Software and Technical

AutoTURN is a swept path analysis software package developed by Transoft Solutions. It runs as a plugin within AutoCAD, Civil 3D, MicroStation, or as a standalone application. The user selects a vehicle from the software's library, positions it on the site layout, and uses the simulation tools to drive the vehicle through the required manoeuvre. The software calculates the vehicle's swept path in real time, showing the tyre tracks and body outline as the vehicle moves.

For UK planning applications, AutoTURN should be configured to use UK vehicle units (metres), UK vehicle standards, and the appropriate vehicle library for the application type. The software should be set up to display results in metric dimensions with scales appropriate for the output drawings. The software's UK vehicle library includes standard vehicles for residential, commercial, and construction applications validated against UK highway standards.

AutoTURN's vehicle library contains hundreds of pre-validated vehicle models organised by vehicle type (car, bus, lorry, fire engine etc.) and national standard. For UK applications, the library should be filtered to show UK vehicles. The correct vehicle is selected based on the development type and the local highway authority's requirements. If the specific vehicle needed is not in the standard library, custom vehicles can be built using the vehicle editor.

AutoTURN includes a vehicle editor that allows custom vehicles to be built from first principles using dimensional data from vehicle manufacturers. The key parameters are overall length, width, front and rear overhang, wheelbase, and turning radius or steering lock angle. Custom vehicles can be saved to a personal library for reuse. When using a custom vehicle, the dimensional data should be documented and the source referenced in the drawing.

AutoDRIVE is AutoTURN's interactive steering simulation mode, where the user moves the cursor to steer the vehicle along the desired path and the software calculates the resulting swept path. This is the most commonly used mode for swept path analysis, allowing the analyst to explore different approaches to a manoeuvre and find the optimal path. Results are captured as the swept path is traced and can be displayed and annotated on the drawing.

Path editing mode in AutoTURN allows the analyst to define a vehicle's path as a series of tangent arcs and straight sections, then calculate the swept path along that defined route. This is useful for checking whether a vehicle can follow a specific route — such as a lane centreline — and for producing smooth, reproducible swept paths. It is commonly used for checking junction turning movements and bus routes.

A simulation in AutoTURN is an automated analysis where the software calculates a vehicle's swept path along a defined route or through a defined manoeuvre without manual steering. Simulations can be run in batch mode for multiple vehicles simultaneously. They are useful for checking large numbers of similar scenarios efficiently, such as checking all bends in a road alignment or all bays in a car park.

AutoTURN swept path results are displayed as AutoCAD entities (lines and arcs) within the drawing. The drawing is exported as a PDF for submission to planning authorities and as a DWG file for sharing with the design team. Before export, the drawing should be annotated with a title block, north point, scale bar, vehicle description, drawing reference, and date. The PDF scale should be checked to ensure it is correct for reading at the expected plot size.

AutoTrack is a swept path analysis software package developed by Savoy Computing, historically the dominant UK swept path software. It runs within AutoCAD and uses a UK-focused vehicle library. AutoTrack operates on similar principles to AutoTURN — the analyst selects a vehicle and steers it through the manoeuvre interactively. The two packages produce comparable results and are both accepted by UK highway authorities.

Swept path analysis drawings should be submitted in PDF format at the specified scale (typically 1:200 for site layouts). The PDF file name should include the project reference, drawing title, and revision. Some local planning authorities also request the DWG file. The drawing should be plotted at a size that allows the paths and annotations to be clearly read — A3 or A1 are common sizes depending on the complexity of the layout.

The scale depends on the size of the site and the level of detail required. For individual plots or tight accesses, 1:100 or 1:200 is appropriate. For estate road layouts, 1:500 is common. For large commercial sites, 1:1000 may be needed. The scale should be large enough to show the vehicle positions and swept paths clearly but small enough to fit the drawing on a practical sheet size. Overly small scales make the drawings difficult to read and may not satisfy the highway authority.

A swept path analysis report is a written document accompanying the swept path drawings that explains the methodology, the vehicles and manoeuvres checked, the results, and any conclusions. Not all submissions require a formal report; many planning applications accept the drawings alone. A report is typically produced for complex developments, public inquiries, or where the analysis methodology or vehicle selection needs to be justified.

AutoTURN's standard UK passenger car model is approximately 4.7 metres long and 1.8 metres wide, with a turning circle of approximately 11–12 metres between kerbs. These dimensions represent a mid-range family car. For checking parking bay dimensions, the UK parking standards vehicle (typically 4.8 metres long and 1.8 metres wide) is often used. Different local authorities may specify different design cars, so the correct vehicle should be confirmed.

The kerb-to-kerb turning circle is the diameter of the circular path traced by the outer front tyre of a vehicle when turning at full lock in an open space. It represents the minimum circular area the vehicle needs to turn around. The kerb-to-kerb turning circle is typically smaller than the wall-to-wall turning circle (which includes the overhang of the vehicle). AutoTURN uses the kerb-to-kerb circle as the basis for its swept path calculations.

The wall-to-wall turning circle is the diameter of the circular path traced by the outermost point of the vehicle body (usually the front corner of the cab or bonnet) when turning at full lock. It is larger than the kerb-to-kerb turning circle and represents the minimum circular area needed when there are obstructions at the outer edge of the turning area. Wall-to-wall clearances must be checked when obstructions such as walls, posts, and buildings are present.

Swept path clearance is the distance between the vehicle's swept path and any obstacle such as a kerb, wall, post, or parked vehicle. The minimum acceptable clearance depends on the vehicle type and the obstacle. A clearance of 300mm is a common minimum for rigid vehicles passing a fixed obstacle; more clearance is preferable to allow for driver positioning tolerances. The highway authority may specify minimum clearance standards in their design guide.

Vehicle overhang is the part of the vehicle body that extends beyond the axles at the front and rear. Front overhang extends forward of the front axle; rear overhang extends behind the rear axle. During a turning manoeuvre, the rear overhang sweeps an arc outside the wheel track, and the front overhang sweeps an arc inside the track. These overhangs must be accounted for in the swept path analysis as they can strike obstacles that the tyres clear.

The fifth wheel is the coupling point between an articulated lorry's tractor unit and semi-trailer. The position of the fifth wheel (its distance from the rear axle of the tractor) significantly affects the trailer's swept path on a turn. A fifth wheel positioned further forward reduces the trailer cut-in; one positioned further back increases it. AutoTURN accounts for fifth wheel position in its articulated lorry models.

Trailer cut-in is the phenomenon where the rear of a semi-trailer cuts to the inside of the arc traced by the tractor unit during a turn. This means that the area immediately inside the trailer's path is swept by the rear corner of the trailer, which can collide with kerbs, vehicles, or pedestrians that are clear of the tractor's swept path. Trailer cut-in is critical in tight spaces such as loading docks and junctions. It is one of the main reasons why articulated lorry access is more demanding than rigid vehicle access.

A vehicle tracking simulation in AutoTURN or AutoTrack produces an animated or step-by-step representation of the vehicle moving through the manoeuvre. It shows the vehicle body at multiple positions along the path, illustrating how the vehicle moves through the space. Simulations are useful for understanding complex manoeuvres and for presenting the analysis to non-technical stakeholders such as planning committee members.

At a junction, a swept path drawing shows the vehicle's position as it approaches the junction, the swept path of the front and rear of the vehicle as it turns, the clearance from the opposite kerb and any pedestrian crossing features, and the vehicle's position after completing the turn. Multiple vehicles may be shown simultaneously to demonstrate that opposing traffic can pass safely during the turning manoeuvre.

A passing place is a widened section of a narrow road that allows vehicles travelling in opposite directions to pass each other. Swept path analysis for passing places checks that two design vehicles can pass simultaneously within the widened section, that the transition from the narrow road to the passing place is safe, and that the passing place is positioned correctly along the road.

To check whether two vehicles can pass each other, both vehicles are shown simultaneously on the drawing, one travelling in each direction. The combined swept paths of both vehicles must fit within the road width without overlapping. AutoTURN allows multiple vehicles to be placed on a drawing, making it straightforward to demonstrate simultaneous vehicle movements.

A static swept path shows the vehicle at a fixed position, illustrating its body dimensions and any overhang. A dynamic swept path shows the vehicle's path through a manoeuvre, illustrating the area swept during the movement. Both types of output are used in swept path analysis drawings: static positions show the vehicle at critical points such as the start and end of a manoeuvre; dynamic paths show the area swept between those points.

FTA stands for the Freight Transport Association (now Logistics UK), which has published standard vehicle specifications used in UK transport planning. FTA design vehicles are a set of standardised vehicle dimensions used as reference vehicles for checking access design. They are commonly referenced in UK highway standards and used in AutoTURN's UK vehicle library. The FTA vehicle dimensions provide a consistent basis for comparing swept path requirements across different projects.

BS EN standards are European standards adopted in the UK that specify vehicle dimensions and performance requirements. For swept path purposes, the relevant standards specify maximum legal vehicle dimensions including length, width, height, and axle loads. AutoTURN's vehicle library includes vehicles complying with EU and UK legal dimensions. Using vehicles within BS EN limits ensures that the swept path analysis reflects legally compliant vehicles that could realistically use the access.

A design vehicle is the representative vehicle used to check that access geometry is adequate. It should reflect the largest or most demanding vehicle type that will regularly use the access. For residential developments, the design vehicle for swept path purposes is typically the refuse collection vehicle or fire engine. For commercial developments, it may be an articulated lorry. The design vehicle should be confirmed with the local highway authority before carrying out the analysis.

Some highway design standards reference the 98th percentile vehicle — the vehicle that is larger than 98% of vehicles in a particular category. Using the 98th percentile vehicle as the design vehicle ensures that the access will accommodate all but the very largest vehicles in that category. This approach is more conservative than using an average or typical vehicle and is appropriate for access roads serving high-traffic commercial developments.

Good practice in AutoCAD management for swept path drawings includes using separate layers for the vehicle body, the swept path, the site layout, and annotations. Layer names should be consistent with the project's CAD standards. Using named layers allows the swept path to be frozen or turned off when it is not needed on other drawings derived from the same CAD file. AutoTURN creates its own default layers which should be renamed to match project conventions.

A reversing manoeuvre swept path shows the vehicle moving backwards through a turn or into a space. The swept path of a reversing vehicle is different from a forward-turning swept path because the front of the vehicle sweeps an arc when reversing around a corner. AutoTURN can simulate reversing manoeuvres, including articulated lorry reversing into a loading dock, which requires the trailer to be aligned first before the tractor unit can straighten.

A multi-point turn (commonly called a three-point turn or K-turn) is a vehicle manoeuvre used to reverse direction in a confined space. The swept path analysis of a multi-point turn shows each movement of the manoeuvre — forward, stop, reverse, and forward again — and confirms that all movements are within the available space without mounting kerbs or obstructions. This is used to size turning heads and hammerheads in residential layouts.

GVW stands for Gross Vehicle Weight — the maximum permissible weight of a vehicle including its load. While GVW does not directly affect the swept path (which is based on geometry not weight), the GVW of a vehicle determines whether the road surface and any structures such as bridges or weight-restricted roads can accommodate it. A heavy vehicle with a large swept path may also be restricted from certain roads due to weight limits.

Wheelbase is the distance between the front and rear axles of a vehicle. A longer wheelbase produces a larger swept path on a turn because the rear axle is further behind the front axle. For the same turning circle, a vehicle with a longer wheelbase will cut in more on a bend than one with a shorter wheelbase. Wheelbase is one of the most important parameters in determining a vehicle's swept path.

Steering angle is the angle to which the front wheels of a vehicle can be turned. A larger maximum steering angle (full lock) produces a tighter minimum turning circle and therefore a smaller swept path. Vehicles with limited steering angle — such as some heavy goods vehicles — have large minimum turning circles and may struggle with tight junctions and access layouts. AutoTURN uses the vehicle's maximum steering angle to calculate the tightest possible swept path.

The turning radius is the radius of the arc traced by a vehicle's inner rear wheel when turning at full lock. It is determined by the wheelbase and the maximum steering angle of the vehicle. The turning radius governs the minimum radius of any curved road section, roundabout, or junction that the vehicle must navigate. Swept path analysis verifies that the actual radii in the layout are adequate for the design vehicle.