What is the mandatory action required when a driver encounters a steady amber (yellow) light at a signalized intersection?

1. Stop before the stop line, unless the vehicle is already so close that stopping safely cannot be achieved without risking a collision
2. Accelerate quickly to clear the intersection before the red phase begins
3. Continue at the same speed because amber has the same legal meaning as green
4. Come to an immediate emergency stop regardless of the proximity of vehicles following behind