How Far Should the Distance Be in the Rearview Mirror to Change Lanes?
3 Answers
You can change lanes when the distance in the rearview mirror is less than 9 meters. Judging the distance to the car in front during traffic jams: A following distance of about 2 meters is generally appropriate. Being too close can easily cause a rear-end collision, while being too far may allow other vehicles to cut in. Under normal circumstances, the distance can be judged based on the position of the rear bumper and tires of the car in front as seen from the contour line of your car's front: seeing the upper edge of the rear bumper—distance is 1m; seeing the lower edge of the rear bumper—distance is 2m; seeing the lower edge of the rear tires—distance is 3m. Judging the distance to the stop line when leading: When you can see the stop line aligned with the 5 cm point of the front door corner through the car window, your car is aligned with the stop line.
I've been driving long-haul trucks for twenty years, and judging the distance when changing lanes by looking in the rearview mirror is quite an art. Generally speaking, when the following vehicle only occupies a small portion in the mirror, the distance should be at least 100 meters to be safe, especially on highways where higher speeds require even greater distances. I always use the three-second rule: pick a reference point, like a road sign, and after the following vehicle passes it, I count to three before making my move—this ensures enough reaction time. Always remember to check the blind spot by turning your head. When I was younger, I once nearly caused a rear-end collision because I didn’t check. Now, in bad weather like heavy rain, I increase the distance even more to account for slippery conditions. When the truck is loaded with cargo, I’m even more cautious—I’d rather wait a few extra seconds to observe more. Getting home safely is more important than anything. Overall experience has taught me that distance needs to be adjusted flexibly—don’t just rely on rules recklessly.
As a driving instructor for over a decade, my fundamental principle for teaching students lane changing is ensuring sufficient reaction space through rearview mirror distance checks. Typically, when the following vehicle occupies no more than one-third of the mirror's field of view, it equates to an appropriate distance of 80 to 100 meters. For every 10 km/h increase in speed, the distance should be extended by 10 meters. Safety steps: first check the rearview mirror to confirm distance, then quickly glance over your shoulder to scan the blind spot area, and only after confirming no vehicles are present, signal for at least 3 seconds before gradually changing lanes. A common mistake during practice is impatient lane cutting, which is why I emphasize doubling the distance during rainy or nighttime conditions. When students master this judgment combining speed and road conditions, their accident rates significantly decrease.
