To me it appears as if the added forward mass of her considerably larger than average mammory glands caused her to have a further forward center of gravity than the bi-wheeled human powered locomotion device was designed for.

With all that added weight pulling her forward and the slow speed of her vehicle it caused the front wheel of the bicycle to turn sharply to the side. This sharp turn caused her forward momentum due to her being "top heavy" to become even more forward momentum, while the turning wheel of the bicycle caused it to have a sudden dramatic reduction in velocity.

This caused her to lunge forward out of control over the stalling human powered bi-wheeled locomation device and fall forward on to the asphalt coated travelling surface.

I guess it was a good thing she has built in air bags;... but the way I see it they actually contributed greatly to her accidental unplanned meeting with the road surface.

This just goes to show you how dangerous being well endowed can be...

So be careful people, big knockers can cause you pain!
(especially when their boyfriends catch you staring at them)