What are the green lasers on the highway used for?

[Hector]

The row of green laser lights on the highway are anti-fatigue laser lights. The purpose of turning on anti-fatigue laser lights on the highway at night is to remind drivers to stay alert and avoid fatigued driving. Here is some relevant information: 1. These green laser beams have a long irradiation distance and are particularly noticeable at night. The laser lights come in two forms: constant-on and strobe, with a range of 2 kilometers, which can effectively stimulate the driver's brain and use this method to avoid fatigue. These lasers are generally only installed on relatively straight sections of the road. 2. The installation of anti-fatigue laser lights on the highway can provide visual stimulation through changes in light, thereby altering the visual fatigue caused by monotonous driving conditions. After multiple on-site surveys and concentrated discussions, highway traffic police have placed the laser lights on relatively straight sections of the road that are prone to fatigued driving, adjusting the lasers to ensure sufficient brightness while also providing a certain visual impact to effectively prevent drivers from fatigued driving. Anti-fatigue laser lights are just one of the many anti-fatigue measures implemented by highway traffic police.

[StIan]

Oh, I've seen this kind of green laser many times on highways. The first time I encountered it was during a long night drive. From afar, I saw several green beams scanning overhead and initially thought it might be some military base. Later, I learned from a traffic police friend that this device is technically called an anti-fatigue laser warning light, specifically installed in accident-prone areas or long straight sections of road. The green light flashes at different frequencies and has strong penetration, directly entering the driver's cabin. Its purpose is to suddenly stimulate your visual nerves when you're drowsy or driving in a fixed position for too long, giving you a quick jolt of alertness. Especially during the most sleep-prone hours like 3-4 AM or 1-2 PM, this laser serves as a reminder to take a break at service areas, preventing accidents caused by drowsy driving. In fact, some road sections have warning signs several kilometers ahead, indicating that you're about to enter a laser alert zone, but many drivers overlook these small details.

[NorahDella]

During a self-driving trip, I paid special attention to these green laser devices. They are typically installed at tunnel entrances and long downhill sections, with projection equipment placed approximately every 200 meters. These lights use green lasers with a wavelength of 520 nanometers, as the human eye is most sensitive to this color. The devices are equipped with automatic recognition systems—they deactivate during daylight when illumination is sufficient and activate at dusk when light dims. The installation positions are also carefully chosen, mostly mounted on overhead gantries about ten meters above the road, ensuring the light penetrates the windshield without directly shining into the driver's eyes. Some newer models even include radar modules that adjust the flashing frequency based on traffic flow: slower, steady beams during peak hours and rapid sweeps late at night when traffic is sparse. The actual effectiveness is far superior to standard broadcast alerts or roadside reflectors, at least they won’t be drowned out by background noise.

[VonKyle]

Last week while driving on the highway with my family, we encountered green lasers. My wife and kids initially thought it was some kind of stage light show. The primary function of these installations is to prevent drowsy driving by providing visual stimulation to keep drivers alert. The green light is particularly noticeable in dark environments, prompting drivers to instinctively look up at the road. Many provinces have installed these systems in accident-prone drowsy sections, such as certain long straight stretches of the Shanghai-Kunming Expressway and Beijing-Harbin Expressway. Maintenance of these devices is typically handled by local road authorities, who regularly check the angles of the laser emitters to prevent obstruction by tree branches. Interestingly, different provinces have different preferences for laser usage—Shandong tends to use fixed beams, while Zhejiang prefers dynamic sweeping lights, possibly due to terrain differences. Personally, I think besides this, it's best to combine it with other methods like adjusting the AC temperature or opening windows for ventilation to stay alert.