Guide to Traffic Impact Assessment
The Guide to Traffic Impact Assessment provides guidance for development proponents on how to assess the traffic impacts of a proposed development on the state-controlled road network.
The guide outlines the principles and the framework for undertaking a traffic impact assessment and provides advice on mitigation strategies to address traffic impacts. The guide provides advice for both development proposals assessable under the Planning Act 2016, as well as for major development assessed under other assessment frameworks (usually subject to an environmental impact statement, or a notifiable road use).
Several tools are available to assist industry in understanding and applying the Guide, including answers to frequently asked questions and videos about the guide, intersection delay assessments, pavement impact assessments and road safety assessments.
The Guide to Traffic Impact Assessment Case Studies provide step-by-step guidance for completing a traffic impact assessment in four different scenarios:
- high density residential development in an over capacity road network
- large hardware retailer in an under capacity road network
- large quarry in a rural area (view video), and
- small residential development in an under- capacity road network (view video).
The Pavement Impact Assessment Practice Note provides further guidance on how to prepare a pavement impact assessment, including step-by-step examples for a number of different development scenarios.
The department also can provide road asset data used in traffic impact assessments and information such as marginal cost rates for pavement impact assessments. To obtain access to this data please complete the Road Asset Data Request Form and submit to your local region or RoadAssetData@tmr.qld.gov.au.
View the embedded videos for further information.
Overview to Guide to Traffic Impact Assessment
When we put this together, there were four outcomes that we wanted to achieve in terms of explaining what the new guide is about.
Number one. It's about understanding what a traffic impact assessment is and what it doesn't cover.
Secondly, understanding what has changed with the release of the new guide - so what's different from GARID.
Then a bit on understanding how to manage a traffic impact assessment and the process that that involves.
And finally understanding where to find and who to contact for more information.
Okay, so in terms of the overview and context, I'm sure many of you know, but we thought it might be useful to explain again what a traffic impact assessment has been defined as in the guide.
So it's really identifying impacts of a development or a major project on our state-controlled road network and on our infrastructure.
It's also about how we go about impacting those, how we go about mitigating those impacts.
There's three broad outcomes that we're seeking to achieve and those are: safety, infrastructure condition and efficiency.
Those outcomes are consistent with the outcomes that we seek to ensure that we protect through SDAP: the state development assessment provisions.
Just quickly this slide goes through some of the process. That's a bit of a timeline of the development of our guide and GARID.
I won't go through that in a lot of detail but all I'll say is that this review has been going for some time - since 2013. There's been a number of iterations to get where we are with the current guide.
There's a number of key things that we wanted to do in terms of bringing the guide up–to-date, in terms of making it contemporary with current impact assessment, taking consideration of the current legislation and the planning instruments and planning framework under which it operates.
These were some of the objectives and drivers for the review of the guide.
I've talked briefly about some of these just now.
There's also some organisational changes that we wanted to reflect.
A stronger safety emphasis.
We'll talk a bit more about that and particularly at the next session on Thursday there will be a bit more detail on the new safety assessment process.
We're also cognisant of the changed funding outlook under which government is providing its services.
Where we can, we want to make the guide provide a more standardised and consistent approach to how we do these assessments across the state.
Some of the principles and changes from GARID. So that's GARID: the Guidelines for Assessment of Road Impacts of Development.
As I said it's been around for over 10 years now so it's definitely ready for a review.
This is our new guide so it will replace GARID.
It's currently available internally as a consultation draft.
We've made some amendments to that consultation draft just over the last couple of weeks based on some more feedback we've got from some of the questions that have come in, and particularly some of the external stakeholders and some of their feedback.
Nothing too significant though in terms of changes.
The plan is for the new guide to take effect on the 3rd of July the same time as the new Planning Act and other planning instruments.
This is a summary of what's changed from GARID.
These are four of the features that aren't being continued.
The bring forward methodology. There wasn't much support for that.
That was basically a methodology that sought to try to capture the costs associated with bringing forward programmed works that TMR had planned to do at a later date, but it wasn't very successful from all the feedback we received.
We've got a new pavement assessment methodology that uses the FAMLIT methodology which has been developed by ARRB, the Australian Road Research Board, I think that is.
We'll talk more about that as well in particularly on the session on Thursday.
We've gotten rid of design horizons for efficiency impacts other than an access intersection.
Basically we're no longer requiring a development to build in and design capacity for ten years of growth post opening of the final stage of development.
We've actually got a fact sheet specifically on that issue because there's been a lot of questions about that.
At the end of the presentation we'll talk about where you can find fact sheets.
Some of the assessment of other impacts that are currently found in GARID has been removed from the new guide and that's simply because that is now dealt with through SDAP and some of the supporting guides that take effect under SDAP.
Some of the features that are new under the guide – it has a new name so - Guide to Traffic Impact Assessment which we think better reflects the function of the guide.
It's modernised for legislation and the planning framework.
There's a stronger focus on safety so all triggered development now needs to undertake some form of safety assessment and that begins with a risk assessment process.
We'll talk more about that - there is a stronger emphasis on this but it doesn't in all cases mean that there's a detailed road safety audit that's necessary.
There's a mitigation hierarchy which we've adopted and that's consistent with similar hierarchies that are used in the environmental space and elsewhere in government.
We want to avoid impacts first of all, before managing impacts, and then finally we can mitigate impacts, and that usually means constructing infrastructure, or as a final step that could be a monetary contribution.
Some other changes there's the no worsening principle, so all triggered development now needs to avoid, manage, or mitigate impacts to achieve no worsening.
There's an intersection delay assessment process.
The focus is no longer about intersection capacity and basically now we're saying if you're a development that adds more than 5% of traffic to any movement that will be captured in an impact assessment area, that then forms part of the assessment.
Damien will definitely talk about this but just to be clear, I think one of the things we've realised with the guide that probably wasn't clear is that there will be instances where development is triggered for assessment, intersections are part of that assessment, but if the traffic generated by the development is less than 5% this is the aggregate, sorry this is the traffic delay, so the aggregate delay is less than 5%, then there would be no mitigation required under those circumstances.
We have the updated pavement impact assessment methodology.
And we also have a preferred input parameters schedule that's attached to the new guide that provides some of the inputs that we would hope that nine times out of ten will be standard and if used will hopefully reduce some of the contestability and back–and-forward that can happen.
In terms of access assessments, there's really not a whole lot of change to do with this.
There's a bit of clarity provided in terms of you know, needing to consider the impacts on existing cycling, pedestrian and other infrastructure.
The new guide has six principles that operate in a hierarchy.
Principle one overrides principle two and that works its way all the way through.
Some of these are very consistent with what happens under GARID, and some of them are a little bit new.
Particularly the no worsening principle number two and the mitigation hierarchy principle number three.
So I'm just going to quickly go through each of these principles.
For safety. Development must not compromise safety on the state-controlled road network.
Safety has been recognised as something that we want to improve upon in terms of how we assess impacts on safety.
To do that, this diagram from the guide explains the process that we need to follow.
It begins at the top there where it says 6.3.2 Risk Assessment.
We're asking all development to do an initial risk assessment to identify current safety risks that may need to be mitigated and secondly to look at new safety risks that can be introduced by the development.
All triggered development needs to do that risk assessment.
Following from there, there's the second stage, if there are safety impacts that need to be mitigated, depending on the traffic volume and the speed of the corridors, you would either need to do a road safety assessment or a road safety audit. The guide talks a bit about that and we'll talk again about safety in our session on Thursday.
For no worsening, this is principle number two.
Development should seek to achieve no worsening to safety or infrastructure condition, and no net worsening to efficiency across the impact assessment area.
So in terms of no worsening of safety and infrastructure condition, hopefully that's pretty straightforward in terms of what we're trying to achieve.
For no net worsening that really has application to intersection delay and that's where we're recognising that across an impact assessment area, there might be some intersections that we allow delay to worsen if we can achieve no worsening – no net worsening by improving other intersections in that impact assessment area.
This slide explains what typically happens currently under GARID, where we're considering capacity of intersections.
So you can see under scenario one, that's an intersection where the intersection is operating under capacity.
Development is added in terms of that yellow (pink) block and because the intersection is still under capacity we currently would not seek to get any contribution from a development proponent.
In the third scenario where the capacity is already over capacity, and this can happen a lot in some of our urban intersections, the development worsens it, but it was already wrecked so it comes down to a bit of a question then as to whether a development contributes for their impact or fixes it and brings it back to an under capacity level. Or whether they make the argument strong enough that they don't need to make any contribution.
There is a bit of inconsistency in terms of how this is currently handled.
In scenario two, that is typically the scenario where under GARID we will get some sort of contribution whether works or monetary contribution from a proponent.
So that's where an intersection is under capacity and that's being pushed over capacity with the additional traffic.
There's a bit of inequity there because that development that does that, will get 100% of the works to upgrade that intersection, whereas other developments might have contributed to the impact but have not contributed to the mitigation.
Under the new guide to traffic impact assessment, you can see that we're now seeking to get all developments under all three of those scenarios to mitigate their impacts.
So whether it's under capacity or over capacity we want them to account for the aggregate delay they add to the impact assessment area.
The approach is really a shift from thinking in terms of degree of saturation to the aggregate delay on the community.
The third principle is about avoiding impacts and using the mitigation hierarchy.
Firstly avoiding, secondly managing, and finally mitigating impacts.
In some ways this is already reflected in GARID - it's just that this makes it a bit clearer in terms of this is the sort of place where we want to move to.
We want to push any strategy that can lead to avoidance of additional traffic as our first priority.
This is the hierarchy – it's pretty straightforward. It's from the guide so again, we're trying to avoid impacts to begin with.
'Manage' can be things such as scheduling, programming to manage the impacts, and then finally mitigating through new works or a monetary contribution.
Principles four, five, and six.
Principle four and five are about access.
With principle four, where we're essentially trying to capture that we want access to be consistent with a function of the road and any access limitation requirements that may be on that road.
Principle 5 is essentially similar to what happens under GARID, so development proponents will continue to be responsible for all access and frontage works.
And finally principle six is about out-of-sequence development.
We're saying, proponents are responsible for all works required to connect to out-of-sequence development to the current and future state-controlled network while not compromising implementation of planned transport infrastructure.
Out-of-sequence. This principle number six again links into our approved planning policy and brings home the need to be able to shift important planned upgrades or future corridors to category C or D so we can use that planning and it can be considered in DA.
The traffic impact assessment process and statutory framework – I'm just going to go through that.
The key document for applications under the planning framework is the state development assessment provisions.
As you would know there is a new SDAP version 2.0 that starts from the 3rd of July.
It has modules that are mode based for transport.
So there's a state code one: development in a state-controlled road environment and a state code six: protection of state transport networks.
These modules refer to our new guide.
They refer to it as an editor's note so it typically says it's recommended you undertake a traffic impact assessment in accordance with the guide.
As I said earlier SDAP seeks to achieve the same outcomes that we are doing in this guide.
That's about safety operating conditions or efficiency and infrastructure condition.
Outside of the Planning Act there are other ways that a development might need a traffic impact assessment.
They are somewhat complex depending on what it is.
Generally a lot of that will happen through an EIS process and that can happen in two different ways under the State Development and Public Works Organisation Act or could be an EIS subject to the Environmental Protection Act.
Generally projects requiring an EIS will assess transport impacts.
Another key mechanism is a Notifiable Road Use and that as I understand intends to pick up projects that are not captured through an EIS or the Planning Act.
It's where fifty thousand tonnes is transported per annum, and it only deals with safety and pavement impacts so you're not assessing intersection delay and some of the other things through that.
We've also mentioned there can be other planning schemes that can require consideration of traffic impact assessments, so under an SDA or a PDA.
Generally TMR is nominated as a referral agency or asked to provide input.
And finally an Infrastructure Designation so that was formerly known as a Community Infrastructure Designation.
DILGP may consult with TMR on traffic impact assessment matters.
We've been talking to DILGP about that.
The impact assessment area is a key concept under the new guide and this is the area that is basically assessed.
For each of the six impact types that we've identified, it's defined slightly differently, but generally it's about where development is introducing an increase in traffic of five percent.
That can be at an intersection for intersection delay or road safety, and can also be along road links for some of those other impacts like pavements and road link capacity.
Then we have an impact assessment year.
Generally that's pretty consistent now - it's the year of opening of each stage including the final stage.
*fire alarm sounds*
We're just getting a building announcement.
I guess a key point to note is that for an access intersection, you would still need to design for ten years of capacity post opening of the final stage.
Monetary contributions - we have actually made a slight change in the last couple of weeks based on some of the feedback we got on how monetary contributions would be applied.
With monetary contributions we had a lot of feedback about the concept we're referring to as 'breaking the nexus'.
We wanted to be able to use monetary contributions across the impact assessment area where, for whatever reason, we are not able to or do not wish to or don't have enough money to do some works at that point where the monetary contribution has been collected.
So there has been a lot of feedback about that, saying that probably doesn't meet the reasonable and relevant legislative tests.
What we've done is we've kept that in there as an option.
So we're saying where there's agreement of all parties - and that's the key proviso - so where all parties agree, the monetary works could be used at a different location within the impact assessment area, or in a different way.
That's certainly I think where we would like to shift eventually.
However, for the moment, the position that's currently adopted in GARID is largely the same in that where we collect the monetary contribution it will be collected for works to occur at that point at a point in time when TMR is able to do that.
We've had questions about how you can determine the value of a monetary contribution.
There's no easy answer to that but we've said that it should be based on the construction value of the theoretical works that would be required.
You would have to base that on other works that you've undertaken to get a cost per square metre. For example – the square metres of turn lanes if turn lanes are required, that sort of thing.
We're saying exclude land costs in that calculation.
There is a FAQ document that we're putting together and this is one of the questions that we're hoping to provide a bit more information on.
Case Study 1 - Quarry in a rural area
Ok, so I'm now handing over to Damien Bitzios. He's going to take us through two case studies.
Okay, thanks Andrew.
The first case study we'll go through today is for a large quarry development in a rural environment rural area.
As we normally do, we would collect some background information.
And in this particular case it's quite a remote rural intersection that is being primarily impacted and the quarry site is just to the south of that at that intersection.
As we'd ordinarily do, we would identify the land uses around the subject site and in this case it's undeveloped rural land except for of course the development site.
The speed of the road is quite important in this context because it's called up a few times in the GTIA and requiring different types of assessments, based on the speed of the fronting road.
In this case the two major roads are at 100 kilometres an hour and 80 kilometres an hour posted speeds.
Some of the key input information we also need are: traffic volumes, some of the existing intersection performance, the road safety conditions and the site access location.
From a preliminary scan we identify there was no current road safety issues on that section of highway, and there was some recent traffic survey data that we could use.
One of the key issues in this particular case is a steep grade on the frontage of the site.
In this particular case again there's been some recent pavement works done to upgrade the road and in terms of the types of assessments it's not relevant for assessment for public transport or active transport being in a quite remote rural area and there's no site parking considerations that would influence the state-controlled network.
The focus of this assessment for this type of develop application is primarily on pavement and transport infrastructure impacts as well as access configuration.
Just some details around this hypothetical development, in this case study.
A 2019 year of construction with 2022 as being the notional new of opening and a 20-year operational life for the quarry with direct access onto the state-controlled road.
One of the first steps is to identify the traffic generated by the development and in this particular case the quarry's predicted to output 250,000 tonnes per year.
Both the heavy vehicles and light vehicle needs need to be identified so in terms of staff, both in the construction phase and the operational phase.
Types of vehicles we're also needing, that's also under the current GARID assessment that are usually input in to these types of assessments.
Those types of parameters are required to able to calculate the number of truck trips both loaded and unloaded that need to access the site.
In terms of the intersection-based assessment, the additional traffic passing through that intersection number one is greater than five percent for through traffic movements and the intersection delay threshold is therefore triggered.
That intersection is considered within the impact assessment area.
For a quarry, there's a construction impact for this particular case, there's a construction impact period as the buildings on site and so on are developed.
The impact assessment includes road safety impact, access and frontage, intersection delay and so on, for both the construction and the operating periods.
In terms of the traffic distribution.
Sorry. Moving on to the traffic safety assessment.
The first step in the safety assessment is to identify any potential risks.
In this particular case southbound vehicles turning left into the site are identified as a potential risk for rear-end crashes - primarily for rear-end crashes and given the speed of the road.
With the development, obviously without the development there is no left turning traffic, and with the development there is a significant increasing likelihood for those left turn crashes.
Similarly for right turn movements out of the site, there is a significant increase in likelihood because there is nothing there at the moment.
Potential mitigation measures to – to channelise a left turn, to separate out the left turning vehicles from the following through vehicles.
And for the right turn movements, to upgrade the intersection configuration to again separate those right turning movements, provide acceleration lane for the trucks to get up to speed to merge.
With those two mitigation measures in place the risk assessment has resulted in the risk score returning back to the low level.
With those works being identified as being required to the risk assessment process, and considering that the speeds are in the 80 kilometre an hour environment, with a lower than 8,000 vehicle AADT, we trigger the medium road safety environment rating category.
And given that it's a major development, and in a medium road safety environment rating, a road safety audit has been identified for the design of the left-turn channelised intersection and the right turn seagull arrangement.
Those particular works would then go through - a concept design for those works would go through a road safety audit - design based road safety audit.
Moving on to the access and frontage assessment.
We've identified through the safety component of the assessment just completed that we needed a new seagull intersection with the channelised left turn.
The access assessment would then investigate any additional sight line issues that that are required to be addressed.
Although they should have been picked up in the safety assessment in the first case.
Moving on to the intersection impact assessment of intersection number one there. With background traffic the intersection delay is 30 seconds.
Given the low increase in volume and they're primarily through movement increases and it's on a t-intersection, there's marginal increases in delay.
In this particular case even though the traffic volume has increased by more than five percent and has triggered the need for assessment, when it has been assessed there's less than five percent increase in delay and what that means is that no further action is required for mitigating any intersection delay impacts in this case.
A secondary consideration is that the access needs to operate within acceptable performance limits for a 10-year design horizon.
It is part of the frontage works assessment the access must be designed to operate for at least 10 years under capacity.
In this particular case, with the volumes that we have in place that's not a significant issue.
Moving on to the road link capacity assessment, the mid-block level of service has actually decreased with the development traffic.
Now what has been undertaken here?
The reasons for that decrease is primarily due to the additional heavy vehicles that have been added to the highway, and the reduction in level of service from A to B just in that section one.
The assessment would be a TRARR analysis that identifies that some overtaking lanes will be required at the steep grade location to cater for those heavy vehicles.
Once those climbing lanes are introduced the level of service would come back to a level of service A demonstrating a no worsening condition on infrastructure.
Again that piece of work would need to, being in an 80 kilometre environment, as part of the overall package of works, would need to go through a road safety audit process.
Now, that could have been done in one go in effect with the other intersection upgrade requirements.
Moving onto pavement impacts now, the SARs increase in this particular case is a four percent increase, so it doesn't actually trigger any need for further assessment in section three.
When you move closer to the development in section two there is a 9% increase, and closer still in section one there is a 20% increase.
So section one and two are the two sections that require a pavement assessment and this is done through the FAMLIT software process that is referenced in the guide.
We're not going to go through that in too much detail yet as that's still being finalised and completed, but needless to say under this particular case, this example, the development consumes remaining pavement capacity during the mitigation period and some pavement design is required in this case.
Just one more example of how we deal with some nearby transport infrastructure.
We have a bridge that is nearby the development and the development traffic exceeds a 5% increase in background traffic in this particular case.
In that case the bridge is referred to the structural team for further assessment to determine whether the additional loads can be accommodated by the bridge or whether additional works are required.
The overall process then, similar to the other case studies that have been presented previously is to discuss and agree on an impact mitigation measures from that draft assessment completed and to revise and finalise documentation accordingly.
Following submission the usual information request and response process would follow, and then obviously a decision by TMR through to the relevant assessing agency.
Case Study 2 - Small residential development
The last case study is on a small residential development in an under capacity road network.
So, typically on the fringes, potentially of a regional centre or a rural town centre.
In this particular case, this example is in a residential area with a priority controlled intersection.
The development triggers the need for assessment, being due to proximity to the state-controlled road network so assessment needs to be done under the guidelines - under the GTIA guidelines.
Just some details on the frontage road network for the example - it's a six lane fronting road and the side street is a two-lane council road.
In terms of assessing the existing conditions you need to collate traffic volumes again, need to look at the base case intersection and network performance, looking at the road safety condition and identifying where the site access would be.
And collecting traffic data of course at the key intersection.
Being in an urban environment, we would be assessing public transport, walking and cycling as well insofar as the development impacting those particular modes or being able to access those particular modes as a means of mitigating some of its traffic generation impact.
This case study has a 2019 year of opening, so it's a relatively small development of twenty residential townhouses.
Again the trigger for assessment by TMR has been the proximity to the state-controlled network, rather than be the size of the development.
In the context of traffic on the state-controlled network thirteen peak vehicle trips which isn't a lot of vehicle trips, and thirty parking spaces.
For this case study, the access has been assumed to be off the council road which then would feed onto the state-controlled intersection.
The traffic generation is calculated using the conventional trip generation rates for medium density development, with in-out splits to assign that traffic to the road network.
The distribution of that traffic is then determined to and from the development and to and from the subject intersection or the primary intersection that accesses the development.
Looking at development traffic versus background traffic, you can see that for all the movements the development traffic is less than five percent of the background traffic in the opening year.
So in this particular case there is no need to take this any further in terms of intersection assessment at that location.
Intersection Delay Assessment
Okay, just to recap on the current approach in GARID and part of the reasoning why the approach has been modified under the GTIA.
So GARID currently requires essentially a threshold based assessment where the degree of mitigation works required vary depending on where the development sits in relation to the existing capacity.
We'll take the first example on the far left there, where the base condition of the network and near the development is well below the capacity threshold.
The development traffic is added into the network and with that traffic the condition of intersections surrounding the development is still below the capacity threshold.
In that case we would add no impacts and there would be no mitigation to be undertaken.
Moving on to scenario three on the far right hand side in heavily urbanised, congested conditions, which we're obviously having more and more of in Queensland, the base condition may very well be over capacity in peak periods.
The development comes in with its additional traffic and adds to that - adds to those volumes resulting in an even more over capacity situation.
Nevertheless the capacity threshold has been reached and there's typically little that is required to be done on the basis that the problem was already there before the development came along.
So scenario two is the situation where the base case condition is just below the capacity threshold, the development traffic is adding in on top and results in over capacity of the particular intersection.
Now in that case, developments are typically conditioned under GARID to provide the works to bring the intersection or intersections under capacity.
So, these various scenarios demonstrate that the inconsistencies with the same size development depending on where they are, the maturity of the network, or the level of congestion of the network, and the potential for works all contribute to which developments in which locations require upgrade works and conditions. So it can be quite inequitable.
Under the new approach, under the GTIA, there is essentially a continuum of impact mitigation.
So regardless of where you are and where the network level of capacity is, there is some contribution towards upgrade works.
In all three scenarios, in this particular example comparing to the previous slide there are works required to bring the whip development condition back to the condition that the network was in prior to the development being there.
Just to breakdown intersection impact into a little more detail, we typically in travelling back to systems under GARID have been considering intersection impact in terms of degree of saturation or level of service.
But when you really break down what intersection impact is doing to the community, it really is adding to delay.
Pavement Impact Assessment
Good morning all. Previously, Mano Manoharan, a member of our team was to give this presentation in the previous session. He's on annual leave until 29th of this month, so I'm presenting this information on his behalf.
If there are any questions please feel free to send it to the planning policy email, we'll try our best to address your queries.
Okay, in terms of the pavement impact assessment, the marginal cost methodology is primarily based on the FAMLIT model, depending upon the pavement type, traffic volume etc, so that's what has been used in the Guide to Traffic Impact Assessment.
I'll run through some of the information which are used in the guide in terms of the pavement impact assessment.
As I said, this is the methodology which is in the guideline and it's primarily called marginal cost methodology.
In terms of the methodology, we are using the FAMLIT tool which is the freight axle mass limit investigation tool.
In terms of the method, a marginal cost analysis is done based on FAMLIT, and then the cost goes into our databased - the ROADLINK database, and then the pavement impact assessment tool is used to calculate the damage as a result of the new development and the pavement structures and then the PIA (pavement impact assessment) tool.
Because this is going to be used for the first time based on this marginal cost methodology, we'll be providing training to all the relevant staff who are going to be involved in the development assessment activities.
Primarily with this methodology there are a number of steps - a number of things we need to be aware of.
The main thing is this nationally accepted whole of life cost calculation (WOLCC) method which is based on FAMLIT and there are a number of technical things we need to be aware of.
Primarily, measuring the road condition data which is, for example, roughness, rutting etc and also the pavement properties in terms of the material, the subgrade and the pavement materials and also how the road segments will be performing as a result of these traffic impacts.
Also in terms of the environmental factors as well, we'll be considering those things in the analysis.
Recognition of road specific differences, as a result of the traffic volumes and depending upon the pavements.
Also, the results related to physical segments - so each segment which has the deflection data will be considered in the analysis so we'll be checking in to all those segments and then used in the calculation method.
Now what is the time period for the calculation of the marginal cost as a result of the road wear?
There are a number of maintenance activities on a segment of a road. For example routine maintenance, program minions maintenance, rehabilitation.
A very simple sequence of the routine maintenance is done every year. Program maintenance it varies, for example from ITS to 10 years, for reseal, then it goes up to 14-15 years for asphalt.
So less than average we will go for 10 years the rehab, normally it's designed for the pavement, when the pavement is designed it's normally taken for 20 years. So routine maintenance, program maintenance and then the rehab, and then another cycle goes on.
Instead of using a very short period for cost analysis, we do go for 50 years which is a long enough year to come up with the equivalent annual uniform cost.
In the EAUC calculation, there are number of things we need to know.
It's SAR - which is standard axle repetitions, equivalent standard axles and so those things are used in conjunction with the pavement material, then the model is developed.
Now this graph shows the relationship between SAR and EAUC – equivalent annual uniform cost.
The graph was developed by using various calculations at various stages.
For example minus 40, minus 20, plus 20, plus 40 percent, and the line that line was run out. The equation, which you can see is y = a + bx, 'b' being the slope which is the MC - marginal cost.
So for each increment of the SAR - standard axle repetition –there's an EAUC increment so that's what is called a marginal cost. The increment as a result of the additional traffic impact due to development activities.
This one just shows the model structures for the lifecycle cost and analysis, which is incorporated in FAMLIT. So, road description and then we need to know traffic loading, and then because of that extra traffic it leads to deterioration and as a result of the deterioration the works treatment will be triggered, and what sort of treatment will be done - that will obviously cost money and all the various treatments are taken into account over the period of 50 years and then the full analysis is done in order to calculate the EAUC.
Now, I'm just going through a little bit more detail.
We have more than 33,000 kilometres of road which include both sealed and unsealed.
We do the deflection survey - it's called TSD - traffic speed deflectometer.
Normally we do about 20,000 kilometres of road survey each year.
Currently we have a little bit more than 17,000 kilometres of the road segments for which I have TSD data.
Sometimes the vehicle cannot go into each road segment, so it's not possible to do the full network for each year, and also because of the cost, we don't target the full network each year but we do include them in a cyclic basis.
The information we need to have is, obviously the road functional class and the location details and in terms of percentages and then the pavement and the surfacing construction - how it is constructed, whether granular or asphalt or the cement is stabilised material.
And also we need to know about information about the climate and the soil reactivity. Some soil in our state road network is reactive, some are non-reactive, and there is also dry reactive and dry and wet reactive.
Normally, four types - dry reactive, dry non-reactive - reactive and non-reactive, wet reactive, and, wet and non-reactive. All that information is taken into account, and also we'll look at the pavement or subgrade strength and also the surface condition as I said previously roughness rutting, and also the associated deterioration for each road segment.
The traffic numbers and compositions - we do have our database we get the traffic info from there. And also we need to know what sort of maintenance treatment is done and what is the cost for each of those maintenance treatments - whether it is routine, program maintenance or rehabilitation.
Now marginal cost is calculated based on all physical segments where the deflection data is available and then by creating the representative segments the remaining physical segments marginal costs were populated using that model - the one I showed you previously.
Then we can develop maps illustrating the spatial distribution of marginal cost and that marginal cost otherwise goes into the road link table and then we develop a database tool to calculate pavement impacts for the network where the development work goes on.
This graph gives you the various impact levels in terms of the marginal cost which is the dollar for SAR per kilometre for various road categories, starting from inter-regional to urban sub-arterial.
As you can see, the higher effect is on the 'regional distributor and connector' role and the 'rural land access'.
Also the graph shows the various impacts in terms of the different material type as well - concrete or cement stabilised or the granular material of the pavement.
In regional and rural roads, normally the pavement design, there is more detailed analysis and more weight is given in terms of the design of the urban roads.
For example the roads which have higher traffic they have asphalt and concrete pavement.
Because of that there is more capacity to resist the traffic impact, whereas the rural roads, the design is fairly simple and some of the roads don't have urban design at all.
That's why it's relatively more impact in terms of the marginal cost due to development activities and those road networks.
Now this graph shows the marginal cost for different traffic volumes, less than 1,500, 1,500 to 5,000, 5,000 to 10,000 and greater than 10,000. Again, also depending upon the material type which is asphaltic concrete, cement stabilised and granular material.
The marginal cost varies depending upon the traffic and the material type as you can see from the graph.
This is the model which is used for calculation of the pavement contribution.
Now the calculation is done taking into account the construction period as well as the operation period for each road segment trigger. Now 'MC' - it's described in the departmental database for each road segment which is per SAR kilometre.
The length is the length of the road segment which is taken into consideration for calculation of the pavement contribution. And 'n' is the number of road segments.
So a section which is impacted will have a number of road segments so calculation is done for each road segment because it will have a different pavement material and also can have different traffic.
Not necessarily the close ones, but definitely when you take into consideration the limit of roads, it will have various types of traffic and pavement material.
This is just an example of the pavement impact assessment, and how the marginal cost tool is used.
The vehicle has six axles with a gross mass load of 4.93 for SAR4 which is the granular and the asphalt complete SAR5 and SAR12 which is the cement stabilised material.
1000 trips per year over ten years and that gives you ten thousand trips all up.
The road sections, 10A and 10B in the gazettal directions, from zero to twenty-three kilometres.
Also, there is a structural number - it's related to the structural model.
In the next page you can see how the PIA tool is used and this is a simple sample. First there is the overall length of the road - 168 kilometres, broken into road 1 and road 2.
In road 1, there is an asphalt section and some cement stabilised.
For example from 0 to 145 kilometres, for 10A there's ten thousand trips; asphalt section 31.14 kilometres, the marginal cost - the SAR, which comes from the database - asphalt is 5.61 and now the marginal cost which is dollars per SAR per trip - that's also from the database - the TMR database for each short segment.
The cost for the entire section is $0.52 times 10,000 times 5.61, that will give you $29,173 approximately, that's the cost the total cost.
Now in terms of the same procedure for the cement stabilised section, which is 99.27 per kilometre the same method is used.
You can calculate the cost separately for asphalt section and the cement stabilised.
When you combine those two, you'll get a total cost for road one.
The road two is a similar matter. The 10B - 0 to 23 kilometres, uses a similar sort of calculation, depending upon different marginal costs from the database and the segments where they are, and what type of material.
Once you know the cost for road two, and then when you combine road one and road two, you get the total overall cost which is that $432,735. That's the total cost as a result of the impact.
That was a very brief rundown in terms of sealed roads, how the model is used and how the calculation is done.
There has been a fair bit of detailed study and analysis of the model development for sealed roads, whereas for unsealed roads, we don't have that detailed tool.
We do have, obviously, a number of unsealed roads adding roughly about 4000 kilometres in our road network.
In terms of the unsealed road there is a model. It's called Australian Local Road Deterioration Study gravel loss model which has been already developed.
That's what it is used to calculate the marginal cost for unsealed roads.
In the next space I will show you a table. You can see this is the marginal cost matrix for unsealed roads.
On the left hand side that's the ADT - average daily traffic, with the percentage of heavy vehicles and also the grading frequency. For example here that's roughly about three times a year.
Then, what is the initial gravel depth of a particular road segment, starting from 75, 125, 175, 200. So different depths of the gravel and also there is a material property as well, and the PF (plasticity factor) and MMP (mean monthly precipitation).
PF that is from 50 to 300, that's what is used in this chart and then the MMP varies from 45 to 188.
So for each initial pavement depth and the specific material type there is a marginal cost figure.
Those costs are obtained based on this particular matrix, and when you add all the costs for all the segments you get the total impact cost for the for the particular length of the road we will be interested in.
That's a general sort of model which is already developed and used, but in terms of sealed roads - the information which I've already presented, it is the one which is used.
So that's a very brief rundown for both sealed and unsealed roads. Please feel free to send your questions and if you have anything with regard this pavement impact study we'll try to answer as much as we can.
As Andrew said the new safety assessment section of the GTIA it was previously in the GARID but to a lesser extent.
So the safety assessment is covered very clearly in principles one and two where development must not compromise safety on the state controlled network and a development should seek to achieve no worsening to safety or infrastructure condition and no net worsening to efficiency across the network.
So really we need to make sure that any development has to make sure that safety is the number one principle before you go on to the next steps.
When looking at safety there's in the document a clear table showing the process go through.
Really it's broken into two components: the risk assessment, and the safety assessment.
The risk assessment, which you do first and is necessary for all developments through a development application goes through the cream-colours here and it's covered by section 6.3.2.
So the risk assessment, its aim is really identifying and assessing existing safety risks. Assess the development proposed impacts that may change those existing safety risks and then look at, will those increase the risk to an unacceptable level or is it already at an unacceptable level and sorry it's also 'will it increase risk from an existing level to a higher level'.
Similar to - throughout the document, I think in Section three in terms of a trigger for a risk assessment it's a five percent threshold. So anywhere where there's a five percent increase in traffic on a movement or a through carrying volume there is need for a safety assessment to be undertaken.
So assuming, and in most cases a risk assessment hopefully will come up with no changes -no need for an infrastructure improvement. If there is no infrastructure improvement needed and you can get around and infrastructure improvement by using the avoid, manage, mitigate.
If you do potentially increase it, you might go through the 'yes' and avoid it, but if you don't need an infrastructure change, the risk assessment is the only assessment that you need under this safety assessment process.
After that, you document it and then you include that risk assessment in the TIA.
If however, there is need for some infrastructure improvements due to the development and/or there's an existing high unacceptable risk on the road network, there's a need now to go to section 6.3.3 the safety assessment, or those sections in blue.
This we'll go through soon, is either a road safety audit or a road safety assessment which will be required, is more expensive and really will form an attachment to the TIA.
First looking at the risk assessment.
The document 6.3 in the GTIA and section 6.3.2 goes through and shows you the risk assessment table looking at the likelihood and consequences of risk.
As you can see there's five levels of likelihood and five levels consequences.
Consequences being the existing consequences of crashes, being property damage, minor injury, medical treatment, hospitalisation and fatality.
Whereas a likelihood; there's no clear direction given on what an 'almost certain' and a 'rare' is because it really depends on the development you're undertaking.
There is a number of documents such as Austroads Guide to Road Safety: Part Six on Road Safety Audits which gives good guidance on the likely understandings of these words.
For instance 'rare' might be the likelihood might be an event occurs once or twice a year, whereas 'almost certain' might be it happens every day. That might be for a big development whereas for a smaller development, it's very unlikely you might have a fatality every day, but for its size is the risk level quite high.
So the consequences of having a property access onto a motorway. Yes you won't die every day but, it's almost certain that that incident would occur as a very high severity outcome crash if you had that development access in a very high volume road. So, you have to consider the development in the situation.
So once you've gone through this risk assessment, and identified if it's a 'low', 'medium' or a 'high' for the existing risk without the development, you look at with the development in place will that risk level change.
In identifying risks you look at all the different potential safety risks that that development might be contributing to, or existing risks. In Section 6.3.2, Figure 7 examples of risk assessment. They have one such as there might be more left turning traffic into a property so you've increased the risk potentially of rear-end crashes or maybe more right turning pockets so the right turning traffic might extend past the end of the turning bay.
Or there might be slight distance constraints that might have to be addressed, maybe due to foliage in the way or parking in areas which may hinder where a driveway might be going in.
Once the risk assessment has been undertaken, we look at the need for a further analysis if this is triggered.
As I said there are two potential requirements: a road safety audit or a road safety assessment.
The road safety audit and road safety assessments, determining if they are the level which is required is based first off the lower table which looks at what the speed of the road is and the volume of the road.
So for a high volume, high speed road you will have the high need and for the lower volume, lower roads, the lower need and then medium is in between.
Then you look at if it's a major development an EIS-type development or is it just a Planning Act development which is majority of developments.
If it's for the majority of development you probably going to low and mediums so you require a road safety assessment. It's only really for those major developments and those ones that trigger the 'high' that you require those road safety audits as shown in this table which again is in tables eight and nine of the GTIA.
Depending on the level of audit or road safety assessment required a road safety assessment or road safety audit who is able to do that assessment varies.
For a road safety audit it has to be an accredited road safety auditor from Queensland.
The document refers to where a list of these auditors are so you would require at least one of these to undertake this assessment. In terms of the independence of this person, they have to be independent of the development application, but they can be still in the same company.
For better understanding of how that independency is highlighted the Austroads Guide to Road Safety Part 6 goes through that in more detail, and the fact sheets we have has that in a bit more detail.
In terms of the road safety assessment these in terms of what they are it's a little bit unclear but it is really a step down from that road safety audit requirement, so the road safety audit is very clearly stated what it is in the Austroads document.
Whereas for the road safety assessment we've written in Section 6.3.3 what's the role of that, and it really is to look at existing issues and any new issues introduced by the changes and designs and look at the measures to address the safety issues identified within the design.
Who can do one of these? It's either a road safety auditor again can undertake these or someone who is an RPEQ - with experience in road safety.
So the requirements are a bit lower but they still at the end of the day it's either an RPEQ signing off on the road safety assessments who will be approving this, or if you have a road safety audit done and the road safety audits don't necessarily have to be an RPEQ, whoever's doing the TIA, the outcomes of the road safety audit will always be given back to the TIA component.
So there will be at least someone at the road TIA levels signing off who is an RPEQ.
Superseded guide versions
Guide to Traffic Impact Assessment (commenced July 2017, replaced October 2018).
For general enquiries about the guidelines, please contact:
Director (Corridor Management and Protection Unit)
Transport Strategy and Planning Branch
Transport and Main Roads
For technical enquiries please contact your local region.
- Last updated 30 July 2019