Historian, Sir (or Madam),
Thank you for your detailed, positive critique. Your analysis is considered and thoughtful.
The imagery and conceptualizations provided in “You Deserve to Know More” are of necessity simplified to cater for a general audience. The devil is always in the detail.
20m is an absolute constraint for 2km.
Physical survey establishes this constraint. There is variability up to 20.3 but for the sake of simplicity 20m is taken as the design constraint.
This constraint primarily exists between Murrumbeena station and Cosy Gum Rd, near Grange Rd in Carnegie, a rounded up distance of 2,000 metres. The total 20 km engineering conception between Caulfield and Dandenong is essentially influenced by this 2km choke. The Alternative works for the 20km but incorporates a 20m wide resolution for the short 2km as well.
Temporary Protection Fences.
A 3,600mm corridor is required for the CFA piling system contemplated in Skyrail.
A 1,500mm frontal offset from the pile is required for bored piles contemplated in Cut & Cover. So both systems require the temporary use of some of the backyards of residents in the 2km choke corridor. Under Planning Law, no resident has the right to prevent the demolition of their back fence and the erection of a Temporary Protection Fence. Later, the LXRA must make good, but an espaliered apple tree on brick fence will be replaced with an apple sapling. The choice for residents here is whether the disruption will result in a 10 m high elevated structure with elevated freight and Metro trains on their back fence or the ‘disappearance’ of trains under a cover altogether. On behalf of the residents I can vouch for more support for the latter. So the 20m absolute constraint has a temporary remedy for construction purposes only, that does not require compulsory acquisition.
In the Cut & Cover Alternative, the tie beam running along the top of the piling system effectively becomes part of the rear boundary fence of an abutting property in the choke corridor. This acts as a collision barrier in case somebody accidently accelerates in reverse in their carport. A thoughtful LXRA might offer residents thus impacted a set of steps and a gateway in their new back fence to bring their bike up to the new linear park behind them.
In two stage Cut & Cover, for Stage 1 two tracks, you only need Temporary Fencing on one side of the corridor. For a two track Skyrail solution, you are affecting both sides of the corridor, and you are still left with future works hanging. While the Alternative does allow a budget conscious, two track staged solution, it really asks for all four tracks to be put in at once. That is what the corridor needs for Metro and Regional passenger services to really improve and the economy needs in terms of freight.
Unless you correct me, 1,300mm from nearest rail is required for trackwork OHS, which is generally in line with the existing steel postwork supporting existing electrical supply. Columns for Skyrail have been spun inline with the elevated section, a weaker design outcome, grappling with this constraint. Thus any construction workzone can only be between this safety fencing and residential fencing, bringing us back to Temporary Protection Fences in this 2km choke corridor.
Springvale Station and Burke Rd Glen Iris are recent projects that exemplify what is possible. The tie beam, running along the top of shoring is 1,200mm at Springvale and 800mm at Burke Rd, based on 600mm diameter piles. Some say that Springvale is over engineered, being a first project for a contractor, and Burke Rd is optimized, based on an experienced contractor. The Alternative runs with experience, using the 800mm dimension for wall thickness.
Offsets – Rail centerline to Constraint.
Springvale up to Dandenong cutting shows an offset of 3,000 mm from wall to rail centerline, and this offset dimension is taken up in the Alternative model, based on track on slab and a straight run.
Centre line to CL clearance for Metro is 4,000mm. For freight, the Alternative ran with 4,300mm clearance, giving an overall 19,900mm for the Choke Corridor. We need to have a beer and work out where 4,500mm comes from, but accepting it means accepting 20,100mm, which allows us to slide a cigarette paper between Victrack and resident. I would contend that you would even have community support for 500mm of compulsory acquisition if the outcome was Cut & Cover rather than Skyrail.
Two Versions of Cut & Cover.
The 20km Version of Cut & Cover is optimized for ‘Value Capture’ above. A central pier or shoring wall allows more load bearing for more options above. Even cyclists will need to stop and go to a café or toilet. The 20km solution needs 23m of space, which is available for 18 km. So your analysis of dimensions based on this Standard version is correct.
The 2km Version of Cut and Cover is developed within the 20m constraint in the Choke Corridor. The essential difference is no central pier or shoring wall and a segmented arch cover. It can only be used for grassed open area, playgrounds and blue sky bicycle tracks.
Both these variations will be posted on noskyrail.net over the weekend under a report called “The Choke Corridor”. You can find this under the tab "You Deserve to Know More". The capacity to comment via facebook or twitter has also been setup. There are reports there about how thoughtless station car parking options are, problems with gas pipes, and better bike tracks. They are intended to start a conversation, involve the community in the difficult process of compromise involved in the development of infrastructure in built up areas and hopefully generate better outcomes.
The Choke Corridor.
Constructing the Choke Corridor has some magnificent challenges. There are two ways to do this : the hard way and the easy way. The hard way means running existing services on two tracks. For the trades, it means playing a game of twister. It is doable, but you need a shot of grappa every time you clock off.
The easy way means running existing services, for 2km only, on a single, bi-directional track. You may bite the bullet and do this single bi directional Oakleigh - Caulfield. This is an easily accepted concept for road works, controlled by temporary traffic lights or flag men. For rail, this would require further refinement.
In simple terms there are three peak uses of the rail corridor ; (a) Metro am inbound, (b) Metro pm outbound and (c) Freight.
Managing this and keeping boom gates up as long as possible requires slotting Freight into an envelope outside of Metro am and pm peak. Then the Metro am inbound peak should use 100% of the single bi directional track while Metro am outbound, with lower demand, should terminate and use buses. There are enough buses to handle the lower demand in one direction and express back for more punters. The reverse in Metro pm peak.
All a pain, but doable, and nothing worse than attempting to drive down the Tullamarine Freeway corridor for the next 18 months.
All this Skyrail stuff is concocted by Daleks in Vicroads anyway.
Not much thought into the rail side of things.
Nice to see the Easter Bunny hanging out of Steamrail this morning.