The car was moving at a terrific rate of speed, up grade, and down grade.
You business people are on the up grade just now, and you know it.
A half-hour went by, and still the car rattled on, up grade and down, without once slacking its speed.
Then No. 999 struck the edge of the up grade in safety, past the danger line, gliding along on clear tracks now.
Twelve miles an hour ...