onto the Gardiner Expressway was spontaneous (even though it bears some resemblance to a similar but much smaller Los Angeles freeway ride from two weeks ago), and was not intended to be a huge statement: as Reis put it, the groupthink was more along the lines of "Here we are. Let's take the Gardiner."
The cyclists started off in the merging lane, then gradually took over the rest of the lanes, controlling all of them by about the time they reached York Street. "We basically became like one giant automobile," Reis says. Fellow participant Nick Syperek told Torontoist that "it was exhilarating to see Toronto from that angle." Reis saw no confrontations between cyclists and motorists, characterizing the entire thing as "very very civilized, [and] very peaceful."
Here is the article and plenty of pics.