A Request for Information (RFI) from council regarding your traffic generation figures can bring a Development Application (DA) to a standstill. For mixed-use developments, this challenge is common, and often stems from a failure to provide a robust multi-trip purpose justification. Standard trip generation rates frequently overestimate traffic by failing to account for internal trips between different land uses on a single site. This leads councils to question the data and demand potentially excessive road upgrades or infrastructure contributions.
By correctly applying this methodology, you can present a realistic and defensible assessment of your development’s true traffic impact. This guide provides a clear framework for understanding and implementing a justification that satisfies council requirements. We will detail how to avoid unnecessary DA delays, reduce your Section 7.11/94 contribution costs, and ensure your car parking and access facilities are accurately sized for real-world demand. The result is a more robust application and a more efficient project outcome.
What is Multi-Trip Purpose Justification in Traffic Engineering?
A multi-purpose trip occurs when an individual completes multiple tasks or visits several destinations within a single journey. For example, a person might leave home, drive to a mixed-use development, park their car once, visit a medical centre, pick up groceries, and then have coffee before returning home. This contrasts sharply with a standard single-purpose trip, which involves travelling from an origin to a single destination and back again (e.g., home to a shop and back home).
This behaviour of linking stops is known as ‘trip chaining’. In the context of a well-designed development, trip chaining means visitors can satisfy multiple needs without moving their vehicle and generating additional traffic on the external road network. This concept is fundamental to accurately forecasting the traffic impact of modern developments.
To better understand the broader context of traffic impact analysis, the following video provides a helpful overview:
For mixed-use developments that intentionally co-locate retail, commercial, and residential uses, understanding trip chaining is critical. Standard traffic generation rates often treat each land use in isolation, which can grossly overestimate the total number of vehicle trips and the required parking supply. A multi-trip purpose justification provides a more realistic and accurate assessment.
Standard Trip Generation vs. Factored Rates
The baseline for traffic assessment in New South Wales is typically the RMS (now TfNSW) Guide to Traffic Generating Developments. This guide provides standard rates for Trip generation that assume each visit to a specific land use is a unique, single-purpose trip. However, for mixed-use sites, a reduction factor is applied to these rates to account for internal trips. This is not guesswork; it is a calculated discount based on established methodologies and evidence of shared trips between complementary land uses.
Why Councils Scrutinise Trip Generation Data
Local councils have a statutory responsibility to protect the performance and safety of the surrounding road network. Inaccurate traffic forecasts that underestimate impact can lead to future congestion, degrading local amenity and potentially requiring costly infrastructure upgrades. A well-prepared multi-trip purpose justification demonstrates professional due diligence. It gives the consent authority confidence that the development’s traffic impact has been rigorously and realistically assessed, rather than simply relying on conservative, unadjusted figures.
The Critical Role of Justification in Your Development Application
A Traffic Impact Assessment (TIA) for a mixed-use development must go beyond applying standard, high-level traffic generation rates. The primary goal is to achieve a more realistic and accurate traffic impact projection by accounting for internalised journeys. A robust justification is not merely a supplementary document; it is a critical component that can prevent council Requests for Information (RFIs) and expedite Development Application (DA) approval. This involves moving beyond default assumptions to a site-specific analysis, a principle validated by academic research on multi-purpose trip effects, which quantifies how visitors combine activities within a single location.
Reducing Infrastructure Contribution Costs
A key financial benefit of a detailed justification relates directly to infrastructure contributions. Under planning legislation, councils levy Section 7.11 (formerly Section 94) contributions based on the projected traffic impact of a development. By providing a well-researched multi-trip purpose justification, you can demonstrate lower external traffic generation. This can lead to substantial cost savings. For example, if a council contributions plan levies A$20,000 per additional peak hour trip, reducing the projected impact by just 10 trips could save A$200,000 in contributions and avoid paying for unnecessary upgrades to local intersections.
Optimising On-Site Parking and Access Design
Accurate trip data is fundamental to an efficient on-site design. A justified, lower traffic volume directly informs the car parking demand assessment, ensuring compliance with Australian Standard AS 2890.1 without over-provision. This prevents the significant capital expenditure associated with excavating and constructing surplus parking spaces. Furthermore, it allows for the appropriate design of driveways and access points, ensuring they are scaled for realistic traffic flows-not inflated theoretical maximums-thereby aligning the final design with actual, expected usage patterns.
Strengthening Your DA Against Third-Party Objections
Traffic congestion and parking availability are among the most common grounds for public and third-party objections to new developments. A TIA that relies solely on generic rates is vulnerable to challenge. In contrast, a report containing a thorough justification grounded in site-specific data and established methodologies is a robust, defensible document. It provides council planners with the technical confidence to support and approve the application, and it stands up to scrutiny in planning panels or the Land and Environment Court, demonstrating a proactive and responsible approach to traffic management.
Methodology: How We Justify Multi-Purpose Trip Reductions
Developing a parking demand assessment for a mixed-use site is a detailed analytical exercise, not a simple calculation. Our methodology is designed to be transparent, repeatable, and grounded in accepted traffic engineering principles. The objective is to produce a clear and defensible multi-trip purpose justification within the Traffic Impact Assessment (TIA) report, providing council authorities with the necessary evidence to approve a reduced parking provision.
Citing Official Guidance and Accepted Surveys
The credibility of any parking reduction argument rests on its foundation. We base our analysis on official industry documents, primarily the Transport for NSW (TfNSW) Guide to Traffic Generating Developments and relevant Austroads publications. By referencing data from these recognised transport studies and surveys, we ensure our approach aligns with industry best practice and regulatory expectations, establishing a robust framework for the assessment from the outset.
Calculating Internal Capture Rates for Mixed-Use Sites
A critical component of the analysis is quantifying ‘internal capture’. This refers to trips made between different land uses within the development that do not use the external road network. For example, a resident walking downstairs to visit an on-site retail store or cafe is an internally captured trip. We calculate these rates based on the specific mix and scale of land uses (e.g., residential, commercial, retail), as the interaction between them directly influences shared parking potential and reduces overall external traffic generation.
Presenting a Defensible Argument to Council
The final output is a logical and clearly written justification that a council assessment officer can follow and accept. Every assumption made during the analysis is explicitly stated and supported by the cited data and survey evidence. We utilise tables and diagrams to summarise complex information, presenting the results of the multi-trip purpose justification in a concise and accessible format. This meticulous approach ensures the argument is not only technically sound but also easily understood, minimising delays in the approval process.
Need a robust justification for your TIA? Contact our experts.
Common Scenarios: Where Multi-Trip Justification is Essential
Applying standard, isolated traffic and parking generation rates to each component of a mixed-use development invariably results in an over-provision of parking and an overstatement of traffic impact. A robust multi-trip purpose justification is the formal process used to accurately quantify the real-world interaction between complementary land uses. This analysis is critical in a number of common development scenarios.
Large Shopping Centres and Retail Hubs
Major retail centres are a primary example where trip chaining is fundamental to their operation. A single vehicle trip to a shopping centre can facilitate visits to multiple tenancies, such as a major supermarket, a bank, specialty retailers, and a food court. Calculating parking demand based on the sum of each individual tenancy’s requirements would grossly overestimate the necessary provision. The role of anchor tenants as primary trip generators must be correctly factored in, making this justification a standard component of any major retail Traffic Impact Assessment (TIA).
Integrated Mixed-Use Developments
The classic mixed-use model-residential apartments above ground-floor retail and commercial offices-thrives on internal trip capture. This synergy is a core design benefit that must be quantified for council assessment. Common internal trip examples include:
- Residents accessing on-site supermarkets, cafes, and services without using a car.
- Office workers utilising on-site gyms, childcare facilities, and restaurants during their lunch break.
A professional multi-trip purpose justification provides the evidence-based data required to justify a reduction in parking rates based on this efficiency, reducing construction costs and improving project viability.
Medical Centres Co-located with Other Facilities
Health and medical precincts frequently involve linked trips. For instance, a patient may drive to a facility for a GP consultation, then walk to the co-located pharmacy to fill a prescription and visit the on-site pathology clinic for tests. Without a detailed analysis, this would be incorrectly counted as three separate vehicle trips, leading to a significantly overstated traffic impact. Our extensive experience assessing medical centres demonstrates that accounting for these chained trips is essential for presenting a realistic traffic assessment and securing development approval.
If your project involves any of these complex land use interactions, a professional assessment is vital. Contact ML Traffic Engineers to ensure your parking and traffic strategy is accurate and defensible.
Partnering with an Expert for a Council-Ready Justification
Formulating a parking demand assessment for a mixed-use development is a specialist discipline within traffic engineering. The success of a Development Application (DA) often depends directly on the quality and credibility of the accompanying Traffic Impact Assessment (TIA). Submitting a poorly researched or unsubstantiated claim for reduced parking is often more detrimental than submitting none at all, as it can undermine the integrity of the entire project proposal in the eyes of council assessors.
Choosing a qualified traffic engineering consultant is therefore one of the most critical decisions in the pre-lodgement phase of your project. An expert-prepared multi-trip purpose justification is not an expense; it is a crucial investment in achieving a timely and cost-effective project approval.
Risks of an Inadequate or Unsubstantiated Claim
An attempt to reduce parking requirements without robust, professional backing exposes a development to significant commercial risks. The consequences extend far beyond a simple disagreement over parking bay numbers and can include:
- Immediate Rejection or RFIs: A weak justification is a primary trigger for a lengthy Request for Information (RFI) process from the council, halting assessment and causing delays.
- Loss of Credibility: If the traffic report is easily dismissed, council officers may scrutinise other aspects of the DA more harshly.
- Higher Contribution Costs: Councils may default to their highest parking rates, forcing developers to pay substantial infrastructure contributions or construct expensive, unnecessary parking spaces.
- Costly Project Delays: Every week a project is delayed waiting for approval has direct financial implications, impacting timelines and budgets.
The ML Traffic Approach: Data-Driven and Authoritative
ML Traffic provides the technical authority required to navigate the council assessment process successfully. Our principal engineers have over 15 years of direct experience preparing and defending parking demand assessments for complex mixed-use sites across Australia. Our approach to a multi-trip purpose justification is built on a foundation of verifiable data and accepted industry methodologies recognised by state and local government authorities.
We present our findings clearly and logically, ensuring our reports are robust, defensible, and structured for a smooth assessment. To ensure your development application is supported by an authoritative and council-ready traffic assessment, contact the principal engineers at ML Traffic.
Achieve Council Approval with a Defensible Traffic Assessment
As we’ve outlined, a well-executed justification for multi-purpose trips is not merely a technicality; it is a critical component for demonstrating the true traffic impact of your development. By accurately accounting for linked trips in mixed-use or retail centres, you can present a realistic traffic generation profile, significantly strengthening your Development Application and avoiding unnecessary council objections or infrastructure costs.
Navigating the specific requirements for a council-ready multi-trip purpose justification demands specialised expertise. At ML Traffic Engineers, our principal engineers bring over 15 years of specialised experience across Australia to every project. We have a proven track record of securing DA approvals with robust Traffic Impact Assessments because the consultant who provides the quote, does the work. This direct access ensures your project receives the senior-level attention required for a successful outcome.
To ensure your development application is built on a solid, defensible foundation, Contact ML Traffic Engineers for a Defensible Traffic Assessment Report.
Frequently Asked Questions
What is the difference between multi-purpose trips and pass-by trips?
Multi-purpose trips are internal trips made between different land uses within a single mixed-use development. For example, a resident of an apartment building walking downstairs to the on-site cafe. These trips do not add new vehicles to the external road network. Pass-by trips are made by vehicles already on the adjacent road network that choose to stop at the development en route to another primary destination. Both reduce the total new traffic generation compared to standalone developments.
Can I just apply a standard 10% reduction for my mixed-use site?
No. Applying an arbitrary reduction is not considered a robust methodology and will be rejected by most consent authorities. A defensible parking reduction requires a site-specific analysis based on the proposed land use mix, operational hours, and supporting data from recognised sources like the TfNSW (formerly RTA/RMS) guidelines or ITE Trip Generation Manual. The justification must be transparent, evidence-based, and tailored to the unique characteristics of your development to be approved by council.
Which councils in NSW or Australia are most stringent about trip justification?
Major metropolitan councils with high development density and traffic congestion are typically the most stringent. In NSW, authorities such as the City of Sydney, City of Parramatta, and North Sydney Council have rigorous assessment criteria. Similarly, major capital city councils like the City of Melbourne and Brisbane City Council require detailed, first-principles analysis to justify any proposed reduction in traffic generation or parking provision for mixed-use sites. These councils demand a high standard of evidence and justification.
How much does a multi-trip purpose justification add to the cost of a TIA report?
A detailed multi-trip purpose justification is a specialised component that adds to the base cost of a Traffic Impact Assessment (TIA). Depending on the project’s complexity and the number of land uses involved, this analysis typically adds between A$2,000 and A$5,000 to the total professional fees. This investment is often offset by significant savings in construction costs and a more efficient site layout achieved through justified parking reductions, delivering substantial value to the project.
What information do you need from my project team to begin this analysis?
To commence an accurate assessment, we require a comprehensive project brief. Key documents include current architectural plans with a detailed Gross Floor Area (GFA) schedule for each proposed land use (e.g., retail, residential, commercial). We also need the proposed hours of operation for each use and, if available, information on the intended tenant mix. This foundational data allows our senior traffic engineers to model the interaction between uses and calculate a defensible parking demand.
Is a multi-trip justification required for smaller developments?
The requirement is determined by the mix of land uses, not just the overall size of the development. Even smaller sites with complementary uses, such as ground-floor retail beneath a small office or residential component, can generate significant internal trips. If you are seeking a parking provision below the standard council rates based on this interaction, a formal multi-trip purpose justification will be necessary to satisfy the consent authority’s assessment requirements, regardless of the development’s scale.
