Gravel Roads - GENERAL FACTS AND F.A.Q. RESPONSES
Unsealed Roads – Varied Lifecycles
Unsealed roads vary considerably in condition because they are exposed to sun, rain, wind and traffic.
They pothole when wet, and when dry they become loose (unravel), corrugate, and create a dust
nuisance.
Changes in surface condition are highly variable due to exposure to the natural elements and this is
compounded further by traffic loads, which often fluctuate due to changing land use.
Grading of roads is an attrition-based maintenance treatment that, despite the best efforts by the
grader driver, will always result in disturbance of the existing gravel being spilled from the ends of the
grader blade.
Grading roads contributes to gravel loss costing Councils more money in the long run, so current
maintenance strategies look to defer grading for as long as reasonably possible, with emphasis on
localised pothole filling where practical.
New Specifications - Unsealed Road Wearing Course (UWC)
Different gravels have different uses with larger ‘cleaner’ stone used on logging routes due to its ability
to support heavy loads. Routes mostly used by light vehicles suit smaller gravel sizes.
National industry standards now specify Unsealed Road Wearing Course (UWC). The new UWC replaces
traditionally stony, loose, unsealed road gravels. UWC will help reduce the frequency of corrugations,
minimise the extent of potholes and deliver a more consistent, smoother road surface with less grading
costs.
National standards for aggregate on unsealed roads encourage the blending of materials in the gravel to
improve cohesion. Some gravels can appear red or orange-brown and drivers have raised concerns
about UWC gravels appearing muddy. Retaining and/or addition of clays, silts and other fine materials
into the gravels is required to meet the UWC specifications.
Concerns sometimes raised over ‘muddy’ roads being unsafe to drive on when wet are taken seriously
by Council staff. Where we receive reports of cars skidding in the mud, our engineers will conduct skid
resistance and traction tests. Invariably, these tests show that braking and steering performance is the
same, if not better, than on dry, loose, stony surfaces.
Natural Product – Gravel is natural and safe
Some people have raised concerns about the safety of roading materials. Gravel that is used in road
construction is an inert, naturally occurring mineral and there is little evidence that rain runoff from
unsealed roads contaminates waterways. Stormwater runoff can result in localised deposits of gravel at
culvert outlets and on private properties. These deposits are not harmful to the health of people, crops
or livestock. Where these deposits are assessed to be a nuisance or impact private property, they can be
removed by Councils contractors.
If you still have concerns about the safety of these materials, please contact the Regional Council which
has responsibility for air and water quality.
Gravel Roads - GENERAL FACTS AND F.A.Q. RESPONSES
Environment – gravel roads are dirty
The exposed nature of unsealed roads means they are dirty when wet and dusty when dry. Dirty
vehicles (dusty when dry, muddy when wet) is an unavoidable consequence of driving on unsealed
roads.
We often get comments about ‘clean’ looking gravel vs ‘muddy’ looking gravel and the impact this has
on road traction. Traditional stony and loose road gravels often make it difficult for vehicles to gain
traction, particularly on inclines when conditions are dry. Traction is much less of a problem for new
UWC road materials that appear bound and smooth in the dry and slushy during wet conditions. It is
common that the top 30-40mm of freshly applied UWC gravel presents as ‘muddy’ during rain. This is
superficial and reduces over time as the UWC gravel consolidates and wears in.
Vehicle Care – Punctures and Wear-&-Tear
Unsealed road conditions change rapidly, and all drivers should drive to the conditions.
Gravel road surfaces can be loose when dry, affecting vehicle traction and making punctures more
common. It has been identified that some low-cost brands of tyres that are primarily rated for sealed
road can be more susceptible to punctures.
Complaints of ‘sharp’ stones are taken seriously by the Council and all gravels used on our roads are
tested for compliance by quarries and contractors. The Council also conducts verification testing on
gravel when required. Differences in crushed stone often relates to the method of crushing (e.g. cone vs
jaw) and the Council works closely with suppliers to ensure aggregate quality complies with national
industry standards.
The blending of clays and fines materials to improve cohesion of UWC gravels provides smoother
unsealed road surfaces. This reduces vehicle wear and tear. However, vehicle owners are encouraged to
check their vehicle regularly and to undertake regular servicing to ensure vehicles are mechanically
sound.
Summer Grading – grading dry roads
Sections of unsealed roads often become loose (unravel) over summer because there is not enough
moisture in the fines to bind larger stones together. This unravelling causes rutting and corrugations.
Grading is an attrition-based maintenance treatment. Despite the best efforts by the grader driver
grading unsealed roads will always result in disturbance of the existing gravel being spilled from the
ends of the grader blade. This is further exacerbated in dry weather conditions.
Applying metal and grading hard, dry roads will cause further problems and usually results in an increase
in road-user complaints.
Gravel Roads - GENERAL FACTS AND F.A.Q. RESPONSES
Surface defects can only be effectively dealt with by cutting to a depth greater than the defect. Doing
this while the road is dry only provides relief for a few days but then creates more unravelling and
damage. That is why road users will often notice a reduction in grading or metalling over summer when
roads are very dry.
Grading of dry roads creates increased dust nuisance and also accelerates gravel loss, costing Councils
more money in the long run.
Grading with a Roller – Compaction
Wet-grade-roll treatments is up to 10x more expensive than normal grading, so it is done sparingly
within budget constraints.
Wet-grade-roll is typically limited to hill sections that have traction difficulties and/or focused on
unsealed roads with very high traffic use.
Compacted unsealed roads have a limited lifecycle before becoming loose (unravelling) and corrugating
when dry or potholing when wet. A road that has been graded and compacted with a watercart and
roller may last less than 3 months, depending on the type of gravel, the terrain and traffic volumes.
It is also common for the Regional Council to place water-take restrictions on many rivers and streams,
during summertime periods, preventing Council from directing the Contractor to grade a road with a
water cart and roller.
Health & Safety – dust and speed management
Vehicle speed and size are major contributors to road dust – the bigger and faster the vehicle, the more
dust created.
A regional review of speed limit bylaws is currently underway, and communities will have an
opportunity to provide input on proposed speed limit changes. Speed reductions will result in less road
dust being created.
Councils work with forestry companies to manage the impact of trucks on log harvest routes. These
companies are very aware of the impact their trucks have on unsealed roads and the dust they create.
Many haulage operators have placed self-imposed speed restrictions on their drivers, including
additional roadside warning signage and GPS vehicle tracking to educate drivers on slowing down in
front of residential homes.
Council works with Forestry partners for summertime dust suppression, entering into co-funding
agreements to assist in the application of dust suppression product in front of affected homes on some
busier designated haulage routes.
Gravel Roads - GENERAL FACTS AND F.A.Q. RESPONSES
Sealing of Roads – dust matrix
There are three funding options available to the Far North District Council for the sealing of roads:
1) Non-subsidised sealing (i.e. 100% funded from rates)
2) Subsidised sealing (i.e. 67% subsidised by Waka Kotahi NZTA
[69% from 1 July 2021] )
3) Community Funded Sealing (i.e. Policy No. 4112).
The Far North District Council prioritises road sealing based on criteria that ranks the impacts of road
dust according to the number of houses impacted and severity, as well as economic and other benefits.
1. Non-subsidised sealing (i.e. 100% funded from rates)
The Dust Matrix measures 22 criteria relating to road sections (Treatment Lengths). Below are the 22
criteria we measure, including types and numbers of traffic movements and speeds, number of houses
and distance from the road, the terrain/exposure of houses, and the function/hierarchy of the road, etc.
There are more than 1,840 sites (treatment sections) creating in excess of 40,500 records.
Due to continuous updating of information, the rankings can change. The Far North District Council uses
this tool to prioritise and select its annual road sealing programme based on the best information
available at the time. This includes considering other works nearby and cost savings that may be
possible by co-ordinating this work.
2. Subsidised Sealing (i.e. 67% subsidised by Waka Kotahi NZTA)
The Dust Matrix measures 11 criteria relating to Waka Kotahi’s
NZTA General Circular 16/04 criteria as
shown in the table below.
Its is increasingly difficult for the Councils to gain funding assistance from Waka Kotahi under that
criteria, mainly due to the volumes of truck movements being lower than Waka Kotahi’s requirements.
3. Community Funded Sealing (Policy No. #4112)
The Far North District Council will consider sealing a section of road where 75% of property owners
and/or ratepayers directly impacted by the work agree to fund the work.
Gravel Roads - GENERAL FACTS AND F.A.Q. RESPONSES
Dust Suppression – Summertime treatments
The Far North District Council has a limited budget for the application of dust suppression products on
sections of unsealed road during summer months. The Dust Matrix is used to select dust suppression
sites based on the following four criteria:
1. Target building is within 25m from the road
2. More than 130 vehicles per day
3. More than 30 trucks per day
4. Vehicle speed assessed at more than 65kph.
This product has a lifespan of around three months and is applied before Christmas.
The Council works with the forestry industry to co-fund the application of dust suppression products
along key harvest routes.
The Far North District Council has identified over 150 sites across the district that meet its dust
suppression criteria.
Dust Suppression – can be paid for by Individuals
The Far North District Council has agreed to support individuals who fall outside the criteria above by
covering the cost of applying the dust suppression products when it undertakes its summertime work.
The cost of the product is borne by the individual. Product to treat a 100m long x 5m wide stretch of
unsealed road typically cost approximately $750 - $800 + GST based on current market rates.
Where the individual pays for the product, the Council will add this site to its work programme and pay
for the contractors to apply it.
To arrange privately funded dust suppression, contact the Contractor directly:
Gravel Lock Ltd
Anneke Koens
Office Manager
021 506 337
