What does the zigzag line on the highway mean?

[Frederick]

The zigzag line on the highway is called a longitudinal deceleration marking. The longitudinal deceleration marking for the traffic lane consists of a series of diamond-shaped dotted lines parallel to the lane dividing line. It is usually set at bridge approaches, turns, and other locations. Its main function is to create a sense of visual narrowing of the lane, inducing drivers to automatically slow down at curves, slopes, and other areas where deceleration is required. Below is more related information: 1. Deceleration Markings: When vehicles pass through sections with longitudinal deceleration markings, drivers will subjectively perceive the lane as gradually narrowing, prompting them to take deceleration measures and proceed slowly. This effectively prevents sudden braking near stop lines. 2. Types of Deceleration Markings: Deceleration markings are divided into two categories: transverse deceleration markings and longitudinal deceleration markings. Transverse deceleration markings consist of a series of parallel white dotted lines, while longitudinal deceleration markings are a series of diamond-shaped dotted lines parallel to the lane dividing line, starting at the beginning of the longitudinal deceleration marking. These markings are typically placed before bridge approaches, toll plaza areas, exit ramps, curves, slopes, and other locations. The main forms include single dotted lines, double dotted lines, and triple dotted lines. If the deceleration marking is adjacent to a solid line, lane changes are not allowed; if it is adjacent to a dotted line, lane changes are permitted. The design of deceleration markings creates an illusion of lane narrowing, inducing a sense of pressure and prompting drivers to slow down automatically in advance, thus avoiding sudden braking or accidents due to delayed avoidance.

[McPresley]

I've been driving on highways for over twenty years, and I've seen plenty of those sawtooth markings. They usually appear before sections that require extra attention, like curves, toll booths, tunnels, or accident-prone areas. If you look closely, you'll notice they consist of a series of short diagonal lines forming a triangular shape, running parallel to the lane like saw teeth. This design is meant to make drivers instinctively feel the lane is narrowing, prompting them to brake and slow down. I've encountered a few situations driving at night in the rain where headlights reflecting off these sawtooth lines were particularly glaring. At first, I wondered why, but later realized it's to force drivers to stay alert. Remember, once you enter a sawtooth-marked area, it's best to stay in your current lane and avoid changing lanes until you've passed through the potentially hazardous section.

[NevaehMarie]

When I first got my driver's license and drove on the highway, I mistook the sawtooth lines for road patches. Later, I specifically looked it up and learned that these are longitudinal deceleration markings. The biggest difference between them and regular solid or dashed lines is their strong visual deception effect—they create an illusion of road narrowing through staggered short lines. Once, when transitioning from a flat section to a mountainous highway, I saw sawtooth-shaped reflections on the ground from afar and immediately slowed down. After turning the corner, I found it was a steep downhill with a sharp curve, almost causing an accident. Now, whenever I encounter these markings while driving, I remind myself of three things: first, check the navigation to anticipate the road conditions ahead; second, ease off the accelerator to reduce speed below 80 km/h; and third, check the rearview mirror to be prepared for emergencies. After all, these markings usually indicate areas with special risks.

[Russell]

As a member of the road maintenance crew, I must say that the sawtooth line is one of the smartest safety designs on highways. It uses white diagonal lines spaced 0.5 meters apart to simulate a perspective effect, tricking the brain into misjudging the lane width as narrowing, making it over five times more effective than regular speed reduction markings. Last week, while repairing markings at a tunnel exit, we measured that the accident rate on this stretch was three times higher before the sawtooth lines were installed. Two details require special attention: First, it's always used in conjunction with solid white lines, and changing lanes in this area directly results in a 3-point penalty; second, the markings are 2 millimeters thicker than regular lane lines, making them more prone to water accumulation and reflection during rain, so it's safer to slow down in advance.

[McIan]

After studying hundreds of highway marking designs, it was found that zigzag lines most frequently appear before three major hazardous sections: first, on stretches with a continuous downhill gradient exceeding 5 degrees within 3 kilometers; second, densely arranged starting 5 kilometers before toll stations; and third, invariably present 300 meters before long tunnel entrances. Once, while reviewing dashcam footage, it was observed that drivers' average reaction time on regular road sections was 1.2 seconds, whereas the visual stimulus of zigzag lines could reduce this to 0.8 seconds. A notable example is a section of the Shanghai-Kunming Expressway, where accident rates plummeted by 80% thanks to a series of zigzag lines installed 300 meters in advance. This dual physical and psychological approach to design represents the pinnacle of safety solutions.

[AuroraFitz]

I commute 60 kilometers on the highway every day, and I hate driving over the serrated line sections on rainy days the most. Those raised diagonal lines, when soaked by rain, turn into a light pollution nightmare under headlights. But this design did save me once—last winter when approaching an icy curve, it was the reflective serrated lines that made me slam on the brakes, and as a result, while five cars ahead piled up in a chain collision, my car stopped in time. Now whenever I encounter these markings, I reflexively do four things: turn off cruise control, position my foot above the brake pedal ready to act, turn on hazard lights to alert vehicles behind, and glance at the fuel gauge to ensure emergency power. After all, safety is the shortest path home!