A woman drives a bike wearing a white blouse with her brown hair blowing in the wind.
The woman is riding her bike to conserve fuel use.
Just because a women is driving a bike does not mean she is riding her bike to conserve fuel use.
The woman might be riding her bike for recreation or exercise, not necessarily to conserve fuel use.
Sentence 1 gives no reason why the woman is driving a bike, only describes the act of her driving it. Nothing suggests she is trying to conserve fuel use.