Auckland Transport (AT) is responsible for the management and maintenance of around 7,500km of the road network.
Approximately 800km of the network is unsealed and is operated as a gravel road. AT has a programme to progressively improve the performance of its unsealed road network, including in some cases converting gravel roads to become sealed roads. This is known as a seal extension.
In general, gravel roads service sparsely populated rural areas. Around 80% of Auckland’s gravel roads are within the former Rodney area. The remaining 20% is located mainly in Franklin, Hauraki Gulf Islands, and Waitakere*.
However, recent increases in the number of lifestyle blocks and development in rural areas has meant a higher number of people are now being exposed to dust effects from these unsealed roads. For economic reasons, new rural houses tend to be built closer to the public road than traditional farmhouses. As a result, AT has updated is management approaches to unsealed roads.
* The Waitakere Ranges Heritage Area Transport Design Guidelines will be considered when considering the sealing of any unsealed roads in this area. These state that: “existing unsealed roads should remain in an unsealed state, unless there are overriding health or road-safety reasons”.
How we prioritise road sealing
AT prioritises sealing unsealed roads using the criteria contained in the Unsealed Road Improvement Framework which is maintained by the Chief Engineer.
The current criteria for prioritising the upgrading of unsealed roads include traffic volume, including heavy commercial vehicles, houses and amenities close to the road, safety (traffic accidents), road gradient (steepness), public health risks, school bus routes and local community feedback.
AT also uses guidance materials published by Waka Kotahi / NZTA.
The prioritisation produces a ranking of all the unsealed roads compared to the available budget in the Auckland Council's Long-term Plan (LTP). The LTP for the three years 2018 to 2021 allocated $25 million in total for improvements to gravel roads. AT has also applied to the Government under the Covid-19 Stimulus Package for additional funding for increasing the unsealed roads improvement programme.
Images: Matakana Valley Road before and after road sealing.
AT is updating its programme of unsealed road improvements based on the year 2020 datasets. Also, AT as sought to include other dust management technologies on the approved road maintenance interventions list.
Cost of sealing
There is no typical or standard cost per kilometre to seal an unsealed road. Sealing a gravel road changes its physical characteristics, a driver's expectations and can encourage travelling at higher speeds.
To mitigate these changes, it is often necessary to widen the road, undertake geometric and safety improvements including increasing the radius of bends and corners, the provision of road markings and road signs, and strengthening the road foundation. Land acquisition or the construction of retaining structures is a feature of many sealing projects. It is also necessary to improve the collection and disposal of stormwater to prevent water from getting into the foundation layers. This prolongs the life of the sealed road.
The current costs of converting a gravel road to a sealed road range between $500,000 - $1,000,000 per kilometre. The annual cost of maintenance for a sealed road is approximately $20,000 per km and for an unsealed road approximately $5,000 per km.
A trial of dust suppressants and other low-volume road treatments is currently being carried out in partnership with other road controlling authorities throughout Aotearoa.