Artificial intelligence (AI) offers a cost-effective alternative for government bodies to address urban heat by accurately calculating shade from roadside trees without compromising road safety. Traditionally, International Road Assessment Programme (iRAP) assessments involve trained officers manually assessing road safety at 100m intervals. Digitally stripping information from mobile LiDAR point cloud surveys then creating a digital twin is a viable alternative. In this virtual world, existing trees can be grown to maturity and additional mature trees inserted and assessed against a Star Rating.
Australian Local Government Association (LGA) Blacktown City Council contracted Australian geospatial software company, Anditi to develop a methodology where road assessment, tree location suitability and shading could be analysed synchronously. A pilot project was completed for a 3km stretch of Palmyra Avenue in Western Sydney.
Using mobile LiDAR and 360-degree imagery, Anditi calculated an AiRAP Star Rating for existing conditions as well as for when the trunks of recently planted trees grow to 10cm in diameter. A suitability analysis was also prepared for the location of recently planted trees as well as proposed additional trees. The analysis identified 867 suitable locations for the additional trees without significantly affecting the AiRAP Star Rating.
By incorporating this methodology into their road safety management plans, governmentscan identify suitable locations for trees as well as assess how the shading of an individual tree affects road surface temperatures. This approach enables governments to successfully address the critical challenges of urban heat and road safety using the same data source, greatly improving efficiencies.
Blacktown City Council is a LGA located in Western Sydney, NSW, Australia (Figure 1). The area of Western Sydney suffers from extreme heatwaves over summer, with temperatures above 40°C not uncommon, causing significant health and environmental issues. Blacktown currently have some of the lowest urban canopy coverage in NSW, with just under 20.2% total canopy, and some of the highest urban heat in all of NSW
Blacktown City Council is one of Australia’s most culturally diverse and fastest growing LGAs, with over 2,000 new houses being built each year. The pressure for new housing and limited available space results in the vast majority of these houses being built tightly packed together in relatively homogeneous housing estates. The construction of these estates has resulted in the removal of existing trees and vegetation and the condensed nature of the housing offers little opportunity for replanting. Added to this, the rooves of most of these houses are dark grey and heat absorbing in colour and combined with the black road surfaces of the neighbourhood, exacerbating the urban heat issues that the area is facing. Figure 2 provides an example of a recently developed housing estate in Blacktown, highlighting the high proportion of darker, heat absorbing materials and the lack of canopy cover.
To minimise the negative environmental impacts of these new housing developments and to improve liveability for residents, Blacktown City Council has investigated different methods of reducing urban heat, with a focus on reducing surface temperature of roads and buildings. Some of these methods included using cool surface paint and improving shading through planting trees along the road corridor. Figure 3 shows the application of the Cool Roads treatment to a road with the results displayed in Figure 4.
The results in Figure 4 show a 7°C reduction in surface temperature after application, however this is minor compared to the 25°C reduction in surface temperature from shade. There was also a notable difference in surface temperature reduction between dark and terracotta roof material.
Based on the results of the shading and Cool Roads analysis, Blacktown City Council is developing a Street Tree Master Plan aimed at planting new trees along the road corridor and appointed Australian geospatial analytics company Anditi to conduct a pilot project on 3km of Palymra Rd (Figures 5 & 6) to analyse the impact that the proposed trees would have on road surface shading and whether the trees may be a contributing negative effect on road safety.
As shown in Table 1, Blacktown City Council recorded an 8.5% increase in crashes in 2022 compared to 2021. 45% of injury causing accidents occurred on 60 and 70km/h roads which comprise just 7% of the total road network. For this pilot project, Palymra Road was chosen because it is a high-risk 60km/h road with minimal canopy coverage, addressing the main project goal that street tree planting strategy must not decrease road safety.
The project goals were defined as follows:
The International Road Assessment Programme (iRAP) is a charity aimed at saving lives and preventing serious injuries on the world’s roads in line with the United Nations Sustainable Development Goal of halving road deaths and injuries.
One of the tools that iRAP uses towards this goal is Star Ratings, which are an objective measure of the level of safety ‘built-in’ to the road through more than 50 road attributes that influence risk for vehicle occupants, motorcyclists, bicyclists, and pedestrians. Star Ratings reflect the risk as it relates to an individual road user. 1-Star roads have the highest risk and 5-Star roads the lowest risk.
In 2019, iRAP announced the introduction of AiRAP (Accelerated and Intelligent Road Assessment Program) for data collection, capture and coding. AiRAP is a modern approach to road safety assessments which uses AI/ML techniques to extract data from LiDAR and imagery and increases accuracy and objectivity. Anditi are an AiRAP accredited organisation who specialise in 3D LiDAR point cloud analysis including digital twin modelling.
The methodology for deriving an AiRAP Star Rating from mobile LiDAR and imagery starts with extracting the necessary attributes from the data as shown in Figure 7.
This extracted data was then converted into 2D format to enable future tree planting analysis, as shown in Figure 8.
After further analysis and AiRAP components, the finished Star Rating is then available in Anditi’s RoadViewer portal for desktop analysis, as shown in Figure 9. This initial Star Rating was used as the pre-Street Tree Planting benchmark and is shown in Figure 10.
With the existing Star Rating calculated, the next stage involved Anditi using Council guidelines such as the below to generate the street tree plan:
A section of this plan is shown in Figure 11.
Following the creation of the street tree planting plan, the next stage involved analysing the shading impact of the proposed and existing trees, with the steps taken as follows:
A sample tree modelled in a point cloud is displayed in Figure 12
Shading analysis was conducted at three times of day (9am, 12pm, 3pm) across four different seasons of the year (December, March, June, September). Examples are shown below in Figures 13 and 14.
This shading analysis was then applied across the entire project area to understand the proposed net impact of the entire street tree planting plan. Examples of this analysis are shown at Figures 15 and 16.
The creation of the street tree planting plan identified 867 locations for the planting of additional and growth of recently planted trees across the 3km pilot project area. These combined trees resulted in the average shading of road increasing from 10-30% to 40-60%.
Of these 867 trees, only two trees had a negative impact, resulting in Segment 5 reducing from 4 stars to 3 stars, as shown in Figure 17.
Figure 18 below provides a summary of the street tree planting plan, with potential tree planting locations identified along the 3km length of the Palmyra Rd pilot area, with Figure19 highlighting an overview of the potential shading impact in March.
This pilot project has demonstrated that it is possible to achieve Blacktown City Council’s potential conflicting core goals of increasing street tree canopy to reduce urban heat without negatively affecting road safety. Of the 867 locations that were identified as possible for tree planting based on Council guidelines, only 2 had a negative impact on the Star Rating, giving Council a simple decision to make on whether to plant those two trees or not. The positive impact on shading and subsequent reduction in road pavement surface temperatures for a substantial portion of the project area shows a clear accomplishment of Council’s main priority.
Some findings of note are that trees on southern side have minimal effect on shading due to sun positioning, and that intersections are highly constrained with restricted opportunities for tree planting.
The repeatable and scalable nature of the AiRAP process allows modelling of multiple scenarios such as the tree planting example demonstrated in this pilot project.
Another available scenario involves using Anditi’s ability to calculate carbon storage in vegetation from LiDAR. An extrapolated expansion of this calculation across the entire LGA is estimated to offset Council’s carbon output, resulting in further benefits from this methodology.
Other benefits of the proposed tree planting include enabling and encouraging more residents to engage in exercise alongside the road corridor with the subsequent improvements in health, liveability and happiness that entails.
Overall, this pilot project has proven that the mobile LiDAR and imagery data collected for the AiRAP Star Rating methodology enables the creation of a digital twin that allows many other types of analysis from the same data, improving efficiencies and ROI, and allowing multiple project goals to be achieved concurrently.
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