How to Determine the Following Distance?
4 Answers
Methods to determine the following distance are as follows: 1. Use the rearview mirror to judge the distance of the vehicle behind: According to the physical principle that objects appear larger when closer and smaller when farther away, when the image of the following vehicle occupies one-third of the rearview mirror, the distance should be approximately 12 meters. When the image occupies half of the mirror, the distance is about 9 meters. If the image fills the entire mirror, the distance is roughly 3 meters. 2. Judging the distance to the vehicle ahead during urban driving: A general following distance of 3 meters is appropriate. When the rear bumper of the vehicle ahead is visible from the driver's seat, the distance is about 1 meter. When the lower edge of the bumper is visible, the distance is approximately 2 meters. Seeing the rear tires of the vehicle ahead indicates a distance of around 3 meters. 3. Utilize roadside reference objects: On highways, where following distances are greater, the above methods may not apply. In such cases, fixed objects like lamp posts can serve as references to estimate distance and maintain proper spacing. Typically, the distance between two adjacent lamp posts is equal and measures 50 meters, so three lamp posts represent the standard highway following distance of about 100 meters. Pay close attention when observing; if the time it takes for the vehicle ahead to pass from one lamp post to the next decreases, it indicates rapid movement, allowing for acceleration. Conversely, if the time increases, reduce speed appropriately.
Here's a practical tip for judging following distance while driving: observe the rear position of the vehicle ahead. When you can fully see where the rear tires of the preceding car contact the ground, the distance is approximately 5 meters; if only the lower edge of the bumper is visible, it's about 3 meters; when even the bumper's lower edge is obscured, the distance is less than 2 meters and you should immediately decelerate. Another method is the '3-second rule': pick a fixed reference point like a road sign, and when the front vehicle passes it, silently count '1001, 1002, 1003' - if you haven't reached the reference point by the time you finish counting, you're at a safe distance. On highways, extend this to 4 seconds, and add another second in rainy conditions. Personally, I maintain at least half a car length gap in heavy traffic to allow braking reaction time.
The key to judging following distance is leaving enough reaction space. When driving at 40 km/h in urban areas, I maintain at least 15 meters from the car ahead, equivalent to three car lengths. At 100 km/h on highways, I keep over 100 meters distance. The simplest test method is performing a full brake on dry pavement – stopping from 60 km/h requires about 20 meters, which helps me calculate safe distances at different speeds. Whenever I see the leading car's brake lights, I immediately release the accelerator and prepare to brake. Many modern vehicles' active safety systems can also assist monitoring, with dashboard warnings for collision risks, but never rely entirely on electronic aids.
As a beginner, I was most afraid of rear-end collisions while learning to drive. My instructor taught me to use the windshield as a reference for distance judgment. For example, when waiting at a red light, if the bottom of the rear wheels of the car in front just disappears below the hood, the distance is about 2 meters; if the entire tire is visible, it's more than 4 meters. While driving, I like to reference the lane markings: each dashed line segment on urban roads is 5 meters long, and maintaining a distance of three segments is safest. Another simple method is to buy a small bear magnet and stick it to the edge of the windshield—aligning it with a specific part of the car ahead can help estimate distance. Remember, following distance shouldn't be rigid; leave an extra 10 meters for trucks and add one-third more spacing on rainy days.
