[Brian R.]

This is the caution you must exercise when you have a manual transmission. It is understood that a car in neutral may roll.

The only way to be sure that it won't move is to shut off the engine, place the transmission in reverse, and use the handbrake (or chock the wheels for maintenance). The handbrake by itself is not designed to ensure against rolling on a hill, since a hill may have any slope, whatsoever. This is the reason for driving safety courses to emphasize that, when parking on a hill by a curb, you turn the front wheels so that if your car rolls, it hits the curb immediately and does not roll further.

If you were a car manufacturer, would you install another safety feature in your cars which cost everyone who buys one an additional $100? Even in this day of way too much safety consciousness, there is a limit to ridiculous add-ons for those with no common sense.