Sleeper Locks

In the New Zealand railway system sleeper locks were used in conjunction with Woods keys and lever locks to provide a low cost form of interlocking. As far as I know, in 2004 the only extant sleeper locks and woods keys are at Masterton. Masterton is the terminal of the Wairarapa's diesel hauled commuter passenger trains and this is probably the reason that the equipment has not been scrapped. This page describes the Masterton installation, which is unique in having the sleeper locks parallel to the rails.

Thanks to Masterton Locomotive Engineer Bruce Scott for his help. Thanks also to Ken O'Reilly of the Wairarapa Railway Restoration Society Inc. for his help. When I took the Masterton photographs on this page I had a cab pass, was wearing a hi-viz jacket and was under the supervision of Toll Rail staff.


Spring Points In Main Line

At Masterton spring points (with flush levers) are used in the loop to main crossover next to the platform, rather than frame levers. I assume that this is for safety reasons. Consequently lever locks cannot be used to lock the mainline points or interlock the points with signals.

Sleeper locks are used to provide the locking function.

Masterton Configuration

Two sets of points must be unlocked with one key. The key must be impounded in the mainline points when they are locked reverse. The result is a configuration in which the lock is parallel to the rail and the lock bar sits in a notch on a stretcher bar.

Contrast this with the photograph in Semaphore To CTC. In the latter the lock bar is parallel to the sleepers and wedges against the switch.

Masterton Sleeper Locks

Masterton Photographs

6 Main to Loop Cross-Over

The points are spring operated with a flush operating lever.

The A Woods key is used to first unlock A6B loop points (left). The key is not impounded in A6B and can be taken to A6A spring points in the Main (right) to unlock them. The key is impounded in A6A. While the key is impounded it cannot be used to unlock the Up Home signal.

The photograph was taken looking in the Up direction (to Woodville).  

Bruce Scott photo.

Points Locked By Sleeper Lock

A6B points in the loop. A sleeper lock is mounted parallel to the rails. A locking bar sits in a notch in a spreader bar, locking the points normal.

This is an unusual (unique?) configuration. Usually the sleeper lock is installed parallel to the sleepers and the bar rests against the switch.

Points Locked Reverse

Sleeper lock in A6B loop points. The points have been reversed. The "normal" (left) and "reverse" (right) notches are of the same depth so the points can be locked either normal or reverse and the key removed. This is unusual as normally a sleeper lock will only lock the points normal.

Note the flat faces on the end of the lock bar. This is another unusual feature of the Masterton installation - usually the end of the bar is circular.

The Woods key has been taken to A6A Main points where it will be impounded unless the points are locked normal.


The keyhole of the sleeper lock on A6A main line points. The position of the small notch indicates that it accepts an "A" Woods key.

On the "B" key the small notch is in line with the larger notch. In total there were five patterns of Woods keys ("A" to "E"), although only "A" and "B" are used at Masterton.

Bruce Scott Photo

Unlocking Points

The A Woods key has been inserted in the A6A lock and turned anti-clockwise. This moves a horizontal sliding plate which frees the lock bar.

The lock bar has been thrown back, unlocking the points. When the lock bar is in this position the horizontal plate cannot move, which in turn stops the Woods key from being turned. The key is therefore impounded in the lock.

Unequal Slots In Stretcher Bar

The stretcher bar on A6A sleeper lock. The points can be locked normal or reverse by placing the lock bar in the slot.

In this photograph the points are reversed but not locked.

The right hand slot (points reversed) is shallower than the one on the left (points normal). Because the locking bar cannot be placed completely horizontal in the right hand slot the Woods key cannot be turned and is impounded in the lock.

Locking Bar

A6A points unlocked and reversed. The rectangular section that sits in the spreader bar slot is on the left. The rectangular section is unique to Masterton. In the centre is a substantal nib that is engaged by a sliding plate to lock the bar down. On the right is a small slot in the disc. Unless a pin can slide into this slot the key cannot be turned and so is impounded.

On the far right is the slot in the spreader bar.

Last Updated: Saturday, December 31, 2005

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