Why is it important to leave extra space behind a large vehicle when stopped on a hill?

• The large vehicle may roll forward when the driver releases the brakes.
• The large vehicle may roll backward when the driver releases the brakes.
  Explanation:

  "When stopping behind a large vehicle on a hill, it’s important to leave extra space because the vehicle may roll backward when the driver releases the brakes. "
• The large vehicle might not stop at the red light.
• The large vehicle does not need to stop at a red light.