This old thread being revived has prompted me to feel the need to comment . . .
Never intentionally lay your motor down to avoid a collision!
A sliding bike produces less than half the friction force of a braking bike.
Example: At 35 mph a sliding motor will require a minimum of 102 feet to stop.
A braking motor (skill dependent) requires a minimum of 45 to 54 feet to stop. A huge difference!
Braking could save you from an impact or at least greatly reduce your impact speed and injury exposure.
Additionally, when you are down and sliding, cage bumpers and wheels are much more hazardous than flying over your bars.