Night service, sometimes also known as owl service, is a mode of public transport service operated during the night hours. As an intermediate approach – between providing full service around the clock and stopping services altogether – it provides more limited service during times of lower passenger volume, saving resources and allowing for maintenance on primary transportation systems. They typically offer fewer routes and less frequent service. Night-based services may be differently branded compared to daytime services. Examples are London and Chicago, where overnight buses are prefixed with an "N" for "night". Another common way to distinguish night services from their daytime counterparts is dark-colored line numbers. Some cities apply a different fare structure for night services from their daytime services. Characteristics 24-hour, continuous rapid transit operation is practiced in some cities, most notably the subway in New York City, which essentially renders night services unneeded. Many of New York City's buses also have 24-hour operation; and around the world, night services may be provided by virtue of 24-hour services on daytime routes, as does Berlin on its "Metrotram" routes. Where it exists, night service is generally much more limited in geographic coverage than daytime services, with fewer lines and perhaps routes over different paths from daytime services; routes serving more stops than during the daytime; or the night terminus may be in a different place. Networks may run longer routes than daytime services, sometimes combining two or more daytime routes, which may use interchanges to reach the same outlying districts. Night services usually also run less frequently. For example, according to the New York City Transit Authority's Service Guidelines Manual, New York City buses are required to operate at least every 30 minutes all times except late nights. Local bus frequencies during late night times (defined as 1a.m. – 5a.m.) are required to operate at least every 60 minutes. Because of much longer intervals between services than during the day, night routes often offer guaranteed transfers to other lines or transit modes (such as regional and intercity rail). To ease planning, many cities use a central hub where all lines converge at a specific time. This makes the line map of many night services look like a wheel with radial lines to the center and some additional lines connecting the outer ends (or running along a ring road outside of the city center). For example, many London night bus