Final answer:
Safe lane merging requires a 4-second gap, allowing sufficient reaction time and translating into several car-lengths. Adjust this timing based on speed and road conditions for optimal driving safety.
Step-by-step explanation:
When merging or changing lanes, it is recommended to have a gap that allows for at least a 4-second rule between you and the vehicles in the lane you are entering. This rule can be applied by picking a stationary object on the road, such as a sign or a tree, and counting the time it takes for you to reach the same point after the car in front of you passes it. If it takes at least four seconds, then you likely have enough space to merge safely.
This time gap provides sufficient distance to react and stop if necessary, which translates into several car-lengths depending on your speed and road conditions. It's essential to consider speed limits, traffic density, and visibility to adjust this timing for safety. On a freeway, if you are moving at a high speed, this distance will be greater than in a city with lower speed limits.