Glossary of Terms

This is a quick reference guide to some of the terminology used in the transportation industry and within our software.

Term	Description
Active Hitch	A type of rear axle consisting of a drawbar with the bar facing rearwards linked to the front axle or articulation point (hence 'active').
Actual Wheelbase	The distance between the innermost axles on a tractor, or the distance from kingpin or drawbar pivot point to the innermost rear axle on a drawbar or semi-trailer.
Apron (or Overrun Area)	A zone provided outside the Central Island for larger vehicles to track over. Note: The Apron is considered by some standards to be a part of (i.e. within) the Central Island and by others as part of the Circulatory Width (i.e. outside the Central Island). Either way, the outer limit of the Apron is the normal offside limit for normal vehicles turning 270 degrees.
Arm	A road that connects to a junction. Known in some parts of the world as a leg.
AutoDrive	A means of driving the vehicle in which the path from a given position is calculated automatically as you move a target point (the cursor).
Authorisation code	A code needed to update the hardware lock to run each new version. May also be needed when you purchase extra features.
Axle Spacing	The distance between adjacent axles in a multi-axle group at the front or rear of a component.
Baseline	The baseline is the line that passes along the back of a row of parking bays.
Bay markings	The bay markings include the painted lines, symbols and hatching used to delineate the preferred position of the car.
Bay style	Each different composition of markings, safety zones, symbols and parking accessories is call a bay style.
Bay symbol	Bay symbols are the graphics painted within the bay and used to indicate, for example, bay usage.
Bend island	Bend islands are placed where a row of parking bays changes direction.
Blend Point	The point on a junction arm alignment at which it joins, or blends with, the existing road.
Castor Steering	Wheels that are part of a fixed axle group but that are free to rotate. Sometimes referred to as self-steered wheels.
Cats Whiskers	See Predictive Turning.
Central Island (or simply Island)	The normal offside limit (possibly kerbed) for vehicles turning 270 degrees. Note: In some standards there may be an Apron within the Central Island. AutoTrack treats the Central Island as the limit of turning for all vehicles if there is no apron or te apron is defined outside the island and as the limit for normal sized vehicles if there is an apron defined inside the island.
Circulatory Width	The Inscribed Circle radius minus the Island radius. Note: The preferred physical vehicle path limit will typically be inside this.
Cramp Angle	A term (seemingly used only by US fire departments) for the maxium wheel angle. See also 'Wheel Cut'.
Cut-in Point	The point at which the spine of the element is tangential to the arc that it transcribes.
Cut-in Radius	The radius of the arc traversed by the Cut-in Point.
Definition Line	A virtual line representing a roadway limit. The physical Kerb Line may or may not coincide with this line.
Dongle	Slang name for a Hardware Lock.
Drag Lines	Lines drawn from the grips used to extend the path to the front most and rearmost grips on the vehicle. These lines vary in length according to the vehicle size and can be switched off.
Drawbar	A rigid towing bar attached rigidly to an axle. The bar and axle turn as one unit.
Drawbar Articulation Angle	The angle subtended at the axle pivot of a drawbar by the drawbar and associated trailer spine.
Drawbar Length	The length of a drawbar is measured from the centre of turning of the relevant axle group to the physical end of the drawbar. The coupling at the remote end must be defined separately in AutoTrack.
End island	End islands are non-parking areas placed at the ends of rows of parking bays.
DXF File	DXF stands for Drawing Exchange Format, a text file format used to transfer data between dissimilar CAD systems. Supported by many CAD systems.
Dynamic Edit	See Dynamic Editing.
Dynamic Editing	Editing a path by dragging the grips at target points (and / or intermediate points) to new locations. The path updates automatically when the grip is dropped.
Effective Fixed Axle	The effective fixed axle is the single axle that would have the same effect on the vehicle swept path as the fixed axle group. It is the centroid of the group after the effects of retracted and self-steered axles are taken into account.
Effective Front Axle Offset	The offset of the effective front axle from the reference datum. Positive if the effective axle position is behind the reference datum.
Effective Front Track Width	The distance between outer faces of the front wheels to be used in path calculations.
Effective Rear Axle Offset	The offset of the effective rear axle from the reference datum. Positive if the effective axle position is behind the reference datum.
Effective Rear Track Width	The distance between outer faces of the rear wheels to be used in path calculations.
Effective Steered Axle	The effective steered axle offset is the single axle that would have the same effect on the vehicle swept path as a given steered axle group. It is the outermost axle of the steered axle group, i.e. the furthest forward on a front axle group and the furthest back on a rear axle group.
Effective Wheelbase	The distance between the Effective Front and Rear Axles.
Envelope	A single line representing the maximum body or wheel movement. In the case of vehicle bodies it is the outer limit of movement of any point on any body. In the case of wheels it is the outer limit of travel of any wheel.
Exit Overturn	An exit overturn is when a vehicle continues past the point at which it would normally start the turn (i.e. delays the start of the turn) prior to turning back and exiting the turn. The lateral deviation from the normal path is the exit overturn distance.
Fastest Line	The Fastest Line is the centreline of the path taken by a vehicle travelling as fast as possible through the junction. It is defined by various standards in different ways but usually there is a minimum offset from the apex of the path at entry, exit and island. There are also often specified starting and ending positions.
Fifth Wheel	A horseshoe shaped coupling device on a tractor that connects to a pin on a semi-trailer called a kinpin.
Flare Lane	An extra lane added at the entry to a roundabout used to manage vehicle movements.
Follow	A means of driving a vehicle in which you specify a required path as a polyline and let the vehicle attempt to follow it.
Grips	Small squares that appear when an object is selected. Grips can be selected and moved using the mouse.
Hairpin marking	A type of parking bay marking comprising twin sidelines connected at the entrance.
Hardware Lock	A hardware lock or dongle is a security device that must be plugged into the parallel port of your computer to allow AutoTrack 5 to run.
Head up display	A display of data that the user can see without diverting his or her gaze from the task in hand.
HUD	See Head up display.
In bay numbering	In bay numbering is when bay numbers are placed within each marked parking bay.
Independent Bogies	Multiple linked bogies arranged along a unit each with their own turntable. Also known as Tandem Axles. See also Pendel Axles.
Inscribed Circle	The Definition Line representing the outer limit of the Circulatory Width.
Intermediate Grips	Transient editing grips that are displayed along the path between Target Points to make path editing easier. An Intermediate Grip becomes a Target Point if it is selected.
Kerb Line	A line representing the roadside edge of the physical kerb.
Kerb Offset	The distance that the Kerb Line is offset (outside) the Definition Line.
Kerbside numbering	Kerbside numbering is when the bay numbers are placed adjacent to the bay.
Kerb-to-Kerb Turning Circle Radius	The radius of the smallest circle within which the vehicle's wheels can turn. It is assumed that this occurs when full steering lock is applied.
Kingpin	A pin on a semi-trailer that connects to a horseshoe shaped coupling device on a tractor called a fifth wheel.
Lane Line	A line between lanes of traffic travelling in the same direction.
Layer	A means of grouping objects together within an AutoCAD drawing. The properties of layers (e.g. visibility) may be controlled independently of the objects they include. See also Level, the equivalent in MicroStation.
Level	A means of grouping objects together within a MicroStation drawing. The properties of layers (e.g. visibility) may be controlled independently of the objects they include. See also Layer, the equivalent in AutoCAD.
Linkage Proportion	The linkage proportion is the proportion of the articulation or wheel angle at one end of a unit that is applied to the axle group at the other end. The proportion may be specified in terms of angles or tangents of angles. In arithmetic terms if the linkage is on an angular basis the linkage proportion would be:- LinkageProportion = LinkedAngle/PrimaryAngle If the linkage is on a tangential basis the linkage proportion would be:- LinkageProportion = tan(LinkedAngle)/tan(PrimaryAngle) We understand that the latter is the more common form of linkage and in this case the effective cut in point offset is fixed for all primary angles.
Loci	The plural of locus. See Locus.
Lock	Steering angle; thus, maximum left lock is the maximum steering possible when turning left and right lock is the maximum when turning right.
Lock to lock time	Lock-to-lock time is the time that it takes the driver of the vehicle to turn the steering from the maximum angle (full lock) in one direction to maximum angle (full lock) in the opposite direction in a single continuous movement.
Locus	The path of a moving point in space. In the context of AutoTrack the path of the wheel tracks or the body vertices. Referred to in AutoTrack in it's plural form loci.
Manual Drive	A means of driving a vehicle that uses a control overlay displayed on screen. The vehicle moves forwards, reverse, left and right according to the position of the cursor on the control overlay.
Maximum Drawbar Articulation Angle	The largest Drawbar Articulation Angle permitted.
Maximum Wheel Angle	The maximum angle of any wheel in a group, i.e. at the front or at the rear. This is normally the inside wheel on the innermost axle but may be otherwise if the widths of the axles in the group vary. See alse 'Cramp Angle' and 'Wheel Cut'.
Minimum Cut-in Radius	The radius of the arc traversed by the Cut-in Point when the vehicle is turning at the Maximum Steering Angle.
Model Settings	The criteria that control the how a specified vehicle should behave in a specific situation. For example, a lower limit might be placed on the allowable lock rate.
Object enabler	An AutoCAD add-on that allows third party entities, like AutoTrack path entities, to be regenerated but not edited.
Offset Envelope	The envelope of maximum body or wheel movement with a further margin added. This may represent a safety or clearance margin.
Overrun Area	See Apron.
Overturn	A technique for reducing the vehicle cut-in on corners whereby the vehicle either turns temporarily in the opposite direction (side overturn) or delays the exit from the turn (exit overturn).
Overturn angle	When performing an overturn (side or exit) the overturn angle is the angular deviation of the wheels from the path the same vehicle would take if performing a non-overturn manoeuvre.
Pendel Axles	Multiple linked bogies arranged both across and along a unit that turn in much the same manner as Ackerman axles, i.e. those axles furthest away from the centre of turn follow the widest radius arc.
Predictive Turning	Predictive Turning is an AutoDrive feature that displays the limits of the vehicle path from the last position placed and the limits of body or wheel envelope from the ghosted unselected position. Also known as ÒCat's WhiskersÓ.
Primary Axle	The innermost axle of a group, i.e. the rearmost axle of a front axle group and the front most axle on a rear axle group.
Privacy post	Privacy posts are used to prevent use of parking bays by unauthorized personnel.
Rail wheels	Wheels designed to run on rails typically with an inner flange to prevent the wheel from derailing.
Retracted Axle	An axle that is present but not in contact with the road surface. Retracted axles are ignored when AutoTrack calculates the effective axle positions.
Safety post	Safety posts may be placed at the ends of parking bays to prevent vehicles from overshooting.
Safety zone	Safety zones are areas of extra space provided to meet special requirements and are measured from the centres of the bay side and entrance lines.
Script	A means of driving a vehicle by issuing commands such as; forwards 10 metres, turn left 30 degrees, continue for 5 metres.
Secondary steering	A turning axle group whose angle is controllable but which is not the main steering for the vehicle. The axle may be linked to another axle or independently controllable.
Secondary steering angle	The angle of an imaginary wheel at the centre of a secondary steering axle. See Secondary Steering.
Self-steering	Wheels that are part of a fixed axle group but that are free to rotate. Sometimes referred to as castors.
Separator Line	A line between lanes of traffic travelling in opposite directions.
Service type	The different usages of parking areas are called service types.
Side Overturn	A side overturn is when a vehicle starts a turn with opposite lock for a short distance prior to making the turn. The lateral deviation from the normal path is the side overturn distance.
Splitter	The splitter is formed by the boundaries of the entry and exit roadway Definition Lines and the Inscribed Circle.
Splitter Island	The Splitter may include a Splitter Island, especially if there are pedestrian crossings. The physical limits of the Splitter Island are normally inside the Splitter.
Steering Angle	The angle of an imaginary wheel at the centre of the controlling axle or coupling.
Stub axle	An axle carrying wheel(s) at only one end.
Stub axle length	The length of a stub axle is measured from the pivot point to the centre of the wheel group.
T-markings	A type of parking bay marking consisting of a T painted at the entrance between each adjacent parking bay . The leg of the T runs a short distance down the side of the bay and the cross runs part way along the entrance line.
Tandem Axles	See Independent Bogies.
Target Point	A point through which the vehicle must travel.
Tracking Point	The Tracking Point is the point on the vehicle that must pass through the specified Target Points. It is the point on the vehicle that you move and position when you use AutoDrive and also the point that follows the line in the Follow drive mode.
Tyred Wheels	Wheels with tyres fitted.
Vehicle class	Vehicles using parking areas are grouped into classes; vehicles with similar parking requirements.
Wall-to-Wall Turning Circle Radius	The radius of the smallest circle within which the vehicle's body can turn. It is assumed that this occurs when full steering lock is applied.
Wheel Cut	A term (seemingly used only by US fire departments) for the maxium wheel angle. See also 'Wheel Cramp'.
Wheel Diameter	The diameter of the outer face of the tyre.
Wheel stop	Wheels stops are placed at the ends of bays to prevent the vehicle from overshooting.
Wheel Track	The distance between the outer faces of the wheels on an axle.

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