Yes. The less you press your foot on the gas, the less fuel is used to accelerate. It will take more time, but it does conserve fuel.
"like an arrow presently to his home in the green world beneath"
Answer:
I didn't read the book or know the story but I can imagine that if it is meant to be literal, he/she said it because having the disease made him/her more careful and weary.
Explanation:
It is kind of like what happened with this Corona. We heard about the "disease" and became more weary and careful. Also: sharpened our senses.