What is the "only two points" on the roadside in expressway?

In windy, rainy and snowy weather, there is usually a yellow speed limit of 60, which reads "Only 2 o'clock" below, which refers to the small yellow circle sign on the middle isolation belt of the road, with a distance of 30m, which is available all over the road. Only two are seen in bad weather, that is, the visibility is 60 m.

Other high-speed signs are generally 0,50, 100, which are only available at intervals or when you need to slow down before turning. Only in this bad weather can the whole road have yellow speed signs, and the spacing is shortened to 30 m.

Bad weather; ; ? Tempest): refers to the local weather conditions that are unfavorable to human production activities or destructive.

Such as fog, extremely low clouds, storms, sandstorms, snowstorms, severe thunderstorms, hail, tornadoes and so on. The standard of bad weather often varies with different human activities.

1, thunderstorm and gale

Thunderstorm and gale refers to the weather phenomenon that the wind reaches or exceeds level 8 (≥ 17.2m/s) in the case of lightning and rainstorm. Sometimes thunderstorms and strong winds are called storms. During a thunderstorm and gale, dark clouds roll, thunder and lightning, accompanied by heavy precipitation and sometimes hail, and the wind speed is extremely high. Generally, it only covers a few kilometers to dozens of kilometers.

2. Hail

Hail is also called "Hail", commonly known as hail, and it is called "Lengzi" in some areas, which is the most common in summer or at the turn of spring and summer. It is some ice particles as small as mung beans and soybeans and as big as chestnuts and eggs. Except for Guangdong, Hunan, Hubei, Fujian, Jiangxi and other provinces, there is less hail weather in China, and every place suffers from different degrees of hail disasters every year. Especially in the mountainous and hilly areas in the north, the terrain is complex, the weather is changeable and there are many hail, which is very harmful to agriculture. Heavy hail destroyed crops and houses, injured people and killed livestock. Extraordinary hail can be even bigger than grapefruit, which will kill people, destroy a large area of farmland and trees, and destroy buildings and vehicles. It has powerful lethality. Hail disaster is one of the most serious disasters in China.

3.tornado

Tornado is a strong wind vortex accompanied by a funnel-shaped cloud column rotating at high speed, which is produced by strong convection of air in extremely unstable weather. The wind speed near the center can reach 100 m/s ~ 200 m/s, with a maximum of 300 m/s, which is several times larger than the maximum wind speed near the center of typhoon (generated at sea). Tornadoes are extremely destructive. Where they pass, they often pull up trees, overturn vehicles, destroy buildings and even suck people away.

4. Local heavy rainfall and snowfall

Heavy rainfall is generally called rainstorm in meteorology, or heavy precipitation, which refers to rain with great precipitation intensity. So is the heavy snow.