52-vehicle Pile-up On A Highway A31, Emsland Autobahn, Germany

Causes
Pile-ups generally occur in low-visibility conditions as drivers on freeways are sometimes caught out by driving too close to the vehicle in front and not adjusting to the road conditions.
Due to the high traffic speeds on the road, if one car develops a problem and suddenly halts, those behind it cannot stop in time and may hit it. Considering that these roads often have high traffic volumes, more cars are forced into braking and skidding, darting into other lanes and in front of oncoming traffic and so more vehicles become involved, creating a chain reaction effect.