The Secondary Line refers to a transportation route that serves as a backup or alternative to the primary line in a transportation network. It is designed to handle excess traffic, provide redundancy, or serve areas not directly accessible by the primary line. In the United States, the concept of Secondary Lines is particularly relevant in the context of public transportation, such as rail systems and road networks.

The importance of Secondary Lines can be attributed to several factors. Firstly, they enhance the overall efficiency and reliability of the transportation system. According to a study by the American Public Transportation Association (APTA), the presence of secondary lines can reduce delays by up to 20% during peak hours. This is because they provide an additional route for passengers to choose from, thereby distributing the load more evenly across the network.

Secondly, Secondary Lines contribute to improved accessibility. For instance, in urban areas with growing populations, the expansion of public transportation networks often requires the addition of secondary lines to serve new neighborhoods or to connect with existing ones. This is evident in cities like New York, where the subway system has multiple secondary lines that connect different boroughs and provide access to various destinations.

Data from the Federal Highway Administration (FHWA) supports the significance of Secondary Lines in road networks. The FHWA reports that adding secondary roads can reduce traffic congestion by up to 15% in urban areas. This is due to the分流作用，即Secondary Lines allow drivers to choose alternative routes when the primary road is congested, thereby reducing the overall traffic volume on the main artery.

Moreover, Secondary Lines play a crucial role in disaster response and emergency management. In the event of a major incident, such as a natural disaster or a catastrophic accident, the secondary lines can be utilized to reroute traffic and ensure the safe evacuation of affected areas. This is particularly important in densely populated regions where the primary transportation routes may become overwhelmed.

In conclusion, the Secondary Line is a vital component of transportation networks in the United States, providing redundancy, enhancing accessibility, and improving overall efficiency. The data from APTA and FHWA underscores the importance of these lines in ensuring the smooth operation of public transportation and road networks, as well as their role in emergency management and disaster response.