New England Highway Roundabout
Author 1 (Joseph, Marstella)
Department of Transport and Main Roads Author 2 (Rodney, Moss)
Department of Transport and Main Roads
Abstract:
The southern access to Stanthorpe has in the past experienced an unacceptable crash history. Prior to construction, the intersection was a non-conventional multi-crossleg intersection at grade. Following planning and submission for development funding under the targeted road safety scheme, works were implemented to construct a roundabout.
Through the early stages of design, points of ingress and egress were assessed to ensure smooth transition from the existing road environment to a roundabout at crossfall. Transitions, ARNDT Analysis and multiple reviews were undertaken to ensure the practicality of the design. The design intent was to ensure driver awareness and redirection of the travelled path through a carriageway change were safe for driver negotiation.
Due to political interest, works were staged to commence early construction that facilitated free flowing traffic management. Safety being a key deliverable on this project, works were undertaken to ensure minimal impacts to the public. Rock, subterranean moisture and climatic weather effects were all challenges the construction team worked collaboratively to overcome.
Keywords: Roundabout, Safety, Rock, Stanthorpe, New England Highway
Stanthorpe’s southern access has recorded 11 crashes since 2003. This includes the record of two fatal incidents which relate to the failure to give way and negotiate oncoming traffic when crossing the direct path of the New England Highway. In late 2016 and early 2017 The Department of Transport and Main Roads (TMR) Darling Downs District commenced planning development on the implementation of an intersection improvement project. This planning proposed four options which consisted of:
1. Upgrade of the intersection to a controlled T intersection.
2. Implementation of a Roundabout.
3. Augmentation of the existing intersection (incorporating acceleration and deceleration lanes).
4. A grade separated interchange.
Of the four options considered the BCR of the roundabout option (3.7) was chosen to progress to design. This planning development process involved the securing of targeted road transport safety funding under the land transport safety unit.
Detailed design commenced and resulted in the consideration of many options. The design looked in detail at the points of ingress and egress on the roundabout. Points of intersection and the apex of design control lines were considered to ensure smooth driver transitions and negotiation of vehicles through the road environment. Location of the roundabout footprint was considered to avoid as much rock as possible while also ensuring the road horizontal and vertical geometry could negotiate and support the national heavy vehicles that utilise this route. Design also made consideration for future proofing the proposed intersection treatment. This would ensure that a future grade separation interchange could be constructed to meet future traffic growth and demand needs if design/planning was undertaken.
During the final stages of design, early construction works commenced to facilitate pavement widening and clearing so that traffic management would be free flowing throughout the project delivery phase. Once design was complete, RoadTek Downs South West commenced construction on site. A collaborative working relationship was developed between the Administrators team and the delivery team. As works progressed it became apparent that the presence of granite rock and sub- terranean moisture would lead to some challenges.
The pavement design implemented on the project incorporated a rock mattress subgrade treatment (to mitigate the effects of moisture and act as a drainage layer/working platform). A cement treated subbase material was then placed and a deep lift asphalt pavement was used for the base course and surfacing treatments.
Various strengths of rock caused delays in delivery. Most rock was able to be avoided; however, between different rock outcrops, natural springs were present which ensured the need for the chosen pavement drainage design option. Although challenging at times to manage traffic changes and switches, the project was delivered by early July 2019.
Quality challenges that arose from site was the conformance of different asphalt types, use of local materials, sealing in cool and hot weather, protection of pavements to limit rework, ensuring safe and seamless traffic flow and limiting delays to the public. Overall expectation of the local
community was met, and the project was delivered to the required design and business case intent.
One of the main project “safe system” outcomes was the implementation of guidance landscaping to ensure vehicle glare, visibility and maintenance minimisation was enhanced. Use of local materials to place rock and guidance vegetation ensured that vehicle operators were given an experience of road user comfort and awareness. Electrical lighting installed at the project site is to the current LED standard and ensures that night time operation of the intersection is safely supported.
Overall there have been a number of learnings recorded from this project. These include the
resource of design, the application of design standards, the consideration of drainage design and the implementation of landscape planning. Through delivery, learnings were related to: dealing with hard rock outcrops (the use of saws and rock breakers in confined areas), management of water resources and construct a pavement to mitigate future effects of moisture. Management of traffic switch planning and protecting works from the effects of hot and cold weather. The team worked collaboratively together and has implemented a safe intersection outcome.
Acknowledgements
RoadTek Downs South West
Department of Transport and Main Road Darling Downs Technical Services Team Department of Transport and Main Road Darling Downs Delivery Team
Department of Transport and Main Road Darling Land Transport and Safety Unit
References
• Arndt, O. (1994). Relationship between roundabout geometry and accident rates. Brisbane:
Queensland University of Technology ePrints.
• Lee, G. (2004). Treatment of Crash Locations. Melbourne: Austroads publications.
