The planning for the John Gorton Drive Bridge has come out of the shadows – The funding promised at the ACT Election has been announced and the development application documents have been released. The construction costs will be about $177 million (June 2020 estimate).
4 more years
John Gorton Drive Bridge is a strategic link connecting the Molonglo Valley estate development on the north with the south side of the Molonglo River. Belconnen lies about 10 km north of the river and Weston Creek just to the south.
Timeline for the development
“The project could be completed by 2024 or 2025.
The 1.7 km final Stage 3C will connect Stage 2A, completed in 2018, and 3B, currently under construction, and includes a 227.5-metre long, high-level bridge which will be capable of carrying light rail, and link back up with the northern section of Coppins Crossing Road.”Government moves ahead with Molonglo River bridge, The RiotACT Ian Bushnell, 16 December 2020
Detail design in progress
Transport and City Services Minister Chris Steel said detailed design work should commence in 2021 and take about 12 months to complete, followed by a two to three-year construction period.
He said the (ACT) government’s Jobs and Economic Recovery Plan included the $175 million for the final stage of John Gorton Drive. The Commonwealth Government later contributed $87.5 million to the project in its 2020-21 Budget.Government moves ahead with Molonglo River bridge, The RiotACT Ian Bushnell, 16 December 2020
Underpass not certain
The John Gorton Drive is a wide and busy arterial road and crossing it is difficult for pedestrians, cyclists and people on scooters. The John Gorton Drive Bridge development application shows an underpass between the suburbs of Molonglo and Denman Prospects (see below). The underpass is, however, not part of the development application.
A development application is not for the bridge construction but rather for its approval. If we want the underpass it must be included in the detail design happening right now.
There is no guarantee that we will get the underpass or that it is particularly suited, i.e. safe, for cyclists. For example, an underpass on the north side of the Molonglo River on John Gorton Drive was never realised, although schools will be built adjacent to this road.
Molonglo Valley planning in 2021
Planning the cycling infrastructure
Recently a development application was released for Denman Prospect beside the bridge showing the active travel routes in the area (this is a requirement of every estate development). The John Gorton Drive Bridge site is a hole in the landscape. The development of the area around the bridge in both Denman Prospect and Molonglo are being deferred until the bridge will be completed.
Cyclists’ Main Community Routes are important for getting around and serve to thread suburbs together in hopefully logical and sensible ways. Principal Community routes are for cross city travel and most commonly used for work and education commuting. They are commonly known as CBR Cycle Routes and at this time there are few and funding is poor. The 2020-2021 ACT Budget has no funding for Principal Community Routes. The ACT Greens at the 2020 ACT Election promised a cycling “revolution”. Hopefully, their plans will be funded in the next 2021-2022 ACT Budget. This budget must be in the works now.
Principal Community Route (PCR) –A subset of Main Community Routes (MCR) that form direct links between town centres. There are routes that are to include route labels and branding.Active Travel Facilities Design – Municipal Infrastructure Standards 05 (MIS05) (ACT Government, April 2019)
Main Community Routes through the Valley
The Molonglo Valley is a 50 m deep ditch. Coppins Crossing at river level is 90 m below William Hovell Drive. Riding to Belconnen from Coppins Crossing is roughly a 130 m climb. Compare this to riding from the gates of the National Arboretum to Dairy Farmer Hill, which is a climb of almost exactly 100 m. The John Gorton Drive Bridge flattens the river crossing by about 24 m – the separation between the bridge deck and the river level. In comparison, the nearby Butters Bridge has a 25 m deck height.
|Height||Ridge height||Coppins Crossing level||Rise|
|William Hovell Drive||642 m||512 m||130 m|
|Coulter Drive||655 m||512 m||143 m|
|Aranda CBR C5||639 m||512 m||127 m|
Coppins Crossing has an altitude of 512 m above sea level using the data from the Digital Elevation Model (DEM) from OpenMTBMap (a OpenStreetMap derivative). From this source we also know the elevation on the ridge between Belconnen and the Molonglo Valley at the most common crossing points. This differs to the development application as the survey for the development application is much more precise (a few metres versus a few millimetres).
|Molonglo River||506 m|
|10 year flood level||510 m|
|100 year flood level||513 m|
|Dam break flood||522 m|
|Bridge deck level||530 m|
We want Main Community Routes to be as direct and flat as possible with gradients of no more than 5% (Austroads design standard AGRD06A). Such low gradients can be difficult to achieve across low level river crossings but are possible across high level river crossing over bridges. The gradients on the Coppins Crossing Road reach 10%.
The most direct and flattest route between the group centre at Molonglo and West Belconnen is through an underpass on the approaches to John Gorton Drive Bridge, across Butters Bridge, through the Namarag Molonglo Special Purpose Reserve, past Whitlam and along Deep Creek. This route is shown by the BLUE line below. The RED line shows the location of the John Gorton Drive Bridge.
A recent Denman Prospect Development Application from February 2021 shows the Main Community Route crossing the Molonglo River at a low level crossing west of Namarag Molonglo Special Purpose Reserve. This route is more arduous and steeper than the Butters Bridge alternative suggested above.
As discussed previously, it is necessary to reserve such corridors if they are to have any chance of being included in the estate development application for Molonglo or Denman Prospect. The current development application for the west section of Denman Prospect is incomplete as it does not include the John Gorton Drive Bridge (released in 2020).
Views of the bridge captured from the development application.
The John Gorton Drive Bridge features a 3 m wide shared bike path on both side of the roadway.
The John Gorton Drive is a wide road and a barrier for pedestrians and cyclists moving between the adjacent suburbs of Denman Prospect and Molonglo, which includes the town centre. An underpass is proposed close to Butters Bridge, but is not part of the John Gorton Drive Bridge development application. It would need to be included in the detailed planning in 2021.
Whitlam will end in the footsteps of the bridge. The bridge construction appears to be from the south side. The Whitlam development may progress dependent on the staging of road works on the north side.
The construction method for the bridge is similar to the one that was used to construct Butters Bridge, but the design is only optically similar. The girders will slowly be pushed over the gap.
The John Gorton Drive Bridge is a box girder design. Three girders support the road with a shared path on each side. The light rail is supported by another two in the middle.
Coppins Crossing Road remains for river access.
The bridge has a low profile design with the road deck 24 m above the river and 8 m above the expected flood level should the Scrivener Dam fail. The central span is 93 m and those adjacent shorter.