A school bus with flashing red signals has stopped ahead. What must you do?

When a school bus has stopped with its flashing red lights on, vehicles on both sides of the road must stop at least 20 feet from the bus. They must remain stopped until the bus has switched off its flashing red signals or resumed its motion. [When Red Overhead Lights are Flashing, School Buses: What do the Flashing Lights Mean?, 5 Sharing the Road Safely - Be Courteous!, What Every Driver Must Know]