In public transport, a short turn or turn-back is an earlier terminus on a bus or rail line that is used on some scheduled trips that do not operate along the full length of the route. Some agencies, such as the Washington Metropolitan Area Transit Authority use the term "cut route" for the same thing.
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Short turns are practical in scheduling when the short-turning bus can proceed through its layover at the short turn loop, then start a run in the opposite direction, all while reducing the number of buses needed to operate all trips along the route as opposed to if all scheduled trips operated to the terminus of full-length trips.
Short turns require the availability of a separate loop on the bus or rail line where the vehicle can turn around and lay over. On bus routes, this could be streets that can accommodate bus traffic. On a rail line, this means a location where the layover does not interfere with other rail traffic.
On rail lines, short turns are more limited due to the number of crossovers between tracks.
Demand for services
Short turns are used on bus routes and rail lines where there is a lower demand for service along the part of the route not served by the short-turning trips. This helps in reducing operating costs. While more economical, these short turns do not necessarily reduce the number of buses needed to operate the full amount of service along the route.
Crowd management
Short turns can aid in reducing overcrowding of buses. By scheduling uneven intervals between full-length and short turn trips, this may lead to accommodation of more riders on the trips coming out of the short turn layover location.
Short turns can be used to reduce bus bunching.
Branches
Some bus and rail routes have multiple branches serving different locations, but are otherwise identified with the same designation. These separate branches are not officially short turns, but in such an operation, the common part of the route has more service than the individual branches, just like a short turn service.
Some multi-branch routes have approximately the same number of trips along each branch. Other routes have a main branch where the majority of service operates, along with selected trips to other locations. Such trips sometimes only operate during certain hours of the day, peak hours, on certain days of the week, or to meet the needs of a particular employer.
An example of a multi-branch service is the MBTA's Green Line, which operates on four branches. The branches fan out on surface tracks west of the downtown region, but operate through the Tremont Street Subway tunnel in downtown. Approximately three-quarters of inbound trains also short-turn in the downtown tunnel; only "E" Branch trains run through the full length of the tunnel to the Green Line's terminus at Lechmere. "B" Branch trains short-turn at Park Street, while trains running through from the "D" Branch turn around at Government Center (one stop beyond Park Street), and trains from the "C" Branch turn two stops later, at North Station. Additionally, some outbound "E" Branch trips short-turn at Brigham Circle to avoid traffic on the street-running outer section of the line, from Brigham Circle to the branch's terminus at Heath Street (before 1985, when the "E" Branch ran through to Arborway, some outbound trains also short-turned at Heath Street).