January 1937 Railway Signaling (Chicago IL)

Automatic interlocking in Canada

An installation at crossing of Canadian National and Canadian Pacific includes an automatic release on all the routes

Home signal on Canadian National

An automatic interlocking has been installed by the Canadian National at Coniston, Ont., where a single-track line, extending northwest from Parry Sound, crosses a similar line of the Canadian Pacific that extends eastward from Sudbury to Ottawa and Montréal. This interlocking is equipped with automatic releasing apparatus which is effective for both approaches on each line to provide for trains stopping at the passenger stations and passing sidings located near the home signals, as well as to permit release of the crossing during switching operations.

The new interlocking displaced a 13-lever mechanical plant which had been in service since the construction of the Canadian National in 1905. Although this plant was kept modernized, it was expensive to operate and maintain, in comparison with a modern automatic interlocking, resulting in the decision to abandon the old facilities. The principal disadvantage of an automatic scheme at Coniston was due to the location of the passenger stations and passing tracks near the crossing. Without special apparatus it was obvious that a train doing station work on one line would obstruct traffic unreasonably on the other. However, the experience of these two railroads in minimizing delays resulting from such conditions at other automatic crossings, by the use of special time-release equipment, effectively demonstrated the practicability of a similar scheme as applied to the Coniston crossing, even though a passenger station and a freight yard on the Canadian Pacific and a passenger station and a passing siding on the Canadian National were involved.

At present, the traffic over the Canadian Pacific comprises two passenger trains each way daily, a tri-weekly local, two regular daily freight trains in each direction, a small amount of switching and a few freight extras. On the Canadian National the traffic is approximately one-half of this amount. With this traffic, it was apparent that if an automatic plant could be successfully designed, it would avoid the expense of a manually-operated, full-time interlocking. The new arrangements are quite in harmony with the operating conditions from an economic standpoint and, after a year of use, have been found to amply meet the requirements of both roads.

Layout of signaling

In place of the mechanical semaphores, modern searchlight signals were installed on the existing masts of the four home signals. Three-aspect approach signals of the same type, manufactured by the Union Switch & Signal Company, were also installed on all four routes. The home signals display either red or green, those on the Canadian Pacific also displaying a second continuously-red light so as to conform to the standard for interlocked home signals on that road. However, each of the Canadian National home signals displays, as is the practice elsewhere on this road, a lunar-white marker light below the main unit to distinguish it from other automatic or interlocked signals. A special rule definition and special trainman's instructions have been adopted for the "red over lunar-white" aspect, as explained in the September issue of Railway Signaling for the LaChevrotiere, Que., interlocking.

Home signal on Canadian Pacific

Operating Features

The general idea of operation, with which the Coniston plant was designed, is that a train making a through movement will normally encounter no interference from a subsequent train on either line. However, if a train approaches the home signal but does not promptly accept the proceed indication and cross the other line, it will surrender, after a six-minute time interval, its privilege to use the crossing to trains of the other road, should they appear. In making this surrender, the home signals on both railroads must show stop for a minimum time interval of one minute before any other signal is allowed to show the proceed aspect. In case a reverse move is contemplated, it can be made on a signal indication provided the use of the crossing is not required by a later train on the other road.

The home signals are normally de-energized or set at stop and the approach signals energized for the yellow aspect. Upon the approach of a train, the plant being otherwise unoccupied, the home and the approach signals for that train both change to the green aspect. The interlocking of one road against the other is accomplished by two relays, designated CPHR and CNHR, which cannot be energized simultaneously owing to each being checked through a back contact of the other. The releasing of a route to the other road is accomplished by the picking up of one of two route stick relays (designated CP-RSR and CN-RSR), which opens the path to negative battery from the HR relay of the first road.

Control circuits for automatic interlocking

The circuits are so arranged that, whenever a train occupies any part of the interlocking, one of two DT-10 time-element relays (designated CP-TER and CN-TER), depending upon which road is involved, begins to measure the time. After six minutes have elapsed, the picking up of this TER relay energizes the corresponding RSR. provided, however, a train on the other road has occupied the plant in the meantime. This in turn drops the corresponding HR relay, breaks the signal control circuit, and sets the home signal at stop. If no such second train approaches, the green signal is retained until it is accepted. Of course, if the train leaves the limits of the interlocking, for instance it may take a siding, before or after the six-minute interval has elapsed, the timing relay immediately becomes de-energized and nothing controlled by it influences the operation of the circuits and the plant immediately becomes normal. If the train on the other road had occupied the plant prior to the first train clearing the center track circuit, the route-stick relay is energized through a back contact of the center track circuit relay and the home signal governing a reverse movement of the first train is held at stop behind the train so the signal will be set green for the other road, which then has the privilege of using the crossing.

For the purpose of imposing a time when all home signals are at stop, when one road is surrendering the privilege to use the crossing to the other road, the route relay, together with the timing relay, energizes a second timing relay of the thermal type. After a half-minute interval, the thermal relay functions to energize a "thermal-stick" neutral relay, which remains energized through its own front contact and the route-stick and timing-relay contacts in series in addition to cutting off the energy to the thermal unit. In cooling to close its normal contact, the thermal relay imposes another half -minute interval on the system, making a total delay of one minute. At this point the second train is given preference and, all home signals having remained red for one minute, the home signal governing the second train indicates proceed.

Special Push-Button Release

Ordinarily, the above procedure will provide for the proper operation of all trains by signal indication with out flagging or undue delays and, furthermore, with perfect safety. However, it is possible that both roads may have southbound trains and the second train, after waiting for the signal throughout the two delay periods totaling a maximum of seven minutes, would not accept the signal and proceed over the crossing. In this event, the plant would be tied up for both southbound trains, because after the second six-minute period had elapsed the signal would again be restored to normal. However, to avoid flagging, a push-button station to be operated by the trainmen has been provided at each of the two home signals nearest the sidings and stations. The first push button that is operated clears the adjacent signal a once, locks out the other road and relieves the situation.

The other two approaches are not provided with push-button releases, as a back contact on the track relay in the rear of the home signal serves to take the place of the push buttons. It may so happen that a southbound train on either road may be holding its main track to be met by a north bound train that is to take the siding, and a train on the other road at that moment has outstayed its seven-minute privilege of using the crossing. In such cases it is desirable that the third or opposing northbound train should receive a proceed indication to cross the diamond without any action on the part of the crew. To provide for this operation, the push button mentioned above, on each road, is paralleled by a back contact of the track relay for the section to the rear of the northward home signal. This multiple path also includes a back contact of a directional-stick relay which is energized for every southbound train that passes the northward home signal, thus preventing the back contact of the track relay from energizing the push-button stick relay if the track relay has been dropped by a southbound train.

On any approach, in the event of failure of the signal apparatus to operate as intended, the trainmen are governed by special instructions for flagging over the crossing, as at the LaChevrotiere interlocking previously mentioned. For this purpose, a box at the crossing diamond is opened by a trainman, which causes an indication lamp for each of the unoccupied approach sections to be lighted. With the assistance of these lights, the trainman makes sure that no trains are approaching the crossing and then opens a knife switch to de-energize all signals. His train then proceeds over the crossing diamond at his hand signal, after which the knife switch is restored to normal and the box is locked.

The southward home signals on both roads are made to block to the end of the plant by carrying the signal armature circuits through the track-repeater relays. The northward home signals, however, block only to the opposite home signals in order to allow use of the sidings as explained in a previous paragraph. The approach signal operating circuits are pole-changed by green-repeater relays of the associated home signals. These signal armature circuits are also run through the track relays for the purpose of blocking.

The relays are housed in a large sheet-metal case at the crossing.

Signaling equipment

The signals on this interlocking are of the d-c. low-voltage, searchlight type, with permanent field magnets. Each signal is equipped with a 10-volt, 10-watt, single-filament lamp, the lamps being lighted on approach control.

The interlocking control relays are housed in a large-size, sheet-metal case, located near the crossing, as shown in one of the views. This case has a door on each side with a partition dividing the case, except that the lower section of the partition is cut away to allow space for the large relays, such as the time-element relays. The underground cables are brought in through a hole in the foundation and are terminated on the lower section of the board.

From the central case the circuits are distributed to each home signal in 14-conductor, No. 14, parkway cable made to A.A.R. Signal Section specifications, the make-up of which includes lead sheath and two wraps of steel tape. This cable is laid in a trench 36 in. deep and is surrounded with 3 in. of sand. Beyond the home signals, the line circuits are No. 10 Copperweld wire, with double-braid weatherproof covering, run on the pole line.

The connections to the rail are No. 9, single-conductor parkway. The make-up of this cable includes two wraps of steel tape but no lead. At the rail, the cable is brought up through a cast-iron riser and into an outlet box. The end of the cable conductor is joined and soldered to two No. 9 Copperweld bond wires. This joint is left in the head of the outlet so as to be readily inspected. The two bond wires extend out through a hole so arranged with a duplex channel pin and a split fiber tube that the wires are held firmly when the cover is bolted on.

A 110-volt a-c. power circuit is extended from the crossing to each of the home and approach signals where G.R.S. transformers and Type BX-116 rectifiers are used to charge storage cells. At each signal, a set of five 85-a.h. lead storage cells is used for the operation of the signal and control circuits. Two cells of the same type in multiple are used for each track circuit within the approach signal limits. A three-cell set of 500-a.h. primary battery is used to feed the track circuit on each of the four approach sections.

This automatic interlocking was planned by C. H. Tillett, signal engineer. Central Region, and in stalled by E. L. Baker, supervisor of signals of the Canadian National at North Bay, Ont. The operation of trains by the automatic plant has been entirely satisfactory, with no complaints as to train delays.

Railways: C.N.Rys., C.P.Ry.

Stations: Coniston