What must you do before changing lanes?

Before changing lanes, it is essential to check your mirrors and blind spots to ensure the lane is clear and safe for you to merge into. This crucial step helps you assess the speed and distance of vehicles around you, particularly those that may be in your blind spots, which are areas not easily visible in your mirrors. By performing a thorough check, you minimize the risk of collisions and enhance your safety and that of others on the road.

The other options do not align with safe lane-changing practices. For example, switching on emergency lights is not relevant when simply changing lanes, as those lights are intended for emergencies or when your vehicle is not operational. Similarly, waiting for five seconds is unnecessary and may disrupt traffic flow, and driving on the shoulder is unsafe and generally against traffic laws unless directed by road signs in specific scenarios. Thus, checking your mirrors and blind spots is the correct procedure for safely changing lanes.