What is a swerve, and when is it the right crash-avoidance choice?

1. A series of S-shaped weaves to slow down — used in all emergencies
2. Two quick consecutive counter-steering presses to change path around an obstacle — used when there is no time to brake to a stop
3. A skidding turn used only on gravel
4. A maneuver only legal in Maine on motorcycles with ABS