Secret: I didn't know the difference between "farther" and "further" until today.
FARTHER denotes physical advancement in distance.
FURTHER denotes advancement to greater degree, as in time.
The correct answers to the above examples follow:
It is farther down the road. (For distance physically traveled.)
You read further in the book. (To a greater degree than where you are now.)
You further your education. (To a greater degree than what you have now.)
Thanks, LessonTutor.com!