Between 4,000 and 5,000 cyclists have flocked to the Adelaide suburb of Glenelg for a Lance Armstrong led Twitter ride.
Cycling stars Lance Armstrong and Robbie McEwen took over the coastalAdelaide roads on Saturday morning with their impromptu social ride.
Using the social network Twitter, the pair announced two days ago that they were leaving from Glenelg's Wigley Reserve at 9am.
Police estimate the ride attracted a massive crowd of between 4000 to5000 cyclists of all abilities, who rode north along the coast toSemaphore and back.
About a dozen officers on motorbikes used a rolling stoppage to shut down the roads.
There were predictably crashes, but SA Police Traffic PlanningCo-Ordinator Senior Sergeant Harry McCallum said there were no majorincidents.
"We got through safely, our people managed it to their satisfaction," McCallum said.
"In reality, it was like Brown's Cows, but our plan allowed for that."
South Australian Premier Mike Rann, who is up for re-election soon, greeted McEwen and Armstrong before the ride started.
"Hey, where's your bike? Look at all these voters!," Armstrong told the premier.
Armstrong, from Texas, has won a record seven Tours de France, while McEwen is one of Australia's greatest cyclists.
Armstrong has held similar rides in other cities, but this one was by far the most popular.
He has usually announced them with only a few hours' notice, but thistime Armstrong confirmed it at a Thursday media conference.
Armstrong is in Adelaide to compete in the Tour Down Under, whichstarts on Sunday with the standalone Cancer Council Classic street raceat Adelaide's East End.
The six-day Tour starts on Tuesday.
McCallum said the SA Police had assumed Armstrong would hold a Twitter ride in Adelaide and had done plenty of planning.
"Two or three months ago, we had no doubt he would do one," McCallum said.
"By Thursday, we'd worked out where it would go.
"We knew it was coming, it was just a matter of getting the logistics in place."
Once Armstrong left, it took about 15 minutes for the rest of the riders to leave Glenelg.
The ride initially went at a slow pace, but Armstrong, McEwen and theother ProTour riders at the head of the massive bunch soon realised thedanger.
Some riders were trying to ride next to Armstrong andtake their picture, so the leaders ramped up the pace to string out thebunch.
Other top riders who took part included Armstrong'slong-time friend George Hincapie, former Australian professional PatJonker and Australian champion Amber Halliday.
Team-mates ofArmstrong (RadioShack) and McEwen (Katusha) also rode. "I'm justsurprised by the sheer numbers, this is out of control," McEwen said.