What caused that multi-car pileup?

As I was getting onto the ANZAC bridge this afternoon, I spotted a police paddy waggon stopped on the city side of the bridge. It seemed an odd spot to stop - the bridge is four lanes wide each way, and traffic thunders across at a good clip. Stopping and stepping out of a vehicle, even a police car, is an open invitation to become a former Australian.

As I reached the crest of the bridge, I noticed that traffic was banking up in two of the lanes heading into town. The second lane was blocked because a white van had rear ended a small hatchback (not surprising - white van drivers tend to be amongst the most reckless and aggressive drivers on our roads). Then, to my surprise, I found that slightly further on, the third lane was blocked by a three car pile up. None of the damage looked particularly severe - I couldn't even see any dents in any of the five cars involved. They appear to have been moving just fast enough to break a lot of glass and plastic - the road was carpeted in it.

Two blocked lanes was not a good thing. As I tried to take a photo of the scene (and failed, due to bigger vehicles blocking my view of the crashed cars), I watched the traffic rapidly grind to an almost halt all the way back to Victoria Road.

I don't know if the stopped police car was the cause of all that carnage, or whether it had stopped because of it. I can imagine people panicking when seeing a cop car up ahead and slamming on the anchors, and that causing some rear-end shunts further back down the line.

Whatever. My bike lane was clear from end to end. I clipped into my pedals and kept on moving, homeward bound.