Contract Report
Great Western Highway upgrade (Mount Victoria to Lithgow) Winter weather related issues
by Adrian Runacres & Paul Hillier for Roads and Traffic Authority (RTA) of New South Wales (NSW)
NC74503 – July 2009
Great Western Highway upgrade (Mount Victoria to Lithgow) Winter weather related issues for Roads and Traffic Authority of New South Wales
Reviewed
Project Leader
PP Quality Manager
NC74503 – July 2009 GWH upgrade (Mt Victoria to Lithgow) - Winter weather issues
Summary
The Roads and Traffic Authority (RTA) of New South Wales (NSW) is committed to the upgrade of the Great Western Highway (GWH) between Mount Victoria and Lithgow in the Blue Mountains region of the state.
The existing road section has a difficult geometry given the challenging local topography and road safety concerns have historically been expressed. Many of these concerns can be related to the adverse weather conditions experienced in the region, particularly during the winter season. Localised sections of the existing route are prone to frost and ice formation with the potential to create hazardous driving conditions. Fog can also be a concern, both in winter and summer months.
In 2008, as part of the preliminary routing and design of the upgrade, the RTA commissioned ARRB Group to apply recognised microclimatological principles together with the undertaking of a desk study and local site visits to identify the microclimatical (weather related) constraints present within a defined study zone. These constraints were considered alongside a number of others, including environmental impact and heritage.
This led to four preferred Route Corridors being identified early in 2009 that have since been subject to further technical investigation and community consultation, including a workshop at Mount Victoria on Saturday 13 June 2009. The workshop provided local residents with information regarding the management of adverse weather on road networks from around the world as well as the constraints within the study zone itself. Residents were also able to provide the ARRB Group team with valuable local perspectives on the weather patterns and influences within the study zone.
The RTA is seeking to use the findings of, and opinions and recommendations provided by, ARRB Group to minimise the propensity of frost, ice and fog to form Although the Report is on the new route, where such conditions can be reasonably foreseen. Experience believed to be correct at has shown that this can be achieved through, wherever possible, avoiding the time of publication, ARRB Group Ltd, to the locations that are susceptible to ice formation and by choosing route alignments extent lawful, excludes all that minimise the extent of elevated sections and steep slopes. Similarly, road liability for loss (whether formations and structures can be designed such that the likelihood of frost and ice arising under contract, tort, statute or otherwise) formation on the running surfaces is reduced. Where the risks of frost and ice arising from the contents of formation cannot be completely mitigated, road authorities can consider the the Report or from its use. Where such liability cannot adoption of proactive winter maintenance programs and/or the adoption of road be excluded, it is reduced user warning systems. to the full extent lawful. Without limiting the foregoing, people should Sound maintenance practices can also play an important role in reducing the apply their own skill and propensity for frost or ice to form on a road surface, by ensuring that surface judgement when using the information contained in drainage provision is adequate and functioning and that wheelpath rutting does the Report. not lead to standing water on the surface. Additionally, ensuring that water does not run off onto the highway from adjacent land and that roadside vegetation is maintained can also play an important part in keeping a road surface free from frost and ice.
ARRB Group has concluded:
• There are climatological concerns regarding all of the four modified route corridors proposed, but these concerns are not considered insurmountable, and therefore, all of corridors are considered potentially viable when only climatic constraints are taken into account.
GWH upgrade (Mt Victoria to Lithgow) - Winter weather issues
• It is essential that a formal weather data collection regime be undertaken during the winter of 2009 to provide additional, highly localised data to further inform the route selection and design process [NB. the data obtained will also be valuable to the RTA’s local Lithgow office in the design and determination of future network maintenance programs and the placement of any future road user warning systems].
• The regime adopted should take the form of a formal thermal mapping exercise to include the study zone and beyond, with coverage being from Mount Boyce in the east to Yetholme in the west.
GWH upgrade (Mt Victoria to Lithgow) - Winter weather issues
Contents
Summary
Summary...... 1
1 Introduction...... 1 1.1 Improvements to the Great Western Highway - Mount Victoria to Lithgow ...... 1 1.2 Consideration of ice formation...... 2 2 Method ...... 4 2.1 Specialist advice...... 4 2.2 Investigation and consultation ...... 4 3 Ice hazards ...... 6 3.1 Introduction...... 6 3.2 ‘Black ice’...... 6 3.3 Hoar frost...... 6 3.4 Ice prone sites ...... 7 3.5 Climate change...... 9 4 Data from the study area...... 11 4.1 Climatic data...... 11 4.2 Accident data...... 13 5 Winter maintenance of roads in NSW...... 15 5.1 Current practice in the Lithgow area ...... 15 5.2 Current winter maintenance practice in other RTA regions ...... 16 6 Current alignment of the Great Western Highway between Mount Victoria & Lithgow ...... 17 6.1 Ice prone sections ...... 17 6.2 Fog...... 18 6.3 Wind...... 19 7 Potential new alignments of the Great Western Highway between Mount Victoria & Lithgow ...... 20 7.1 General observations ...... 20 7.2 Modified Orange Corridor (including common elements of all corridors) ...... 21 7.3 Modified Red Corridor ...... 24 7.4 Modified Green Corridor...... 26 7.5 Modified Purple Corridor...... 27 7.6 Summary ...... 29 8 Comments and recommendations concerning the future maintenance of the GWH between Mount Victoria & Lithgow ...... 31
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8.1 Winter maintenance...... 31 8.2 General maintenance and other issues...... 32 9 Recommendations for further work...... 33 9.1 Thermal mapping...... 33 9.2 Static weather station ...... 35 9.3 Mobile weather station...... 36 9.4 Mobile road condition state and/or road surface temperature sensors ...... 36 9.5 ‘Spot’ road surface temperature measuring equipment ...... 37 9.6 Potential further ARRB assistance ...... 37 10 Summary and conclusions...... 39 10.1 Summary ...... 39 10.2 Conclusions ...... 39 11 Appendices...... 42 Appendix A - Presentations (3 of) to RTA in June 2008 and community consultation workshop in June 2009 – (MS Powerpoint slides)...... 43 Appendix B - Presentation to community consultation workshop at Mount Victoria on Saturday 13 June 2009 ...... 82 Appendix C – Meteorological Data ...... 90 Appendix D: Summary of winter maintenance practices in NSW on state roads...... 112 Appendix E – Summary of winter weather monitoring options...... 119
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1 Introduction
1.1 Improvements to the Great Western Highway - Mount Victoria to Lithgow
The RTA is committed to the upgrade of the 18 kilometre section of the Great Western Highway (GWH) between Mount Victoria and Lithgow in the Blue Mountains of NSW.
One of the primary objectives of the upgrade is to improve safety outcomes, as the existing section of the GWH has a relatively poor safety record along its current route and comprises both steep slopes and a meandering horizontal geometry. The route is a major regional road connecting Sydney and Bathurst and carries a significant proportion of heavy vehicles. The impact of any accident related delays along the route can be highly significant and disruptive.
The inherent geometric features of the route are exacerbated by the cool weather conditions experienced in the region during the winter season, with there being periods of the year when frost and ice can form on the road pavement and on bridges with the potential to create hazardous driving conditions. Fog can also be an issue along the route, both in winter and summer months.
As part of the preliminary design stage of the upgrade during 2008, the RTA commissioned expert advice from ARRB Group with respect to adverse (winter) weather and specifically, the microclimates within a defined study region, to identify any constraints to the planning of the new route and its design. Other specialist inputs (e.g. environmental, cultural, geological) were also procured. The inputs ultimately led to the identification of four preferred route corridors in early 2009, which have been the subject of further technical investigation. The route corridors have also been subject to community consultation during May and June 2009. A community consultation workshop on Saturday 13 June 2009 provided local residents with information regarding the effect of adverse weather on road networks, in general, and then more specifically, with respect to the study zone.
This report provides observation and professional opinions with respect to microclimates and winter weather for both the study zone as a whole and then the four preferred route corridors. The observations and opinions given reflect recognised microclimatological principles together with the findings from a combination of desk study (data analysis) and site visits (including valuable local anecdotal evidence derived from the workshop on 13 June 2009).
Figure 1: Position of the Blue Mountains of New South Wales in relation to Sydney (source: Google map)
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Figure 2: The Great Western Highway (Route 32) between Mount Victoria & Mount Lambie, via Lithgow (source: Google map)
1.2 Consideration of ice formation
As a part of its commission, ARRB Group was requested to provide technical and operational information regarding frost and ice formation on roads and its significance, as well as providing an insight into available strategies for prediction, prevention and mitigation.
Ice formation on a road surface is dependent upon the propensity of the surface to experience sub- zero temperatures at the same time as exhibiting sufficient moisture for ice to form.
Many of the factors that influence these issues are difficult to control and therefore, in many locations around the world where the climate is such that sub-zero temperatures regularly occur, the management of the road network includes active programs of winter maintenance (also known in some jurisdictions as the ‘winter service’). Such programs usually involve the treatment of the road surface with a de-icing agent (e.g. a salt or an alternative chemical) ahead of icy conditions to keep the road surface ‘clear’ and as a result, help to keep roads safe. However, the programs can also be expensive and difficult, as well as giving rise to environmental concerns. Therefore, it is considered vital that any opportunity is taken to minimise the propensity of ice to form on a new road in geographical areas where such conditions can be reasonably foreseen.
This can be achieved through:
• the routing of new roads with a view to avoiding, wherever possible, locations susceptible to ice formation
• considering route alignments that minimise the extent of elevated sections and steep slopes
• employing detailed design elements that reduce the likelihood of ice formation on the running surfaces
• considering long term winter maintenance programs and the adoption of road user warning systems during the road planning stage.
Notwithstanding, it is recognised that the consideration of ice formation (specifically) and winter weather issues (in general) are only individual elements of the overall planning process for the GWH upgrade, and that a successful route will require the careful consideration of a number of different constraints, e.g. sensitivity to environmental and heritage factors. Trade-offs will result and it is inevitable that further consideration of a winter maintenance regime will be required for any new route determined in this geographical area.
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The content of this report and other advice provided under this commission (outlined in the following section of this report) should assist the RTA in better understanding the factors relating to ice formation and winter weather on the route, and allow the integration of these issues during the planning stage.
Geographic areas that are susceptible to ice formation also tend to experience other weather related hazards to road transport, e.g. hoar frost, snow, high winds and/or fog etc. The pertinent study area is no exception and therefore, although this report focuses on ice formation, these other potential hazards are discussed where geographically appropriate.
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2 Method
2.1 Specialist advice
Following initial site inspections by Sydney based team members, ARRB Group arranged for a UK based micro-climatologist and highway winter maintenance specialist, Adrian Runacres, to provide expert advice under a sub-consultancy arrangement. He has therefore been heavily involved in this investigation, visiting the study zone for short periods in June 2008 and June 2009, and has led on the production of the main project deliverables, including this report, in close association with the ARRB Group’s Project Leader, Paul Hillier. Both Mr Runacres and Mr Hillier attended the community consultation exercise on 13 June 2009.
2.2 Investigation and consultation
Initial investigations and consultations included the following:
• an assessment of preliminary information and images provided by the RTA and collected by members of the ARRB Group’s project team, both before and following a project inception meeting which was held in May 2008 • a full day of presentations and discussion at the RTA’s Head Office (then located at Centennial Plaza, Sydney) on Tuesday 3 June 2008, attended by RTA Head Office and regional staff. The presentations delivered, covered the effects of adverse weather on road network safety (with a particular emphasis on winter weather) and are reproduced in Appendix A of this report • a drive through of the length of GWH in question and immediate environs during the early morning of Wednesday 4 June 2008, with local technical commentary provided by Dion Killiby, then RTA’s Project Engineer on the GWH upgrade • a meeting with local engineers and operational staff from RTA, plus a representative of the local Road Policing Unit, at the Lithgow Area Offices on Wednesday 4 June 2008 • desk study of maps and other information pertaining to the area and the potential improvement scheme • site visits with the aim of further familiarisation of the existing route and the general study area on 4-5 June 2008.
Following the above, further research and liaison activities were undertaken and the following additional information was secured:
• operational data obtained from the RTA Regional Offices concerning the incidence and management of ice on the State Road Network in NSW • operational data concerning winter maintenance operations undertaken on the existing alignment of the GWH in the study zone during the three year period July 2005 to July 2008 inclusive • data relating to personal injury accidents on snow and ice affected roads across the study zone during the thirteen year period 1996 to 2008 inclusive • meteorological and climatological data from various weather stations within the study zone and its immediate environs • community consultation resources on the GWH upgrade from the RTA website.
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In addition to the above, discussions were instigated with Vaisala Limited, a specialist weather monitoring technology company, regarding the undertaking of a data collection exercise during July 2009 which would further assist the RTA in determining the preferred route for the GWH upgrade.
In June 2009, Mr Runacres returned to Australia to undertake further site visits and provide updated specialist advice on the project, culminating in technical input to the community consultation exercise on 13 June 2009, which included the delivery of a short presentation to local residents. The presentation is included in Appendix B of this report. During his visit, additional information and data sources were identified, e.g. amateur meteorology records from the Hartley Valley, anecdotal reports of winter weather conditions from long standing residents, and updated RTA crash reports. These items will be used to further inform routing opinions beyond the delivery of this report.
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3 Ice hazards
3.1 Introduction
Ice and frost are hazardous when present on road surfaces because they have the potential to considerably reduce the level of skid resistance provided by the road surface to the tyres of a vehicle. As with other situations where levels of skid resistance are reduced, incidences are most significant (hazardous) when they occur in situations where drivers are required to brake, accelerate and/or alter direction, such as at intersections, and importantly for this study, when traversing slopes and bends.
In order for ice or frost to form, the road surface temperature (RST) is required to be below zero degrees Celsius (0°C). However, sufficient moisture must also be present in the form of liquid water on the road surface or water vapour in the atmosphere. In situations where there is no surface water and atmospheric humidity is low, RSTs can be significantly below 0°C without ice or frost forming.
As a result, in many geographic areas where maintenance programs are routinely implemented to prevent frost and ice forming, as much consideration is given to the timing and extent of predicted precipitation events and atmospheric humidity levels, as prediction of the minimum RST.
3.2 ‘Black ice’
When liquid water freezes on a road surface, it forms a smooth crystalline ‘sheet’ of ice which is typically transparent, although it can occasionally appear light coloured or white in appearance as a result of small air bubbles entrained within the ice. Usually, these crystalline ‘sheets’ will occur as isolated patches, or as a series of patches along a section of road, where ‘puddles’ or larger areas of surface water have frozen. However, such ice can also extend along and across a relatively large area of road surface if a previously wet road freezes. In such instances, the ice can be so thin that its surface is slightly irregular as a result of the texture of the underlying road surface.
Due to the fact that the constituent materials of a road surface will often appear dark in colour when viewed through the ice, and because the ice can be difficult to see and/or differentiate from a simply wet road (especially at the relatively low viewing angles of approaching drivers), this type of ice is widely known and referred to colloquially as ‘black ice’, or ‘glaze ice’.
As well as being difficult to detect, the skid resistance of ‘black ice’ is typically very low. It is most slippery when its surface temperature is around, or close to, 0°C. This is because at such a temperature the pressure induced by the passage of a vehicle tyre over it can cause the uppermost surface to melt, resulting in a film of liquid water between the tyre and the ice. [The level of skid resistance provided rises at surface temperatures below 0 oC].
Typical Coefficients of Friction (CoFs) for ‘black ice’ range from approximately 0.05 to 0.2, which compares to approximately 0.4 to 0.5 for a sound, bituminous road surface in the wet and approximately 0.7 for the same road surface in dry state.
In summary, as well as being difficult to see, ‘black ice’ is typically very difficult to traverse safely. Vehicular control can be lost relatively easily and, if all of the vehicle tyres lose adhesion, the vehicle will tend to travel in a straight line, regardless of any steering or braking inputs by the driver. Additionally, due to the low level of sliding friction afforded by the ice following a loss of control, the vehicle will tend not to lose speed during its slide, with incident severities then tending to be relatively high if an impact with a roadside object or another vehicle occurs.
3.3 Hoar frost
Hoar frost consists of collections of individual crystals of ice that form on surfaces at a temperature that is both below 0°C and below the temperature at which water condenses out of the air in contact
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with it, i.e. below the ‘dew-point temperature’. In effect, hoar frost is ‘ice dew’ and its distinctive feathery white crystals are commonly seen during cold winter mornings in temperate climates. Hoar frost can form at any time of day or night, but is most commonly formed before or around dawn, as this is the time of day that temperatures tend to be at their lowest and humidities at their highest. Hoar frost often affects grass and metal surfaces, such as road signs and parked cars, as these surfaces are generally colder than other objects given that they have relatively large surface areas compared to their mass and their inherent thermal properties.
In those geographic areas where surface temperatures can fall to 0°C or below, road surfaces can be adversely affected by hoar frost. However, as road surfaces are often relatively warm compared to surrounding surfaces, formation is most common on vegetated roadside verges etc.
Hoar frost itself tends not to be as ‘slippery’ as ‘black ice’. However, when it is trafficked, the action of vehicle tyres often temporarily or partially melts the hoar frost crystals, which then re-freeze due to the sub-zero RST. The result is the formation of patches or strips of ‘black ice’ in the wheel tracks and therefore, when it does form on road surfaces, hoar frost is a potentially hazardous phenomenon.
Additionally, hoar frost is also relatively difficult to predict on road surfaces, as it can form directly onto a dry surface and very soon after a surface temperature falls below the dew-point temperature.
3.4 Ice prone sites
As previously stated, ice formation on any particular section of road is dependent upon just two factors, i.e. its surface temperature and the amount of moisture present. However, both of these variables are influenced by a number of further factors. Therefore, the relative propensity for ice to form at one site, compared to another, is complicated, and dependent upon variables relating to:
• the prevailing weather conditions
• the macro and micro climate of each site
• local geography and topography
• local altitude, latitude and distance from water bodies and/or large conurbations
• the construction of the road itself (such as its depth of construction, its constituent materials, and parameters such as surface profile and texture depth).
In most weather conditions, RST tends to decrease with altitude (and often away from urban areas).
However, during clear and calm winter mornings, the main factors affecting RST relate to the nature and topography of the immediate vicinity of each site. The coldest spots tend to be those located towards the bottom of slopes and/or those other spots that are most affected by radiational cooling and cold air (katabatic) drainage. This is especially the case with those sites that lie towards the bottom of south facing slopes (in the southern hemisphere), as such sites are often in shadow for long periods during daylight hours in the winter months (as the sun is low in the sky) and commence cooling overnight earlier (and from a lower initial temperature) than sites that are in full daylight.
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Figure 3: the principle of katabatic drainage (nb. snow does not have to be present for katabatic drainage to occur)
Elevated sections of road, such as those on viaducts or bridge decks, also tend to be more prone to ice and frost formation than adjacent sections of road, as they tend to radiate heat away relatively rapidly and have less mass below the surface of the road (i.e. a lesser depth of construction and formation) to retain and store the heat received during the day.
Not surprisingly, those sites that are subject to the coldest temperatures combined with the greatest amounts of precipitation or other sources of water, whether by way of surface run-off or atmospheric humidity, are generally those that are most prone to ice formation.
During the planning, design and construction stages of a new road; designers, engineers and planners can influence whether (or not) a road will ultimately be prone to the formation of ice when in service. For example, it is prudent to avoid routing a new road such that its alignment falls within an ice prone area/s or where the frequency that ice will form is greatest.
However, it must be recognised that this cannot always be achieved or is not always possible due to other constraints, and where a new road has to be constructed in an area which experiences freezing temperatures, significant precipitation and/or high humidity, some degree of ice formation will be inevitable in certain weather conditions and this situation will need to be mitigated and managed.
As well as considerations at the design stage, sound maintenance practices play an equally important role in reducing the propensity for ice to form on a road surface, e.g. by ensuring that:
• drainage provision is adequate and functioning
• the cross-fall and longitudinal profile of a road do not lead to puddles forming, or result in larger areas of running or standing water
• surface water does not flow onto the highway from adjacent land
• roadside vegetation is maintained, so that humidity levels are controlled.
As previously documented, affected road authorities will also typically devise and undertake an active program of winter maintenance (winter service) on all or a controlled proportion of their road networks.
The fundamental aim of a winter maintenance program is to prevent ice and frost from forming (and snow from lying) by the judicious application of a salt or other anti-icing chemical ahead of the onset of the conditions. This approach is often referred to as ‘precautionary salting’, ‘precautionary
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treatment’ or ‘pre-treatment’ and such regimes are typically more efficient and environmentally sympathetic than those that are purely reactive, i.e. clearing frost, ice and snow after it has formed.
By their very nature, the success of precautionary winter treatments is entirely dependent upon:
• accurate, reliable weather forecasts
• historical and real time information concerning the condition of the road network
• experienced and trained winter maintenance decision makers and operational personnel
• flexible and effective management
• appropriate anti-icing materials and well maintained (and calibrated) spreading equipment.
It must be noted, however, that even with the best of knowledge and intent and a sound regime, the vagaries of the weather, the complexity of local micro-climates, and the limits of technology will occasionally conspire to lead to ice formation on a road surface. Experience shows that this often occurs when a weather forecast proves to be inaccurate (or is not updated expediently) or during ‘freezing rain’ events (when rain falls onto the road surface and freezes almost instantaneously and is the worst winter weather type faced by a road authority), and in such situations, ice formation becomes inevitable, with the road authority largely powerless or without time to respond.
3.5 Climate change
The latest predictions concerning climate change in NSW (http://www.climatechangeinaustralia.gov.au/nswacttemp1.php ) indicate that, when compared to the climate experienced in the period 1980 to 1999, by the year 2030: average winter air temperatures across the state may be between 0.6 oC and 1.0 oC warmer; average winter rainfall may be reduced by between 2% and 10%; and average humidities may be reduced by between 0.5% and 1.0%. It appears that these trends are predicted to continue to 2070 and beyond.
If taken at face value, these trends would indicate that the incidence of ice, frost and fog in the study area is likely to reduce in the future.
However, the data studied relate to the 50 th percentile projections based on the results from a number of different climate models, and the range of results across the models is significant. For example, for the same period as considered above, the projections vary from average winter air temperatures increase of between 0.3 oC and 0.6 oC (10 th percentile) to between 1.0 oC and 1.5 oC (90 th percentile), and from a reduction in average winter rainfall of between 10% and 20% (10 th percentile), to an increase in average rainfall of between 2% and 5%.
Additionally, the spatial resolution of current climate change models is insufficient to identify the likely different effects of climate change that will occur across areas as small (but as geographically diverse) as the study area in this particular case.
The upshot of the above is that it is currently impossible to predict with any certainty how climate change will affect the propensity for ice, frost and fog to form at locations across the study area.
Although it appears likely that the average incidence of ice, frost and fog will tend to reduce with time as the effects of climate change are increasingly felt (possibly reducing the length of the season when these phenomena would be expected), it is considered highly likely that the study area will continue to be affected by these issues during the winter months well after the new route has been constructed. Therefore, and with regard to existing and future roads within the study area, the issues identified remain important considerations for the safety of road users.
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4 Data from the study area
4.1 Climatic data
A number of recording weather stations were found in the proximity of the study zone, but coverage within the study zone is currently thought to be non-existent. Further enquiries with the Bureau of Meteorology will be made in due course to determine if this is indeed the situation.
Weather stations operated at both Mount Victoria (between 1872 and 1990) and at Lithgow (between 1889 and 2006), but these stations are no longer in operation.
Significantly, no formal climatological data appears readily available from the central area of the study area around Hartley and/or Hartley Vale. However, it was identified at the community consultation meeting on 13 June 2009 that amateur meteorological records for this locality may well be available from two local residents, including daily measurements and observations over the last ten years. This data is currently being transcribed and will become a highly valuable resource in the future conduct of this investigation.
In summary, the lack of weather data from within the study zone has necessitated a focus thus far on site observations, the desk study and anecdotal evidence from residents, moderated by analysis of the available data from the automated (AWS) and manual weather stations located across a wider general region. To this end, monthly climate statistics have been reviewed from the following Bureau of Meteorology stations (the base data is included as Appendix C of this report):
• Mount Victoria (Selsdon Street) [Station Number 063056] : 33.59°S 150.25°E : Elevation 1064 metres
• Mount Boyce AWS [Station Number 063292] : 33.62°S 150.27°E : Elevation 1080 metres
• Katoomba [Station Number 063039] : 33.71°S 150.31°E : Elevation 1015 metres
• Lithgow (Birdwood Street) [Station Number 063224] : 33.49°S 150.15°E : Elevation 950 metres
• Lithgow (Newnes Forest Centre) [Station Number 063062] : 33.37°S 150.24°E : Elevation 1050 metres
• Lidsdale State Forest [Station Number 063046] : 33.45°S 150.05°E : Elevation 975 metres
• Sunny Corner (Snow Line) [Station Number 063079] : 33.39°S 149.90°E : Elevation 1225 metres
• Bathurst Airport AWS [Station Number 063291] : 33.41°S 149.65°E : Elevation 745 metres.
There are significant altitudinal differences across the study area, with the Mount York, Darling Causeway and Mount Victoria areas being approximately 1,050 metres above mean sea level (amsl). The floor of Hartley Valley is around 800 metres amsl and, where the current alignment of the GWH between Mount Victoria and Lithgow crosses the River Lett, the elevation is around 700 metres amsl.
The automatic weather stations from which data has been reviewed also vary in altitude from 745 metres amsl at Bathurst Airport AWS, and 1,080 metres amsl at Mount Boyce AWS.
It can be argued that the weather stations studied exhibit broadly similar elevation differences to those within the study area. In addition, stations such as those at Mount Victoria and at Birdwood Street in Lithgow were located relatively close to the existing route of the GWH between these two settlements.
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Notwithstanding the above, there are potentially significant differences between the micro-climates experienced across the study area and the coverage of the weather stations examined. Additionally, a number of the weather stations are located a distance from the study area and experience somewhat different weather conditions.
The sites of the standard (manual) recording stations examined are typically exposed, and open in all directions, so as to be representative of the conditions being generally experienced in the areas surrounding them, and because information gathered in this way will be of most benefit to forecasting meteorologists. Meteorological recording instruments are also generally positioned in a standardised manner and at a prescribed height above the ground. For example, air temperature and dew point measurements are normally made at a height of 1.2 metres above the ground within a shaded enclosure which allows air movement, such as a Stevenson screen or a white coloured louvred shade. However, the environment of road sections varies significantly, with some being relatively open and exposed and other sections being significantly more sheltered. Therefore, the data that is available from weather stations can only provide a general indication of the climatic conditions experienced along the existing GWH and across the study area as a whole.
Significantly for this study, no ground surface temperature measurements are collected at any of the weather stations in the wider region. Such data is of obvious value in assessing the propensity of ice formation at a location with the greatest level of accuracy possible.
However, despite the limitations in the available weather station data, it is nonetheless useful in demonstrating some of the clear differences that exist across the study area with regard to the propensity for ice formation. For example, the statistics for the Mount Victoria weather station indicate that, at that site, the mean minimum July air temperature is +1.7°C (July being the coldest month), that air temperatures fall to 0°C or lower at this site on 19.3 days per year on average, and that these days mainly occur during the months of May through to September. This is in comparison with the Lithgow (Birdwood Street) weather station site, which experiences a mean minimum July air temperature of +0.7°C, and an average of 43.2 days per year when air temperatures fall to 0°C or lower, with these days occurring mainly during the months April to October.
The above shows that the Lithgow area experiences approximately twice as many days when the air temperature falls to 0°C or lower as the Mount Victoria area, and that the period during which these occasions can be expected to occur commences approximately one month earlier and goes on for approximately one month later in Lithgow than in Mount Victoria.
The data from the weather stations also shows that, although the coldest air temperature recorded at Lithgow (Birdwood Street) during the 30 years to 2006 (when the station was closed) was -8°C, 90% of daily minimum July air temperatures at that site are -3.5°C or higher. The coldest air temperature recorded at the Mount Victoria station during the period between 1962 and 1990 (when that station closed) was -6.3°C, and 90% of daily minimum July air temperatures at that site are -1.0°C or higher.
These regimes indicate that, although winter temperatures across the study area are sometimes cold enough for ice to form (with the frequency varying significantly across the area), whether or not this will occur on any given date of the year will be highly variable, due to the short term weather conditions being experienced.
Under this type of climate regime, relatively small variations of minimum surface temperature can make large differences in the number of occasions that ice is likely to form, and this is exacerbated by the variable nature of precipitation (both snowfall and rainfall) that these areas typically experience.
Whilst this situation is similar to the climate regimes experienced in many other parts of the world, it can exacerbate the tendency of road users to be ‘caught out’ by largely unexpected / unforeseen, adverse winter weather conditions. This is turn makes winter maintenance planning and decision making more difficult than it would be for a significantly colder or warmer climate.
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4.2 Accident data
ARRB Group was provided with a Crash Report that included the Mount Victoria to Lithgow section of the GWH, dated April 2008, and prepared by the RTA’s Road Safety and Traffic Section. Additionally, further specific information was made available relating to crashes occurring on snow and ice affected road surfaces across the study area during the period 1996 to 2008.
In June 2009, a second crash report became available for the five year period 2004 to 2008. However, the coverage of this crash report is limited to the area around ‘the 40 bends’ and River Lett Hill. The content of this report has been examined, but the following commentary relates to the April 2008 crash report only, given that it covers the entirety of the study zone. The findings are:
• During the full years 1996 to 2007 inclusive, there were 136 crashes on snow or ice affected roads in the greater Lithgow and Blue Mountains region.
• Of these 136 crashes, 23 occurred within the study area.
• Of these 23 crashes:
o ten resulted in personal injury, with the remainder ‘damage only’ crashes that involved vehicle ‘tow away’
o 17 occurred on the GWH, of which seven resulted in personal injury. The remaining 6 crashes occurred on local roads (only one of which was unsealed).
Significantly, of the 17 crashes that occurred on the GWH, 12 of them occurred within a relatively short distance of each other (within approximately 2 kilometres) on, or very near to, a location on the GWH known locally as ‘the 40 bends’. [Additionally, one of the local road crashes (at the northern end of the McKanes Falls Road, relatively close to its junction with the GWH) is also in this locality].
The ’40 bends’ section of the GWH is towards the northern end of the study area, to the south and east of South Bowenfels and is oriented approximately east/west as well as being located immediately south of, and along, the foot of a relatively steep and densely vegetated south facing slope, known locally as Hassan’s Walls.
A further cluster of three crashes appear to have occurred on the Brown’s Gap Road, near to the bottom of another relatively steep and densely vegetated south facing slope at Hassan’s Walls.
In summary, it appears that 15 of the 23 snow/ice crashes (65%) on the GWH occurred at locations that are not at a particularly high elevation but are close to the foot of a vegetated south facing slope.
The above findings are entirely consistent with the principles of ice formation on a road surface at such locations, due to the pooling of cold and humid air at the bottom of the slopes during and following relatively clear and calm winter nights. As previously reported, the process of cold air flowing down a slope as a result of its relative density is formally termed ‘katabatic drainage’ and particularly affects south facing slopes (in the southern hemisphere) because these slopes do not receive as much solar radiation during daylight hours as other areas (particularly during the winter months when the sun is lower in the sky) and therefore are generally cooler than other sites. Cold air drainage only occurs during relatively calm conditions and usually occurs when the sky is clear, when nocturnal radiational heat losses are greatest. However, when cold air drainage does occur it can lead to an area at the foot of a slope becoming significantly colder and with significantly greater humidity levels, than the majority of other locations in that general region.
The data provided also indicates that snow/ice crashes had also occurred on the more elevated (higher) sections of Chifley Road. Additionally, a cluster of five crashes is shown to the southeast of Bell, on a series of bends on the Bells Line of Road. Again, this cluster was on a section of road at a
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relatively high elevation. These findings are entirely consistent with the typically experienced general decrease in temperature with elevation.
Interestingly, despite the relatively steep slope and tight bends, only one snow/ice crash occurred on the section of the GWH as it descends to the west of Mount Victoria. It is considered that this may relate to the existing route taking a relatively advantageous (climatologically speaking) alignment along a west and north facing ridge. Such an orientation tends to maximise the effects of direct sunlight and significantly reduces the likelihood of cold air drainage affecting this section of the road.
Further analysis showed that of the total 136 snow/ice crashes that occurred in the wide, greater Lithgow and Blue Mountains region, 98 (72%) of them occurred between 0500hrs and 1000hrs.
This ‘time of day’ pattern is even more marked with the 23 crashes that occurred within the GWH study area, given that all occurred in a 5½ hour period between 0500hrs and 1030hrs, and 19 (83%) occurred within an even ‘narrower’ time period of 3½ hours, between 0530hrs to 0900hrs.
The above findings are consistent with most of these crashes having occurred on road surfaces affected by ice, rather than as a result of snowfall (which can occur at any time). This opinion is supported by the fact that the reported weather conditions are ‘Fine’ in the majority of these instances.
Similarly, this finding is totally consistent with the climatic conditions experienced across the area, and is typical of other geographic areas where minimum winter temperatures ‘hover’ around 0°C. It is entirely logical that ice related crashes most frequently occur during, and after, the period when temperatures are coldest (just before, or around, dawn) and when traffic levels are generally increasing at the start of the day.
Of the 17 snow/ice crashes that occurred on the GWH during the statistical period, 9 (53%) of them occurred at weekends. The GWH is subject to winter maintenance from the Bowenfels Depot and this finding may benefit from further investigation.
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5 Winter maintenance of roads in NSW
5.1 Current practice in the Lithgow area
Discussion with RTA engineers based at its Bowenfels (Lithgow) office indicates that a modest program of winter maintenance is in effect on the pertinent section of the GWH. However, the policies and systems governing this program do not appear to be formally documented in a specific ‘Winter Maintenance Plan’ or similar document and it is recommended that this be addressed.
It is understood that the current program is based on the spreading of salt (sodium chloride, NaCl) during early evenings as an anti-icing operation on pre-determined lengths on the GWH. It was explained that the operation encompasses approximately 41 kilometres of carriageway (82 lane km). It appears that ‘Go/no go’ decisions are made daily by the local RTA staff during the winter months.
The extent of the winter maintenance season (often operationally known as the ‘winter period’ in other countries) does not appear to be formally defined. Daily decision making appears to be heavily reliant on a core team of experienced staff using the limited information sources available to them. These sources do include, however, the considerable local knowledge that the team have developed over time, weather forecasts available through normal media channels, as well as patrols and inspections.
The anti-icing salt is spread from a multi-purpose drop sided truck fitted with a small demountable spreader and hopper system. The salt is procured in bags (25 kg) and loaded onto the vehicle on pallets. A full vehicle load is approximately 1.3 tonnes of salt. The bags require opening and the hopper is filled by hand as the vehicle traverses its route.
The salting route consists of carriageway sections pre-determined by local knowledge as being those sections where ice and frost hazards are most likely. The route is traversed in both directions, with salt being applied to a single carriageway/lane during each pass. It appears from operational records that the rate of spread of salt averages at around 4 g/m² (typical spread rates are around 10 g/m 2 for such operations in other countries of the world).
It does not appear that the width of spread and/or spread pattern of the salt can be easily adjusted during a salting operation, rendering it difficult to cope with varying carriageway widths (e.g. at overtaking and turning lanes etc.).
In addition to the above proactive operations, it is understood that reactive winter maintenance is possible, e.g. using road graders on fallen snow together with the spreading of salt, as and when reports of adverse conditions and/or adverse weather related incidents have been received. It appears that such reports usually come from the Police who conduct overnight patrols of the GWH. It was explained that the GWH can be closed temporarily until the hazard is satisfactorily dissipated.
The winter period in Australia extends from June to August inclusive. However, it appears that is not uncommon for ice, frost or snow to be experienced on the GWH outside of these months and it was explained that historically, operations have been undertaken in every month, except February.
The information provided by RTA includes winter maintenance operational data out of the Lithgow Depot during the years 2005 to 2008 inclusive. The data was analysed year on year.
During 2005, operations were undertaken on 45 separate dates between 4 July and 27 October 2005, with the GWH ‘salted’ on 30 of these dates. Other roads ‘salted’ included Bells Line of Road (28 dates), Jenolan Caves Road (24), Mitchell Highway (four) and the Mid Western Highway (eight). Snow signs were erected on the Mitchell and Mid Western Highways during this winter season.
During 2006, operations were undertaken on 18 dates between 2 June 2006 and 7 September 2006. The GWH was ‘salted’ on nine occasions and Mid Western Highway, six dates. Bells Line of Road and Mitchell Road were ‘salted’ on four dates, and the Jenolan Caves Road was ‘salted’ on three dates. It appears that snow / ice signs were utilised on all of these roads during this period.
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During 2007, operations were undertaken on 21 separate dates between 14 June and 21 July 2007. The GWH was ‘salted’ on 16 occasions, as was the Mid Western Highway. Mitchell Highway was ‘salted’ on 13 dates, the Jenolan Caves Road three dates, and the Bells Line of Road on two dates. During this season, the Castlereagh Highway was also ‘salted’ on five dates. It is understood that snow / ice signs were employed on the GWH and Bells Line Road during the season.
It appears that the 2008 winter season started relatively early in the Lithgow area, with the first operation being undertaken on 28 April 2008, which included treatment of the GWH.
The large variation found in the number and timing of treatments per year is considered entirely consistent with the overall climatic regime, where minimum temperatures ‘hover’ around 0°C.
More detailed information was provided regarding operations undertaken in July 2008 and shows that ‘the 40 Bends’ section of the GWH was ‘salted’ on six dates during that month. This is considered indicative of staff at the RTA’s Lithgow depot being very aware of the propensity for this road section to be affected by ice, and that this fact is recognised when planning operations in this area.
5.2 Current winter maintenance practice in other RTA regions
Appendix D of this report provides a summary of winter maintenance practices currently adopted in other RTA Regions. The data includes some information regarding the incidence and severity of ice, frost and snow formation in each of the regions.
It is clear that winter maintenance / ice management practices vary significantly across the state, which is not unexpected given the range of climatic conditions and weather regimes experienced.
It appears that as well as in the Lithgow Region, precautionary salting also takes place at known problem sites in the Orange District of Western Region, as well as in the RTA’s Southern Region. The latter uses an alternative de-icing agent, calcium chloride (CaCl), on major routes, but sodium chloride (NaCl) is also occasionally spread in isolated areas.
It appears that decisions regarding precautionary ‘salting’ operations are mainly based on local knowledge and experience, together with use of general media weather forecasts. It appears that the Southern Region also procures a specific winter forecast from the Bureau of Meteorology.
As well as proactive operations, a number of regions undertake reactive salting operations in response to reports of ice or snow.
It is reported that within the Sydney region, where ice and snow do not generally occur, sand is occasionally spread in response to potentially icy conditions being reported.
Warning signs are generally utilised in all of the RTA regions where ice and/or snow conditions are experienced and, occasionally, the closure of ice affected road sections is used to protect road users.
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6 Current alignment of the Great Western Highway between Mount Victoria & Lithgow
6.1 Ice prone sections
As previously introduced, the ’40 bends’ section of the current GWH is of most interest regarding the formation of frost and ice. Whilst it is noted that this road section falls within an active program of winter maintenance ex Lithgow depot, a significant ice related accident record exists for the location.
This road section has a number of sharp bends and lies towards the bottom of, and in close proximity to, the densely vegetated south facing slopes of Padley’s Pedestal and Hassan’s Walls and the road safety challenges faced are eminently foreseeable. The incidence of frost and ice on the road surface at this location is directly attributable to a combination of long periods in the winter months when the road surface will remain in shadow in daylight hours, with the effects of cold air drainage during calm winter nights, along with consistently high relative humidity levels due to dense vegetation nearby.
As this section is likely to be most prone to ice formation during clear and calm winter nights and mornings, it will exhibit ice and frost formation when many other sections of the current GWH between Mount Victoria and Lithgow remain ice/frost free, and also potentially when other areas of the GWH to the north and west of Lithgow remain ice free. Therefore, it is considered possible that such situations are sometimes difficult to predict and/or identify early, by staff at the local Lithgow depot, especially as the depot’s immediate area does not exhibit the same micro-climate.
It appears that it will ultimately be impractical for future routes for the GWH to avoid this particular area. Therefore, the RTA is advised to further consider relatively cost-effective and practical measures in reducing the potential for ice/frost formation on ‘the 40 Bends’ section of the current alignment. These measures include cutting back the vegetation adjacent to the road, improving the characteristics (e.g. texture depth, skidding resistance etc.) of the running surface of this section and installing, for example, road weather and condition monitoring equipment to aid awareness and decision making, as well as perhaps considering real-time driver information warning systems.
It is considered that the general alignment of the current GWH immediately to the west of Mount Victoria follows a line that is relatively favourable in terms of climatology when compared to some alternative routes. Notwithstanding, it is considered that the top and (to a lesser extent) bottom bends on the slopes west of Mount Victoria are potentially prone to the occasional formation of ice or frost.
Other sections of the GWH in the study area, such as the slopes of River Lett Hill and the bridge over the River Lett (near Hartley) are also considered to be potentially prone to the formation of ice or frost. However, the propensity to be affected is certainly not to the same extent as ‘the 40 Bends’ section.
Notwithstanding these differences, it is currently recommended that these other sections may also benefit from similar operational measures to those considered for adoption at ‘the 40 Bends’ section.
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6.2 Fog
The weather data analysed; site observations and discussions with local residents all indicate that certain sections of the current GWH can be affected by fog formation, even to the extent where fog reduces visibility such that it has an adverse effect on road safety.
The main types of fog that are likely to affect the study area are orographic fog (referred to colloquially as ‘hill fog’) and radiation fog:
• Orographic fog is caused by air cooling and reaching its saturation point as it is forced to ascend due to the terrain. Therefore, it mainly affects higher ground and tends to occur most commonly when there is a wind blowing onto the slope.
• Radiation fog mainly forms on clear and calm nights as a result of localised cooling of the ground through nocturnal radiation processes. Therefore, it tends to form most commonly and is densest at lower level sites that are subject to cold air drainage and/or that are also ‘frost hollows’.
Figure 4: Orographic fog
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Figure 5: Radiation fog
It has been found that radiation fog causes the greatest difficulty for road users, as it tends to form at localised sites and its density can vary significantly over short distances and timeframes. Therefore, drivers can be ‘caught out’ by suddenly finding themselves in fog when previous sections of their route have been completely fog free.
Radiation fog can occur at any time of the year and, when it occurs during the summer months, it tends to form overnight or during early mornings over low ground, particularly in proximity to water bodies or along water courses. Typically, summer fogs are dispersed and evaporated as the ground and lower atmosphere are warmed by the effects of the morning sun.
Research and experience indicates that when fog (regardless of its type / formation) reduces visibility levels to below 200 metres (which is the threshold for the formal meteorological definition of ‘thick fog’) significant problems can occur on high speed roads.
In addition, fog prone sites also tend to experience generally higher humidity levels, which as previously reported, can increase the propensity of ice formation during winter months.
Improved road lighting systems and/or ‘active’ reflective road studs have been used to assist in ameliorating problems caused by fog, but in some instances it appears that the most effective method of reducing the number of occasions that fog forms around a road is an active program of cutting vegetation roadside edges, in order to encourage air movement and reduce local humidity levels.
Advance fog warning systems (possibly linked to speed reduction measures when activated) have the potential to improve road user safety on the more fog prone sites across the study area. It is noted that a fog warning sign system has already been deployed on the GWH to the west of Lithgow.
6.3 Wind
Strong winds were not highlighted by local RTA staff as being a recognised hazard on the current alignment of the GWH in the study area. Indeed, the meteorological data from the general region indicates that strong winds do not generally occur at most locations across the study area. Notwithstanding, the relatively high altitude of some of the sections of the route and the nature of the local topography do tend to indicate that strong wind gusts could be a hazard to road users from time to time at certain, exposed, locations on the route.
The climatological data reviewed does not include maximum wind gust speeds. However, the data from both the Mount Boyce and Mount Victoria weather stations, as well as that located at Bathurst airport, shows mid-afternoon mean hourly wind speeds of up to and around 20 kilometres per hour. Whilst wind speeds of this strength (Beaufort Force 4 ‘Moderate Breeze’) would not typically cause any significant problems to road users, it is known that gusts can be strong enough to cause drivers of high sided and two wheeled vehicles some difficulty on occasion, although this would only tend to be in those locations that are most exposed and at the highest elevations across the study area.
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7 Potential new alignments of the Great Western Highway between Mount Victoria & Lithgow
7.1 General observations
The ‘40 bends’ section of the current alignment of the GWH is of the most climatological concern. Although conditions can be managed and improved at this location to some extent, it is strongly recommended that new alignments should avoid this area or be subject to careful selection.
An immediate response would appear to be to devise an alignment some distance to the south of the existing road, so as to move it away from the influences of the foot of the slopes of Hassan’s Walls and Padley’s Pedestal. Such an initiative would improve the micro-climatic characteristics of the new route considerably and significantly reduce its propensity for ice formation. However, it is also noted that the presence of settlements and gully formations to the south may be a constraint in the exact distance that a route can be considered at the foot of Hassan’s Walls.
The current alignment of the GWH to the west of Mount Victoria generally follows the ridgeline of Victoria Pass. It is considered likely that any alignment option identified immediately to the west of Mount Victoria and including a section south of the existing road and south of Mitchell’s Ridge, would likely suffer from significant ice/frost issues, due to the shadowing effects of the ridge that would then lie immediately to the north of such an alignment. This situation would also be exacerbated by the altitude factor and the presence of dense vegetation, and be most significant if the alignment chosen included any elevated sections of road (which would appear likely given the topography).
Any route option to the south of Mitchell’s Ridge would be more prone to ice and frost formation than the existing line of the GWH between Mount Victoria and Lithgow.
It is also considered likely that potential alignment options including an east-west crossing of Fairy Dell Creek significantly north of Mount Victoria and/or Kerosene Creek, are likely to experience issues with regard to ice/frost formation, especially if major (elevated) structures are required (which would be likely given the topography faced).
Potential alignment options that include lengthy elevated sections, either at the east or west end of the study area, are also likely to be prone to ice/frost formation. These issues can be ameliorated to some degree by careful structural design, adequate maintenance regimes, and road user warning systems. Consideration should be given to emerging technologies, e.g. surface heating options (solar, geothermal power) and/or already ‘tried and tested’ technologies such as automated chemical spray systems, for discrete lengths of road. These technologies were introduced to RTA engineers during ARRB Group’s presentations in June 2008.
Additionally, due to their general exposure, elevated sections of road tend to experience stronger winds than other road sections. Therefore, further research may be required to identify whether strong winds might adversely affect any elevated sections of road designed within the study area.
Adverse weather issues for each of the four modified route corridors are discussed below (NB. commentary on the Modified Orange Corridor includes common issues for all corridors).
It is important to recognise that the opinions expressed are based upon the data and information currently available; recognised micro-climate principles and specialist professional experience. However, an important recommendation of this project (discussed in detail later) is that further field work (in the form of a data collection exercise) should be undertaken to obtain further and location specific information concerning the variation in temperatures and climatic regimes experienced across the study area. This further information will significantly improve understanding of the climatic issues relating to the study zone and route corridors, and hence, greatly assist with final route selection.
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The construction of any major route will involve the modification of the environment in its immediate vicinity. For example, slopes will typically be ‘smoothed’ by the use of cuttings and embankments etc., and these modifications will in turn affect the micro-climates of these sites to a degree. The effects can end up being incidental or significant in the performance of the road in winter. As the overall climatic regime of the study zone sees temperature fluctuations around 0°C, relatively minor modifications to this regime caused by the alignment and design of a new road could potentially influence the propensity for ice to form at some localities within the route corridors. It must be recognised that at this stage in the project, such effects can only be considered in a very general manner, with specific guidance only being possible when preferred alignments have been devised.
Figure 6: The four Modified Route Corridors (source: RTA web site)
7.2 Modified Orange Corridor (including common elements of all corridors)
The south-eastern ‘ends’ of all of the modified route corridors initially follow the line of the existing GWH but then bend to the north to cross, or join, the general line of Darling Causeway.
The principles of micro-climatology suggest that due to elevation, the study area around Mount Victoria would be susceptible to the formation of orographic fog and that this is likely to be dense enough to affect road users on occasion. Whilst the data obtained and personal observations on site support these statements, local knowledge (RTA officers and residents) will be extremely valuable.
It is noted that all corridors involve travelling over, or under, the Main Western Railway Line and avoid the heritage listed Mount Victoria Railway Station. Whether or not the road is carried over the railway line or vice versa (e.g. by way of a bridge) will have some significance to its propensity for ice/frost formation. The design of any bridge, its size, height and precise alignment will all affect this and at this project stage it is impossible to provide detailed comment. However, appropriate planning, design and maintenance should mitigate the increased risk of ice formation posed by the bridge.
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After crossing the Darling Causeway, the Modified Orange and Red Corridors curve toward the west and bypass Mount Victoria around its northern side. These corridors cross the upper slopes of Fairy Dell Creek and the broad ridge to the north of the main built-up area of Mount Victoria. The corridors traverse a more rural environment than the existing line of the GWH, which passes through the settlement, and it is considered likely that this section of the two corridors will exhibit some climatological differences to the equivalent section of the existing GWH. However, it is not considered that these differences will lead to major problems with ice formation. Notwithstanding, as with the current alignment west of Mount Victoria, ice formation may become an issue on isolated occasions.
The defunct Mount Victoria weather station was located in, or near to, Selsdon Street which is close to the southern boundary of both the Modified Orange and Red Corridors.
After bypassing Mount Victoria, there are two alternative options, which are shared by both the Modified Orange and Red Corridors for descending the upper slopes of Butlers Creek. These alternatives merge together once more in the area around the upper bend of Victoria Pass.
The more northerly of the two alternatives includes a 300 metre long tunnel under Mount York Road, which runs along a ridge from Mount Victoria to the north-west. It appears that a tunnel would be orientated approximately east-west. Assuming that any tunnel is appropriately designed, drained and ventilated, there are no particular concerns regarding ice formation within, or in the immediate vicinity of, the tunnel. Indeed, it is likely that RSTs within the tunnel would be significantly higher than those outside the tunnel during the coldest winter nights. Notwithstanding, the precise orientation and slopes of the tunnel entrances and exits require careful thought, as experience suggests that glare from a ‘low’ sun can potentially be an issue for drivers in such situations (in early January the sun rises in the ESE and sets in the WSW, and in late June it rises in the ENE and sets in the WNW). Experience also suggests that drivers can be adversely affected by the large changes in light levels that can occur when entering and exiting tunnels on bright and sunny days.
To the west of any tunnel, the northern alternative continues in a direct line towards, and just north of, the upper bend of Victoria Pass, where it rejoins the more southerly of the two corridor alternatives. In doing so, the route descends and crosses the relatively steep slopes of the Butler’s Creek valley.
The southern alternative sweeps around the western side of Mount Victoria and joins the general line of the current GWH at its intersection with Mount York Road. The route then follows the existing alignment towards the upper bend of Victoria Pass, with the two alternative corridors then merging.
Due to the steepness of the slopes in this area, it is expected that any new road through this section (along either the northern or southern alternatives) and further west towards the valley floor of Butler’s Creek will require a major viaduct.
It is considered likely that any large elevated structure in this area will prove significantly more prone to ice/frost formation than the current alignment along the ridgeline of Victoria Pass. Therefore, if this option is selected, the issues faced must be mitigated by careful and specific structural design, appropriate winter maintenance, and possibly, the provision of a road user warning system.
This particular area may also be susceptible to fog formation, affecting road users on occasion, although any elevated structure would tend to reduce the likelihood of this hazard.
The Modified Orange Corridor descends westwards to the Rosedale area and encompasses the existing alignment of the GWH, and follows this to the northwest towards Little Hartley and Hartley.
In the vicinity of the Rosedale Historic Site, the Modified Orange Corridor traverses an area of ground that exhibits a number of pools of water that are up to two to three hectares in size. It is considered that this may exacerbate any tendency for fog and/or ice/frost formation in this vicinity.
Before reaching Little Hartley, the Modified Orange Corridor reaches an area of higher ground that lies to the south of the existing route of the GWH. This ground reaches an elevation of 909 metres, which is 80 metres or so higher than the existing route present at its northern edge. From a
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climatological perspective, it would be beneficial for a new route to skirt the lower part of the northern slope or, alternatively, any cuttings or other terrain modifications through this area should retain the road’s exposure towards to north, so that solar heating potential is maximised in the winter months.
As the Modified Orange Corridor traverses northwest and bypasses the heritage sites south of Browns Gap Road and HartIey Historic Village, the nature of the terrain is such that it is not considered that this section will exhibit any significant issues with ice/frost formation.
West of Hartley, the Modified Orange Corridor crosses the River Lett and ascends the east facing slopes of River Lett Hill. Although this section of the current GWH alignment experiences issues with ice/frost formation periodically, the modified route, which follows a line to the west of Boxes Creek, is likely to experience more favourable climatic conditions than a route to its east, which would cross Finnigan’s Creek and ascend the slopes of Boxes Creek. However, it is considered important that the route does not ascend any further ‘up’ River Lett Hill than is necessary.
Once to the north of River Lett Hill, the Modified Orange Corridor curves to the west and joins all three of the alternative modified corridors, traversing around the foot of the steep and densely vegetated slopes of Hassan’s Walls. It is noted that the corridor is relatively wide at this point and its northern boundary closely follows the existing line of ‘the 40 bends’ section of the GWH.
As discussed earlier, it is strongly recommended from a micro-climate perspective that any new route in this locality is located a considerable distance to the south of the existing alignment of the GWH, i.e. the new route would benefit climatologically from following the southern boundary of the Modified Route corridor. Such an alignment would minimise the propensity for ice formation, by maximising the amount of solar heating during daylight hours as well as avoiding, as far as possible, areas affected by katabatic drainage and cold air pooling. In comparison with the existing line of the GWH, the southern boundary of the Modified Route Corridor is approximately a kilometre further from the foot of the steepest slopes of Hassan’s Walls, leading to considerably less marked shadow effects.
At the western end of Hassan’s Wall, the Modified Orange Corridor curves to the north following the existing line of the GWH towards South Bowenfels.
At the point where the Modified Orange Corridor reaches the western end of the steep slopes, their detrimental effects are substantially reduced and there are no particular climatological concerns with the final section of this corridor as it heads north.
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Figure 7: Modified Orange Route Corridor (source: RTA web site)
7.3 Modified Red Corridor
The Modified Red Corridor commences in the south-east of the study area coincident with the Modified Orange Corridor, and these corridors ‘combine’ until the Modified Red Corridor curves toward the north-west across the valley floor of Butler’s Creek.
The proximity of water sources and the relatively confined nature of the valley at this location indicate that this section of the Modified Red Corridor is likely to be susceptible to periodic fog formation, together with an increased likelihood of ice/frost formation. When compared to the Modified Orange Corridor, these issues are likely to be more marked and affect a longer length of road. Additionally, the lower ground in this vicinity (which is close to areas of water) may well be prone to periodic summer fog, although local knowledge will be important in verifying this observation.
The Modified Red Corridor continues to the north-west until it is north of Little Hartley, where it curves further toward the north and follows the line of Butler’s Creek towards the Hartley Vale Road. In this way, the Modified Red Corridor skirts the foot of the steep and densely vegetated south-west and west facing slopes of Berghofer Pass and Mount York.
Due to the wider and more open aspect of the valley at this point, and the fact that the slopes are generally west facing, it is considered unlikely that this section of the Modified Red Corridor will be greatly affected by katabatic airflows. Nonetheless, consideration should be given to avoiding the north-eastern boundary of the corridor as it traverses close to the steep slopes of Mount York.
This section of the Modified Red Corridor follows the general line of Butler’s Creek. It is considered likely that the localities adjacent to the watercourse would be more susceptible to fog formation than other areas in the vicinity. Therefore, it is recommended that any route alignment devised for this Corridor is separated from the creek line and follows a slightly higher line across the valley.
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The next section of the Modified Red Corridor, which traverses north-west towards, and continues north-west of, Blackman’s Creek does not exhibit issues relating to frost, ice or fog formation.
The Modified Red Corridor includes a crossing of both River Lett and Blackman’s Creek and any resultant bridges may well be prone to the formation of frost and ice. As a result, careful consideration should be given to mitigating these effects during design, and in any future operations.
To the west of Blackman’s Creek, the Modified Red Corridor curves toward the west-south-west, traversing the base of the steep, densely vegetated slopes of Hassan’s Walls and Padley’s Pedestal. This section of the Modified Red Corridor then merges with the Modified Green and Modified Purple Corridors, which follow the same line across this area.
It is considered highly likely that the steep slopes to the north of this section, which are mainly south- south-east facing, will create nocturnal katabatic airflows and cause cold air to pool over the area at their base during clear and calm winter nights. This area is considerably more open and exposed toward the east than the area of ‘the 40 bends’ section of the current GWH, and therefore, it is likely that the sun will cause these flows and pools of cold air to dissipate earlier during the day than they currently dissipate on ‘the 40 bends’ section. However, ice/frost formation will still pose a significant problem along the foot of these slopes and therefore, if this route is chosen, the line of the route should tend to follow the southern boundary of the route corridor and avoid the northern boundary.
South of Padley’s Pedestal, the Modified Red Corridor meets the Modified Orange Corridor and traverses around the base of Hassan’s Walls and then north to South Bowenfels.
Figure 8: Modified Red Route Corridor (source: RTA web site)
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7.4 Modified Green Corridor
The Modified Green and Purple Corridors follow the lines of the Modified Orange and Red Corridors until reaching (and possibly crossing) the Main Western Railway and the Darling Causeway.
At this point, the Modified Green and Purple Corridors continue north along the line of the railway and Darling Causeway, and skirt the edge of the Blue Mountains World Heritage Area.
This section of the Modified Green Corridor traverses at a relatively high elevation and is likely to be susceptible to orographic fog formation. However, the accident data provided indicates that the Darling Causeway does not experience any particular issues with the formation of frost and ice.
The Modified Green Corridor then curves to the north-north-west and leaves the line of the railway and Darling Causeway (as well as the Modified Purple Corridor) to traverse and descend towards Hartley Vale. This section initially follows and descends a ridgeline that is currently heavily vegetated, until it then reaches an area where it descends relatively steep slopes which may well require significant earthworks and/or a viaduct to keep the grade (vertical alignment) of a new road within required limits.
This section of the Modified Green Route is likely to exhibit issues with fog formation and, particularly if a viaduct is required, frost and ice formation may be a risk given the local topography, requiring careful attention during design.
The lower part of the descent towards the north-north-west lies adjacent to Walton’s Road. This area is sheltered by higher ground to its south-west and north-east. Due to its aspect (even given that some nocturnal katabatic drainage may occur) it is unlikely that frost or ice formation would be an issue.
The Modified Green Corridor bypasses the Hartley Vale settlement to its east and north, before curving sharply towards the west, continuing across relatively level terrain. This area presents no particular climatological concerns.
Where the Modified Green Corridor reaches Browns Gap Road, it converges with the Modified Red Corridor and continues to its immediate north-north-east. It is not considered that this section of the route corridor is likely to exhibit any particular issues with frost, ice or fog formation.
However, similarly to the Modified Red Corridor, crossings of the River Lett and Blackman’s Creek appear likely and bridges may be prone to the formation of ice and frost. Careful consideration of these effects is required during the design process, and in managing them during operation.
After crossing Blackman’s Creek, the Modified Green Corridor curves to the west and merges with the Modified Red Corridor for the remainder of its length.
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Figure 9: Modified Green Route Corridor (source: RTA web site)
7.5 Modified Purple Corridor
The Modified Purple Corridor follows the line of the Modified Green Corridor until that route curves to the north-north-west away from the line of the Main Western Railway and Darling Causeway.
At this point, the Modified Purple corridor continues to head north along the ridgeline followed by the railway and Darling Causeway, although the corridor also includes an area of the west facing slope on the west side of the ridge. It is not expected that this section will experience any significantly different climatological issues from that further to the south, as shared with the Modified Green Corridor.
In the vicinity of the intersection between the Darling Causeway and Hartley Vale Road, the ridgeline curves towards the north-north-east. At this point, the Modified Purple Corridor leaves the ridge and continues north so that its western boundary follows the existing Hartley Vale Road as it descends down towards Hartley Vale itself. East of this road, the corridor encompasses the adjacent valley, a steep sided ridge/bluff that is in the centre of the corridor, as well as the valley to its immediate east.
This suggests that the Modified Purple Corridor could potentially follow the line of the existing Hartley Vale Road and valley, or a line through the parallel valley to its east, which is on the opposite side of the ridge/bluff that runs along the centre of the corridor.
Due to the north facing aspect of these valleys, frost and ice formation is unlikely to pose a significant problem. However, on occasion, the valley floors may be subject to katabatic airflows and therefore, if this option is selected, it is recommended that the alignment is part way up one of the slopes.
This section of the Modified Purple Corridor is also potentially prone to the formation of fog, with both of these valleys being relatively constricted and densely vegetated.
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North of the ridge/bluff, the Modified Purple Corridor curves sharply to the west and follows the Lett Valley. At the curve, the corridor reaches the River Lett, its intersection with Kangaroo Corner Creek and the Sassefras Swamp. This locality also lies to the south of steep, south facing slopes from considerably higher ground. Therefore, this area is likely to be subject to katabatic airflows and the pooling of cold air. High humidity levels are also likely, combining to increase the propensity for frost, ice and fog formation.
The Modified Purple Corridor encompasses the meandering line of the River Lett and it is recommended that any alignment chosen within this Corridor does not lie immediately adjacent to the watercourse and remains separated from it, preferably along higher ground. In this respect, even ground a few metres higher than the watercourse is currently considered likely to be less at risk of ice, frost and fog formation than the lowest ground immediately adjacent to the river.
This locality will be susceptible to the occasional formation of summer fogs, most frequently on the lowest ground in the vicinity of the River Lett. However, further investigation is required to confirm the magnitude of the potential issues currently envisaged with this locality.
The Modified Purple Corridor will require a crossing of the River Lett, and it is considered that any bridging point will be prone to the formation of frost and/or ice. The likelihood of this arising will vary significantly with the exact position of the crossing and careful consideration of this issue is required during the design stage.
The northern boundary of this section of the Modified Purple Corridor runs along the foot of a series of steep and vegetated south facing slopes to the east and west of Reedy Creek before it merges with (and continues along) the Modified Green Corridor. Due to the likely effects of katabatic drainage and cold air pooling, the alignment of a new road should ideally be some distance to the south of the northern boundary of the route corridor, along the entire length of the slopes.
Figure 10: Modified Purple Route Corridor (source: RTA web site)
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7.6 Summary
The above individual commentaries show that there are certain climatological concerns regarding each of the four modified route corridors. However, it is important to note that all of the currently proposed modified corridors are considered to be potentially viable when only climatic concerns and issues are taken into account. As previously indicated, the concerns and issues identified will need to be given careful consideration during the on-going route planning and design stages of this road upgrade. The collection of additional weather data will be valuable in this process, and will also assist with the framing of future road maintenance programs and the placement of any road user warning systems adopted.
Main climatological issues affecting all four modified corridors
• Orographic fog formation concerns in Mount Victoria area
• Moderate frost and ice formation concerns regarding bridge over Main Western Railway Line north of Mount Victoria and other bridges across watercourses
• Critical frost and ice formation concerns regarding ‘the 40 bends’ section of the existing GWH alignment, which is included within all modified corridors (although an alignment at or close to the southern boundary of the route corridor would considerably reduce these concerns).
Modified Orange Corridor
• Serious frost and ice formation concerns regarding the large viaduct that is likely to be required west of Mount Victoria
• Moderate fog formation concerns in the vicinity of the Rosedale Historic Site
• Moderate frost and ice formation concerns regarding crossing of the River Lett
• Moderate frost and ice formation concerns regarding ascent/descent of eastern slope of River Lett Hill.
Modified Red Corridor
• Serious frost and ice formation concerns regarding the large viaduct that is likely to be required west of Mount Victoria
• Moderate fog formation concerns regarding the area north of Rosedale Historic Site
• Moderate frost and ice formation concerns regarding the section that skirts the foot of Berghofer Pass and Mount York (although an alignment away from the foot of the slopes would considerably reduce these concerns)
• Moderate fog formation concerns relating to the immediate vicinity of the Butler’s Creek watercourse (although an alignment away from the watercourse, and preferably along slightly higher ground, would considerably reduce these concerns)
• Moderate frost and ice formation concerns regarding crossings of the River Lett and Blackman’s Creek
• Serious frost and ice formation concerns regarding the section that skirts the foot of Hassan’s Walls and Padley’s Pedestal (although an alignment away from the foot of the slopes would considerably reduce these concerns).
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Modified Green Corridor
• Moderate orographic fog formation concerns until the route reaches open ground at lower elevation
• Serious/moderate frost and ice formation concerns during steepest parts of descent to lower ground, especially if a viaduct is required
• Moderate frost and ice formation concerns regarding crossings of the River Lett and Blackman’s Creek
• Serious frost and ice formation concerns regarding the section that skirts the foot of Hassan’s Walls and Padley’s Pedestal (although an alignment away from the foot of the slopes would considerably reduce these concerns).
Modified Purple Corridor
• Moderate orographic fog formation concerns until the route reaches open ground at lower elevation
• Moderate frost and ice formation concerns during lower descent section south of Kangaroo Corner Creek (although an alignment away from the valley floor would reduce these concerns)
• Serious frost, ice and fog formation concerns in Sassefras Swamp area (although careful alignment may reduce these concerns)
• Moderate ice, frost and perhaps more significant fog formation concerns regarding the line of the River Lett (although an alignment away from the watercourse, and preferably along slightly higher ground, would reduce these concerns)
• Serious/moderate frost and ice formation concerns regarding the crossing of the River Lett (dependent upon the location of the crossing)
• Serious frost and ice formation concerns regarding a relatively long section of the corridor that skirts the foot of steep south facing slopes, which is longer than all other modified corridors (although an alignment away from the foot of the slopes would considerably reduce these concerns).
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8 Comments and recommendations concerning the future maintenance of the GWH between Mount Victoria & Lithgow
8.1 Winter maintenance
An active program of winter maintenance, in the form of spreading salt and physically removing snow, is considered to be of crucial importance to the on-going and future management of the existing GWH between Mount Victoria and Lithgow. It is clear that the existing strategy and program, although not formally documented, already play an important role in terms of both road user safety and in keeping traffic flowing, and it is considered likely that its importance will only increase, as projected traffic flow figures indicate heavier usage of the GWH in future years. Elements of the proposed new route alignments, such as the need for large viaducts and river crossings/bridges, will also increase the importance of a sound and active winter maintenance program, even given the careful consideration (and wherever possible, elimination) of such issues during the design stage.
Given that the design and construction of a new route between Mount Victoria and Lithgow will take some years, it is strongly recommended that the current winter maintenance strategy and program be comprehensively reviewed and ultimately, formally documented.
The winter maintenance regime provided on both the existing GWH and on any new route would be significantly improved by procuring specialist forecasts of frost and ice formation and snow falls, RST and road surface condition, and basing initial daily ‘go/no go’ anti-icing decisions on these predictions. This allows an emphasis on preventive treatments, applied before the onset of adverse conditions. Preventive treatments are both more effective and environmentally sensitive than reactive regimes.
Accurate predictions of other adverse weather hazards, e.g. high winds, intense rainfall, hail storms and fog, can also be important to the management of roads throughout the year. The road authority can also help increase the weather forecast providers’ knowledge of the local road network and the issues faced by road engineers and this will in turn significantly improve the advice they are able to offer engineers and the quality of the weather forecasts that they produce for those purposes. It is therefore recommended that close liaison occur between the RTA and the weather forecasting organisation (BoM or a similar commercial provider) regarding the on-going delivery of the winter maintenance program in this area.
The installation of additional weather and road condition monitoring equipment at particularly prone sites such as ‘the 40 bends‘ would significantly improve the accuracy of forecasts for maintenance purposes; and assist with winter maintenance decision making and the monitoring of road conditions.
The use of automated road user warning systems for adverse weather is not a new development, and indeed they have been used on the GWH and other strategic roads operated by the RTA, e.g. the automatic warning systems for ice and fog currently in place to the west of Lithgow on the GWH.
The active use of weather specific forecasts and road weather and surface condition monitoring equipment tends to naturally lead to interest in a Road Weather Information System (RWIS). Such systems are extensively used in the Northern Hemisphere to further improve the delivery of winter maintenance programs and the dissemination of road condition data to staff and road users alike.
It is considered that winter maintenance operations out of the South Bowenfels Depot would benefit from review (including the materials currently used) as well as the procurement and use of specialist equipment, such as modern belt feed spreaders.
The opinions expressed above are not unique to winter operations on the GWH between Mount Victoria and Lithgow and it is recommended that serious consideration be given to undertaking a wider review of adverse winter weather policy and operations on other sections of the GWH and other areas of NSW that experience significant adverse winter weather conditions, e.g. NSW snowfields.
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Such a process would also allow the RTA to develop a documented policy to be implemented consistently statewide with regard to the management of adverse winter weather.
8.2 General maintenance and other issues
Site inspections under this commission highlighted that the current surfacing of the pertinent section of the GWH varies considerably along its length both in terms of materials and condition.
Ensuring road surfaces have adequate surface texture and are effectively drained (i.e. they are as free as possible from surface water) are crucial considerations for the safety of road users in winter conditions. Therefore, it is recommended that such issues are given particular emphasis when considering surfacing options for both existing and any future sections of the GWH, as well as during the management of routine and cyclical maintenance on the pertinent section of the highway.
With regard to surfacing options, experience with UK road constructions indicates that concrete carriageways are commonly slightly warmer and less prone to frost and ice formation than asphalt surfaces. This is attributable to the thermal retention properties of concrete and reduced surface moisture levels. Anecdotal evidence from local RTA engineers seems to suggest that their experiences with Australian road constructions are similar.
It is recommended that further monitoring be undertaken of RSTs and surface condition states on different surfacing types on the current GWH. Notwithstanding, the differences between surfacings found are likely to be slight and, based on past experience, other considerations, such as carriageway noise, performance in extreme heat and future maintenance requirements, may ultimately prove more significant constraints in material selection.
A number of sections of the existing GWH alignment exhibit vegetation growing relatively close to the road and, in some instances, this vegetation is dense. A program of cutting back vegetation from the carriageway edges on such sections prior to the onset of winter can reduce the propensity for frost and ice to form on the adjoining road, given that this reduces humidity levels close to the road surface, as well as potentially increasing surface heating from the sun during daylight hours.
Active driver warning information systems and variable speed limits for adverse road surface conditions (such as when the surface on particular sections is wet) already form part of the management system for the GWH, albeit outside of the study area. Consideration should be given to extending these systems to include such matters as ice, frost and fog formation on both the current and future routes of the GWH in this locality by way of automated or manually controlled VMS signs. Such signs are triggered by conditions detected in real time and/or those predicted by a Road Weather Information System (RWIS), which can include both precipitation and fog detectors.
It is also considered that CCTV cameras could also assist in the management of the existing and future GWH, as well as providing a means of disseminating road condition information to the public.
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9 Recommendations for further work
This report has provided commentary and recommendation concerning the routing and management of the planned GWH upgrade through the study area based on climatological principles, site observations, local anecdotal evidence, operational data (including crash studies) and available weather data. However, as previously documented, the extent of specific climatic and road weather condition information available from within the study zone was / is very limited.
Therefore, it is recommended that a data collection program be implemented in the study zone during the winter of 2009. ARRB Group has already started assisting the RTA with the preliminary design and likely implementation of such a program and in analysing the resulting data, but final arrangements have yet to be made. The advantage of such an approach is that the data will be of great benefit in both the development of preferred route alignments (and ultimately the design and specification of the final preferred alignment) as well as in optimising current maintenance operations on the existing GWH.
Appendix D of this report provides a table summarising a range of options for the winter weather data collection and monitoring regime for further consideration. The table includes approximate costings for each option, which are also discussed below.
9.1 Thermal mapping
The primary purpose of thermal mapping is to determine and demonstrate the variations in road surface temperature that occur over a given length of route or a given area of network. Due to the fact that the surface temperature variation pattern alters under different weather conditions, thermal maps are produced for each of the three principal winter weather types (which in turn relate to patterns of minimum temperatures attained overnight) and include ‘cloudy and windy’ and ‘clear and calm’ nights.
During cloudy and windy conditions, RSTs generally vary along a route or across an area as a result of macro-scale variables such as altitude, latitude, distance from large urban areas or the coast etc. During these conditions, RSTs along a route or across an area will tend to vary only gradually, and these conditions are therefore often referred to as ‘damped’ thermal conditions.
Conversely, during clear and calm conditions, the principal influencing factors on road surface temperature are micro (or local) in nature and relate to issues such as whether a site is exposed or sheltered, or whether it is subject to katabatic airflow. During such conditions, point to point variations in RST along a route or across an area can be very marked and large variations (of up to several degrees Celsius) can occur over relatively short distances, e.g. over 20 to 40 metres or so. As a result, these conditions are often referred to as ‘extreme’ thermal conditions.
Figure 11 below shows a typical variation in RST along a route during two nights when the weather conditions were cloudy and windy (‘damped’). The upper part of the Figure shows topography and shows that, as the route ascends (and, in this instance moves away from an urban area), the RST decreases. It is a relatively gradual variation with distance and altitude.
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Figure 11: Typical thermal trace during cloudy and windy (‘damped’) conditions
Figure 12 below shows the typical variation in RST along the same route as in Figure 12. However, this Figure shows the variation on two nights when the weather conditions were clear and calm (‘extreme’). It shows a greater ‘point to point’ variation than when conditions are cloudy and windy, and that the patterns of RST along the route are very different.
Figure 12: Typical thermal trace during clear and calm (‘extreme’) conditions
Thermal mapping is therefore a very powerful tool in determining and demonstrating the variation of RST from one location to another, and is thus extremely useful in determining the varying propensity for frost and ice formation of different locations along a route or across an area.
It is strongly recommended that consideration be given to undertaking a thermal mapping exercise on the GWH commencing at Mount Boyce in the east and extending to Yetholme in the west (i.e. including the section of interest from Mount Victoria to South Bowenfels) during the winter of 2009.
Extending the thermal mapping exercise beyond the study area, will allow linkage with the road weather warning system located at Mount Lambie. This will in turn allow an assessment of whether data obtained from Mount Lambie can also be of assistance/relevance to maintenance operations between Mount Victoria and Lithgow.
Undertaking a thermal mapping exercise within the entire study area will also provide detailed information concerning RST variations in areas away from the existing GWH and the larger settlements, i.e. this should provide information for those areas that are perhaps less well known and understood. Therefore, it would be important for this exercise to include a number of existing local
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roads across the area that are close to, or encompassed by, the various Modified Corridor options, e.g. Hartley Vale Road, Browns Gap Road, Mid Hartley Road, and the Darling Causeway.
The results of a local thermal mapping exercise would also help to verify (or reject) the current observations concerning the propensity of certain areas to be subject to katabatic airflow and radiational cooling. This would provide great assistance in developing understanding of the diversity of micro-climatic regimes and propensity for frost and ice formation across the study zone.
A secondary (and very useful) purpose for thermal mapping is to assist in determining the required number and most appropriate locations for the installation of future static weather stations. Because thermal mapping provides data concerning the relationship between the temperature of one section of road compared to another, analysis of the data will highlight those sites that are typically the coldest and those sites that are representative of large proportions of the network.
A future consideration is that the digital data files from the thermal mapping exercise can be linked to an RWIS and calibrated by ‘real time’ information recorded by static weather stations. As a result, the outputs can visually demonstrate the likely variation in RST that is occurring at any particular time and therefore serve as an extremely valuable tool in operational / winter maintenance decisions.
In summary, a thermal mapping exercise will assist significantly with understanding of the microclimates of the study zone and hence the propensity for frost, ice and fog formation across the area, as well as providing outputs that can inform future maintenance operations on the GWH.
9.2 Static weather station
Static weather stations typically provide detailed information concerning RST and road state condition, air temperature, humidity, wind speed and direction at a single location. Other sensors, such as those that measure solar radiation, precipitation and visibility can also be incorporated.
Such stations can be configured to store data for subsequent retrieval and analysis, or they can communicate (via wireless or telephone link etc.) with remote computers to provide data in ‘real time’. Often, networks of these stations provide data through an RWIS or similar, to assist in the active management of road networks.
Information from such stations is a vital component in many winter maintenance programs around the world, as the information that they produce significantly improves the accuracy of weather forecasts and allows engineers to actively and continuously monitor RST and road surface conditions.
It is considered that the installation of a single static weather station would have limited application in developing an understanding of the micro-climatology of the study zone unless adopted in conjunction with thermal mapping, which would allow extrapolation from a spot location to a road network.
Notwithstanding, the installation of a number of static weather stations positioned at carefully chosen locations across the study area would significantly assist in gaining a better understanding of the range of weather conditions experienced. This could be undertaken with, or without, the additional benefit of thermal mapping.
Potential sites for static weather stations on the GWH across the study area could include:
• ‘the 40 bends’ sections
• bends on Victoria Pass
• crossing of the River Lett;
• east facing slope of River Lett Hill.
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Potential sites away from the GWH could include:
• intersection of Browns Gap Road and Hartley Vale Road
• intersection of Hartley Vale Road and Darling Causeway.
The placement of a static weather station on ‘the 40 bends’ section of the current GWH, together with specialist weather forecasts, would significantly help winter maintenance decision makers during winter months. However, to maximise the potential use of the data from such a station, appropriate data management protocols would be needed to ensure data is routinely monitored.
If the option of static weather stations is favoured, it is recommended that further detailed investigation be undertaken, which could include joint RTA/ARRB site inspections, and could also potentially include representation from the manufacturers of the weather station equipment, before decisions are made concerning the number and location of static weather stations to be installed.
Given the observations in this report concerning potential fog formation issues, consideration should be given to including visibility sensors on any static weather stations that may be installed.
9.3 Mobile weather station
A mobile weather station typically provides information concerning standard meteorological parameters (NB. but not RST or road condition state) from a single point which could be varied across an area. Such stations would be installed at a specific location of interest and then operated for a set period of time, before being moved to an alternative location of interest.
The advantages of such an approach include that, over a period of time, data can be obtained from a series of locations that potentially exhibit different climatic characteristics using a single station.
However, a downside is that as weather patterns change with time, comparing data sets between locations can prove difficult. This can be overcome by considering data from other sources (such as a static weather station located within the study area, or permanent weather stations operated by the Bureau of Meteorology in the region) or by utilising more than one mobile weather station.
A further advantage of mobile weather stations is that their deployment is not limited to existing roads, i.e. with this project, they could be deployed at a wide range of ‘off road’ locations across the study area, which would enable coverage of locations of interest within the four modified route corridors.
Data obtained from mobile weather stations would prove useful in developing a better understanding of the range of weather and micro-climatic conditions experienced across the study area. However, it is also considered that an inability to measure RST is a significant disadvantage of this technology for the specific applications being considered.
It is recommended that, if mobile weather stations are to be deployed to assist with this project, the installation program and data comparison methods should be carefully considered prior to placement.
Finally, it is understood from manufacturers that mobile weather stations are a relatively new development and the best mode/s of operation may well require on-going development.
9.4 Mobile road condition state and/or road surface temperature sensors
Mobile road condition state and/or RST sensors are vehicle mounted systems that allow continual measurement of these parameters along a route or a network. ‘Road condition state’ means whether the road surface is dry or wet, or whether it is affected by ice, frost or snow.
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Vehicles equipped with either or both of the sensors can be driven across the whole of the existing road network within the study area (i.e. on the GWH and other local roads) on multiple occasions. Theoretically, the data from such exercises would assist with the development of a better understanding of which locations within the study area are most subject to ice/frost formation.
It is also considered that ‘real time’ data available from these sensors could significantly assist those responsible for managing the network in this area during winter conditions.
However, the measurement of surface condition state alone would tend to limit the potential usefulness of the technologies to this study. It is also known that mobile RST sensors constitute relatively new technology, and manufacturer confidence in such equipment has some way to go.
9.5 ‘Spot’ road surface temperature measuring equipment
Typically, such equipment consists of hand held infra-red thermometers, as deployed in a wide variety of industrial applications.
One of the downsides of this equipment type is that the operative is required to pre-set the appropriate emissivity value for the surface type that is being measured. The emissivity values typically utilised for these purposes are determined from published tables that provide generic values. However, actual surface emissivity varies with a number of factors (e.g. whether or not a surface is clean or contaminated with dirt or dust) and therefore, can vary from the published value. This in turn can affect the accuracy of the resultant measurement.
In addition to surface emissivity, experience indicates that the RST values using such equipment are also dependent upon surface texture and the angle of the incident infra-red beam to the surface.
In most weather conditions, the typical variation in RST from one location to another within the same general area is often only a few degrees Celsius. Experience indicates that, although such variations can be important for considerations regarding ice formation, this constitutes a relatively small variation when compared to the potential errors that can arise from use of hand held infra-red thermometers when measuring RSTs. Therefore, experience indicates that use of this method often results in unreliable measurements that cannot be appropriately analysed or corrected.
Notwithstanding, sound operative training and careful use of this technology could result in useable data being obtained to help better understand variations in RST across the study area. Indeed, the ARRB Group has some experience in measuring RSTs using equipment mounted and hand held infra-red equipment as part of its Falling Weight Deflectometer (FWD) testing of road pavements.
If this method is ultimately adopted, a definitive schedule of temperature measurement must be pre- determined and rigorously adopted so that the data obtained provides value.
9.6 Potential further ARRB assistance
In addition to assisting the RTA with data collection, monitoring and analysis options, ARRB Group is able to provide further assistance to the project team and to the RTA in general, including:
• development of (review of current) RTA guidelines for the management of roads and structures subject to adverse weather conditions (frost, ice, snow, fog etc)
• input to the design of the new GWH between Mount Victoria and Lithgow (including its structures)
• input into the selection of materials for pavements and bridges
• development of winter maintenance protocols for new routes
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• development of road user warning systems to advise motorists of adverse road conditions.
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10 Summary and conclusions
10.1 Summary
The RTA has commissioned ARRB Group to provide specialist technical advice regarding adverse weather issues relating to alignment, design and operation of a potential upgrade of the Great Western Highway between Mount Victoria and Lithgow. This report has been prepared with the input of Adrian Runacres, a micro-climatologist and road winter maintenance specialist based in the UK.
This report provided commentary on ice, frost and fog formation issues within the existing GWH alignment as well as within four proposed route corridors (Modified Orange, Red, Green and Purple) that are currently being investigated and are subject to formal community consultation. The report also provides opinion on current and future programs of winter maintenance on the GWH.
10.2 Conclusions
All of the proposed four modified corridors are considered viable from a climatological perspective.
However, there are potential alignments within each of the four corridors that give rise to climatological concern and present issues that will need to be addressed during the further planning and design stages for the new route. Similarly, scope exists for improvement to the current winter maintenance program and further deployment of road user warning systems.
Main climatological issues affecting all four proposed route corridors
• Orographic fog formation concerns in Mount Victoria area
• Moderate frost and ice formation concerns regarding bridge over Main Western Railway Line north of Mount Victoria and other bridges across watercourses
• Critical frost and ice formation concerns regarding ‘the 40 bends’ section of the existing alignment, which is included within all modified corridors (although an alignment along or close to the southern boundary of the route corridor would considerably reduce these concerns).
Modified Orange corridor
• Serious frost and ice formation concerns regarding the large viaduct that is likely to be required west of Mount Victoria
• Moderate fog formation concerns in the vicinity of the Rosedale Historic Site
• Moderate frost and ice formation concerns regarding crossing of the River Lett
• Moderate frost and ice formation concerns regarding ascent/descent of eastern slope of River Lett Hill.
Modified Red corridor
• Serious frost and ice formation concerns regarding the large viaduct that is likely to be required west of Mount Victoria
• Moderate fog formation concerns regarding the area north of Rosedale Historic Site
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• Moderate frost and ice formation concerns regarding the section that skirts the foot of Berghofer Pass and Mount York (although an alignment away from the foot of the slopes would considerably reduce these concerns)
• Moderate fog formation concerns relating to the immediate vicinity of the Butler’s Creek watercourse (although an alignment away from the watercourse, and preferably along slightly higher ground, would considerably reduce these concerns)
• Moderate frost and ice formation concerns regarding crossings of the River Lett and Blackman’s Creek
• Serious frost and ice formation concerns regarding the section that skirts the foot of Hassan’s Walls and Padley’s Pedestal (although an alignment away from the foot of the slopes would considerably reduce these concerns).
Modified Green corridor
• Moderate orographic fog formation concerns until the route reaches open ground at lower elevation
• Serious/moderate frost and ice formation concerns during steepest parts of descent to lower ground, especially if a viaduct is required
• Moderate frost and ice formation concerns regarding crossings of the River Lett and Blackman’s Creek
• Serious frost and ice formation concerns regarding the section that skirts the foot of Hassan’s Walls and Padley’s Pedestal (although an alignment away from the foot of the slopes would considerably reduce these concerns).
Modified Purple corridor
• Moderate orographic fog formation concerns until the route reaches open ground at lower elevation
• Moderate frost and ice formation concerns during lower descent section south of Kangaroo Corner Creek (although an alignment away from the valley floor would reduce these concerns)
• Serious frost, ice and fog formation concerns in the Sassefras Swamp area (although careful alignment may reduce these concerns)
• Moderate ice, frost and perhaps more significant fog formation concerns regarding the line of the River Lett (although an alignment away from the watercourse, and preferably along slightly higher ground, would reduce these concerns)
• Serious/moderate frost and ice formation concerns regarding the crossing of the River Lett (dependent upon the location of the crossing)
• Serious frost and ice formation concerns regarding a relatively long section of the corridor that skirts the foot of steep south facing slopes, which is longer than all other modified corridors (although an alignment away from the foot of the slopes would considerably reduce these concerns).
The main body of this report provides a number of specific comments and recommendations concerning the alignment and management of the GWH improvement through the study area.
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Whilst the comments and recommendations made are based on sound climatological principles, the findings of site visits, operational data provided and anecdotal evidence secured from local residents, the volume of meteorological data available from within the study area was (and remains) very limited. The available data does not include RSTs or road state condition.
As a result, the implementation of a data collection regime is considered essential during the winter of 2009. It is strongly recommended that the regime takes the form of a thermal mapping exercise which covers the GWH across the study area, i.e. from Mount Boyce in the east to Yetholme in the west. The exercise should also thermally map a schedule of other RTA roads (e.g. the Darling Causeway and Bells Line of Road) and prominent local Council roads located within the initial study area.
Options for the data collection regime are discussed within this report. ARRB Group is actively assisting RTA in identifying and securing the most appropriate regime in terms of:
• the type and extent of data to be collected
• the value of the data in determining preferred alignments for the GWH upgrade
• the value of the data in supporting the on-going maintenance and operation of the existing (and future) GWH;
• the cost of the regime.