I appreciate what you're saying, but am not that worried about it. If you are in a crash, a flexible fishing rod bopping you in the head will be the least of your concern. Of course there are many variables that play into a collision such as speed, deceleration (how soft the object you hit is), driver mass, etc.. A general back of the envelope calculation shows that for a 30mph crash, an average sized driver may experience as "little" as 3,000 pounds force, up to 24,000 pounds force for a particularly severe stop. That's just the force on the driver from the seat belt, steering wheel, airbag, or whatever stops their body. It's not a perfect calculation since it assumes the person's body is rigid and makes many assumptions, but is decent for an approximation.
The force from a fishing rod that was accelerated due to an airbag could be calculated using a similar method. However keep in mind that fishing rods also absorb energy, like many other things, and are in many ways designed to do so. Think about selecting the appropriate rod stiffness so you don't snap line. My math shows a typical rod would probably smack you with about 150 pounds of force. It'd hurt like Hell, sure.
My point is that a fishing rod is probably the least of my concern in a crash.