Botanic Gardens Trust, Sydney, Australia

Department of Environment, Climate Change and Water NSW

Frequently Asked Questions

One of the conditions of approval for the Cross City Tunnel was that traffic noise and its visual impacts in the Royal Botanic Gardens and the Domain be mitigated. Some time ago the Trust suggested building sound barriers along both sides of the Cahill Expressway that would reduce noise, but on the Domain side not interfere with the views across the top of the expressway to the Gardens (any extension to the wall on the Gardens side would be mostly obscured by existing vegetation). Based on feedback from stakeholder meetings late in 2004, four options (including not building a wall on the Domain side) were tested during February and March in focus groups, on-site interviews, web-based surveys and Friends’ questionnaires.

A decision has now been made to erect sound barriers on both sides of the Cahill Expressway: a higher timber fence to replace the one beside the service road on the Royal Botanic Gardens side (with a transparent section on the existing picket fence at the western end), and a sandstone-lined concrete wall on the Domain side. The Premier has announced that the Domain garden wall will be a memorial to Australian servicemen and women who have died overseas while on non-combatant duty.

Is there a noise problem?

  • Staff and users of the Domain and Gardens near to the expressway have always found the noise intrusive. When interviewed on site, most respondents appreciated the problem and felt it should be addressed in some way.
  • An acoustic report (see website) shows that the noise levels are 10 decibels above EPA goals for passive recreation land.  A variation of 10 decibels represents a doubling or halving of noise.
  • Few people use the area beside the expressway for picnicking due to the noise and visual intrusion. For those walking along the nearby path, which the Pedestrian Council of Australia lists as one of the most well used paths in Sydney, the experience will be greatly enhanced.
  • The Domain Management Plan specifically calls for a mitigation of the intrusive effects of the Cahill Expressway, suggesting the use of hard structures and plantings.

Why walls?

  • Mounding, plantings and walls were investigated, but due to underground utilities large trees cannot be planted close to the expressway.
  • In addition, a forest of about 50 m would be needed to achieve the same reductions in noise levels as a 2.5 metre high wall.
  • Due to existing paths and the many and long-standing uses of the Domain (e.g. lunch-time sport, concerts in the Domain) the open space needs to be maintained.
  • It is also worth noting that there will be new garden beds created beside the walls and it is our intent to create a new ‘botanical walk’ experience for Sydney. This very popular thoroughfare will become a popular destination for its own sake, with the traffic intrusion removed and new shrubs and gardens lining the sandstone wall.
  • Our community consultation showed overwhelming support for a wall of some sort along the expressway.

What options did the Trust consider?

  • The Trust has always favoured a solution that will reduce noise and visual impact while retaining the connection between the Royal Botanic Gardens and the Domain. All options include raising the height of the timber fence along the Royal Botanic Gardens to 4 m (this will be barely visible from the expressway and inside the Gardens due to existing plantings) and attaching a transparent barrier to the existing picket fence near the Tropical Centre.
  • For the Domain side, our Board of Trustees gave approval last year for a 2.5 m high, 250 m long, sandstone wall, as did the Heritage Office. It was considered a good solution to reducing the noise and visual impact of the expressway, and was one of the options put to the community during our period of public consultation.
  • A transparent wall option (made of glass and metal) was raised in some stakeholder workshops we held towards the end of 2004. The Trust considered the transparent walls a reasonable alternative but they do have some limitations (all of which were raised during the consultation period):
    • Traffic still visible through the wall (an intrusion in itself and will increase the ‘perception’ of traffic noise).
    • Introduces a new structural element in the Domain area which is seen as more obtrusive than a sandstone face that compliments the nearby buildings and statue bases.
    • Difficult to keep clean and attractive.
    • Possible risk for birds (although glass can have horizontal lines on it to make this risk minimal).
    • Reverberation of sound from concerts (including the very popular free concerts as part of Sydney Festival) into the Hospital. Acoustic advice provided by one of the respondents suggested that reverberation would be greater from glass than from a sandstone face.
  • Another option was a combined glass and sandstone-lined wall. It consisted of a solid concrete/sandstone wall at either end with a short stretch of glass in the middle. Depending on your perspective, it has all the advantages and/or disadvantages of the other two options.
  • The fourth option has walls only on the Royal Botanic Gardens' side.
  • For more information about these options and the Gardens’ wall, see our website or the large signs in the Gardens and Domain.

Will 2.5 m walls on the Domain side make any difference?

  • All of the options proposed should reduce sound levels by 5 dB, which will result in a drop in noise levels by about a quarter. This is considered a significant reduction.
  • With the sandstone wall, the visual impact of the expressway will also be reduced and this would add to the feeling of separation from traffic, leading, we are told, to an even greater perception of tranquillity.
  • The acoustic modelling tested a 3.5 m high wall. The noise reduction was almost the same as a 2.5 m high wall (see the acoustic report on our website).

What will the walls look like from the Domain?

  • The David Chesterman designed walls are all very elegant.
  • A sandstone face on the Domain side will be in keeping with the materials used throughout this precinct, such as the Art Galley, the Library and the base of our statues. It will be made from formed concrete sections lined with sandstone on the park side. The design of the wall and the sandstone surface is modern, and not ‘faux-heritage’.

What about the view from the expressway?

  • First up, our primary concern is for the 4 million people using the Domain each year and the 3 million visitors to the Royal Botanic Gardens. Noisewalls are part of the 21st century driving experience and our visitors shouldn’t miss out on the benefits of this protection.
  • Creepers (climbing fig) will be planted along the expressway side and in some areas, garden beds created. This will create a soft, green connection to the larger trees overhanging the wall. With the median strip plantings and lush vegetation on the Gardens side, drivers will still experience a sense of passing through a green oasis. Concrete rather than sandstone is the most durable surface for the road side, but it will soon be covered by vegetation.

What about public safety?

  • The presence of a wall should not make the public any less safe when walking through the Domain, and nearby plantings will be designed to minimise the potential for dark spaces.
  • In addition, in response to concerns about safety raised during the public consultation we will introduce lighting to keep the areas well lit at night.
  • More generally, the Trust is also working with our neighbours (such as the Art Gallery and Opera House) to improve security in the Domain, including enhanced lighting, security cameras and control rooms.

Will the walls effect sound quality of concerts in the Domain (e.g. Carols and Opera)?

  • Event organisers did not request the building of these walls. Indeed they were concerned about possible reverberation.
  • Our acoustic report confirms that no audible reverberation is anticipated from the planned walls.
  • During the consultation period, event organisers expressed concern about reflection of noise from glass walls and did not support that option.

Can further regrading of the asphalt surface of the Cahill Expressway reduce the need for noise walls?

  • Recent resurfacing of the expressway is a welcome move which helps but does not solve the noise problem.  The visual impact of traffic in the parkland and noise levels above EPA goals for passive recreation land remain.
  • The acoustic report on our website is based on levels following the re-sheeting of the road surface closest to the Domain.

Will existing trees and gardens be affected?

  • Two small trees, Tuckeroos (Cupaniopsis anacardioides), will be removed and there will be a temporary impact on the existing garden beds along the Domain side of the expressway.
  • New beds will be established, including trees where possible (taking into account  existing utilities). It is intended that the new garden beds will create a sense of a ‘botanical walk’ beside the new wall.
  • The Trust has a general goal of increasing our tree plantings (as we did along Hospital Road), focussing on interesting and appropriate tree species.
  • New garden beds will be created on the road-side of the Domain wall in sections set back from the picket fence.

Does the Trust have the necessary approvals?

  • Noise protection walls were approved under Part 5 of the Environmental Planning and Assessment Act 1979 and in the Ministerial Consent Conditions for the Cross City Tunnel.
  • The Heritage Council has already approved the sandstone-faced concrete wall for the Domain and the timber wall on the Royal Botanic Gardens side. The Heritage Council asked that the existing picket fence be retained.
  • The Board of Trustees and the Trust’s Botanic Gardens Committee (including external experts) support the wall designs, and in earlier meetings (prior to the stakeholder meetings) approved the sandstone option.

Who is paying for the walls?

  • A condition of approval for the Cross City Tunnel is that traffic noise and its visual impacts in the Royal Botanic Gardens and the Domain be mitigated.
  • As such, the Cross City Motorway Consortium provided the funding for the construction of the proposed sound barrier.
  • This is similar to arrangements made with residents and neighbours in all new road developments where the developer pays for the road infrastructure.

How widely have we consulted?

  • Relevant Trust staff, the Board of Trustees and the Trust Botanic Gardens Committee
  • Road and Traffic Authority
  • ERM (acoustic specialists)
  • Jackson Teece & Chesterman (architects)
  • Stakeholder meetings inviting representatives from the following groups:
    • Australian Garden History Society
    • NSW Heritage Office
    • City of Sydney Council
    • Australian Institute of Landscape Architects
    • Friends of The Gardens
    • Sydney Harbour Foreshore Authority
    • Event organisers and sporting users
    • Sydney Festival
    • State Library Of New South Wales
    • Department of Infrastructure, Planning and Natural Resources
    • Office of Protocol Dept of Premier and Cabinet
    • Members of Parliament
  • On-site briefings with members of the above groups, and others (e.g. National Trust of Australia [NSW]), as requested or by invitation
  • During February and early March 2005, the Trust sought community feedback including:
    • Large noticeboards in the Domain and Royal Botanic Gardens - drawing 25 responses by phone, fax, email or letter
    • Community research by professional market researcher, including focus group of 8 residents, 101 on-site interviews, 300 participants in a web-based survey and 126 questionnaires by members of the Friends of the Gardens
    • Copies of the posters sent to more than 150 local residents and businesses
    • Information on the Trust website
    • Media release on 14 February 2005
    
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