When a traffic accident or breakdown occurs on an urban expressway or elevated highway, what is the mandatory distance to place the reflective warning triangle behind the vehicle?

1. 1 meter behind the bumper
2. At least 150 meters (150米以外) behind the vehicle on expressways (and 50–100 meters on regular urban roads), with hazard warning flashers turned on
3. On top of the vehicle front windshield wiper
4. No warning triangle is needed if the driver stands behind the car waving their arms