Rail transit refers to a type of transportation vehicle or system that requires operating vehicles to travel on a specific track. The most typical rail transit is a railway system composed of traditional trains and standard railways. With the diversified development of train and railway technology, rail transit has emerged in an increasing number of types, not only distributed over long-distance land transportation, but also widely used in medium and short distance urban public transportation. Common rail transit systems include traditional railways (national railways, intercity railways, and municipal railways), subways, light rails, and trams. New types of rail transit systems include maglev track systems, monorail systems (straddle track systems and suspension track systems), and passenger automated rapid transit systems. In the Chinese national standard "Common Terminology of Urban Public Transport", urban rail transit is defined as "a general term for fast and high-volume public transportation that is usually powered by electricity and operates on wheels and rails." According to differences in service scope, rail transit is generally divided into three categories: national railway system, intercity rail transit, and urban rail transit. Rail transit generally has advantages such as large volume, fast speed, dense schedules, safety and comfort, high punctuality, all-weather, low freight costs, and energy conservation and environmental protection. However, it often comes with high initial investment, technical requirements, and maintenance costs, and often occupies a large space. In a broad sense, rail transit refers to various road transportation vehicles composed of trains, railways, stations, and scheduling systems (including scheduling equipment and personnel), including all traditional railway systems and new rail systems. The main body of general rail transit is traditional railways, including high-speed railways. Narrowly defined rail transit generally refers to two types of urban rail transit, namely intercity rail transit and urban rail transit, such as the Pearl River Delta intercity rapid rail transit and Dongguan rail transit. Generally speaking, rail transit is commonly used to refer to various medium and short distance passenger railway systems newly built in economically developed areas. In the early days, some local governments or mass media were unaware that many intercity rail transit systems were constructed using the national railway system, namely intercity railways, abbreviated as urban railways. Therefore, many factual intercity railways were habitually referred to as intercity railways, abbreviated as urban railways, such as the Guangzhou Zhuhai Metro and the Dongguan Huizhou Metro. In fact, to be precise, they belong to the category of intercity railways in intercity rail transit and are a component of the national railway branch network