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 curb 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 Center 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 center island diameter. Apron Width The Apron Width is the difference between the radius of the Apron that of the Center 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. Center Island (or simply Island) The non-traversable island at the center 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 center island to include an overrun area for large trucks. Junctions regards this overrun area as falling outside the center island.