A siding, in rail terminology, is a low-speed track section distinct from a running line or through route such as a main line or branch line or spur. It may connect to through track or to other sidings at either end. Sidings often have lighter rails, meant for lower speed or less heavy traffic, and few, if any, signals. Sidings connected at both ends to a running line are commonly known as loops;[1][2][self-published source?] otherwise they are known as single-ended sidings or dead end sidings,[3] or (if short) stubs.[4]


Sidings may be used for marshalling, stabling, storing, loading and unloading vehicles.[5][self-published source?]

Common sidings store stationary rolling stock, especially for loading and unloading. Industrial sidings go to factories, mines, quarries, wharves, warehouses, some of them are essentially links to industrial railways. Such sidings can sometimes be found at stations for public use; in American usage these are referred to as team tracks (after the use of teams of horses to pull wagons to and from them). Sidings may also hold maintenance of way equipment or other equipment, allowing trains to pass, or store helper engines between runs.

Some sidings have very occasional use, having been built, for example, to service an industry, a railway yard or a stub of a disused railway that has since closed. It is not uncommon for an infrequently-used siding to fall into disrepair.

Passing siding

A particular form of siding is the passing siding (international) or passing loop (U.K.). This is a section of track parallel to a through line and connected to it at both ends by switches (points in international usage).

Sidings allow trains travelling in opposite directions to pass, and for fast, high priority trains to pass slower or lower priority trains going the same direction. Sidings are very important for operating efficiency on single track lines, and add to the capacity of other lines.

A siding may have lighter rail than the main track. The rail used may not be continuous welded rail but rather joined by angle bars. The railway owner may place less emphasis on the quality of the ties and the ballast used on the siding as compared to that on its main track. A siding may not receive or may not require, the same degree of scrutiny and maintenance that the more heavily travelled main track may receive. It could be because of these factors that a siding may have a lower authorized train speed or it could be a business decision to operate at a lower speed on the siding that facilitates the cost saving on materials and maintenance.

Though a siding on a class one railroad in Canada is primarily used for the meeting and passing of trains, the term "passing siding" is not part of the official Canadian railroad terminology. The Canadian Rail Operating Rules edition effective May 28, 2008 uses the single word "siding" and defines such as "A track adjacent and connected to the main track which is so designated in the Time Table, GBO or Operating Bulletin." No mention is made of the number of switch connections to the main track such a siding may have.

This same naming convention for sidings is followed in the US rules for railroad operation. The General Code of Operating Rules Seventh Edition effective April 1, 2015 defines a siding as "A track connected to the main track and used for meeting or passing trains. Location of sidings are shown in the timetable." The definition is interesting in that it appears to attach a single purpose to a siding and makes no mention of other possibilities such as the storage of rail cars or equipment on a siding. Like their Canadian counterparts, there also is no assigned number of main track switch connections in this definition of a siding.

The employee time table for these Canadian railroads also uses the single word "siding" to describe this section of track. A designated siding in the railroad's employee timetable is shown with a siding capacity which is its usable length as measured in feet. Typically the track centre for a siding or any track adjacent to the main track is a standard distance to allow the safe passage of trains including trains that may be handling dimensional shipments. At the two ends of the siding, that distance is compromised as the siding joins the main track. As such the railway will display an appropriate stopping point on both the main track and the siding track to ensure the safe passage of both trains.

In early Canadian Pacific Railway employee timetable editions,[6][7] the capacity of a siding was not shown. As locomotives became more powerful, and train size increased, there became a need for this feature. In later employee timetable editions, the capacity of a siding was shown in car lengths. A siding capacity would be indicated as being "70 cars". This information was valid as long as all the rail cars were of the same length. With the introduction of rail cars that had specific assigned uses, such as a bi or tri-level auto carrier car, the standard length of the rail car became indeterminate.

The time table also displayed the type of siding, such as "Signalled Siding" or "Non-signalled Siding" so that all employees are aware of the rules that apply to that piece of track. If signalled, the time table would indicate the type of signal system thereby again reinforcing which rules would be in effect for the siding and its occupancy.

After the introduction of Centralized Traffic Control (CTC) on Canadian Pacific's Schreiber Division, the sidings between Cartier at the east end and Current River as the western-most location now were all signalled sidings but still varied greatly in length. The signalled siding at Carry designated as Mile Post or MP50.0 on the White River Subdivision was the shortest at 4735 feet[8] while fifteen miles to the east the signalled siding at Bolkow designated as MP35.7 White River Subdivision, was the longest on the Division at 8008 feet.[9]

To best demonstrate the changes in sidings, here are a series of examples as taken from various years of employee timetables for the Nipigon Subdivision which runs from Schreiber Ontario MP 0.0 to Fort William/Thunder Bay Ontario MP 132.9 Nipigon Subdivision.

According to page 12 of the Canadian Pacific Railway Algoma District Employee Timetable number 70 effective on September 27, 1931,[10] the single track portion of the Nipigon Subdivision was broken by three pieces of double-track territory. One section of double track ran from Selim to Pays Plat. Then there was a stretch of single track Absolute Staff System from Pays Plat to Cavers followed by another piece of double track from Cavers to Gurney. The last portion of double track territory ran from Navilus into Fort William. The remainder of the subdivision was single track with 19 stations which appear to have passing tracks. In this timetable edition, there are no siding lengths indicated which can be used to identify the placement of sidings. Instead, the only alternative is the use of a "star" symbol to show which stations do not have passing tracks. From that one information, one assumes that the other stations have sidings. The longest distance between two sidings was the 6.3 miles between sidings Mackenzie and Navilus.

According to page 12 of Canadian Pacific Railways Algoma District Employee Timetable number 91 taking effect on February 16, 1941,[11] the single track portion of the Nipigon subdivision was 126.5 miles in length and consisted of 24 designated sidings. The longest siding, Nipigon, showed as being 100 cars in length. The shortest siding, Horn, showed being 31 cars in length. The longest distance between two sidings was eight miles in length between Rossport and Pays Plat. That section of the subdivision from Current River to Thunder Bay is shown as double track Manitoba District. Schreiber Division train dispatchers were responsible for issuing the train orders between Fort William and Current River.

According to page 20 of Canadian Pacific Railway's Eastern Region Smiths Falls, Sudbury and Schreiber Divisions Employee Timetable Number 56 effective on October 30, 1966,[12] the single track portion of the Nipigon Subdivision from Schreiber to Current River was 126.5 miles in length and consisted of 18 designated sidings. Two of these sidings, Rossport and Navilus, were the longest at 100 cars in length; one was 98 cars in length; another 96 cars in length; one siding was 88 cars in length; three sidings were 87 cars in length; 9 sidings were 85 cars in length; and lastly, the shortest siding, Hurkett, was 79 cars in length. The longest stretch between two sidings was from Pays Plat to Gravel a distance of 10.7 miles. This interval would be due to the fact that in this area, the railroad was hindered by Lake Superior on the south side and the Canadian Shield on the North side. Drilling, blasting of rock and the creation of two tunnels was necessary in this portion of the route to carve out just the single track path for the railway. The section of the subdivision from Current River to Fort William is displayed as two track territory Prairie Region. From Current River to Selim, Automatic Block System (ABS) rules apply. From the east switch Selim to west switch Schreiber, Centralized Traffic Control (CTC) rules apply. The Special instructions dictate that "Schreiber Division Train Dispatchers will issue train orders between Fort William and Current River."

According to page 25 of Canadian Pacific Railway’s Eastern Region Sudbury and Schreiber Divisions Employee timetable Number 56 effective at October 28, 1979,[13] the single track portion of the Nipigon Subdivision was 126.5 miles in length and now consisted of 12 designated sidings. The sidings capacities were now measured in feet. The longest siding was Navilus at 7643 feet in length. Two sidings were 6685 feet in length. Two sidings were over 6400 feet in length at 6425 feet and 6493 feet. One siding was 6385 feet in length. Six sidings were between 6200 and 6300 feet in length. The longest distance between any two sidings was 12.3 miles which occurred between sidings Selim and Pays Plat. That section of the subdivision from Current River to Thunder Bay is now shown as two track ABS territory Prairie Region. The 126.5 miles of track, both main track and sidings, from Schreiber to Current River are now all shown as being under Centralized Traffic Control rules.

According to page 29 of the CP Rail System Algoma District timetable number 40 effective at June 9, 1996,[14] The single track portion of the Nipigon Subdivision from Schreiber to Current River now showed as consisting of 126.0 miles of main line track and twelve designated sidings. Siding lengths were displayed in feet and the longest siding was Navilus with a length of 7643 feet. The shortest sidings were Dublin and Bowker each with 6235 feet in length. The longest stretch of track between two sidings was the 12.3 miles between sidings Selim and Pays Plat. A new section of the timetable had been created which is called Thunder Bay Terminal. It extends from Mile 126.0 Nipigon Subdivision to Mile 8.0 Kaministiquia Subdivision. From Mile 126.0 to Mile 126.6 Nipigon Sub, single track CTC rules apply. From Mile 126.6 to Thunder Bay station Two Track ABS Rules apply. Footnote number 6.1 states that the CTC between Mile 126.0 and Mile 126.6 is now controlled by the Nipigon Subdivision RTC, Toronto.

With such variations in the siding lengths and to avoid serious train delays, it became very apparent that train size was to be a major concern.

The first element of controlling train lengths was to place a cap on train size. To avoid train meets where both trains were overlength for a siding’s capacity, an instruction was issued to the Thunder Bay yardmasters to ensure that eastward trains leaving their terminal for the Nipigon Subdivision did not exceed a length of 6200 feet. This capping of the length of eastward trains also tacitly acknowledged that westward trains would have no length restrictions.

When first implemented, this length target was difficult to meet as there was no process in place to deliver an accurate train length measurement. Thus sometimes there were surprises when, on a planned meet, a train did not fit into a siding. In such instances, the excess length would have to be moved into the siding’s back track, if possible, until the opposing train had passed. Under such a scenario, delays could be incurred by both trains.

Canadian Pacific Railway took train length determination a step further and implemented on the Division a basic process to capture actual train lengths and pass this information along to the train dispatcher to assist in train planning while limiting train delays.

The strategy was to gather train length information from two locations; Schreiber Ontario would gather length information on eastward trains while Cartier Ontario would collect this same information on westward trains. Both locations would advise their respective train dispatcher of this information. This information would then be recorded on the dispatcher's train sheet.

The unfortunate part of this plan was that as the measurement did not take place until Schreiber, the Train Dispatcher worked the 126 miles of the Nipigon Subdivision with no accurate train measurement for Eastward trains. A very crude method of determining such train length on the Nipigon Subdivision was developed using the features of the CTC panel. If, while en route, an eastward freight train showed on the CTC panel as occupying both the east and west switches of a siding at the same time, then, knowing the length of that siding, it could be assumed that this train would be overlength for a siding of similar size. This was a very primitive and potentially inaccurate methodology as it was dependent upon the quickness of the CTC electric signal relays to indicate such occupancy on the dispatcher's CTC panel. If there were other train activities occurring at the same time, the reaction time of the relays could be delayed and an occupancy displayed briefly when there was no such occupancy.

In both locations, Schreiber and Cartier, a designated site was chosen where the trains were instructed to stop for their crew change. From that point, the engineering department then measured in the appropriate direction. Distances from this designated stopping point were identified. Marker signs bearing a length number were then constructed and attached to the corresponding adjacent telegraph pole at the matching distance from the stopping point. A series of such markers were installed, each with the corresponding distance painted on it so that they would be visible to a train crew in a caboose.

At Schreiber, the chosen spot was the water standpipe at the east end of the station platform. When the arriving eastward train stopped at this location, the arriving head-end train crew would disembark and the outgoing crew would board the locomotive. This new crew would then advise the train crew in the caboose by radio that they were on board. The caboose crew would acknowledge this message and advise the new head-end crew if sixty pounds of air pressure was displayed in the caboose air pressure gauge. If this number had been attained, then the caboose crew member would direct the head-end crew to start the train brake testing process which was done at every station during these years. The caboose crew would also note the location of the caboose in relation to a measurement sign and communicate that information to the local yard office and from there to the dispatcher.

For example, if the caboose of an eastward train stopped at Schreiber was close to a marker that read 5930, then this information was given to the Schreiber yard office personnel and relayed to the train dispatcher as "5930 feet" in length. The distance measuring markers at Schreiber only went as far as 6050 feet from the assigned stopping point for the train. If the crew on the caboose could not see a marker when originally stopped, then when the train resumed movement after the head-end crew change and brake test, the caboose crew would count the number of telegraph poles until the marker was spotted. In such cases, the length would be announced as "6 pole lengths west of marker 6050". Each pole length could be calculated as being fifty feet in length. An accurate train length was not determined but the information still assisted the train dispatcher in the planning of meets with opposing trains.

The weakness in this process was that not every train stopped at the designated spot and the crew in the caboose that was providing the train length information were not aware of this discrepancy, therefore the accuracy of this length information could be impacted.

While this crew change and brake testing were taking place, the local supervisor would do a walk-around of the bottom of the locomotives checking the wheels, journals and running gear for obvious defects and then climbing onto the running board to do a quick inspection of the lubrication and water levels and topping off such levels if required. Thus the short stopping time at the crew change station was well utilized.

This same method of information gathering was employed at Cartier Ontario, the easternmost point on the Schreiber Division when a westward train stopped there for a crew change. This system was employed until the actual length of the rail cars was incorporated into an electronic database. The information from the UMLER database was then used to compile train consists detailing each car number, weight, destination and length along with other pertinent information. The train consist information was then broadcast and made available to all rail employees for information purposes. From these consists, the operating employees were made fully aware of the true lengths of each train. The Canadian Pacific Railway later refined this train length information by showing on these train consists, the actual length of each locomotive and car that composed the train along with a new length that calculated a three percent increase for slack action within the train as caused by the stretching and compressing of the drawbars between each car. It was felt that this number was necessary due to the increased use of cushioned drawbars on rail cars.

This new train length information which incorporated the 3% factor presented a quandary to the train dispatcher. Prior to the creation of this additional length information, if an eastward freight train was shown as 6000 feet in length on the train consist and a train meet planned at a siding that was 6077 feet in length such as Middleton siding on the Heron Bay Subdivision, then the train dispatcher would make the train meet there based on the basic information that the train would clear. Typically there would also be radio contact with that train's engineer apprising him/her of the situation and asking if they were comfortable fitting the train into that siding. If the engineer agreed, then the meet was made at Middleton. Middleton is a curvy but fairly flat siding sitting on a shelf above Lake Superior. The train's skilled engineer would enter the siding there using a braking technique that would keep the cars on the train "bunched up". The personnel in the caboose would be keeping the engineer informed of the train's progress by counting down the number of cars to go before the switch was cleared.

Now, however, the train dispatcher/RTC uses the length with the 3% factor included. The train length of the 6000 foot train is now expressed as being 6180 feet in length when the 3% factor is included and thus the train is now considered as oversize for a siding such as Middleton which is 6077 feet in length. Given this new and longer train length, the train dispatcher would have to pull the train meet back to a siding which would accept a train of this newly expressed train length of 6180 feet. To present this information in another format, the actual length of a train to fit into Middleton siding would now have to be 5895 feet in length in order for the 3% factor to be 6077 feet.

This system of gathering train length information may have been unique to the Schreiber Division. The Lakehead Division to the west of Thunder Bay was two track territory decreasing the issue of train length. East of Cartier, Ontario, the Sudbury Division had "long", or over 7000 foot sidings again reducing concern regarding train lengths. The Schreiber Division though had siding lengths that, as mentioned previously, varied greatly in length. It was this variation in siding length and the potential delay to traffic, that resulted in this strict awareness of train lengths.

If a railway has a "Hot Box Detector" system in place, the location of such a device will be indicated in the employee timetable. Typically the next siding is considered as the set-off point for any suspect car. The use of backtracks for storage of equipment took on new importance as a result of being designated as set-off points. Track machines that would previously have filled backtracks to capacity when not in use now had to be placed such that there was sufficient room at the appropriate end of the designated backtrack for a train to set off a suspect rail car.

The distance between designated sidings may vary from railroad to railroad. The actual length of a railroad's designated sidings may also vary widely. The distance between sidings is a huge factor in train delay. The further a train has to travel to meet another train, the larger the delay for the stopped train.

The argument can always be made as to whether siding capacity is the issue or would it be the train size. Previously, in some parts of Canada, the trains were made to fit the sidings and the sidings were equidistant from each other. This meant more trains were operated but overall with fewer delays. The increasing length of freight trains resulted in the extending of selected sidings on each subdivision. This could be a tricky exercise in some instances as different barriers would have to be considered. There could be physical barriers such as rock or water which had limited the placement and size of the original siding. There could be population growth or infrastructure projects in place that would impede any alteration to an existing siding.

Now, the development of ever-more powerful locomotives with improved traction capabilities allowed the building of longer trains handling more tonnage. Longer trains meant that overall fewer trains had to be operated. Reducing the number of trains also decreased operating costs as less locomotives and fewer train crews were required. Such trains may be overlength for the present designed siding capacity.[6] Consequently, the inferior train will be held back at a siding which has the capacity to hold its length.

Being cognizant of both a territory's siding capacity and the train length of all trains operating over a territory is a very important part of a train dispatcher/rail traffic controller's job. It may be necessary for trains to be held back at sidings which can contain them. Presently, in 2016, there is no system in place to prevent the meeting of two trains at a siding in which neither train could fit. That responsibility lies solely with the train dispatcher/RTC. Should such an event occur, the process and ensuing delay can be quite onerous. When such an occasion does happen, the excess length of one train would have to be moved to another track or ultimately to another location to permit the passing of the superior train.

While sidings are used for the meeting and passing of trains, it must be noted that trains can carry cargo of varying dimensions which may impact such passing or meeting. According to the Canadian Pacific Railway RTC (Rail Traffic Controller) Manual of May 28, 2008, a Dimensional Shipment is one which exceeds the maximum standards of size, weight, and/or height of centre of gravity. Such oversize shipments are identified, measured and classified from 00 to 10 according to a Dimensional Shipment chart. The chart advises whether the meeting or passing of such shipments can be done at track speed or with specific restrictions.

The increase in the handling of a variety of large shipments has been expressed by the establishment of instructions to all involved in Dimensional Shipments. On Canadian railroads, there has also been a recognition that there are sections of track where the distance between the main track and the siding may be larger than the norm. These wider segments are now identified as a "Dimensional Bulge" and, due to the distance separation between the main track and the siding, now are acknowledged to be areas in which dimensional restrictions can be relaxed or removed.[15]

Refuge siding

Single-ended (or dead-end) siding with similar purpose to passing loop.

See also


  1. ^ Jackson (2006), p. 192.
  2. ^ Ellis (2006), p. 207.
  3. ^ Jackson (2006), p. 87.
  4. ^ Jackson (2006), p. 337.
  5. ^ Ellis (2006), p 324.
  6. ^ Canadian Pacific Railway, Ontario District, Employee Time Table 45, effective Sunday June 5, 1921
  7. ^ Canadian Pacific Railway, Eastern Region, Employee Time Table 51, effective October 25, 1959.
  8. ^ CP Rail, Eastern Region, Sudbury and Schreiber Division, Time Table 56, Effective Sunday October 28, 1979.
  9. ^ CP Rail, Eastern Region, Sudbury and Schreiber Division, Time Table 56, Effective Sunday October 28, 1979.
  10. ^ Canadian Pacific Railway Algoma District Employee Timetable number 70 effective on September 27, 1931
  11. ^ Canadian Pacific Railways Algoma District Employee Timetable number 91 taking effect on February 16, 1941
  12. ^ Canadian Pacific Railway's Eastern Region Smiths Falls, Sudbury and Schreiber Divisions Employee Timetable Number 56 effective on October 30th, 1966
  13. ^ Canadian Pacific Railway’s Eastern Region Sudbury and Schreiber Divisions Employee timetable Number 56 effective at October 28th, 1979
  14. ^ CP Rail System Algoma District timetable number 40 effective at June 9, 1996
  15. ^ Canadian Pacific Railway, General Operating Instructions, Section 10, Dimensional Traffic


  • Jackson, Alan A. (2006). The Railway Dictionary, 4th ed., Sutton Publishing, Stroud. ISBN 0-7509-4218-5.
  • Ellis, Iain (2006). Ellis' British Railway Engineering Encyclopaedia. Lulu.com. ISBN 978-1-8472-8643-7. 
  • Riley, Joseph E. and Strong, James C., "Basic Track", AREMA, 2003
  • Solomon, Brian, "Railway Signalling", 1st Edition, Voyageur Press.