Swept Path Analysis: When Councils Demand It and Why It Pays

There is a moment on many NSW projects when a design that looked resolved suddenly is not: the council engineer asks for swept path analysis, the turning templates go over the basement ramp, and the B99 vehicle clips a column, a wall, or the boundary. Now the basement needs replanning, the parking count drops, and the DA clock keeps running.

Swept path analysis — the computer simulation of the space a vehicle actually occupies while turning — is one of the cheapest pieces of engineering on a project and one of the most expensive to skip. This article explains what it is, when NSW councils demand it, which design vehicles matter, and how running the checks early protects the two most vulnerable parts of any urban project: the basement and the driveway. It is written by the team at Sweptpaths, the traffic engineering consultancy within the Rouse Hill–based Contrive group.

What swept path analysis actually is

When a vehicle turns, its body sweeps a wider envelope than its wheelbase: the front overhang swings outside the front wheels’ path, and the rear wheels track inside the front wheels (“cut-in”). Swept path analysis uses specialised software to drive a specific design vehicle — with its real dimensions, steering geometry and turning behaviour — through your proposed layout, and plots the envelope of body and wheel paths over the drawings.

The output is a set of swept path plans showing, unambiguously, whether the vehicle can perform each required movement: enter from the street, descend the ramp, turn into the aisle, park, and leave — usually in a forward direction — with the clearances the standards require. It replaces guesswork and “looks about right” with demonstrated geometry, which is exactly why assessing engineers ask for it.

The design vehicles that drive your layout

Swept path analysis is always run for nominated design vehicles, and choosing the right ones is half the job. In NSW work the usual cast includes:

B85 car — the “85th percentile” passenger car used for general parking manoeuvres under AS 2890.1, the Australian Standard for off-street car parking.
B99 car — the larger 99.8th percentile car, used where a single failure is unacceptable: critical accessways, blind aisles, and situations where a vehicle cannot reasonably back out. Many councils require B99 checks on basement ramps and tight driveways.
Vans and service vehicles — courier and trade vehicles for loading areas.
Small and medium rigid vehicles (SRV/MRV) — under AS 2890.2 for commercial vehicle areas: removalist trucks, delivery vehicles, small waste vehicles.
Heavy rigid vehicles (HRV) and waste collection vehicles — councils typically specify their own waste vehicle dimensions; if the truck enters the site, it must be simulated.
Fire appliances and emergency vehicles — where required for access to buildings or through estates.
Articulated vehicles and B-doubles — for industrial subdivisions, warehouses and loading docks.

The design vehicle question is where projects most often understate their needs: a childcare centre that forgot the linen delivery van, an apartment building whose waste contractor runs a bigger truck than the plan assumed, an industrial unit whose tenants’ 19-metre semis were “someone else’s problem”. Confirm the realistic largest vehicles for each function first, then design for them.

When NSW councils demand swept path analysis

There is no single statewide trigger — requirements sit in council DCPs, in assessment practice and in the standards themselves — but the situations are predictable. Expect to need swept path plans when your project includes any of the following:

Basement or undercroft parking. Ramp entry and exit from the street, internal circulation, movements into and out of critical spaces, and turning bays where dead-end aisles require them.
On-site waste collection. If the collection vehicle enters the site — as it must on most apartment and many townhouse projects — councils want proof it can reach the collection point and leave in a forward gear. This pairs directly with the waste management plan our Contrive Consultants colleagues prepare.
Loading docks and service areas for commercial, industrial and mixed-use projects, assessed against AS 2890.2.
Tight or constrained driveways — battle-axe lots, shared driveways serving multi-dwelling housing, narrow frontages, and corner sites with awkward entry angles.
Childcare centres, medical centres and other traffic-generating uses where pick-up/drop-off areas must demonstrably work.
Subdivision road networks — cul-de-sac heads sized for waste and fire vehicles, intersection geometry, and bus route checks.
Works on or near the public road — new driveways on classified roads, or anywhere Transport for NSW is a referral authority.

Even where a council does not explicitly demand it, a competent assessing engineer will test doubtful geometry with templates — so the practical rule is simpler: if a reasonable person would wonder whether the vehicle fits, submit the swept paths before being asked.

How swept path analysis saves your basement

Basements are where swept path failures cost the most, because every dimension is structural. The ramp grade transitions, the column grid, the aisle widths and the core location are all locked together; discovering a turning failure after structural design means expensive rework. The recurring rescue scenarios:

Ramp/street interface. The B99 entering from the kerbside lane while another car waits to exit — checked early, this sizes the ramp width and splay geometry correctly; checked late, it can require moving the ramp, which moves everything.
Column placement. A column 300 mm further along the grid can be the difference between a compliant turn into the end space and a dead parking bay. Running swept paths during structural coordination keeps every space usable — and parking counts are yield.
Blind-aisle turnaround bays. Where vehicles cannot exit in reverse to the street, a turning bay must genuinely work for the B99, not just appear on plan.
Grade changes and scraping. Alongside plan geometry, ground clearance checks along the ramp profile catch designs that would scrape long-wheelbase cars at grade transitions — an AS 2890.1 check that is far cheaper in design than in defect claims.

The same logic protects driveways on smaller projects: a dual occupancy with a narrow shared driveway, a townhouse row where visitors must pass a parked car, or a steep frontage where the driveway profile, checked against the surveyed kerb levels, determines whether cars bottom out. Small jobs fail geometry just as readily as big ones — they just fail cheaper, provided someone checks.

Timing: when to run the analysis

The value of swept path analysis is inversely proportional to how late it happens.

Concept design: quick-pass checks on ramp location, aisle layout and waste servicing strategy. This is where whole design approaches get validated or discarded at minimal cost.
DA documentation: the formal swept path plans submitted with the traffic report and waste management plan, covering every movement council will question.
RFI response: the reactive case — still valuable, but by now changes are costly. Most of our rescue work happens here, re-planning basements that were never geometry-checked.
Construction documentation: re-verification after structural and services coordination moves columns, hydrants or bulkheads.

Within the Contrive group, the traffic engineers at Sweptpaths sit alongside the architects at ARQI and the civil team at Contrive Consultants, so ramp grades, driveway levels and vehicle geometry are reconciled in design coordination rather than discovered in assessment. That integration is the difference between swept paths as insurance and swept paths as ammunition for an RFI.

Frequently asked questions

Do I need swept path analysis for a duplex or dual occupancy?

Often, yes — particularly for shared or narrow driveways, battle-axe access, corner lots or steep frontages. Councils increasingly ask for turning and, on steep sites, ground clearance checks even on small projects. The analysis is quick and inexpensive at this scale, and it prevents the genuinely awkward outcome of an approved dwelling whose residents cannot comfortably get a car in.

What is the difference between B85 and B99 vehicles?

They are the two standard design cars from AS 2890.1: the B85 represents the 85th percentile Australian passenger car and is used for routine parking manoeuvres; the larger B99 (99.8th percentile) is used for critical movements where failure is unacceptable, such as basement ramps and layouts where a vehicle cannot reasonably reverse out. Councils commonly expect B99 checks on accessways and B85 checks into parking spaces.

Council asked for waste vehicle swept paths — what do they want to see?

Simulation of the council’s (or contractor’s) nominated collection vehicle entering the site, travelling to the collection point, standing to load, and leaving in a forward direction, with acceptable clearances throughout. Height clearances to basement entries and awnings, pavement adequacy and grades come with the package. The swept path plans should match the waste management plan exactly — mismatched documents are an RFI classic.

Can swept path analysis recover a failing design without losing car spaces?

Frequently. Failures are often localised — one column, one tight splay, one ramp width — and targeted adjustments recover compliance without losing yield. That is the real payoff of doing the analysis with designers in the room: the software shows precisely where the envelope fails, so the fix can be surgical rather than wholesale.

Check the geometry before council does

Sweptpaths (sweptpaths.com.au) provides swept path analysis, parking and traffic advice for developments across NSW as part of the Contrive group in Rouse Hill — coordinated with civil, waste, architectural and planning services under one roof. Browse the group’s services or contact us before your layout is locked: +61 497 848 111, info@contriveconsultants.com.au.