Infringements and out-of-gauge loads

The clearance standards describe the space the railway intends to keep. Reality falls short of them in many places: old structures built to earlier gauges, platforms built close to trains on purpose, track that has moved, a new structure squeezed into a constrained site, a load too big for its loading outline. None of these is automatically dangerous, but each reduces the margin the standards intend, and each must be known, judged, approved by someone with the authority to do so, and recorded. The rules for doing this are as important to safety as the standards themselves, because they decide which shortfalls are accepted, on what conditions, and whether anyone remembers them.

This chapter explains how infringements are classified by the margin that remains, follows the approval and record-keeping that the NSW standards required, and works through the running case’s out-of-gauge transformer move, including how a speed restriction recovers part of the margin.

Classifying infringements

ARTC’s NSW standard for infringements of transit space, BDS 14, identified the things that can infringe the approved transit space: rolling stock, loads, structures, track centres, and track or vehicle tolerances being exceeded. It then classified infringements by what they reduce.

Figure 1Classes of infringement in ARTC BDS 14

	What it means	Approval or action described in BDS 14 (2005)
Operational infringement	the safety margin beyond the kinematic envelope is reduced below 200 mm	approval needed when proposed or identified to remain permanent
Below the base operating standard	the margin is reduced below 100 mm	action to be taken under the base operating standard
Service corridor infringement	the agreed service dimensions are not provided	approval needed for any permanent service corridor infringement
Field infringement	track relocated or its geometry altered from its approved position	managed under track examination procedures; approval if it is to remain
Design infringement	a new or renewed structure cannot achieve the structure gauge	evidence of inability to comply; approval and a recorded approval form

The distinction between safety and service is the same as in Chapter 6. A service corridor infringement means the railway has less room to operate and maintain itself than it wanted; an operational infringement means the margin that protects trains from contact is reduced. The second is far more serious, and the reduction to below 100 mm, half the standard margin, triggers action rather than mere approval.

Temporary and permanent

Infringements can be temporary, such as a scaffold during construction, track that has moved and is awaiting correction, or a load passing once, or permanent, such as an old tunnel that will not be rebuilt. ARTC’s code of practice for SA, WA and Vic stated that permanent infringements where the contingency gap between kinematic envelopes, or between an envelope and a structure, is less than 150 mm should be approved by ARTC and permitted only in special circumstances, such as platforms, tunnels or substandard track centres, and that track at such locations may need higher inspection or maintenance levels, including datum markers. It also called for track positions to be monitored where the gap could fall below 250 mm.

Approval and records

An infringement that nobody recorded is an infringement that will be forgotten, until the next maintenance job moves the track a little further or the next wider vehicle arrives.

Figure 2Handling a design infringement, following the pattern in ARTC BDS 14

1. 1Show inability to complytechnical and financial evidence that the structure gauge cannot be achieved
2. 2Calculate the marginkinematic envelope at the structure; minimum clearance to it laterally and vertically
3. 3Seek approvalfrom the position with authority, with any special conditions proposed
4. 4Record the approvalan approval form with location, infringement details, minimum clearance and conditions
5. 5Register itan entry in the corridor's infringement register, issued to corridor managers and maintainers
6. 6Maintain the conditionsinspection, track monitoring, speed restrictions or vehicle restrictions as approved

BDS 14 used two forms for this: an approval form, recording the location by line and kilometrage, the maximum infringement of the structure gauge and the minimum clearance to the kinematic envelope on each side and vertically, the reason and the conditions of approval; and a register of approvals for each corridor, issued to corridor managers and maintenance staff. The forms matter less than the principle: every accepted shortfall is written down where the people who might change the track or the traffic will see it.

Who decides

The approval of infringements sits at a senior level for a reason. A designer under deadline, a maintainer with a track possession ending, or an operator with a customer waiting all have reasons to accept a smaller margin, and none of them sees the whole corridor. The person who approves an infringement must be independent of the pressure, must know the corridor’s other infringements, which may combine at the same place, and must have the authority to impose conditions on operations and maintenance. BDS 14 placed the approval of permanent operational and service corridor infringements with a senior engineering manager of the infrastructure manager, not with the people proposing them.

Exceedances by vehicles and loads

Infringements can come from the vehicle side too. ARTC’s code for SA, WA and Vic described exceedances of the static rolling stock outline, including out-of-gauge loads, and of the dynamic limits or track tolerances used to determine the kinematic envelope, and noted that approval may be subject to conditions such as speed restrictions or tightened track tolerances. BDS 14 required any rolling stock or load permanently infringing the approved outlines to be approved, with evidence of inability to comply.

Special loads

Some loads cannot fit the standard loading outline: transformers, large machinery, bridge girders, mining equipment. Railways handle them in two ways. The NSW standards provided special load gauges, larger outlines whose kinematic envelope, according to BDS 17, lay wholly within Structure Gauge 1994, so loads within them could move under special conditions without infringing structures. Loads larger still are out of gauge, and each move is checked against every structure on its route, with conditions. BDS 17 made operations responsible for ensuring that nothing outside the special load gauges travelled without approval, and made the structures representatives responsible for advising operations of any temporary infringement that reduced the margin below 100 mm.

The running case: the transformer

This is an illustration. A power utility needs to move a transformer along the corridor, under the new overbridge and through an old tunnel further along the line. Loaded on a well wagon, the transformer’s top corners are 1,600 mm from the centreline, wider than the 1,500 mm loading outline, and 4,300 mm above rail. The operator’s out-of-gauge planner checked the load’s kinematic envelope at every structure on the route, using the load’s own dimensions and position on the wagon, the curve and cant at each structure, and the standard allowances.

Under the overbridge, with its piers at 4,300 mm, the load cleared easily. The critical structure was the old tunnel, on straight track, whose wall at 4,300 mm above rail is 2,000 mm from the track centreline.

Figure 3Margin between the transformer's kinematic envelope and the tunnel wall

At line speed161 mm of clear space at 4,300 mm above rail

At walking pace216 mm of clear space at 4,300 mm above rail

Standard safety margin200 mm of clear space at 4,300 mm above rail

At line speed, the transformer’s corner could reach about 1,839 mm from the centreline, leaving about 161 mm to the tunnel wall: less than the 200 mm margin, so an operational infringement, but above the 100 mm at which action would be required. At walking pace, with the dynamic roll and bounce reduced, it reaches about 1,784 mm, leaving about 216 mm. The infrastructure manager approved the move through the tunnel at walking pace, with the track’s position in the tunnel checked against its datum markers the day before, no other train on the adjacent track while the load passed, and an observer at the tunnel.

Planning the route

An out-of-gauge move is planned structure by structure. The planner lists every structure on the route that could come near the load: bridges over the line, tunnels, platforms, signal posts and gantries, overhead wiring, walls, cuttings and adjacent tracks. Each is checked with the load’s envelope at that location, using the curve, the cant and the structure’s surveyed position from the clearance records of Chapter 10. Where the records are incomplete or old, structures are surveyed before the move. The result is a list of critical locations, each with its remaining margin and any condition needed, and sometimes a decision that the route is impossible and another must be found.

Long loads on curves

A long load behaves like a long vehicle. Its position on the wagon decides its throw: a load whose ends lie between the wagon’s bogies swings inward at its middle like the wagon’s body, but less at its ends; a load that overhangs the wagon’s ends swings outward beyond them. For the transformer, sitting 8 m long in the middle of a well wagon with bogie centres of 14 m, the load’s middle on the 400 m curve sits about 61 mm inside the centreline, the wagon’s centre throw, and its ends, 4 m from the middle, about (14,000² − 4 × 4,000²) ÷ (8 × 400,000) ≈ 41 mm inside, because they lie well within the bogies. A load overhanging the wagon would have needed its end throw calculated as well.

The adjacent track

An out-of-gauge load can infringe the space of trains on the next track as well as structures. Its envelope plus the envelope of a train on the adjacent track, plus the margin, may exceed the track centres. Where it does, the condition of the move is that no train runs on the adjacent track while the load passes the critical location, which needs coordination with train control and is written into the move’s conditions, as it was for the transformer in the tunnel.

Telling the people who run the train

Conditions are useless unless the people running the train know them. An approved out-of-gauge move is issued with a written notice to the train crew and train control listing the route, the speed restrictions and where they apply, the locations where adjacent tracks must be clear, any observers, and what to do if something goes wrong. The planner checks that the conditions are practical, such as a walking-pace restriction that the locomotive can actually hold on the grade, before they are issued.

Learning from contacts

When a vehicle or load does strike a structure, the investigation compares the calculated envelope with what happened: was the vehicle within its outline, the track within its tolerances, the structure where the records said? Each answer points to a different correction: the loading check, the track maintenance, the clearance records. Strikes are rare, but each is a free test of the clearance system, and the lessons are fed back into the standards and procedures.

Why speed helps, and when it does not

Speed restrictions reduce the dynamic parts of the envelope: the roll and bounce that rough track excites at speed. They do not reduce the throw, the cant tilt, the wear or the track tolerances, which are geometric. On a canted curve, a slow train has cant excess and leans further inward on its springs, so slowing down can make clearance on the inside of a canted curve worse, not better. A speed restriction is a valid condition only where the analysis shows it reduces the movement that matters at that structure.

Field infringements found in service

Infringements are also found, not designed: a track recording run shows that a track has moved towards a platform; a clearance survey finds a structure closer than recorded; a new vehicle is found to be wider than assumed. The response depends on the remaining margin. With a margin still above the base operating standard, the infringement is recorded and corrected in planned maintenance; below it, immediate action is needed, such as a speed restriction, a restriction on wide vehicles, or correcting the track before trains run. BDS 14 placed field infringements found by track examination under the track examination procedures.

A failure: the forgotten approval

This is an illustration. An old overbridge on another line had a lateral clearance infringement approved many years earlier, with a condition that the track beneath it be held to its position by datum markers. The approval was recorded on paper in an office that was later closed, and never entered in the corridor’s register. When the track was renewed decades later, the new track was laid to the design centreline without reference to the markers, which had been removed, and ended up 40 mm closer to the bridge pier.

A clearance survey after the renewal found the margin at the pier had fallen below the base operating standard. Wide stock was restricted until the track was moved back, and the infringement and its conditions were entered in the register, where the next renewal team found them.

Exercise: classifying three locations

Three locations on a corridor are surveyed, with the kinematic envelope of the critical vehicle calculated at each. At location A, the minimum clear space to a structure is 180 mm; at B, 95 mm; at C, 230 mm, but the structure is 2,600 mm from the centreline where the corridor requires a service dimension of 3,000 mm. Using the classes in this chapter, classify each.

Location A, with 180 mm, is below the 200 mm safety margin but above 100 mm: an operational infringement, which needs approval and recording if it is to remain, with any conditions.

Location B, with 95 mm, is below the 100 mm base operating standard: immediate action is needed, such as a restriction, and it may be accepted only temporarily while it is corrected. Location C has a full safety margin, 230 mm, but does not provide the 3,000 mm service dimension: a service corridor infringement, needing approval if permanent. This is an illustration; the governing standard defines the classes and the authorities.