What are the regulations for sight distance on different classes of highways?
3 Answers
Stopping sight distance is the most basic requirement, and all classes of highways should ensure stopping sight distance. Sight distance for other highways: Expressways and first-class highways only need to ensure stopping sight distance; other classes of highways should meet the requirements for meeting sight distance, which should not be less than twice the stopping sight distance. For two-lane highways with opposing traffic, sections ensuring passing sight distance should be set up based on terrain as needed. Concept of sight distance: Sight distance is a traffic engineering term, meaning the visible distance for drivers during driving. Sight distance is an important factor affecting traffic safety, mainly including stopping sight distance, passing sight distance, and meeting sight distance.
Having driven for over a decade and traveled on various roads, I understand the importance of sight distance. On highways, where speeds are high, the stopping sight distance must be at least 210 meters because high-speed emergency stops require sufficient distance to see obstacles ahead. For national highways and expressways, it's typically around 160 meters; for provincial highways and urban arterial roads, about 110 meters; and for rural roads, the minimum is 75 meters, though curves and slopes can affect actual sight distance. Overtaking sight distance is even stricter—on two-way two-lane roads, a distance of over 350 meters is needed for safe overtaking. Once on a mountainous provincial road, the sight distance suddenly shortened, and I nearly rear-ended the car ahead—fortunately, I had slowed down in advance. These regulations are based on vehicle braking performance and human reaction time, and following them can prevent many accidents. I recommend drivers familiarize themselves with road conditions and maintain proper following distances.
As someone who frequently designs roads, I'm well-versed in the sight distance standards for various road classes: minimum stopping sight distance is 210 meters for expressways, 160 meters for Class I highways, 110 meters for Class II, 75 meters for Class III, and 55 meters for Class IV. Sight distance types include stopping, overtaking, and meeting sight distances; overtaking sight distance requires higher standards, such as over 300 meters on flat sections to safely judge overtaking opportunities. These regulations are calculated based on vehicle braking distance and a driver reaction time of 0.75 seconds to ensure stopping capability during emergencies. Sight distance deteriorates when road gradients exceed 3% or curve radii are small, so we achieve compliance through proper gradient design and obstacle clearance in engineering projects. Neglecting these factors increases accident risks.
