Towrang to Marulan

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This sector involves some difficult terrain, with the Wollondilly River winding between hilly country. The existing alignment has seven curves with a radius of 600m, four of which are reverse curves with minimal or no transition. These curves must be bypassed with a new alignment. However, as that new alignment will require tunnels and bridges, the existing freight railway will be left in its present position. Thus means we will have to provide grade separations for all instances where the new alignment crosses the old.

The eastern part of the alignment approaching Marulan is unproblematic; curves are minimal and there is even a former trackbed on the north side of the tracks that can be reutilised for most of the length, except for the final approach to Marulan. In order to accomodate triple track, the northern platform at Marulan Station will have to be relocated.

Alignment design

Three corridor options were considered for this sector. The first (solid line) utilises a maximum length of existing rail while smoothing out the curves around Towrang at the expense of two substantial tunnels and two long-ish bridges; the new section achieves a radius of 3000m, although the minimum radius for the sector is 2000m due to the curve near Lynwood Quarry near Marulan.

The second option (dashed line similar to first option) limits the radius of the new section to only 2000m, due to the existing limitation near Marulan. This would enable a TGV-style train to travel 250km/h – more than sufficient for our near-term purposes, but unable to accommodate future speed increases. It is identical to section 5 and 6 of the first option, and section 1 and 2 of the third option, and has the lowest capital costs of the three options due to avoiding the need for any tunnelling.

The third option is a very fast alignment (dashed line to the south) which pretty much bypasses the entire section. It eliminates the curves at both Towrang and Marulan, achieving a minimum radius in excess of 5000m. As it traverses less difficult terrain, only a single, smaller tunnel is needed, and therefore the capital costs are lower than for the first option.


Option 1 – Two Tunnels


1 – First Wollondilly crossing

Section length 3100m, sector start. Begins with two high-speed tracks on the north side of a single dedicated freight track. Follows the existing track around the gentle curve next to the river, then departs north of the freight line onto a new corridor tangential to the initial curve onto a relatively long floodplain viaduct and bridge over the Wollondilly River.

  • Bridge: twin-track, 760m total length with 20m spans
    • $24.79m
  • Negligible earthworks
  • Track:
    • 2340m – 1 freight track upgraded to high speed, 1 new track added: $4.39m
    • 760m – New dual track: $1.71m
    • 2 low-speed turnouts: $1.4m
  • Signalling – including two turnout signals
    • $8.39m
  • Civil works
    • 4680m of chainlink fence: $234k
    • 2340m of drainage: $468k
    • 1 minor grade separation for Silver Stream Fire Trail: $1.25m
  • Land: 40m corridor for bridge section
    • 1.2ha, $24k

2 – Towrang Tunnel

Section length 1220m, beginning at 3100m. Consists of an 800m dual track, single-bore tunnel and about 400m of approach cuts.

  • Tunnel: 800m, OD 12.4m
    • $49.6m
  • Earthworks: 420m rock cut, avg. 5m depth
    • 35,700m3 and $1.11m
  • Land: Corridor for new cut, approx 1.7ha
    • $33,600

3 – Second Wollondilly crossing

Section length 3170m, starting at 4320m. Earthworks create a new alignment adjacent the existing freight line, with a complex skew grade separation over Towrang road, and a simple one over the freight line. The track proceeds onto the second Wollondilly bridge and a long section of floodplain viaduct. Section ends at the western portal to the Carrick Tunnel.

  • Bridge: 1000m total length, mainspan 27.5m
    • $32.62m
  • Earthworks:
    • 800m fill, 8m depth = $2.46m
    • 465m cut, 8m depth = $2.31m
    • 330m cut, 4m depth = $655k
  • Track: 3170m new dual track = $7.13m
  • Signalling: $403k
  • Civil works:
    • 4340m of chainlink fence:$217k
    • 2170m of drainage: $434k
    • Complex grade separation: $2.5m
    • Simple grade separation: $1.25m
  • Land: Approx. 8.8ha for 40m wide corridor
    • $88,000

4 – Carrick tunnel

Section length 750m, starting at 7490m. Consists of a 750m dual track single bore tunnel.

  • Tunnel: 750m with OD 12.4m
    • $46.5m
  • 750m of dual track: $1.69m
  • Signalling: $95,000

5 – Carrick to Lynwood Quarry

View east from Carrick Rd level crossing. Image: Google Maps

View east from Carrick Rd level crossing. Image: Google Maps

Section length 11,000m starting at 8240m. Alignment rejoins the existing corridor after the first 1.5km; the existing corridor is no longer 3 tracks wide, therefore the existing cuts and fills will require widening by 6m. The first of the two curves at Lynwood Quarry will require easing to R2000m from the existing approx. 800m.

  • Bridges
    • Two identical single lane bridges to add an extra track to the corridor, each with length 100m and spans of 10m: $1.32m each
  • Earthworks
    • 660m balanced cut-and-fill on exit from the Carrick Tunnel: $1.25m
    • About 3500m of balanced cut/fill widening on the existing alignment: $1.26m
    • 600m, 3m high fill on approach to quarry: $648k
    • 700m, 5m deep cut within quarry: $2.50m
  • Track
    • 1400m of new dual track: $3.15m
    • 7900m of 1 new, one upgrade (one unchanged): $14.81m
    • 1700m of new triple track: $5.53m
  • Signalling: $1.4m
  • Civil works:
    • 21600m chainlink fence: $1.08m
    • 10800m drainage: $2.16m
    • 2x minor grade separations: $1.25m each
  • Land: 6ha of premium hobby-farm
    • Assume $250k/acre = $1.5m

6 – Marulan entry

Alignment at Marulan Station, looking west

Alignment at Marulan Station, looking west

Section length 2100m starting at 19240m. Rejoins the existing corridor for the final run into Marulan Station. The two existing tracks will be upgrade to high-speed with a third track for freight added on the north. This can be accommodated within the existing rail corridor but the northern platform of Marulan Station will have to be rebuilt. The existing station is a heritage building and precinct, so it will be retained, but with a major refit to upgrade it to a commuter station, including parking for 100 vehicles on the reserve adjacent Railway Parade. Steel pallisade fencing is used within the township boundaries, otherwise chainlink “cyclone” fence.

  • Earthworks: Negligible
  • Track: 2100m of upgraded dual track with 1 additional
    • $5.26m
    • 2 low-speed turnouts: $1.4m
  • Signalling
    • Cables and balises: $267k
    • Crossover signals: $8m
  • Civil works
    • 1450m steel pallisade fencing: $145k
    • 2750m chainlink fence: $138k
    • Drainage: $420k

The total cost for Option 1 comes to $254.23 million ($11.91m/km).

We’ll look at Option 3 now, because once we’ve done that we can pretty much combine it with parts of Option 1 to make Option 2.

Option 3 – Pipeline easement


 1 – Existing alignment at Murray Flats

Section length 850m, sector start. Consists of the straight section of the existing track, upgraded for high speed, with a new freight track added to the north side (the corridor is already wide enough for triple track, having previously had a third track to the north).

  • Track: 850m of dual upgrade with an added track, including 2 low-speed turnouts
    • $2.99m
  • Signalling: $8.11m (including two turnout signals)
  • Civil works
    • 1700m of chainlink fence: $85k
    • 850m of drainage: $170k
    • Minor grade separation: $1.25m

2 – Wollondilly crossings

Section length 3730m, starting at 850m. Consists of three bridges, two of them crossing and then recrossing an arm of the Wollondilly river. The river is shallow, and usually only narrow, so 20m spans should be sufficient. Some moderate earthworks are required. Although the corridor passes close to two houses, it should be possible to avoid having to demolish them. Farm underpasses shall not be needed due to the frequency of bridges which can serve the same purpose.

  • Bridges
    • Unnamed creek bridge: 100m length with 10m spans: $2.64m
    • First Wollondilly bridge: 160m with 20m spans: 4.77m
    • Second Wollondilly bridge: 220m with 20m spans: $6.56m
  • Earthworks
    • 500m cut, 8m deep: $2.48m
    • 220m fill, 6m high: $443k
    • 300m fill, 5m high: $468k
    • 950m balanced cut/fill, 4m: $1.03m
    • 150m fill, 5m high: $234k
  • Track: 3730m of dual: $8.39m
  • Signalling: $474k
  • Civil works
    • 6500m of chainlink fence: $325k
    • 3250m of drainage: $650k
    • 1x minor grade separation: $1.25m
  • Land: 40m corridor through small farms
    • 14.9ha costs $149,200

3 – Carrick Tunnel west

Section length 2300m, starting at 4580m. Follows the Wingecarribee Pipeline for most of its length, and therefore will probably need to relocate the pipeline in some areas (especially cuts). Consists of a moderate, balanced cut/fill, followed by a 350m tunnel. The section ends at Carrick Road, east of the tunnel.

  • Tunnel: 350m, dual-track single-bore with OD 12.4m
    • $21.7m
  • Earthworks
    • 800m fill, avg 8m high: $2.46m
    • 465m cut, avg 8m deep: $2.31m
    • 330m cut for tunnel approaches, 4m deep: $655k
  • New dual track: $5.18m
  • Signalling: $292k
  • Civil works
    • 3900m of chainlink fence: $195k
    • 1950m of drainage: $390k
    • 2x farm underpasses: $500k each
    • Minor grade separation: $1.25m
    • Utilities relocation: $244k
  • Land: $7.8ha, $78,000

4 – Carrick Tunnel east

View east of the Carrick Tunnel portal, where the pipeline easement crosses Carrick Road. Image: Google Maps

After the Carrick Tunnel portal looking East, where the pipeline easement crosses Carrick Road. Image: Google Maps

Section length 3830m, starting at 6880m. Consists of some pretty substantial cuts and fills as the line descends the other side of the low range, then leaves the pipeline easement and begins the approach to the Narambulla Creek bridge. Only one farm underpass required.

  • Earthworks:
    • 600m cut, 7m deep: $2.47m
    • 700m fill, 4m high: $806k
    • 500m balanced, 2.5m deep: $295k
    • 800m cut, 3m deep: $1.12m
    • 525m fill, 7.5m high: $1.46m
  • New dual track: $8.62m
  • Signalling: $486k
  • Civil works
    • 7660m of chainlink fence: $383k
    • 3830m of drainage: $766k
    • 1x farm underpass: $500k
    • 2200m of utilities relocation: $275k
  • Land: 15.3ha will cost $153,200

5 – Narumbulla Creek crossings

Section length 6920m, starting at 10,710m. Line proceeds through farmland, crossing two creeks with floodplains and then passing south of the quarry to rejoin the existing alignment. Consists of two medium-sized bridges and several cuts as well as approach embankments to the two bridges.

  • Bridges
    • Narumbulla Creek bridge: 450m long with 27.5m spans: $14.68m
    • Unnamed bridge: 350m long with 27.5m spans: $11.42m
  • Earthworks
    • 420m fill, 7m high: $1.06m
    • 1050m cut, 4m deep: $1.06m
    • 330m fill, 4m high: $380k
    • 400m fill, 2m high: $192k
    • 600m cut, 6m deep: $1.06m
    • 2000m balanced, 2m deep: $900k
  • 6920m of new dual track: $15.57m
  • Signalling: $879k
  • Civil works:
    • 12240m chainlink fence: $612k
    • 6120m drainage: $1.22m
    • 1x minor grade separation: $1.25m
  • 40m land corridor: 27.2ha costs $277k

6 – Marulan entry

This section is identical to section 6 of Option 1.

The final cost for Option 3 is $167.93 million ($8.51m/km)

Option 2 – Slow(er) and expensive(ish)

The final option we look at is exactly the same as the final two sections of Option 1, and almost exactly the same as the first two sectors of Option 3 (close enough that we’ll assume exactly the same). They amount to:

  • Existing rail at Murray Flat: $12.6m
  • First Wollondilly crossings: $29.9m
  • Carrick to Lynwood Quarry: $41.8m
  • Marulan entry: $21.3m
    • Sub total: $105.6m

That just leaves 5.8km in the middle to work out. We could go to the bother of analysing it in detail, but I’m pretty sure I already know how this is going to turn out. We can see from the plan view that it’s going to have several long bridges and quite a bit of earthworks, so it’s going to be a mid-range expensive section, definitely over $10m/km. It only has to cost $62 million to kick the total above the $167.9m that the very fast option will cost, and that works out at $10.6m/km. It’s going to be basically the same cost as the much faster option, therefore the very fast Option 3 is the one that we will select.


The total cost of the sector is $167.93 million ($8.51m/km). Considering the proportion of entirely new alignment, and the fairly hilly terrain, this is a pretty good result, especially considering minimum radius has been kept above 5000m, allowing future speed upgrades to well over 300km/h. The earthwork balance for this sector is +15,735m3, an insignificant amount considering the scale of the project, which should easily be able to be utilised for fill nearby.

Component,Cost ($m),Percentage
Civil works,13.0,7.8%

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