What do you think is smooth driving? Here's two of my ideas: 1) Always try to have as little acceleration as possible (either forward/backward for gas/brake or left/right for steering) as possible. That's quite safe I think - no acceleration, no force felt by the passengeers 2) Always try to have as little derivative of acceleration (da/dt=d^3x/dt^3) as possible. I came up with this idea thinking of myself standing on the subway. When the train starts to accelerate, I adjust forces on my hands and feet that make me steady. Now, if the acceleration changes a little, indeed I am able to manage these changes. And if the change is steady, I can even anticipate it. Obviously this is done for a very short time, as having a constant increase of acceleration makes x(t)=ct^3. If the train driver has to stop suddenly, the change is large and this is what causes the discomfort. What's everyone's opinion on this.