After passing another vehicle, it’s crucial to check that you're maintaining a safe distance before merging back into the lane. A useful guideline is to ensure you can see the entire front of the vehicle you've passed, particularly its headlights, in your rearview mirror. This check helps confirm a safe space buffer between you and the vehicle behind, minimizing risks of a collision due to abrupt merges. Maintaining appropriate spacing helps keep the flow of traffic smooth and avoids potential accidents from cutting in too closely.