Glossary of Terms

270 Degree Turn Path Radius
The minimum radius of the fastest vehicle path of a vehicle performing a 270 degree turn, i.e. a right turn for vehicles driving on the left or a left turn for vehicles driving on the right.
270 Degree Turn Path Speed
The speed that corresponds to the 270 Degree Turn Path Radius.
90 Degree Turn Path Radius
The minimum radius of the fastest vehicle path of a vehicle performing a 90 degree turn, i.e. a left turn for vehicles driving on the left or a right turn for vehicles driving on the right.
90 Degree Turn Path Speed

The speed that corresponds to the 90 Degree Turn Path Radius.

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.
Approach Gradient Over 50m
The average gradient over the last 50m of an approach to a roundabout.
Approach Half Width
The width of the approach road, measured at a point in the approach upstream from any entry flare, from the median line to the nearside kerb line.
Approach Stopping Sight Distance
The required line of sight on approaching a roundabout. The approaching driver must be able to see a point on the yield line or the crossing from point far enough back that he can stop if necessary.
Apron
The Apron, or Overrun Area, is a zone provided outside the Centre Island for larger vehicles to track over. The outer limit of the Apron is the offside limit for normal vehicles turning 270 degrees.
Note: In some parts of the world (notably the USA) the apron is considered to be a part of the island, in others (notably the UK) it is considered to fall between the island and the main circulation area. In Junctions the apron is considered to fall outside the central island, i.e. the apron diameter may never be smaller than the island radius.
Apron Diameter
The diameter of the Apron, or overrun, area. The apron diameter is never smaller than the centre island diameter.
Apron Width
The Apron Width is the difference between the radius of the Apron to that of the Centre Island. It may never be less than zero.
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).
Axle Spacing
The distance between adjacent axles in a multi-axle group at the front or rear of a component.
Backward Visibility on Entry
Visibility to the right on entry to a roundabout when driving on the left or to the left on entry to a roundabout when driving on the right.
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.
Centre Island (or simply Island)
The non-traversable island at the centre of a roundabout which is the normal offside limit for vehicles turning 270 degrees.
Note: Some parts of the world (notably the USA) consider the centre island to include an overrun area for large trucks. Junctions regard this overrun area as falling outside the centre island.
Centreline Offset
The perpendicular distance between the tangent to the arm alignment at the ICD and the centre of the island. The offset is positive if the tangent passes the centre of the island on the opposite side to the entry road. Thus, in general, the larger the centreline offset the larger the entry deflection, and vice versa.
Circulating Path Radius
The minimum radius of the fastest vehicle path around the centre island.
Circulating Path Speed
The speed that corresponds to the Circulating Path Radius.
Circulatory Carriageway Median
The path of a vehicle travelling midway between the inscribed circle and the centre island.
Circulatory Width
The Inscribed Circle radius minus the Island radius.
Note: The preferred physical vehicle path limit will typically be inside this.
Conflict Angle
See Entry Angle.
Cramp Angle
A term, seemingly used only by US fire departments, for the maximum wheel angle. See also Wheel Cut.
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.
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 that represents a carriageway limit. The physical Curb Line may or may not coincide with this line.
Distance to Next Arm
The Distance to Next Arm is the straight line distance from the offside end of the give-way line on the current arm to the nearest point of the median marker or island (whichever is nearest) on the next arm after that.
Drag Lines

Lines drawn from the frontmost and rearmost grips on the vehicle that may be used to extend the path. 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 or group of axles. The bar and axles turn as a single entity around a kingpin linking them to the body of the 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 Vehicle Tracking.
DXF File
DXF stands for Drawing Exchange Format, a text file format used to transfer data between dissimilar CAD systems.
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 Flare Length

The Effective Flare Length is the distance l’ in the diagram below.

Note: The Effective Flare Length used by ARCADY for the analysis of mini-roundabouts is the average effective flare length, constructed in the same way as for standard roundabouts but using the MINIMUM approach road half-width instead of the approach road half-width.
Effective Front Axle
A single axle that is equivalent in effect to the actual front axle group defined.
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
A single axle that is equivalent in effect to the actual rear axle group defined.
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 Axle and the Effective Rear Axle.
End Island
End islands are non-parking areas placed at the ends of rows of parking bays.
Entry Angle
The entry angle or conflict angle, F (phi), is a geometric proxy for the angle between entering and circulating streams. It is calculated in one of two ways depending upon whether the entry and exit tangents intersect with respect to the median circulation path.

When the entry and exit tangents intersect ‘inside’ the circulatory carriageway median, the entry angle is the angle between the entry tangent and the tangent to the circulatory carriageway median at the intersection point.

When the entry and exit tangents intersect ‘outside’ the circulatory carriageway median, the entry angle is half the angle between the entry and exit tangents.

Entry Corner Kerb Line Distance
The Entry Corner Kerb Line Distance is the length of the entry corner kerb line, measured from a point on the entry kerb from which a perpendicular would be raised to the offside end of the give-way line, to a point further along the kerb from which a perpendicular would be raised to the offside end of the exit width measurement on the next arm clockwise.
Entry Deflection
The extent to which a vehicle must deviate from a straight line path to negotiate the entry to the roundabout.
Entry Path Radius
The minimum radius of the fastest vehicle path at, or close to, the entry yield line. See also Maximum Entry Path Radius.
Entry Tangent
The tangent to the path of an entering vehicle at the intersection of the entry path and the yield line.
Exit Path Radius
The minimum radius of the fastest vehicle path at, or close to, the exit.
Entry Path Speed
The vehicle speed that corresponds to the Entry Path Radius.
Exit Path Speed
The speed that corresponds to the Exit Path Radius.
Exit Tangent
The tangent to the path of an exiting vehicle at the intersection of the exit path and the ICD.
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 kingpin.
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.
Forward Circulatory Visibility
Visibility around the circulation area.
Forward Fastest Path Visibility
Visibility from an entering vehicle on the fastest path to the conflict point on the fastest entry path from the next arm.
Forward Visibility on Entry
Visibility to the left on entry to a roundabout when driving on the left or to the right on entry to a roundabout when driving on the right.
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.
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.
Junction Sight Distance
Visibility to traffic entering from the previous arm and/or traffic already circulating.
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 Vehicle Tracking the path of the wheel tracks or the body vertices. Referred to in Vehicle Tracking in its 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 Entry Path Radius
The maximum radius that can be drawn tangential to the road alignment at the fastest path start offset and tangential to the offset circle in the circulatory area. See also Entry Path Radius.
Maximum Entry Path Speed
The speed that corresponds to the Maximum Entry Path Radius.
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 also Cramp Angle and Wheel Cut.
Minimum Approach Half Width
The smallest Approach Half-Width, measured anywhere within the final 100 meters of the approach.
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 how a specified vehicle should behave in a specific situation. For example, a lower limit might be placed on the allowable lock rate.
Nearside
The side closest to the passenger in a standard passenger car designed for the region.
Object enabler
An AutoCAD add-on that allows third party entities, like Vehicle Tracking 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.
Offside
The side closest to the driver in a standard passenger car designed for the region.
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.
Pegasus Crossing
See Signalised Pedestrian/Equestrian Crossing.
Pelican Crossing
See Signalised Pedestrian Crossing.
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 "Cat’s Whiskers".
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 unauthorised personnel.
Profile
A profile is a Vehicle Tracking object that lets you display a side or plan view of a vehicle complete with dimensions.
Profile View
A profile view is an AutoCAD Civil 3D object that lets you display ground profiles as graphed lines on a grid. For more details please refer to the AutoCAD documentation.
Puffin Crossing
See Signalised Pedestrian Crossing.
R1
See Entry Path Radius.
R1 Max
See Maximum Entry Path Radius.
R2
See Circulating Path Radius.
R3
See Exit Path Radius.
R4
See 270 Degree Turn Path Radius.
R5
See 90 Degree Turn Path Radius.
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 Vehicle Tracking 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 which 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.
Signalised Pedestrian Crossing
A pedestrian crossing that has signals to stop the traffic. The signals may use detectors to automatically change the lights when pedestrians approach or there may be explicit pedestrian controls. The detector type is known in the UK as a Puffin crossing and the non-detector type as a Pelican crossing.
Signalised Pedestrian/Cycle Crossing
A crossing designed specifically for pedestrian or cycle access that uses signal controls to stop the traffic. Known in the UK as a Toucan crossing.
Signalised Pedestrian/Equestrian Crossing
A crossing designed specifically for pedestrian or equestrian access that uses signal controls to stop the traffic. Known in the UK as a Pegasus crossing.
Splitter
The splitter is formed by the boundaries of the entry and exit carriageway 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.
Toucan Crossing
See Signalised Pedestrian/Cycle Crossing.
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.
Tired Wheels
Wheels with tyres fitted.
Un-signalised Pedestrian Crossing
A pedestrian crossing with no signal controls. Known more commonly in the UK as a Zebra crossing.
V1
See Entry Path Speed.
V1 Max
See Maximum Entry Path Speed.
V2
See Circulating Path Speed.
V3
See Exit Path Speed.
V4
See 270 Degree Turn Path Speed.
V5
See 90 Degree Turn Path Speed.
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 maximum wheel angle. See also Cramp Angle.
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.
Zebra Crossing
See Un-signalised Pedestrian Crossing.