A balloon loop or turning loop allows a rail vehicle or train to reverse direction without having to shunt or even stop. Balloon loops can be useful for passenger trains and unit freight trains such as coal trains.
Balloon loops are common on tram or streetcar systems. Many streetcar and tram systems use single-ended vehicles that have doors on only one side and must be turned at each end of the route, or else haul trailer cars with no driver's cabin in the rear car.
History
Balloon loops were first introduced on metro and tram lines. They did not appear on freight railways in large numbers until the 1960s when the modernising British Rail introduced merry-go-round (MGR) coal trains that operated from mines to power stations and back again without shunting.
Tramways
Balloon loops enable higher line capacity (faster turnaround of a larger number of trams) and also allow the use of single-ended trams which have several advantages, including lower cost and more seating when doors are on one side only. However, double-ended trams also benefit from the capacity advantage of balloon loops, for example on the former Sydney tram system where loops were used from the 1880s until the system's closure in 1961. Initially the Sydney system was operated by single-ended steam trams and then, from the 1890s, by double-ended electric trams. Lines were looped in the Sydney CBD and the other busiest areas of operation, such as the La Perouse, New South Wales and other eastern suburbs lines, as they provided greater turn-around capacity on this very busy system. The Sydney system was possibly the first major example of a looped tramway system. European systems were extensively converted to looped operation in the early twentieth century and most of them changed to single-ended trams.
Examples
Passenger
South Ferry balloon loop
On a balloon loop:
the station is on the balloon loop, and the platform may be curved or straight.
Lower level (suburban) layout of the Grand Central Terminal, showing a balloon loopUpper level (mainline) layout of the Grand Central Terminal, showing a balloon loop
South Ferry (see diagram) was a two-track subway loop station in New York City, with a sharply curved side platform for each track. Due to problems with train length and platform clearance, this station was replaced by a standard stub terminus with two tracks and an island platform (South Ferry), although the original trackage remains in use for turning trains. After the latter station was damaged in Hurricane Sandy, the former station was reopened temporarily to provide service to the ferry terminal until the repairs to the latter station are complete.[1]
69th Street is the western terminus for the Market Frankford Line in Philadelphia, and rapid transit trains use a double-track balloon loop for turning & staging.
Bowdoin Station on the MBTABlue Line in Boston has a wedge-shaped island platform inside a balloon loop. The boarding platform is long enough for only four cars, but all of the trains on the line are six cars so only the rear four can be boarded at Bowdoin.
Mattapan Station on the MBTA Ashmont–Mattapan High Speed Line in Boston, has trolley cars unload passengers at the platform, then uses a balloon loop to return to the same platform to load inbound passengers.
The Eurotunnel Shuttle uses balloon loops: since the two tracks cross over at the French end the whole line forms a figure 8 loop. This evens the wear on the train wheels.
Peasholm on the North Bay Railway in Scarborough, North Yorkshire has a reverse balloon loop, with the "neck" of the balloon facing the buffer stop. The loop is used to allow the locomotive to run round the train and reverse at the same time.
The first Wembley Stadium station in London (opened 1923, closed 1968) was on a balloon loop, but the present station of that name is not.
The Charleroi Pre-metro system features two balloon loops, at Beaux-Arts and Waterloo stations.In the Charleroi Pre-metro, both the Beaux-Arts and Waterloo stations have balloon loops. At Beaux-arts, trains between Sud and Anderlues (line 89, both directions) first run through the station on a platformless track, take the underground balloon loop then stop at the platform leading to their destination. Waterloo station services three lines (54, 55 and 88) going to three directions, on a single island platform. Trains from Gilly station either diverge to the right and end up at the station to continue to Parc station, or diverge to the left to end up on the other end of the island platform to go towards Beaux-Arts. At the station is also a bypass so trains can run from Gilly directly to Beaux-Arts, without halting at the platform. No scheduled trains thus fully run the loop (or the bypass).
The Amsterdam, Rotterdam and The Hague tram systems have balloon loops at the end of all lines. Only Amsterdam line 5 terminus at Amstelveen Binnenhof[5] and The Hague lines branded as Randstadrail do not have balloon loops. Across these city's there are several unused balloon loops that were in use until lines were extended or abolished. These loops however are still maintained for eventual purposes. The municipality of The Hague however plans on removing them and purchase new trams with a drivers cabine on both sides of the tram.
The City Loop or Melbourne Underground Rail Loop, Melbourne, Australia, has five stations. There a four loops, one from the north east and three from the south west, on two levels. The loops are bi-directional. A connection enables one of the south east loops to be used as a circle line. The are no connections between the four loops.
In the Helsinki area, the Kehärata or Ring Rail Line is being built between an existing branch at Vantaankoski and the main line at Tikkurila, primarily to serve the airport which is presently only accessible by road. It is expected to open in 2014. Two existing stopping services (to Tikkurila and Vantaankoski) will be replaced by a single service which traverses the whole loop and returns to Helsinki, stopping twice on opposite sides of Pasila station. Four new stations are planned, but the loop will have a total of 21 stations, not counting Pasila or Helsinki. Roughly half of these stations are on the northbound and westbound mainlines, the loop line leaving them via diving junctions at Hiekkaharju and Huopalahti.
With balloon loop:
The balloon loop is past the station.
Brooklyn Bridge and City Hall stations in New York City.
Bad Herrenalb, Albtalbahn, Germany: the train passes the loop before arrival
Bowling Green on New York City's IRT Lexington Avenue subway line is the southern terminus for 5 service in the evenings & on weekends, with the South Ferry inner loop (see previous section) used to turn trains.
Brooklyn Bridge – City Hall, also on New York City's IRT Lexington Avenue Line, is the southern terminus for Lexington Avenue local service (the 6 and <6> trains), with the City Hall loop (see previous section) used to turn trains.
Howard Station on the CTA Red Line in Chicago uses a balloon loop to turn a northbound train back south. Because the other end of the line does not contain a loop, the wear on the wheels is evened out after two trips.
Kennington tube station, on the London Underground's Northern line: trains from the Charing Cross branch can terminate at Kennington and then run around a loop to return north. Trains from the Bank branch cannot use this loop.
There also are a few loops used for stabling trains, for example west of Invalides and north of Porte de la Villette.
Tram Systems
Balloon loops are used extensively on tramway systems with single-ended trams. Usually located at termini, the loop may be a single one-way track round a block. Single-ended trams have a cab at only one end and doors on one side, making them cheaper and having more space for passengers. On tram systems with double-ended trams balloon loops are not required but may still be used as they can provide greater turn-around capacity than a stub terminus.
The Milan interurban tramway network, although using double-ended trams, had balloon loops at termini within the city limits so that they could be used as backup termini by the single directional trams used on urban service. In Milan, tramway depots are built as balloon loops, just as urban termini.
Another example is in Potsdam, Germany.
Selke Valley Railway (German: Selketalbahn) — Part of the 1,000 mm (3 ft 3+3⁄8 in) gauge Harz Narrow Gauge Railways (German: Harzer Schmalspurbahnen). A balloon loop has been constructed at Stiege to allow freight trains between Nordhausen and the power station at Silberhütte (Harzgerode) to make their journeys without the locomotive having to run round. Passenger trains continue along the branch beyond Stiege to Hasselfelde where they reverse.
New Zealand
Dargaville Branch — Balloon loop providing access to Kirikopuni, 2 km north of the main line. This was eliminated by a bypass in 1943.
Also, the Fife Circle line between Edinburgh and the county of Fife acts like a giant balloon loop, branching off after Inverkeithing and connecting again at Kirkcaldy.
United States
Louisa Generating Station — Coal unloader, south of Muscatine, Iowa
Donner Pass, California - there is balloon loop on either side of the pass. One is in Truckee and the other near Blue Canyon. They are primarily used to facilitate snow removal, allowing the plows and blowers to easily be returned over the pass.
Other
Both the French and the British terminals of the Eurotunnel Shuttle service through the Channel Tunnel consist of balloon loops.
Occasionally, balloon loops are used for reversing trains on lines with heavy grades and tight curves to equalise wear on both sides of locomotives and rollingstock. Such a balloon loop was constructed at Beech Forest on the 2 ft 6 in (762 mm) Victorian Railways line from Colac to Crowes.
Advantages
Advantages of a balloon loop include:
Smooth operation
Trains can arrive in any free platform, while another train is leaving any platform.
Reversal of rolling stock helps even out wear and tear on the wheels.
Eliminates need for brake test if locomotives uncoupled to carry out run around move.
Compared to stations with stub platforms, balloon loops allow:
Fewer tracks and platforms are required
Arrivals into some platforms do not block departures from other platforms
Time is not lost while drivers change ends and reset the train for the other direction
If the driver changed ends and discovers a hidden fault, then delays to trains are less likely
Disadvantages
The major disadvantage is that a balloon loop is very space consuming. Another disadvantage is that the sharp curves cause noise, as well as wear on wheels and rails. Also, if the platform is located on the curve, the gap between the platform and railcar door is a hazard. The former South Ferry station on the New York City Subway solved this problem by using gap fillers that extended out to the railcar door when the train triggered a switch on the tracks. The older station had been closed, but was reopened as a result of damage to the newer station caused by Hurricane Sandy.
On systems where, for reasons of economy, the couplings are made non-reversible (e.g. by fitting the air brake pipe along one side of the car only), the use of a reversing loop will cause a proportion of the rolling stock to face the "wrong" way and it may not be possible to assemble a complete train in a depot, even if sufficient cars are on hand. This was the case on the Charing Cross, Euston and Hampstead Railway (now part of the Northern line of London Underground). After the opening of a loop at Charing Cross (Embankment) in 1914 (replaced in 1926 by the present Kennington loop) car ends were marked "A" or "B" (later, when axles were designated by letters, the "B" car ends became "D" to match the adjacent axle), and it was not permitted to couple cars together if the ends to be coupled bore the same letter. It was found necessary to provide a turntable at Golders Green depot (near the other end of the line), for use when there was an imbalance of car directions.[21]
To avoid this problem, on many systems with a balloon loop the couplings and brake hoses are made reversible.
At coal ports such as Kooragang in Newcastle, New South Wales the space inside the balloon loops is used for storing coal, so that it is not wasted.
At the Olympic Park station in Sydney, the loop is flattened where the platforms are located, so that the platform faces are straight.
^5 Southern & TfL (Map) (3rd ed.). Railway Track Diagrams. Cartography by John Yonge. Trackmaps. November 2008. p. 43 Piccadilly line: South Harrow & Heathrow - Acton Town. D inset. ISBN978-0-9549866-4-3.
^4 Midlands & North West (Map) (2nd ed.). Railway Track Diagrams. Cartography by John Yonge. Trackmaps. March 2005. p. 40 Hunts Cross - Moorfields. ISBN0-9549866-0-1.
^Bruce, J. Graeme (1988). "7. The First of the Standard Tube Stock 1923/25". The London Underground Tube Stock. Shepperton: Ian Allan. pp. 56–57. ISBN0-7110-1707-7.
