VISUALLY COLLAPSIBLE REPRESENTATION OF AN INTERSECTION

Abstract: Method and apparatus for representation of a route to be travelled by a vehicle through an intersection. The route is displayed in a visually collapsed (VC) representation in which the amount of detail shown varies with the direction of approach to, the direction of departure from, and the manoeuvre(s) required to pass through, the intersection. In some situations, an intersection is separated in VC format into two or more perceived intersections that are spaced apart a great distance. Examples of four-way intersections, T-intersections, roundabouts, unusual left turn configurations, crossovers and other patterns are presented to illustrate how a particular intersection would be displayed in a representative VC format.

Description: - 1 - VISUALLY COLLAPSIBLE REPRESENTATION OF AN INTERSECTION This invention relates to accurate representation on a graphical or other display of an intersection of two or more road segments in vehicle navigation. A road network used for vehicle navigation purposes includes at least two types of navigation entities : a plurality of road segments or "links" on which a vehicle may travel in a given region; and one or more intersections or "nodes" at which two road segments come together or cross each other, at which a vehicle operator may have to make a decision and execute a simple or complex manoeuvre in order to pass through the intersection and continue on a chosen vehicle route. As a vehicle approaches a simple intersection, such as a standard four-way intersection with one lane devoted to traffic in each direction, as shown in Figure 1, the operator's choices are simple and limited: (1) continue in a "straight-through" direction; (2) turn left at the intersection; and (3) turn right at the intersection. If the intersection is made more complex, for example, by including additional turn lanes on a road segment on which the vehicle now moves or by including a roundabout at the intersection, execution of correct manoeuvres to pass through the intersection becomes more difficult, especially if the operator is not familiar with this road configuration. The operator will often require some visually perceptible or audibly perceptible prompting before the vehicle reaches the intersection. A map database can provide such visual and/or audible prompting, but if the intersection information is provided in its full complexity, the operator may either misunderstand or misapply the manoeuvres required or may become bewildered and have to stop to study the instructions, or to match what is on the screen with what is visible through the front windshield, - 2 - before passing through the intersection. If the intersection display is too simple, the operator may miss a crucial manoeuvre . What is needed is a graphical representation system for different types of intersections that includes only the important details required to allow the vehicle to pass through the intersection and continue on the chosen route, and that represents the intersection configuration and the required manoeuvres in a visual and/or audible manner that is simple enough that the operator can usually comprehend the manoeuvres with no more than a few seconds observation or a quick glance. Preferably, the details shown should vary with the route through the intersection. The present invention provides a system that (1) receives information on a vehicle's present location, (2) determines a road segment on which the vehicle now travels and the present direction of vehicle travel, (3) identifies a node or intersection that the vehicle will next encounter if the vehicle continues to move on the present road segment in the present travel direction, (4) receives information from a database that displays this next-encountered intersection in a "visually collapsed" or "VC" representation in a visually perceptible or audibly perceptible manner. The visually collapsed representation provides a selected level of detail required for the vehicle to pass through the intersection, and this level of detail optionally varies with the vehicle manoeuvres required and/or with the direction of vehicle approach to and departure from the intersection. As a vehicle approaches an intersection, or a series of closely spaced intersections, the system answers two questions for the vehicle operator: (1) Is a manoeuvre, such as a turn or lane change, needed at this intersection and (2) If the answer to question (1) is "yes," what is the manoeuvre or sequence of manoeuvres required to move through the intersection? - 3 - A node is a junction of two or more road segments at a single location, and an intersection, as used herein, is a collection of adjacent nodes (one or more) and connecting road segments that can or should be perceived as part of a closely related set. An intersection may consist of two or more nodes that are spaced apart by a positive distance d, where d is not too large. An intersection is representable in a "visually collapsible" (VC) format if, from any approach passing through the intersection from any direction, an operator of a vehicle visually perceives passage through the intersection as a single continuous manoeuvre. Representation of an intersection in a particular VC format may depend upon the direction of approach to, the manoeuvre (s) required to pass through, and the direction of departure from, the intersection. An intersection (i.e., a collection of adjacent nodes) that is not visually collapsible may be expressible as the sum of two or more separate perceived intersections, each of which is visually collapsible, where each perceived intersection optionally includes a mutually exclusive collection of closely spaced nodes . The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1A is a schematic view of a standard four-way intersection that might be encountered by a vehicle, with a conventional amount of detail; Figures IB, 1C, ID and IE represent the intersection in Figure 1A, showing direction of approach to, and several directions of departure from, the intersection; Figure 2A is a schematic view of a diverging Y- intersection, with a conventional amount of detail; Figures 2B and 2C represent the intersection in Figure 2A in a VC geometry, showing direction of approach to, and several directions of departure from, the intersection; Figure 3A is a schematic view of a converging Y- intersection, with a conventional amount of detail; Figures 3B, 3C and 3D represent the intersection in Figure 3A in a VC geometry, showing several directions of approach to, and several directions of departure from, the intersection; Figure 4A is a schematic view of an angularly oriented T-intersection, with a conventional amount of detail; Figures 4B represents the intersection in Figure 4A in a VC geometry, showing directions of approach to, and several directions of departure from, the intersection; Figure 5A is a schematic view of a T-node with two displaced, angularly oriented T-nodes and a Y-node, with a conventional amount of detail; Figure 5B represents the intersection in Figure 5A in a VC geometry. Figures 5C, 5D, 5E and 5F are schematic views of the intersection in Figure 5A, decomposed into separate perceived intersections; Figure 6A is a schematic view of a T-node on a curved base, with a conventional amount of detail; Figure 6B represents the intersection in Figure 6A in a VC geometry; Figure 7A is a schematic view of an intersection consisting of a four-way node plus a laterally displaced, angularly oriented T-node, with a conventional amount of detail; Figure 7B represents the intersection in Figure 7A in a VC geometry. Figures 7C, 7D and 7E are schematic views of the intersection in Figure 7A, decomposed into separate perceived intersections; Figure 8A is a schematic view of an intersection consisting of a four-way node and a laterally displaced T- node, with a conventional amount of detail; Figure 8B represents the intersection in Figure 8A in a VC geometry; - 5 - Figures 8C and 8D are schematic views of the intersection in Figure 8A, decomposed into separate perceived intersections; Figure 9A is a schematic view of an intersection that includes a first variety of left turn crossover, with a conventional amount of detail; Figure 9B represents the intersection in Figure 9A in a VC geometry; Figures 9C and 9D are schematic views of the intersection in Figure 9A, decomposed into separate perceived intersections; Figure 10A is a schematic view of a four-way intersection that includes a second variety of left turn crossover, with a conventional amount of detail; Figure 10B represents the intersection in Figure 10A in a VC geometry; Figures IOC, 10D and 10E are schematic views of the intersection in Figure 10A, decomposed into separate perceived intersections; Figure 11A is a schematic view of an intersection that includes a first variety (circular or semicircular) of roundabout with tributaries, with a conventional amount of detail; Figure 11B represents the intersection in Figure 11A in a VC geometry; Figures 11C, 11D, HE and 11F are schematic views of the intersection in Figure HA, decomposed into separate perceived intersections; Figure 12A is a schematic view of an intersection that includes a second variety (polygonal) of roundabout with tributaries, with a conventional amount of detail; Figure 12B represents the intersection in Figure 12A in a VC geometry; Figures 12C, 12D, 12E, 12F and 12G are schematic views of the intersection in Figure 12A, decomposed into separate perceived intersections; - 6 - Figure 13A is a schematic view of an intersection that includes a five-way node plus a first angularly oriented diagonal connecting two of the adjacent approach roads plus a second angularly oriented diagonal as part of the five-way node, with a conventional amount of detail; Figure 13B represents the intersection in Figure 13A in a VC geometry; Figures 13C, 13D, 13E and 13F are schematic views of the intersection in Figure 13A, decomposed into separate perceived intersections; Figure 14A is a schematic view of an intersection that includes a four-way node with road dividers and left turn lanes plus four right turn diagonals connecting pairs of adjacent approach roads, with a conventional amount of detail; Figure 14B represents the intersection in Figure 14A in a VC geometry; Figures 14C, 14D, 14E, 14F and 14G are schematic views of the intersection in Figure 14A, decomposed into separate perceived intersections; Figure 15A is a schematic view of an intersection that includes a four-way node and an angularly oriented diagonal approach road connecting two of the adjacent approach roads plus a T-node, with a conventional amount of detail; Figure 15B represents the intersection in Figure 15A in a VC geometry; Figures 15C, 15D, 15E and 15F are schematic views of the intersection in Figure 15A, decomposed into separate perceived intersections.; Figure 16A is a schematic view of an intersection that includes a five-way node with left turn lanes and road dividers, with two of the approach roads being angularly oriented relative to the other approach roads, with a conventional amount of detail.; Figure 16B represents the intersection in Figure 16A in a VC geometry; - 7 - Figures 16C, 16D and 16E are schematic views of the intersection in Figure 16A, decomposed into separate perceived intersections; Figure 17A is a schematic view of an intersection that includes three laterally displaced four-way nodes that form a triangular obstruction, with a conventional amount of detail; Figure 17B represents the intersection in Figure 17A in a VC geometry; Figures 17C, 17D and 17E are schematic views of the intersection in Figure 17A, decomposed into separate perceived intersections; Figure 18A is a schematic view of a four-way node that includes a curved right turn road connecting two approach roads, with a conventional amount of detail; Figure 18B represents the intersection in Figure 18A in a VC geometry; Figures 18C, 18D and 18E are schematic views of the intersection in Figure 18A, decomposed into separate perceived intersections; Figure 19A is a schematic view of an intersection that includes two four-way nodes and a three-way node that form a triangular obstruction, with a conventional amount of detail; Figure 19B represents the intersection in Figure 19A in a VC geometry; Figures 19C, 19D and 19E are schematic views of the intersection in Figure 19A, decomposed into separate perceived intersections; Figure 20A is a schematic view of an intersection that includes a four-way node with two laterally displaced approach roads, with a conventional amount of detail; Figure 20B represents the intersection in Figure 20A in a VC geometry; Figures 20C and 20D are schematic views of the intersection in Figure 20A, decomposed into separate perceived intersections; Figure 21A is a schematic view of an intersection that includes four three-way, angularly oriented nodes that form a tetragonal obstruction, with a conventional amount of detail; Figure 21B represents the intersection in Figure 21A in a VC geometry; Figures 21C, 21D, 21E, 21F and 21G are schematic views of the intersection in Figure 21A, decomposed into separate perceived intersections; Figure 22A is a schematic view of an intersection that combines two four-way nodes and a three-way node with a diagonal connecting two approach roads, with a conventional amount of detail; Figure 22B represents the intersection in Figure 22A in a VC geometry; Figures 22C, 22D, 22E and 22F are schematic views of the intersection in Figure 22A, decomposed into separate perceived intersections; Figure 23A is a schematic view of an intersection that includes a four-way node and laterally displaced three-way node and a curvilinear road segment connecting two approach roads, with a conventional amount of detail; Figure 23B represents the intersection in Figure 23A in a VC geometry; Figures 23C, 23D and 23E are schematic views of the intersection in Figure 23A, decomposed into separate perceived intersections; and Figure 24 is a schematic view of apparatus suitable for practising the invention. A standard four-way node or intersection, such as shown in Figure 1A, is probably the simplest intersection that a vehicle and vehicle operator will encounter at an intersection. This intersection can be represented in a visually collapsed or VC representation substantially as shown in Figures IB, 1C and ID. Optionally, if the vehicle is to pass through the intersection and continue in the - 9 - present direction, as shown in Figure IB, visual or audible presentation or display of this intersection can be omitted. In Figure IB, a vehicle approaches the intersection along a road segment 1-1B, passes through the intersection in the same direction, and departs from the intersection along a road segment 1-2B toward the top. If the vehicle is to turn right at this intersection, as in Figure 1C or IE, the vehicle approaches along the segment 1-1B, turns right at the intersection, and departs along a segment 1-2C toward the right. If the vehicle is to turn left at this intersection, as shown in Figure ID, the vehicle approaches along the segment 1-1B, turns left at the intersection, and departs along a segment 1-2D toward the left. An "active" intersection, at which a manoeuvre such as a turn or lane change is required, should be displayed in VC format for a time interval of length preferably 5-60 sec or more before the vehicle reaches the intersection, especially if the vehicle must take a traffic-constrained action such as changing lanes before reaching the intersection. Optionally, location and orientation of the vehicle may be indicated using an icon-with-orientation that moves through the intersection shown on the display screen, either continuously or in small increments, as the vehicle itself moves through the intersection. The road segments to be used by the vehicle in approaching, passing through and departing from the intersection are indicated on an electronic map or display that presents an intersection in VC format, for example as shown in Figures IB, 1C, ID or IE. The particular road segments to be used in the selected route: (1) may be shown in bold arrows that are distinguishable from the background, as shown in Figure IB; (2) may be distinguished by use of bars having two or more alternating colours and having arrowheads located at one end of each of the bars, as shown in Figure 1C; (3) may be distinguished by use of bars having arrowheads located at one end of each bar and being arranged - 10 - to flash or intermittently illuminate, as suggested in Figure ID; (4) may be distinguished by use of a single continuous and curving bar with an arrow, as shown in Figure IE, that indicates the manoeuvre required (here, a right turn) , where the curving bar and/or arrow have a distinguishable colour or colours or are caused to lash or intermittently illuminate; or (5) may be distinguished from the background in any other suitable manner. The entire intersection is shown in VC format as a connected collection of straight or curved line segments representing road segments, and two or more of the road segments are distinguished to indicate the segments and directions that the vehicle should follow. In the figures that follow, the direction of an arrow will be used to indicate direction of vehicle travel. However, any suitable method to indicate travel direction can be used here. If the intersection requires that a vehicle approaching the intersection along a particular segment (e.g., 1-1B) comply with a traffic control device or yield the right-of- way to a vehicle approaching the intersection from another direction (indicated by an indicium, such as a rectangle with "S/Y" therein, in Figure 1A) , a similar indicium is optionally included in the corresponding VC representation. Alternatively, the stop or yield command can be deleted or can be replaced by a simple line break at the intersection, as shown in Figures IB, 1C and ID. In the illustrations in Figures 1A, IB, 1C, ID and IE, and in all the illustrations that follow, an S/Y indicium may appear on any approach segment for the intersection illustrated. An intersection is said to be represented in a "visually collapsible" (VC) format if, from any approach passing through the intersection from any direction, an operator of a vehicle visually perceives passage through the intersection as a single continuous manoeuvre, which may require from a fraction of a second to as much as 10-15 - 11 - seconds to execute, not counting time delays due to traffic control devices, such as stop signs and traffic lights. Each intersection in VC format is represented as a collection of adjacent and connected nodes, with a node being the junction of two or more road segments. If passage through an intersection requires a first continuous manoeuvre and then a second continuous manoeuvre, separated by a distance (or an equivalent time interval) that is more than a selected threshold distance dthr, this intersection may not be visually collapsible and may have to be decomposed into two or more subsidiary intersections or separate collections of adjacent nodes, separated in space, in order to represent each subsidiary intersection in VC format. The threshold distance dthr may be chosen in a range given by 5 meters μ dthr μ 250 meters but is preferably chosen in a smaller range given by 15 meters μ dthr μ 100 meters. The threshold distance dthr may be fixed by a navigation program or may be selectable by the vehicle operator at the beginning of, or during, a vehicle trip. Examples of an intersection that may not be VC but that can be decomposed into two or more VC subsidiary intersections may be seen in Figures 5A, 7A, 8A and HA, discussed in the following . Optionally, the width w of a road segment that is part of an intersection can be varied according to the "rank" of that road segment. A road segment can be ranked according to what is the maximum vehicle speed legally permitted on that road segment, or according to the number of lanes provided for vehicle travel in one direction, independent of the presence or absence of a Stop or Yield-right-of-way sign that controls that road segment. If this option is adopted, two or more visually different road segment widths are used to indicate presence of road segments with different ranks at a given intersection. Alternatively, the colour of a road segment on a display screen can be varied with the numerical - 12 - rank of that road segment. A road segment that allows only One Way traffic can be indicated by a special colour or by distinguishable colouring or illumination. Use of a width indicium is illustrated in Figure 2A, where display of a larger width wl for one road segment 2-lA and of a smaller width w2 for another road segment 2-2A, both part of an intersection, indicates that the road segment 2-lA has a larger rank (allows a higher maximum vehicle speed and/or has more vehicle lanes) than does the road segment 2-2A. Figure 2A illustrates a diverging Y-intersection, with a conventional amount of detail shown, optionally including one or more S/Y indicia and a possible island or other visual obstruction BL-2 that separates two arms of the Y- intersection. Figure 2B represents the intersection in Figure 2A in VC format, where a vehicle approaches along a road segment 2-1/1 from the bottom and departs along a segment 2-2/0 toward the top right. Figure 2C represents the intersection in Figure 2A in VC format, where a vehicle approaches along the segment 2-1/1 and departs along a segment 2-3/0 toward the top left. Preferably, presence of a visual obstruction 2-BL (or 3-BL in Figure 3A) is not indicated in a VC format of an intersection, because showing an island would introduce detail that is not needed to negotiate passage through the intersection. However, presence of an island might be included, especially if the island is very large or prevents the intersection from being represented as a single entity in VC format. Figure 3A illustrates a converging Y-intersection, with a conventional amount of detail shown, optionally including one or more S/Y indicia and a possible island 3-BL that separates two arms of the Y-intersection. Figure 3B represents the intersection in Figure 3A in VC format, where a vehicle approaches along a road segment 3-1/1 from the bottom left and departs along a segment 3-2/0 toward the top. Figure 3C represents the intersection in Figure 3A in - 13 - VC format, in which a vehicle approaches along the segment 3-2/1 from the bottom right and departs along the segment 3- 2/0 toward the top. Figure 3D represents the intersection in Figure 3A in VC format, in which a vehicle approaches along the segment 3-1/1 and departs along the segment 3-3/0 toward the lower right. Figure 4A illustrates a standard, possibly angularly oriented, T-node or intersection, with a conventional amount of detail shown, optionally including one or more S/Y indicia. Figure 4B represents the intersection in Figure 4A in VC format, illustrating the six ordered road segments that make up this intersection: 4-1/1 and 4-1/0, representing incoming and outgoing segments from the bottom left; 4-2/1 and 4-2/0, representing incoming and outgoing segments from the right; and 4-3/1 and 4-3/0, representing incoming and outgoing segments from the left. The T-node shown in Figure 4A allows at least six ordered sequences of path segments : 4/1 4-1/1; 4-2/0 4/2 4-1/1; 4-3/0 4/3 4-2/1; 4-3/0 4/4 4-2/1; 4-1/0 4/5 4-3/1; 4-1/0 4/6 4-3/1; 4-2/0 No special manoeuvre is required for the sequences 4/3 and 4/6, and presence of the road segments 4-1/1,0 might be deleted in VC format for these two sequences. As indicated in Figure 4A, the standard T-node need not involve a right angle junction of two or more road segments Figure 5A illustrates a T-intersection facing a Y-node (e.g., an island allowing two-way traffic flow on most or all sides), with conventional detail shown, optionally including one or more S/Y indicia. Visibility may be partly - 14 - or completely blocked by obstructions in a core area 5-BL. Figure 5B represents the intersection in Figure 5A in VC format, illustrating the 16 ordered road segments that make up this intersection: 5-1/1 and 5-1/0, representing incoming and outgoing segments from the bottom; 5-2/1 and 5-2/0, representing intermediate incoming and outgoing segments toward the upper right; 5-3/1 and 5-3/0, representing incoming and outgoing segments from the left; 5-4/1 and 5- 4/0, representing intermediate incoming and outgoing segments from the right; 5-5/1 and 5-5/0, representing incoming and outgoing segments from the top; 5-6/1 and 5- 6/0, representing intermediate incoming and outgoing segments from the left; 5-7/1 and 5-7/0, representing incoming and outgoing segments from the left; and 5-8/1 and 5-8/0, representing intermediate incoming and outgoing segments toward the upper left. The intersection shown in Figure 5A allows at least 24 ordered sequences of path segments : 5/1 5-1/1; 5-2/1; 5-3/0 5/2 5-1/1; 5-2/1; 5-4/1; 5-5/0 5/3 5-1/1; 5-2/1; 5-4/1; 5-6/0; 5-7/0 5/4 5-1/1; 5-8/1; 5-7/0 5/5 5-1/1; 5-8/0; 5-6/01; 5-5/0 5/6 5-1/1; 5-8/0; 5-6/01; 5-4/0; 5-3/0 5/7 5-3/1; 5-4/1; 5-5/0 5/8 5-3/1; 5-4/1; 5-6/0; 5-7/0 5/9 5-3/1; 5-4/1; 5-6/0; 5-8/0; 5-1/0 5/10 5-3/1; 5-2/0; 5-1/0 5/11 5-3/1; 5-2/0; 5-8/0; 5-7/0 5/12 5-3/1; 5-2/0; 5-8/0; 5-6/1; 5-5/0 5/13 5-5/1; 5-6/0; 5-7/0 5/14 5-5/1; 5-6/0; 5-8/0; 5-1/0 5/15 5-5/1; 5-6/0; 5-8/0; 5-2/1; 5-3/0 5/16 5/5/1; 5-4/0; 5-3/0 5/17 5-5/1; 5-4/0; 5-2/0; 5-1/0 5/18 5-5/1; 5-4/0; 5-2/0; 5-8/0; 5-7/0 - 15 - 5/19 5-7; I; 5-8/0; 5-1/0 5/20 5-7; I; 5-8/0; 5-2/1; 5-3/0 5/21 5-7;I; 5-8/0; 5-2/1; 5-4/1; 5-5/0 5/22 5-7/1; 5-6;I; 5-5/0 5/23 5-7/1; 5-6;I; 5-4/0; 5-3/0 5/24 5-7/1; 5-6;I; 5-4/0; 5-2/0; 5-1/0 No special manoeuvre is required for the sequences illustrated in paths 5/6 and 5/23. The road segment pair 5- 1/1,0 may be deleted for the sequences 5/6, 5/7, 5/22 and 5/23. The road segment pairs 5-3/1,0 and 5-5/1,0 may be deleted for the sequences 5/4 and 5/19. The road segment pairs 5-5/1,0 and 5-7/1,0 may be deleted for the sequences 5/1 and 5/10. The amount of detail shown for a particular manoeuvre through the intersection in Figure 5A may vary, depending upon the path to be followed through this intersection . Figure 5A illustrates an intersection encountered, in which two or more subsidiary intersections or nodes are part of the total intersection. If the distance d between the two arms of the triangle split shown in Figure 5A is greater than a selected threshold distance dthr (usually in the range 15-50 meters), as discussed above, or if visibility across the core area 5-BL is blocked, this particular intersection may have to be represented in VC format as the sum of as many as four separate, perceived three-way nodes, as shown in Figures 5C, 5D, 5E and 5F. The necessity for representation of an intersection as two or more separate, perceived intersections will depend upon the direction of approach by a vehicle to the intersection, upon the vehicle manoeuvre required within the intersection, upon the direction of vehicle departure from the intersection, and upon other relevant factors. For example, the threshold distance dthr may vary with the width w of a road segment, upon the angle q of intersection of two - 1 6 - intersecting road segments (as in Figure 5A) and/or upon the manoeuvre required for the vehicle. Preferably, issues such as collapsibility, separability of an intersection into separate nodes or perceived intersections, use of a threshold distance dthr for separability and related issues are controlled by one or more database attributes that account for directions of vehicle approach to and departure from an intersection, any manoeuvre required to pass through the intersection, and local conditions. Figure 5A is the first example of an intersection encountered herein in which (1) a collection of adjacent nodes might be decomposed into two or more mutually exclusive subsidiary collections of nodes, each of which represents an intersection in VC format and/or (2) inclusion of a particular collection of nodes representing an intersection in VC format may depend upon the direction of approach to, manoeuvre through, and the direction of departure, from the intersection. Figure 6A illustrates a T-node with a curved base, with a conventional amount of detail shown, including one or more S/Y indicia. Figure 6B represents the intersection in Figure 6A in VC format, illustrating the six path segments that make up this intersection: 6-1/1 and 6-1/0, which represent incoming and outgoing path segments along the curved segment to the right; 6-2/1 and 6-2/0, which represent incoming and outgoing path segments along the curved segment to the left; and 6-3/1 and 6-3/0, which represent incoming and outgoing path segments along the stem of the "T." The T-node shown in Figure 6A allows at least six ordered sequences of path segments : 6/1 6-1/1; 6-3/0 6/2 6-1/1; 6-2/0 6/3 6-2/1; 6-3/0 6/4 6-2/1; 6-1/0 - 17 - 6/5 6-3 /1 ; 6-1 /0 6/ 6 6-3 /1 ; 6-2 /0. No special manoeuvre is required for the sequences illustrated in paths 6/2 and 6/4, and the "T" stem path segment pair (6-3/1, 6-3/0) shown in these two paths may be omitted in a VC format. Thus, the amount of detail shown for a particular manoeuvre through the intersection in Figure 6A may vary, depending upon the path to be followed through this intersection. Figure 7A illustrates a standard four-way node with a laterally displaced, angularly oriented T-node, with a conventional amount of detail shown, optionally including one or more S/Y indicia. Figure 7B represents the intersection in Figure 7A in VC format, illustrating the 12 path segments that make up this intersection: 7-1/1 and 7- 1/0 (vertical approach from and departure toward the bottom) ; 7-2/1 and 7-2/0 (horizontal approach from and departure toward the right) ; 7-3/1 and 7-3/0 (horizontal approach from and departure toward the right); 7-4/1 and 7- 4/0 (diagonal approach from and departure toward the upper right) ; 7-5/1 and 7-5/0 (vertical approach from and departure toward the top) ; and 7-6/1 and 7-6/0 (horizontal approach from and departure toward the left) . The four-way node and laterally displaced, angularly oriented T-node shown in Figure 7A supports at least 20 ordered sequences of path segments: 7/1 7-1/1; 7-2/0; 7-3/0 7/2 7-1/1; 7-2/0; 7-4/0 7/3 7-1/1; 7-5/0 7/4 7-1/1; 7-6/0 7/5 7-3/1; 7-4/0 7/6 7-3/1; 7-2/1; 7-5/0 7/7 7-3/1; 7-2/1; 7-6/0 7/8 7-3/1; 7-2/1; 7-1/0 7/9 7-4/1 ; 7-2/1 7-5/ 7/10 7-4/1; 7-2/1; 7- -6/0 7/11 7-4/1; 7-2/1; 7- -1/0 7/12 7-4/1; 7-3/0 7/13 7-5/1; 7-6-0 7/14 7-5/1; 7-1/0 7/15 7-5/1; 7-2/0; 7- -3/0 7/16 7-5/1; 7-2/0; 7- -4/0 7/17 7-6/1; 7-1/0 7/18 7-6/1; 7-2/0; 7- -3/0 7/19 7-6/1; 7-2/0; 7- -4/0 7/20 7-6/1; 7-5/0. The side road path segment pair (7-4/1, 7-4/0) might serve as a ramp to enter onto or exit from a divided grade, limited access highway, such as a California freeway, or might serve some other purpose. If the distance d between the four-way node and this side road, shown in Figure 7A, is larger than a first threshold amount, such as 50-200 meters, it may be preferable to represent the intersection shown in Figure 7A as two separate nodes or perceived intersections in VC format, namely as a four-way node (Figure 7C) and as an angularly oriented T-node (Figure 7D) , with the path segments as shown in Figures 7C and 7D. If the distance d is smaller than a second threshold amount, such as 10-50 meters, it may be preferable to delete the path segment pair (7-2/1, 7-2/0) and to replace the representation shown in Figure 7B by the representation shown in Figure 7E. In this instance, the path segments 7- 2/1 and 7-2/0 that are part of the sequences 71, 7/2, 7/6, 7/7, 7/8, 7/9, 7/10, 7/11, 7/15, 7/16, 7/18 and 7/19 would be deleted, but the 20 ordered path sequences would be otherwise unaltered. The representation shown in Figure 7B, or the representations shown in Figures 7C and 7D, or the - 1 9 - representation shown in Figure 7E would be used in VC format for the intersection shown in Figure 7A. Intersection of the two path segment pairs (7-3/1, 7-3/0) and (7-4/1, 7-4/0) is an example of an internal intersection that is part of the overall intersection shown in Figure 7A and that may be shown together with, or separately from, one or more other perceived intersections that are part of the overall intersection. Optionally, the path segment pair (7-4/1, 7-4/0) may be deleted in a VC representation for the paths 7/2, 7/3. 7/4, 7/6, 7/7, 7/8, 7/13, 7/14, 7/15, 7/17, 7/18 and/or 7/20, because this path segment pair plays no role in any of these paths . This illustrates again that the amount of detail shown for a particular manoeuvre through an intersection (Figure 7A) may vary, depending upon the path to be followed through this intersection. If the distance d between the four-way node and the T- node shown in Figure 7A is greater than a selected threshold distance dthr, as discussed above, this particular intersection may have to be represented separately in VC format as the sum of a perceived four-way node and a perceived angularly oriented T-node, separated by the distance d, as shown in Figures 7C and 7D, respectively. If the distance d is very small, the road segment 7-2/1 and 7- 2/0 shown in Figure 7B is or may be omitted, as shown in Figures 7E, because deletion of this road segment should not cause any confusion in these Figures. For some of the paths shown in Figures 7B, the distance of separation d may be irrelevant . Figure 8A illustrates a standard four-way node with a displaced (three-way) T-node and (approximately) parallel road, with a conventional amount of detail shown, optionally including one or more S/Y indicia. Visibility may be partly or completely blocked by obstructions in a core area 8-BL. 20 - Figure 8B represents the intersection in Figure 8A in VC format, illustrating the 12 path segments that make up this intersection: 8-1/1 and 8-1/0, representing incoming and outgoing vertical paths from the bottom; 8-2/1 and 8-2/0, representing incoming and outgoing paths from the right; 8- 3/1 and 8-3/0, representing intermediate vertical paths; 8- 4/1 and 8-4/0, representing incoming and outgoing paths from the right; 8-5/i and 8-5/0, representing incoming and outgoing vertical paths from the top; and 8-6/1 and 8-6/0, representing incoming and outgoing paths from the left. The intersection shown in Figure 8B allows at least 20 possible ordered path segment sequences through this intersection: /l 8-1/] ;; 8-2/0 /2 8-1/] [; 8-3/0; 8-4/0 /3 8-1/] I; 8-3/0; 8-5/0 /4 8-1/] :,- 8-6/0 /5 8-2/] I; 8-3/C ); 8-4/0 /6 8-2/] C; 8-3/C j; 8-5/0 11 8-2/] C; 8-3/1 C; 8-6/0 /8 8-2/] [; 8-3/1 [; 8-1/0 /9 8-4/] [; 8-5/C , /10 8-4/1, 8-3/1, 8-6/0 /H 8-4/1, 8-3/1 8-1/0 /12 8-4/1, 8-3/1 • 8-2/0 /13 8-5/1, 8-3/1 ■ 8-6/0 /14 8-5/1, 8-3/1 ■ 8-1/0 /15 8-5/1, 8-3/1 ■ 8-2/0 /16 8-5/1 ■ 8-4/0 /17 8-6/1 • 8-1/0 /18 8-6/1 ; 8-2/0 /19 8-6/1 ; 8-3/0 ; 8-4/0 /20 8-6/1 ; 8-3/0 ; 8-5/0 No special manoeuvre is required for the sequences 8/1, 8/3, 8/4, 8/6, 8/7, 8/8, 8/13, 8/14, 8//17, 8/18 and 8/20, and the T-node (path segments 8-4/1 and 8-4/0) may be - 2 1 - omitted for these paths in a VC format. This again indicates that the amount of detail required for a particular path segment sequence through an intersection can vary with the path chosen. If the distance d between the four-way node and the T- node shown in Figure 8A is greater than a selected threshold distance dthr, as discussed above, or if visibility across the core area 8-BL is blocked, this particular intersection may be better represented in VC format as the sum of a perceived four-way intersection and a perceived T- intersection, separated by the distance d, as shown in Figures 8C and 8D, for one or more of the path segment sequences. For the situations shown in the sequences 8/1, 8/4, 8/9, 8/17 and 8/18, the distance of separation d may be irrelevant . Figure 9A illustrates a left turn crossover intersection, also known as a New Jersey left turn, with a conventional amount of detail shown, optionally including one or more S/Y indicia. A vehicle operator, approaching the intersection from an approach road segment at the bottom of the page and wishing to turn left at the node, positions the vehicle in the extreme right hand lane, makes a partial right turn a line-of-sight distance d before the actual intersection is reached, executes a looping quarter turn (with turn arc length s) to the left from this right turn lane, and comes to a stop at a traffic light or other traffic control device at the intersection. When the traffic control device permits, the vehicle then moves perpendicularly across the approach road segment, effectively making a left turn from the approach road segment. A vehicle operator, moving along the approach road segment and not wishing to turn left, and a vehicle operator approaching the intersection from any other direction, treats this intersection as a standard four-way node that is controlled by a traffic control device. Visibility may be - 22 - partly or completely blocked by obstructions in a core area 9-BL. Figure 9B represents the intersection in Figure 9A in VC format, illustrating the ten path segments that make up this intersection: 9-1/1 and 9-1/0, representing incoming and outgoing vertical paths from the bottom; 9-2, representing a one-way curvilinear quarter loop path that ultimately approaches the intersection from the right; 9-3/1 and 9-3/0, representing incoming and outgoing vertical paths from the bottom; 9-4/1 and 9-4/0, representing incoming and outgoing paths from the top; and 9-5/1 and 9-5/0, representing incoming and outgoing paths from the left. The intersection shown in Figure 9B allows at least seven possible ordered path segment sequences through this intersection: 9/1 9-1/1; 9-2; 9-4/0 9/2 9-1/1; 9-2; 9-5/0 9/3 9-1/1; 9-3/1; 9-4/0 9/4 9-4/1; 9-5/0 9/5 9-4/1; 9-3/0; 9-1/0 9/6 9-5/1; 9-3/0; 9-1/0 9/7 9-5/1; 9-4/0 No special manoeuvre is required for the sequences 9/3, 9/4, 9/6 and 9/7, and the curvilinear quarter loop (path segment 9-2) may be omitted from these sequences in a VC format. A VC format should indicate that a vehicle planning to follow the sequence 9/1 or 9/2 should be in the extreme right hand lane as the turn-off for the path segment 9-2 is approached. If the distance d shown in Figure 9A is greater than a selected threshold distance dthr, as discussed above, or if visibility across the core area 9-BL is blocked, this particular intersection may have to be represented in VC format as the sum of a perceived partial right turn - 23 - intersection (path segment 9-2) and a separate perceived perpendicular crossing intersection, for the sequences 9/1 and 9/2, as illustrated in Figures 9C and 9D. For the sequence 9/3, 9/4, 9/6 and 9/7, the distance of separation d may be irrelevant. Alternatively, the line-of-sight distance d in Figure 9A may be replaced by an arc length s of the road segment 9- 2, which is compared with a threshold arc length sthr as in the preceding paragraph. Figure 10A illustrates an alternative left turn crossover intersection, with a conventional amount of detail shown. A vehicle operator, approaching the intersection from an approach road segment at the bottom of the page and wishing to turn left at the intersection, positions the vehicle in the extreme right hand lane, passes through the four-way node a first time, executes a three-quarter turn loop back to the right from this right turn lane, merges with cross-traffic moving from right to left, and comes to a stop at a traffic light or other traffic control device at the node. When the traffic control device permits, the vehicle then moves perpendicularly across the approach road segment, thus passing through the four-way node a second time and effectively making a left turn from the approach road segment. A vehicle operator moving along the approach road segment that does not wish to turn left, and a vehicle operator approaching the intersection from any other direction, treats this intersection as a standard four-way node that is controlled by a traffic control device. The distance from the centre of the actual intersection to the entrance looping quarter turn is dl, and the distance from the exit from the looping quarter turn to the centre of the actual intersection is d2. Visibility may be partly or completely blocked by obstructions in a core area 10-BL. - 24 - Figure 10B represents the intersection in Figure 10A in VC format, illustrating the 13 path segments that make up this intersection: 10-1/1 and 10-1/O, representing incoming and outgoing vertical paths from the bottom; 10-2/1 and 10- 2/0, representing incoming and outgoing paths from the right; 10-3/1 and 10-3/O, representing incoming and outgoing paths from the right; 10-4/1 and 10-4/O, representing incoming and outgoing paths from the top; 10-5, representing a curvilinear three-quarter loop; 10-6/1 and 10-6/O, representing incoming and outgoing paths from the top; and 10-7/1 and 10-7/O, representing incoming and outgoing paths from the left. The intersection shown in Figure 10B allows at least 13 possible ordered path segment sequences through this intersection: 10/1 10-1/1; 10-2/O; 10-3/O 10/2 10-1/1; 10-4/O; 10-6/O 10/3 10-1/1; 10-4/O; 10-5;10-7/O 10/4 10-3/1; 10-4/O; 10-5; 10-7/O 10/5 10-3/1; 10-4/O; 10-6/O 10/6 10-3/1; 10-7/O 10/7 10-3/O; 10-1/O 10/8 10-4/1; 10-7/O 10/9 10-4/1; 10-1/O 10/10 10-4/1; 10-3/O 10/11 10-7/1; 10-1/O 10/12 10-7/1; 10-3/O 10/13 10-7/1; 10-6/O No special manoeuvre is required for the sequences 10/1, 10/2, 10/5, 10/6, 10/7, 10/8, 10/9, 10/10, 10/11, 10/12 and 10/13, and the curvilinear three-quarter loop back (path segment 10-5) may be omitted from these sequences in a VC format. A VC format should indicate that a vehicle planning to follow the sequence 10/3 or 10/4 should be in the extreme right hand lane as the turn-off for the path segment 10-5 is approached. - 25 - If the distance dl or the distance d2 shown in Figure 10A is greater than a selected threshold distance dthr, as discussed above, or if visibility across the core area 10-BL is blocked, this particular intersection may have to be represented separately in VC format as the sum of a perceived partial right turn intersection, and/or a perceived merging from the right into another lane (both part of the path segment 10-5) , and/or a perceived perpendicular crossing intersection, for one or more of the situations shown in the separated intersection components in Figures IOC, 10D and 10E. For the situations shown in Figures 10/1, 10/2 and 10/5-13, the distances of separation dl and d2 may be irrelevant. Alternatively, the line-of-sight distance d in Figure 10A may be replaced by the arc length s of the road segment 10-3B, which is compared with a threshold distance sthr as in the preceding paragraph. Figure HA represents a circular or semi-circular or ovular, unidirectional (counterclockwise) roundabout having two or more (here, four) access roads or tributaries. A vehicle approaches the roundabout along one of the radially- inward "spokes", turns right and follows the roundabout in an arcuate counterclockwise direction (or turns left and proceeds in a clockwise direction in some jurisdictions), turns right at the appropriate exit road, and departs from the roundabout in a radially-outward direction. The diameter of the roundabout is d. Visibility may be partly or completely blocked by obstructions in a core area 11-BL. Figure HB represents the intersection in Figure HA in VC format, illustrating the 12 path segments that make up this intersection: ll-l/I and 11-1/0, representing incoming and outgoing vertical paths from the bottom; 11-2/CC, representing a counterclockwise path on the roundabout; 11- - 2 6 - 3/1 and 11-3/0, representing incoming and outgoing paths from the right; 11-4/CC, representing a counterclockwise path on the roundabout; 11-5/1 and 11-5/0, representing incoming and outgoing vertical paths from the top; 11-6/CC, representing a counterclockwise path on the roundabout; 11- 7/1 and 11-7/0, representing incoming and outgoing paths from the left 11-8/CC , representing a counterclockwise path on the roundabout. Counterclockwise paths may be replaced by clockwise paths in Figures HA-llF. The intersection shown in Figure 11B allows at least 12 possible ordered path segment sequences through this intersection: 11/1 ll-l/I; 11-2/CC; 11-3/0 11/2 ll-l/I; 11-2/CC; 11-4/CC; 11-5/0 11/3 ll-l/I; 11-2/CC; 11-4/CC; 11-6/CC; 11-7/0 11/4 11-3/1; 11-4/CC; 11-5/0 11/5 11-3/1; 11-4/CC; 11-6/CC; 11-7/0 11/6 11-3/1; 11-4/CC; 11-6/CC; 11-8/CC; 11-1/0 11/7 11-5/1; 11-6/CC; 11-70 11/8 11-5/1; 11-6/CC; 11-8/CC; 11-1/0 11/9 11-5/1; 11-6/CC; 11-8/CC; 11-2/CC; 11-3/0 11-10 11-7/1; 11-8/CC; 11-1/0 11-11 11-7/1; 11-8/CC; 11-2/CC; 11-3/0 11-12 11-7/1; 11-8/CC; 11-2/CC; 11-4/CC; 11-5/0 The curvilinear one-quarter, two-quarter and three- quarter loops in the roundabout are preferably part of all sequences in a VC format If the diameter d shown in Figure HA is greater than a selected threshold distance dthr, as discussed above, or if visibility across the core area 11-BL is blocked, this particular intersection may have to be represented separately in VC format as two or more separate components drawn from a perceived right turn onto or off of a roundabout, similar to the T-node with curved base shown in Figure 6A, as illustrated in Figures HC, HD, HE and HF. - 27 - For the sequences 11/1, 11/4, 11/7 and 11/10, the diameter d of the roundabout may be irrelevant. Figure HB may be reduced to a representation such as Figure HB', a simplified version of Figure HB. Figure 12A represents a polygonal one-way (counterclockwise) roundabout (here, a pentagon) having two or more (here, five) access roads or tributaries. A vehicle approaches the roundabout along one of the radially-inward "spokes", turns right and follows the roundabout in an arcuate counterclockwise direction (or turns left and proceeds in a clockwise direction in some jurisdictions), turns right at the appropriate exit road, and departs from the roundabout in a radially-outward direction. The diameter of the roundabout is d. Visibility may be partly or completely blocked by obstructions in a core area 12-BL. Figure 12B represents the intersection in Figure 12A in VC format, illustrating the 18 path segments that make up this intersection: 12-1/1 and 12-1/0, representing incoming and outgoing vertical paths from the bottom; 12-2/CC, representing a counterclockwise path on the roundabout; 12- 3/1 and 12-3/0, representing incoming and outgoing paths from the right; 12-4/CC and 12-5/CC, representing counterclockwise paths on the roundabout; 12-6/1 and 12-6/0, representing incoming and outgoing vertical paths angularly from the top; 12-7/CC, representing a counterclockwise path on the roundabout; 12-8/1 and 12-8/0, representing incoming and outgoing paths from the top 12-9/CC and 12-9/CC, representing counterclockwise paths on the roundabout; 12- 10/CC, representing a counterclockwise path on the roundabout; 12-11/1 and 12-11/0, representing incoming and outgoing paths from the left; and 12-12/CC, representing a counterclockwise path on the roundabout. Counterclockwise paths may be replaced by clockwise paths in Figures 12A-12G. The intersection shown in Figure 12B allows at least 20 - 28 - possible ordered path segment sequences through this intersection : 12/1 12-1/1; 12-2/CC; 12-3/0 12/2 12-1/1; 12-2/CC; 12-4/CC; 12-5/CC; 12-6/0 12/3 12-1/1; 12-2/CC; 12-4/CC; 12-5/CC; 12-7/CC; 12-8/0 12/4 12-1/1; 12-2/CC; 12-4/CC; 12-5/CC; 12-7/CC; 12-9/CC; 12-10/CC; 12-11/0 12/5 12-3/1; 12-4/CC; 12-5/CC; 12-6/0 12/6 12-3/1; 12-4/CC; 12-5/CC; 12-7/CC; 12-8/0 12/7 12-3/1; 12-4/CC; 12-5/CC; 12-7/CC; 12-9/CC; 12-11/0 12/8 12-3/1; 12-4/CC; 12-5/CC; 12-7/CC; 12-9/CC; 12-12/CC; 12-1/0 12/9 12-6/1; 12-7/CC; 12/10 2-6/1; 12-7/CC; 12-9/CC; 12-10/CC; 12-11/0 12/11 12-6/1; 12-7/CC; 12-9/CC; 12-10/CC; 12-12/CC; 2-1/0 12/12 12-6/1; 12-7/CC; 12-9/CC; 12-10/CC; 12-12/CC; 2-2/CC; 12-3/0 12/13 12-8/1; 12-9/CC; 12-10/CC; 12-11/0 12/14 12-8/1; 12-9/CC; 12-10/CC; 12-12/CC; 12-1/0 12/15 12-8/1; 12-9/CC; 12-10/CC; 12-12/CC; 12-2/CC; 2-3/0 12/16 12-8/1; 12-9/CC; 12-10/CC; 12-12/CC; 12-2/CC; 2-4/CC; 12-5/CC; 12-6/0 12/17 12-11/1; 12-12/CC; 12/18 12-11/1; 12-12/CC; 12-2/CC; 12-3/0\ 12/19 12-11/1; 12-12/CC; 12-2/CC; 12-4/CC; 12-5/CC; 12-6/0 12/20 12-11/1; 12-12/CC; 12-2/CC; 12-4/CC; 12-5/CC; 12-7/CC; 12-8/0 The curvilinear fractional loops in the roundabout are preferably part of all sequences in a VC format. - 2 9 - If the distance dl or the distance d2 shown in Figure 12A is greater than a selected threshold distance dthr, as discussed above, or if visibility across the core area 12-BL is blocked, this particular intersection may have to be represented separately in VC format by as many as five components, as illustrated in Figures 12C, 12D, 12E, 12F and 12G. These components may include one or more perceived T- nodes. For the sequences 12/1, 12/5, 12/9, 12/13 and 12/17, the distances of separation dl and d2 may be irrelevant. Figure 13A represents a five-way node with a first angularly oriented diagonal road segment connecting two adjacent approach road segments for the five-way node and a second angularly oriented diagonal road segment connecting the five-way node with the first diagonal, optionally including one or more S/Y indicia. The first and second diagonals together form first and second triangles, Tl and T2, with longest lengths dl and d2 , respectively. Visibility may be partly or completely blocked by visual obstructions located within the triangles Tl and/or T2. Figure 13B represents the intersection in Figure 13A in VC format, illustrating the 18 road segments that make up this intersection: 13-1/1 and 13-1/0, representing angularly oriented incoming and outgoing segments from the lower left; 13-2/1 and 13-2/0, representing angularly oriented intermediate incoming and outgoing segments from the lower left; 13-3/1 and 13-3/0, representing angularly oriented intermediate incoming and outgoing segments from the lower left; 13-4/1 and 13-14/0, representing incoming and outgoing segments from the right; 13-5/1 and 13-5/0, representing angularly oriented intermediate incoming and outgoing segments from the lower right; 13-6/1 and 13-6/0, representing intermediate incoming and outgoing segments from the bottom; 13-7/1 and 13-7/0, representing intermediate incoming and outgoing segments from the right; 13-8/1 and 13-8/0, representing incoming and outgoing 30 segments from the top; and 13-9/1 and 13-9/0, representing incoming and outgoing segments from the left. The intersection shown in Figure 13B allows at least 25 possible ordered path segment sequences through this intersection: 13/1 13-1/1, 13-2/1 13-3 /0; 13-4 /0 13/2 13-1/1, 13-2/1 13-3 /0; 13-7 /1 ; 13-8 /0 13/3 13-1/1, 13-2/1 13-3 /0; 13-7 /1 ; 13- 9/0 13/4 13-1/1, 13-2/1 13-5 /1 ; 13-8 /0 13/5 13-1/1, 13-2/1 13-5 /1 ; 13- 9/0 13/6 13-1/1, 13-2/1 13-5 /1 ; 13-7 /0; 13-4 /0 13/7 13-1/1, 13-6/1 13-8 /0 13/8 13-1/1, 13-6/1 13-9/0 13/9 13-1/1, 13-6/1 13-7/0; 13-4/0 13/10 13-4/1; 13-7/1; 13-8/0 13/11 13-4/1; 13-7/1; 13-9/0 13/12 13-4/1; 13-7/1; 13-5/0; 13-2/0; 13-1/0 13/13 13-4/1; 13-3/1; 13-5/1; 13-8/0 13/14 13-4/1; 13-3/1; 13-5/1; 13-9/0 13/15 13-4/1; 13-3/1; 13-2/0; 13-6/1; 13-8/0 13/16 13-4/1; 13-3/1; 13-2/0; 13-6/1; 13-9/0 13/17 13-4/0; 13-3/1; 13-2/0; 13-1/0 13/18 13-8/1; 13-9/0 13/19 13-8/1; 13-6/0; 13-1/0 13/20 13-8/1; 13-6/0; 13-2/1; 13-3/0; 13-4/0 13/21 13-8/1; 13-6/0; 13-2/1; 13-5/1; 13-7/0; 13-4/0 13/22 13-9/1; 13-8/0 13/23 13-9/1; 13-6/0; 13-1/0 13/24 13-9/1; 13-6/0; 13-2/1; 13-3/0; 13-4/0 13/25 13-9/1; 13-6/0; 13-2/1; 13-5/1; 13-7/0; 13-4/0 No special manoeuvre is required for the sequences 13/7, 13/8, 13/9, 13/10, 13/11, 13/18, 13/19, 13/22 and 13/23, and the diagonal path segments 13-2/1, 13-2/0, 13- 3/1, 13-3/0, 13-5/1 and 13-5/0 may be omitted from these sequences in a VC format. Some of the 25 sequences in Figure - 31 - 13B may be followed in a required detour through the intersection . If the lengths dl and/or d2 are larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 13B into as many as four intersection components: the four-way node and second diagonal, as shown in Figure 13C; intersection of the first and second diagonals, as shown in Figure 13D; and intersection of a horizontal approach road and the first diagonal, as shown in Figure 13E; and intersection of the first diagonal and the four-way node, as shown in Figure 13F. Figure 14A represents a four-way node with left turn lanes and with four angularly oriented diagonal right turn segments connecting four pairs of adjacent approach road segments for the four-way node, optionally including one or more S/Y indicia. One of the four approach road segments for the four-way node includes a curve a short distance from the node. The first, second, third and fourth diagonals, together with the connected approach right turn segments, form first, second, third and fourth approximate right triangles, Tl, T2, T3 and T4, with hypotenuse lengths dl, d2, d3 and d , respectively. Visibility may be partly or completely blocked by obstructions located within the triangles Tl and/or T2 and/or T3 and/or T4. Figure 14B represents the intersection in Figure 14A in VC format, illustrating the 22 road segments that make up this intersection: 14-1/1 and 14-1/0, representing incoming and outgoing segments from the bottom; 14-2/1, representing an angularly oriented incoming segment from the bottom left; 14-3/1 and 14-3/0, representing incoming and outgoing segments from the right; 14-4/1, representing an angularly oriented incoming segment from the bottom right; 14-5/1 and 14-5/0, representing incoming and outgoing segments from the - 32 - top; 14-6/1 and 14-6/0, representing angularly oriented incoming and outgoing segments from the top left; 14-7/1, representing an angularly oriented incoming segment from the top right; 14-8/1 and 14-8/0, representing incoming and outgoing segments from the left; 14-9/1, representing an angularly oriented incoming segment from the top left; 14- 10/1 and 14-10/0, representing incoming and outgoing segments from the bottom; 14-11/1 and 14-11/0, representing incoming and outgoing segments from the right; 14-12/1 and 14-12/0, representing incoming and outgoing segments from the top; and 14-13/1 and 14-13/0, representing incoming and outgoing segments from the left. The intersection shown in Figure 14B allows at least 16 possible ordered path segment sequences through this intersection: 14/1 14-1/1; 14-2/1; 14-3/0 14/2 14-1/1; 14-10/1; 14-11/0; 14-3/0 14/3 14-1/1; 14-10/1; 14-12/0; 14-5/0; 14-6/0 14/4 14-1/1; 14-10/1; 14-13/0; 14-8/0 14/5 14-3/1; 14-4/1; 14-5/0; 14-6/0 14/6 14-3/1; 14-11/1; 14-12/0; 14-5/0; 14-6/0 14/7 14-3/1; 14-11/1; 14-13/0; 14-8/0 14/8 14-3/1; 14-11/1; 14-10/0; 14-1/0 14/9 14-6/0; 14-5/0; 14-7/1; 14-8/0 14/10 14-6/0; 14-5/0; 14-12/1; 14-13/0; 14-8/0 14/11 14-6/0; 14-5/0; 14-12/1; 14-10/0; 14-1/0 14/12 14-6/0; 14-5/0; 14-12/1; 14-11/0; 14-3/0 14/13 14-8/1; 14-9/1; 14-1/0 14/14 14-8/1; 14-13/1; 14-10/0; 14-1/0 14/15 14-8/1; 14-13/1; 14-11/0; 14-3/0 14/16 14-8/1; 14-13/1; 14-12/0; 14-5/0; 14-6/0 The sequences 14/2-4, 14/6-8, 14/10-12 and 14/14-16 require no special manoeuvre, and the diagonal path segments (14-2/1, 14-4/1, 14-7/1; 14-9/1) may be omitted for these sequences . - 33 - If the lengths dl and/or d2 and/or d3 and/or d4 are larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 14A into as many as five intersection components: merging of a vertical approach road and the fourth and first diagonals, as shown in Figure 14C; merging of a horizontal approach road and the first and second diagonals, as shown in Figure 14D; merging of a vertical approach road and the second and third diagonals, as shown in Figure 14E; merging of a horizontal approach road and the third and fourth diagonals, as shown in Figure 14F; and the four-way node shown in Figure 14G. Figure 15A represents a T-node plus a four-way node two laterally displaced three-way nodes that form a triangular obstruction ((island) with a longest leg length dl . Visibility across the polygonal areas marked A, B, C and D may be partly or completely blocked by visual obstructions. Figure 15B represents the intersection in Figure 15A in VC format, illustrating the 18 road segments that make up the intersection: 15-1/1 and 15-1/0, representing incoming and outgoing segments from the bottom; 15-2/1 and 15-2/0, representing intermediate incoming and outgoing segments from the left; 15-3/1 and 15-3/0, representing intermediate incoming and outgoing segments from the left; 15-4/1 and 15- 4/0, representing incoming and outgoing segments from the bottom right 15-5/1 and 15-5/0, representing incoming and outgoing segments from the bottom right; 15-6/1 and 15-6/0, representing incoming and outgoing segments from the top right; 15-7/1 and 15-7/0, representing incoming and outgoing segments from the top left; 15-8/1 and 15-8/0, representing incoming and outgoing segments from the bottom left; and 15- 9/1 and 15-9/0, representing incoming and outgoing segments from the left. The intersection shown in Figure 15B allows at least 25 possible ordered path segment sequences through this intersection: 34 15/1 15-1/1 15-2/1; 15-3 /1 ; 15-4 /0 15/2 15-1/1, 15-2/1; 15-3 /1 ; 15-5 /1 ; 15- 6 /0 15/3 15-1/1, 15-2/1; 15-3 / 1 ; 15-5 /1 ; 15-7 /0 15/4 15-1/1, 15-2/1; 15-3 /1 ; 15-5 /1 ; 15-8 /0; 15- 9/0 15/5 15-1/1, 15-2/1; 15-8 /1 ; 15- 6/0 15/6 15-1/1, 15-2/1; 15-8 /1 ; 15-7 /0 15/7 15-1/1, 15-9/0 15/8 15-4/1, 15-5/1; 15- 6/0 15/9 15-4/1, 15-5/1; 15-7/0 15/10 15-4/1; 15-5/1; 15-8/0; 15-2/0; 15-9/0 15/11 15-4/1; 15-5/1; 15-8/0; 15-2/0; 15-1/0 15/12 15-6/1; 15-7/0 15/13 15-6/1; 15-8/0; 15-2/0; 15-9/0 15/14 15-6/1; 15-8/0; 15-2/0; 15-1/0 15/15 15-6/1; 15-8/0; 15-3/1; 15-4/0 15/16 15-6/1; 15-5/0; 15-4/0 15/17 15-7/1; 15-8/0; 15-2/0; 15-9/0 15/18 15-7/1; 15-8/0; 15-2/0; 15-1/0 15/19 15-7/1; 15-8/0; 15-3/1; 15-4/0 15/20 15-7/1; 15-5/0; 15-4/0 15/21 15-7/1; 15-6/0 15/22 15-9/1; 15-1/0 15/23 15-9/1; 15-2/1; 15-3/1; 15-4/0 15/24 15-9/1; 15-2/1; 15-3/1; 15-5/1; 15-6/0 15/25 15-9/1; 15-2/1; 15-3/1; 15-5/1; 15-7/0 In the sequences 15/7 and 15/21, the four-way node and the intermediate diagonal segments (15-2/1, 15-2/0, 15-3/1, 15-3/0) may be eliminated. In the sequences 15/8, 15/9, 15/12, 15/15, 15/20 and 15/21, the approach segments (15- 1/1, 15-1/0, 15-9/1, 15-9/0) and the intermediate segments (15-2/1, 15-2/0, 15-3/1, 15-3/0) may be eliminated. If the length dl and/or d2 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 15B - 35 - into as many as four intersection components: a T-node, as shown in Figure 15C; a three-way node, as shown in Figure 15D; a three-way node, as shown in Figure 15E; and a four- way node, as shown in Figure 15F. Some of the 25 sequences in Figure 15B may be followed in a possible detour through the intersection. Figure 16A represents a five-way node with left turn lanes and right turn lanes, with two of the approach road segments being oriented at non-perpendicular angles relative to adjacent approach roads and being separated by a distance dl . Visibility across the area marked 16-BL may be partly or completely blocked by visual obstructions . Figure 16B represents the intersection in Figure 16A in VC format, illustrating the 12 road segments that make up the intersection: 16-1/1 and 16-1/0, representing incoming and outgoing segments from the bottom; 16-2/1 and 16-2/0, representing incoming and outgoing segments from the right; 16-3/1 and 16-3/0, representing angularly oriented incoming and outgoing segments from the top right; 16-4/1 and 16-4/0, representing incoming and outgoing segments from the right; 16-5/1 and 16-5/0, representing angularly oriented incoming and outgoing segments from the top left; and 16-6/1 and 16- 6/0, representing incoming and outgoing segments from the left. The intersection shown in Figure 16B allows at least 20 possible ordered path segment sequences through this intersection: 16/1 16-1/1; 16-2/0 16/2 16-1/1; 16-3/0 16/3 16-1/1; 16-5/0 16/4 16-1/1; 16-6/0 16/5 16-2/1; 16-3/0 16/6 16-2/1; 16-4/0; 16-5/0 16/7 16-2/1; 16-4/0; 16-6/0 16/8 16-2/1; 16-4/0; 16-1/0 - 36 - 16/9 16-3/1; 16-4/0; 16-5/0 16/10 16-3/1; 16-4/0; 16-6/0 16/11 16-3/1; 16-1/0 16/12 16-3/1; 16-2/0 16/13 16-5/1; 16-6/0 16/14 16-5/1; 16-1/0 16/15 16-5/1; 16-4/1; 16-2/0 16/16 16-5/1; 16-4/1; 16-3/0 16/17 16-6/1; 16-1/0 16/18 16-6/1; 16-4/1; 16-2/0 16/19 16-6/1; 16-4/1; 16-3/0 16/20 16-6/1; 16-5/0 For the sequences 16/1-5, 16/8, 16/11-14, 16/16-17 and 16/20, or where the distance dl is very small, the intermediate road segment (16-4/1,0) can be eliminated, and the intersection can be shown in VC format as illustrated in Figure 16C. If the length dl is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 16B into two intersection components: a left half three-way node, as shown in Figure 16D, and a right half three-way node, as shown in Figure 16E. Figure 17A represents a perpendicular four-way node and two angularly oriented four-way nodes, forming a triangle with leg lengths dl and d2 and hypotenuse length d3. Visibility across the area marked 17-BL may be partly or completely blocked by visual obstructions . Figure 17B represents the intersection in Figure 17A in VC format, illustrating the 18 road segments that make up the intersection: 17-1/1 and 17-1/0, representing incoming and outgoing segments from the bottom; 17-2/1 and 17-2/0, representing intermediate segments oriented right and left; - 37 - 17-3/1 and 17-3/0, representing incoming and outgoing segments from the bottom right; 17-4/1 and 17-4/0, representing incoming and outgoing segments from the right; 17-5/1 and 17-5/0, representing intermediate segments oriented along a diagonal; 17-6/1 and 17-6/0, representing incoming and outgoing segments from the top; 17-7/1 and 17- 7/0, representing incoming and outgoing segments from the top left; 17-8/1 and 17-8/0, representing intermediate segments oriented top to bottom; and 17-9/1 and 17-9/0, representing incoming and outgoing segments from the left. The intersection shown in Figure 17B allows at least 60 possible ordered path segment sequences through this intersection: 17/1 17-1/1; 17-2/0; 17-3/0 17/2 17-1/1, 17-2/0; 17-4/0 17/3 17-1/1, 17-2/0; 17-5/1; 17-6/0 17/4 17-1/1, 17-2/0; 17-5/1; 17-7/0 17/5 17-1/1; 17-2/0; 17-5/1; 17-8/1; 17-9/0 17/6 17-1/1, 17-9/0 17/7 17-1/1, 17-8/0; 17-7/0 17/8 17-1/1, 17-8/0; 17-6/0 17/9 17-1/1, 17-8/0; 17-5/0; 17-4/0 17/10 17-1/1; 17-8/0; 17-5/0; 17-3/0 17/11 17-3/1; 17-4/0 17/12 17-3/1; 17-5/1; 17-6/0 17/13 17-3/1; 17-5/1; 17-7/0 17/14 17-3/1; 17-5/1; 17-8/1; 17-9/0 17/15 17-3/1; 17-5/1; 17-8/1; 17-1/0 17/16 17-3/1; 17-2/1; 17-1/0 17/17 17-3/1; 17-2/1; 17-9/0 17/18 17-3/1; 17-2/1; 17-8/0; 17-7/0 17/19 17-3/1; 17-2/1; 17-8/0; 17-6/0 17/20 17-3/1; 17-2/1; 17-8/0; 17-5/0; 17-4/0 17/21 17-4/1; 17-5/1; 17-6/0 17/22 17-4/1; 17-5/1; 17-7/0 17/23 17-4/1; 17-5/1; 17-8/1; 17-9/0 38 17/24 17-4/1; 17-5/1; 17-8/1; 17- -1/0 17/25 17-4/1; 17-2/1; 17-8/0; 17- -5/0; 17-3/0 17/26 17-4/1; 17-3/0 17/27 17-41; 17-2/1; . L7-1/0 17/28 17-4/1; 17-2/1; 17-9/0 17/29 17-4/1; 17-2/1; 17-8/0; 17- -7/0 17/30 17-4/1; 17-2/1; 17-8/0; 17- -6/0 17/31 17-6/1; 17-7/0 17/32 17-6/1; 17-8/1; 17-9/0 17/33 17-6/1; 17-8/1; 17-1/0 17/34 17-6/1; 17-8/1; 17-2/1; 17- -3/0 17/35 17-6/1; 17-8/1; 17-2/1; 17- -4/0 17/36 17-6/1; 17-5/0; 17-4/0 17/37 17-6/1; 17-5/0; 17-3/0 17/38 17-6/1; 17-5/0; 17-2/1; 17- -1/0 17/39 17-6/1; 17-5/0; 17-2/1; 17- -9/0 17/40 17-6/1; 17-5/0; 17-2/1; 17- -8/0; 17-7/0 17/41 17-7/1; 17-8/1; 17-9/0 17/42 17-7//I ; 17-8/1 ; 17-1/0 17/43 17-7/1; 17-8/1; 17-2/0; 17- -3/0 17/44 17-7/1; 17-8/1; 17-2/0; 17- -4/0 17/45 17-7/1; 17-8/1; 17-2/0; 17- -5/1; 17-6/0 17/46 17-7/1; 17-6/0 17/47 17-7/1; 17-5/0; 17-4/0 17/48 17-7/1; 17-5/0; 17-3/0 17/49 17-7/1; 17-5/0; 17-2/1; 17- -1/0 17/50 17-7/1; 17-5/0; 17-2/1; 17- -9/0 17/51 17-9/1; 17-1/0 17/52 17-9/1; 17-2/0; 17-3/0 17/53 17-9/1; 17-2/0; 17-4/0 17/54 17-9/1; 17-2/0; 17-5/1; 17 -6/0 17/55 17-9/1; 17-2/0; 17-5/1; 17 -7/0 17/56 17-9/1; 17-8/0; 17-7/0 17/57 17-9/1; 17-8/0; 17-6/0 17/58 17-9/1; 17-8/0; 17-5/0; 17 -4/0 17/59 17-9/1; 17-8/0; 17-5/0; 17 -3/0 17/60 17-9/1; 17-8/0; 17-5/0; 17 -2/1; 17-1/0 - 39 - . For the sequences 17/6 and 17/51, presence of the angularly oriented road segments (17-3/1, 17-3/0; 17-5/1, 17-5/0; 17-7/1, 17-7/0) may be omitted in a VC format. For the sequences 17/11-13, 17/21-22, 17/26, 17/31, 17/36-37 and 17-46-48, presence of the perpendicular four-way node (intersection of 17-1/1, 17-2/1, 17-8/1 and 17-9/1) may be omitted in a VC format. If the length dl, d2 and/or d3 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 17B into as many as three intersection components: the perpendicular four-way node, shown in Figure 17C, and the two acute angle four-way nodes, shown in Figures 17D and 17E. Figure 18A represents a four-way node with a curvilinear right/left turn road having two leg lengths dl and d2. Visibility across the area marked 18-BL may be partly or completely blocked by visual obstructions. Figure 18B represents the intersection in Figure 18A in VC format, illustrating the 14 road segments that make up the intersection: 18-1/1 and 18-1/0, representing incoming and outgoing segments from the bottom; 18-2/1 and 18-2/0, representing curvilinear intermediate segments connecting two approach roads; 18-3/1 and 18-3/0, representing incoming and outgoing segments from the right; 18-4/1 and 18-4/0, representing incoming and outgoing segments from the right; 18-5/1 and 18-5/0, representing incoming and outgoing segments from the top; 18-6/1 and 18-6/0, representing incoming and outgoing segments from the left; and 18-7/1 and 18-7/0, representing incoming and outgoing segments from the bottom. The intersection shown in Figure 18B allows at least 24 possible ordered path segment sequences through this intersection : - 40 18/1 18-1/1; 18-2/1, 18-3/0 18/2 18-1/1; 18-2/1, 18-4/1; 18-5/0 18/3 18-1/1; 18-2/1, 18-4/1; 18-6/0 18/4 18-1/1; 18-7/1, 18-6/0 18/5 18-1/1; 18-7/1, 18-5/0 18/6 18-1/1; 18-7/1, 18-4/0; 18-3/0 18/7 18-3/1; 18-4/1, 18-5/0 18/8 18-3/1; 18-4/1, 18-6/0 18/9 18-3/1; 18-4/1, 18-7/0; 18-1/0 18/10 18-3/1, 18-2/0; 18-1/0 18/11 18-3/1 18-2/0; 18-7/1; 18-6/0 18/12 18-3/1 • 18-2/0; 18-7/1; 18-5/0 18/13 18-5/1, 18-6;0 18/14 18-5/1 18-7/0; 18-1/0 18/15 18-5/1 18-7/0; 18-2/1; 18-3/0 18/16 18-5/1 • 18-4/0; 18-3/0 18/17 18-5/1 • 18-4/0; 18-2/0; 18-1/0 18/18 18-5/1 ■ 18-4/0; 18-2/0; 18-7/1; 18- -6/0 18/19 18-6/1 ■ 18-7/0; 18-1/0 18/20 18-6/1 • 18-7/0; 18-2/1; 18-3/0 18/21 18-6/1 • 18-2/1; 18-3/0 18/22 18-6/1 • 18-5/0 18/23 18-5/1 ; 18-4/0; 18-3/0 18/24 18-5/1 ; 18-4/0; 18-2/0; 18-1/0 For the sequences 18/13 and 18/22, presence of the curvilinear turn segment (18-2/1, 18-2/0) may be omitted. For the sequences 18/1 and 18/10, presence of the four-way node may be omitted. If the length dl and/or d2 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 18B into as many as three intersection components : the perpendicular four-way node, shown in Figure 18C, and the - 4 1 - two right turn or left turn approaches, shown in Figures 18D and 18E. Figure 19A represents two four-way nodes, angularly oriented toward each other, and a three-way node, forming a triangle with leg lengths dl, d2 and d3. Visibility across the area marked 19-BL may be partly or completely blocked by visual obstructions. Figure 19B represents the intersection in Figure 19A in VC format, illustrating the 16 road segments that make up the intersection: 19-1/1 and 19-1/0, representing incoming and outgoing segments from the bottom; 19-2/1 and 19-2/0, representing intermediate segments from the lower left; 19- 3/1 and 19-3/0, representing incoming and outgoing segments from the right; 19-4/1 and 19-4/0, representing incoming and outgoing segments from the upper right; 19-15/1 and 19-5/0, representing intermediate segments from the lower right; 19- 6/1 and 19-6/0, representing incoming and outgoing segments from the top; 19-7/1 and 19-7/0, representing incoming and outgoing segments from the left; and 19-8/1 and 19-8/0, representing intermediate segments from the bottom. The intersection shown in Figure 19B allows at least 40 possible ordered path segment sequences through this intersection: 19/1 19-11; 19-21; 19-3/0 19/2 19-11; 19-21; 19-4/0 19/3 19-11; 19-21; 19-5/1; 19-6/0 19/4 19-11; 19-21; 19-5/1; 19-7/0 19/5 19-1/1; 19-8/0; 19-7/0 19/6 19-1/1; 19-8/0; 19-6/0 19/7 19-1/1; 19-8/0; 19-5/0; 19-4/0 19/8 19-1/1; 19-8/0; 19-5/0; 19-3/0 19/9 19-3/1; 19-4/0 19/10 19-3/1; 19-5/0; 19-6/0 19/11 19-3/1; 19-5/0; 19-7/0 19/12 19-3/1; 19-5/0; 19-8/0; 19-1/0 42 - 19/13 19-3/1 • 19-2/0; 19-1/0 19/14 19-3/1 ■ 19-2/0; 19-8/0; 19- -7/0 19/15 19-3/1 ■ 19-2/0; 19-8/0; 19- -6/0 19/16 19-3/1 ■ 19-2/0; 19-8/0; 19- -5/0; 19-4/0 19/17 19-4/1 • 19-5/1; 19-6/0 19/18 19-4/1 ■ 19-5/1; 19-7/0 19/19 19-4/1, 19-5/1; 19-8/0; 19- -1/0 19/20 19-4/1 19-5/1; 19-8/0; 19- -2/1; 19-3/0 19/21 19-4/1 ■ 19-3/0 19/22 19-4/1 19-2/0; 19-1/0 19/23 19-4/1 19-2/0; 19-8/0; 19- -7/0 19/24 19-4/1, 19-2/0; 19-8/0; 19- -6/0 19/25 19-6;I, 19-7/0 19/26 19-6/1, 19-8/1; 19-1/0 19/27 19-6/1, 19-8/1; 19-2/1; 19- -3/0 19/28 19-6/1, 19-8/1; 19-2/1; 19- -4/0 19/29 19-6/1, 19-5/0; 19-4/0 19/30 19-6/1, 19-5/0; 19-3/0 19/31 19-6/1, 19-5/0; 19-2/0; 19- -1/0 19/32 19-6/1, 19-5/0; 19-2/0; 19- -8/0; 19-7/0 19/33 19-7/1, 19-8/1; 19-1/0 19/34 19-7/1, 19-8/1; 19-2/1; 19- -3/0 19/35 19-7/1, 19-8/1; 19-2/1; 19- -4/0 19/36 19-7/1, 19-8/1; 19-2/1; 19- -5/1; 19-6/0 19/37 19-7/1, 19-6/0 19/38 19-7/1 19-5/0; 19-4/0 19/39 19-7/1 • 19-5/0; 19-3/0 19/40 19-7/1 ■ 19-5/0; 19-2/0; 19- -1/0 For the sequences 19/1, 19/2, 19/9 and 19/21, presence of the segments 19-6/1,0 and 19-7/1,0 may be omitted. For the sequences 19/5, 19/6, 19/26 and 19/33, presence of the segments 19-3/1,0 and 19-4/1,0 may be omitted. For the sequences 19/29, 19/30, 19/38 and 19/39, presence of the segments 19-1/1,0 may be omitted. - 4 3 - If the length dl and/or d2 and/or d3 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 19B into as many as three intersection components: a three- way node, shown in Figure 19C, a four-way node, shown in Figure 19D and a four-way-way node, shown in Figure 19E. Figure 20A represents a four-way node with separated parallel approach road pairs, with one approach road pair facing but laterally displaced from another approach road pair. Visibility across the areas marked 20-BL/l and 20-BL/2 may be partly or completely blocked by visual obstructions. Figure 20B represents the intersection in Figure 20A in VC format, illustrating the ten road segments that make up the intersection: 20-1/1 and 20-1/O, representing incoming and outgoing segments from the bottom; 20-2/1 and 20-2/O, representing incoming and out going segments from the right; 20-3/1 and 20-3/O, representing incoming and outgoing segments from the top; 20-4/1 and 20-4/O, representing incoming and out going segments from the left; and 20-5/1 and 20-5/O, representing angularly oriented segments joining the 20-2/1,0 and 20-4/1,0 segments. The intersection shown in Figure 20B allows at least 12 possible ordered path segment sequences through this intersection: 20/1 20-1/1; 20-2/O 20/2 20-1/1; 20-3/O 20/3 20-1/1; 20-5/1; 20-4/O 20/4 20-2/1; 20-3/O 20/5 20-2/1; 20-5/1; 20-4/O 20/6 20-2/1; 20-5/O; 20-1/O 20/7 20-3/1; 20-4/O 20/8 20-3/1; 20-1/O 20/9 20-3/1; 20-5/O; 20-2/O 20/10 20-4/1; 20/1/O 20/11 20-4/1; 20-5/O; 20-2/O 20/12 20-4/1; 20-5/O; 20-3/O - 4 4 - For the sequences 20/1, the road segments 20-3/1,0, 20- 4/1,0 and 20-5/1,0 may be omitted. For the sequences 20/4, the road segments 20-1/1,0, 20-4/1,0 and 20-5/1,0 may be omitted. For the sequences 20/7, the road segments 20-1/1,0, 20-2/1,0 and 20-5/1,0 may be omitted. For the sequences 20/10, the road segments 20-2/1,0, 20-3/1,0 and 20-5/1,0 may be omitted. If the length dl and/or d2 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 20B into two intersection components : the angularly oriented four-way node shown in Figure 20C and/or the angularly oriented four-way node shown in Figure 20D. Figure 21A represents a trapezoid with four approach roads connected thereto, forming four three-way nodes. Visibility across the area marked 21-BL/l, 21-BL/2, 21-BL/3, 21-BL/4 and/or 21-BL/5 may be partly or completely blocked by visual obstructions. Figure 21B represents the intersection in Figure 21A in VC format, illustrating the 16 road segments that make up the intersection: 21-1/1 and 21-1/0, representing incoming and outgoing segments from the bottom left; 21-2/CC and 21- 1/C, representing intermediate segments; 21-3/1 and 21-3/0, representing incoming and outgoing segments from the bottom right; 21-4/CC and 21-4/C, representing intermediate segments; 21-5/1 and 21-5/0, representing incoming and outgoing segments from the top right; 21-6/CC and 21-6/C, representing intermediate segments; 21-7/1 and 21-7/0, representing incoming and outgoing segments from the top left; and 21-8/CC and 21-8/C, representing intermediate segments . - 45 The intersection shown in Figure 21B allows at least 24 possible ordered path segment sequences through this intersection : 21/1 21-1/1 ■ 21-2/CC, 21/3/0 21/2 21-1/1 • 21-2/CC, 21-4/CC; 21-5/0 21/3 21-1/1 ■ 21-2/CC, 21-4/CC; 21-6/CC; 21-7/0 21/4 21-1/1 ■ 21-8/C; 21-7/0 21/5 21-1/1 • 21-8/C; 21-6/C; 21-5/0 21/6 21-1/1 21-8/C; 21-6/C; 21-4/C; 21- -3/0 21/7 21-3/1 ■ 21-4/CC, 21/5/0 21/8 21-3/1 ■ 21-4/CC, 21-6/CC; 21-7/0 21/9 21-3/1 • 21-4/CC, 21-6/CC; 21-8/CC; 21-1/0 21/10 21-3/1 21-2/C; 21-1/0 21/11 21-3/1 21-2/C; 21-8/C; 21-7/0 21/12 21-3/1 ■ 21-2/C; 21-8/C; 21-6/C; 21- -5/0 21/13 21-5/1 ■ 21-6/CC, 21/7/0 21/14 21-5/1 ■ 21-6/CC; 21-8/CC; 21-1/0 21/15 21-5/1 • 21-6/CC, 21-8/CC; 21-2/CC; 21-3/0 21/16 21-5/1 ■ 21-4/C; 21-3/0 21/17 21-5/1 • 21-4/C; 21-2/C; 21-1/0 21/18 21-5/1 • 21-4/C; 21-2/C; 21-8/C; 21- -7/0 21/19 21-7/1 ■ 21-8/CC, 21/1/0 21/20 21-7/1 ■ 21-8/CC, 21-2/CC; 21-3/0 21/21 21-7/1 ; 21-8/CC, 21-2/CC; 21-4/CC; 21-5/0 21/22 21-7/1 • 21-6/C; 21-5/0 21/23 21-7/1 ; 21-6/C; 21-4/C; 21-3/0 21/24 21-7/1 • 21-6/C; 21-4/C; 21-2/C; 21- -1/0 For the sequences 21/1, 21/2, 21/16 and 21/17, the road segments 21-7/1,0 may be omitted. For the sequences 21/7, 21/8, 21/22 and 21/23, the road segments 21-1/1,0 may be omitted. For the sequences 21/13, 21/14, 21/4 and 21/5, the road segments 21-3/1,0 may be omitted. For the sequences 21/19, 21/20, 21/10 and 21/11, the road segments 21-5/1,0 may be omitted. - 4 6 - If the length dl and/or d2 and/or d3 and/or d4 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 21B into one or more of the four three-way nodes shown in Figures 21C, 21D, 21E and/or 21F. Figure 22A represents two four-way nodes and a three- way node, spaced apart, with a diagonal road connecting the three-way node to a road segment connecting the two four-way nodes. Visibility across the area marked 22-BL/l, 22-BL/2, 22-BL/3 and/or 22-BL/4 may be partly or completely blocked by visual obstructions. Figure 22B represents the intersection in Figure 22A in VC format, illustrating the 22 road segments that make up the intersection: 22-1/1 and 22-1/0, representing incoming and outgoing segments from the bottom; 22-2/1 and 22-2/0, representing incoming and outgoing segments from the right; 22-3/1 and 22-3/0, representing incoming and outgoing segments from the bottom; 22-4/CC and 22-4/C, representing intermediate diagonal segments from the lower left; 22-5/1 and 22-5/0, representing incoming and outgoing segments from the right; 22-6/1 and 22-6/0, representing incoming and outgoing segments from the top; 22-7/CC and 22-7/C, representing incoming and outgoing segments from the right; 22-8/1 and 22-8/0, representing incoming and outgoing segments from the top; 22-9/1 and 22-9/0, representing incoming and outgoing segments from the left; 22-10/CC and 22-10/C, representing incoming and outgoing segments from the top; and 22-11/1 and 22-1/0, representing incoming and outgoing segments from the left. The intersection shown in Figure 22B allows at least 84 possible ordered path segment sequences through this intersection: - 47 - 22 / 1 22 - 1 / 1 ; 22 -2 /0 22/2 22-1/1; 22-3/1; 22-4/CC; 22-5/0 22/3 22-1/1; 22-3/1; 22-4/CC; 22-6/0 22/4 22-1/1; 22-3/1; 22-4/CC; 22-7/CC; 22-8/0 22/5 22-1/1; 22-3/1; 22-4/CC; 22-7/CC; 22-9/0 22/6 22-1/1; 22-3/1; 22-4/CC; 22-7/CC; 22-10/CC; 22-3/0; 22-11/0 22/7 22-1/1; 22-11/0 22/8 22-1/1; 22-3/1; 22-10/C; 22-9/0 22/9 22-1/1; 22-3/1; 22-10/C; 22-8/0 22/10 22-1/1; 22-3/1; 22-10/C; 22-7/C; 22-6/0 22/11 22-1/1; 22-3/1; 22-10/C; 22-7/C; 22-5/0 22/12 22-1/1; 22-3/1; 22-10/C; 22-7/C; 22-4/C; 22-3/0; 22-2/0 22/13 22-2/1; 22-3/1; 22-4/CC; 22-5/0 22/14 22-2/1; 22-3/1; 22-4/CC; 22-6/0 22/15 22-2/1; 22-3/1; 22-4/CC; 22-7/CC; 22-8/0 22/16 22-2/1; 22-3/1; 22-4/CC; 22-7/CC; 22-9/0 22/17 22-2/1; 22-3/1; 22-4/CC; 22-7/CC; 22-10/CC; 22-3/1; 22-11/0 22/18 22-2/1; 22-11/0 22/19 22-2/1; 22-3/1; 22-10/C; 22-9/0 22/20 22-2/1; 22-3/1; 22-10/C; 22-8/0 22/21 22-2/1; 22-3/1; 22-10/C; 22-7/C; 22-6/0 22/22 22-2/1; 22-3/1; 22-10/C; 22-7/C; 22-5/0 22/23 22-2/1; 22-3/1; 22-10/C; 22-7/C; 22-4/C; 22-3/0; 22-2/0 22/24 22-2/1; 22-1/0 22/25 22-5/1; 22-6/0 22/26 22-5/1; 22-7/CC; 22-8/0 22/27 22-5/1; 22-7/CC; 22-9/0 22/28 22-5/1; 22-7/CC; 22-10/CC; 22-3/0; 22-11/0 22/29 22-5/1; 22-7/CC; 22-10/CC; 22-3/0; 22-1/0 22/30 22-5/1; 22-7/CC; 22-10/CC; 22-3/0; 22-2/0 22/31 22-5/1; 22-4/C; 22-3/0; 22-2/0 22/32 22-5/1; 22-4/C; 22-3/0; 22-1/0 22/33 22-5/1; 22-4/C; 22-3/0; 22-11/0 - 48 - 22/34 22-5/1 22-4/C; 22-10/C; 22-9/0 22/35 22-5/1 22-4/C; 22-10/C; 22-8/0 22/36 22-5/1 22-4/C; 22-10/C; 22-7/C; 22-6/0 22/37 22-6/1 22-7/CC; 22-8/0 22/38 22-6/1 22-7/CC; 22-9/0 22/39 22-6/1 22-7/CC; 22-10/CC; 22-3/0; 22-11/0 22/40 22-6/1 22-7/CC; 22-10/CC; 22-3/0; 22-1/0 22/41 22-6/1 22-7/CC; 22-10/CC; 22-3/0; 22-2/0 22/42 22-6/1 22-7/CC; 22-10/CC; 22-4/CC; 22-5/0 22/43 22-6/1 22-5/0 22/44 22-6/1 22-4/C; 22-3/0; 22-2/0 22/45 22-6/1 22-4/C; 22-3/0; 22-1/0 22/46 22-6/1 22-4/C; 22-3/0; 22-11/0 22/47 22-6/1 22-4/C; 22-10/C; 22-9/0 22/48 22-6/1 22-4/C; 22-10/C; 22-8/0 22/49 22-8/1 22-9/0 22/50 22-8/1 22-10/CC; 22-3/0; 22-11/0 22/51 22-8/1 22-10/CC; 22-3/0; 22-1/0 22/52 22-8/1 22-10/CC; 22-3/0; 22-2/0 22/53 22-8/1 22-10/CC; 22-4/CC; 22-5/0 22/54 22-8/1 22-10/CC; 22-4/CC; 22-6/0 22/55 22-8/1 22-7/CC; 22-6/0 22/56 22-8/1 22-7/CC; 22-5/0 22/57 22-8/1 22-7/CC; 22-4/C; 22-3/0; 22-2/0 22/58 22-8/1 22-7/CC; 22-4/C; 22-3/0; 22-1/0 22/59 22-8/1 22-7/CC; 22-4/C; 22-3/0; 22-11/0 22/60 22-8/1 22-7/CC; 22-4/C; 22-10/C; 22-9/0 22/61 22-9/1 22-10/CC; 22-3/0; 22-11/0 22/62 22-9/1 22-10/CC; 22-3/0; 22-1/0 22/63 22-9/1 22-10/CC; 22-3/0; 22-2/0 22/64 22-9/1 22-10/CC; 22-4/CC; 22-5/0 22/65 22-9/1 22-10/CC; 22-4/CC; 22-6/0 22/66 22-9/1 22-10/CC; 22-4/CC; 22-7/CC; 22-8/0 22/67 22-9/1 22-8/0 22/68 22-9/1 22-7/CC; 22-6/0 22/69 22-9/1 22-7/CC; 22-5/0 22/70 22-9/1 22-7/CC; 22-4/C; 22-3/0; 22-2/0 - 4 9 - 22/71 22-9/1; 22-7/CC; 22-4/C; 22-3/0; 22-1/0 22/72 22-9/1; 22-7/CC; 22-4/C; 22-3/0; 22-11/0 22/73 22-11/1; 22-1/0 22/74 22-11/1; 22-2/0 22/75 22-11/1; 22-3/1; 22-4/CC; 22-5/0 22/76 22-11/1; 22-3/1; 22-4/CC; 22-6/0 22/77 22-11/1; 22-3/1; 22-4/CC; 22-7/CC; 22-8/0 22/78 22-11/1; 22-3/1; 22-4/CC; 22-7/CC; 22-9/0 22/79 22-11/1; 22-3/1; 22-10/C; 22-9/0 22/80 22-11/1; 22-3/1; 22-10/C; 22-8/0 22/81 22-11/1; 22-3/1; 22-10/C; 22-7/C; 22-6/0 22/82 22-11/1; 22-3/1; 22-10/C; 22-7/C; 22-5/0 22/83 22-11/1; 22-3/1; 22-10/C; 22-7/C; 22-4/C; 22-3/0; 22-2/0 22 /84 22 -11 / 1 ; 22 -3 / 1 ; 22-10 /C ; 22 -7 /C ; 22-4 /C ; 22-3 /0; 22-1 /0 For the sequences 22/1-3,7,13-14,18,24-25,31-33,43- 46,73-76, the road segments 22-8/1,0 and 22-9/1,0 may be omitted. For the sequences 22/1,7-9,18-20.24,49-52,61- 63,67,73-74,79-80, the road segments 22-5/1,0 and 22-6/1,0 may be omitted. For the sequences 22/25-27,37-38,43,49,55- 56,67-69, the road segments 22-1/1,0, 22-2/1,0, 22-3/1,0 and 22-11/1,0 may be omitted. If the length dl and/or d2 and/or d3 and/or d4 and/or d5 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 22B into one or more of the four-way nodes shown in Figures 22C and/or 22E and/or 22F and/or the three-way node shown in Figure 22D. Figure 23A represents a four-way node, including a curvilinear right turn road segment having two leg lengths dl and d2 and a curvilinear leg length d3, a three-way node including the other end of the curvilinear right turn road segment, and another three-way node, spaced apart. - 50 Visibility across the area marked 23-BL may be partly or completely blocked by visual obstructions . Figure 23B represents the intersection in Figure 23A in VC format, illustrating the 14 road segments that make up the intersection: 23/1/1,0, representing incoming and outgoing segments from the bottom; 23-2/1,0, representing incoming and outgoing segments from the right; 22-3, representing an intermediate, one-way curvilinear segment; 22-4/1,0, representing incoming and outgoing segments from the upper right; 22-5/C,CC, representing intermediate segments; 22-6/1,0, representing incoming and outgoing segments from the lower left; and 22-7/C, CC, representing intermediate segments from the left. The intersection shown in Figure 23B allows at least 19 possible ordered path segment sequences through this intersection: 23/1 23-1/1; 23-2/0 23/2 23-1/1; 23-3; 23-4/0 23/3 23-1/1; 23-3; 23-5/CC; 23-6/0 23/4 23-1/1; 23-3; 23-5/CC; 23-7/CC; 23-2/0 23/5 23-1/1; 23-7/C; 23-6/0 23/6 23-1/1; 23-7/C; 23-5/C; 23-4/0 23/7 23-2/1; 23-3; 23-4/0 23/8 23-2/1; 23-3; 23-5/CC; 23-6/0 23/9 23-2/1; 23-3; 23-5/CC; 23-7/CC; 23-1/0 23/10 23-2/1; 23-7/C; 23-6/0 23/11 . 23-2/1; 23-7/C; 23-5/C; 23-4/0 23/12 23-2/1; 23-1/0 23/13 23-4/1; 23-5/CC; 23-6/0 23/14 23-4/1; 23-5/CC; 23-7/CC; 23-1/0 23/15 23-4/1; 23-5/CC; 23-7/CC; 23-2/0 23/16 23-6/1; 23-7/CC; 23-1/0 23/17 23-6/1; 23-7/CC; 23-2/0 23/18 23-6/1; 23-7/CC; 23-3; 23-4/0 23/19 23/6/1; 23-5/C; 23-4/0 - 51 - For the sequences 23/1,2,7,12 the road segments 23- 6/1,0 may be omitted. For the sequences 23/13,19, the road segments 23-1/1,0 and 23-2/1,0 may be omitted. For the sequences 23/1,5,10,12,16,17, the road segments 23-4/1,0 may be omitted. If the length dl and/or d2 and/or d3 is larger than a selected threshold distance dthr, as discussed above, it may be preferable to decompose the intersection shown in Figure 22B into a four-way node shown in Figure 23C and/or the two three-way nodes shown in Figures 23D and 23E. Figure 24 is a schematic view of apparatus suitable for practising the invention. The apparatus 241 includes a location determination (LD) unit 242, including an LD signal antenna 243 and LD signal receiver 244 that receive and process LD signals from one or more LD signal sources (not shown) to estimate the present location of the LD signal antenna. The apparatus 241 also includes a computer 245, including: a microprocessor 246 that receives the present location information from the LD unit 242; a memory unit 247 that contains an intersection database, with information about connected road segments intersections in a selected region, and additional memory for data processing and storage; a data/command entry module 248, such as a keyboard or light pen-driven screen, for entering data or commands into the computer; and at least one of a visual display 249, such as a visually perceptible screen, and an audibly perceptible display 250, such as a loudspeaker. The LD unit 242 may receive and process LD signals from satellites in a Global Positioning System (GPS) , from a Global Orbiting Navigational Satellite System (GLONASS) , from a modified Low Earth Orbit (LEO) system, from a LORAN ground-based system, or from any other suitable location determination system. The LD unit 242 may be portable or may be carried in or on a vehicle whose present location is to be determined. - 52 - The computer 245 receives the antenna present location information from the LD unit 242, compares this present location with road segments in the database 247, and locates the vehicle on a road segment. The computer determines the direction of vehicle travel, for example, by comparing two or more consecutive present locations, and determines the next intersection that the vehicle will encounter if the vehicle continues on its present path. If a vehicle route has been prescribed (and, optionally, stored in the computer memory unit 247), the computer determines the direction of approach to the next intersection, any manoeuvre required to pass through the next intersection on the selected route, and the direction of departure from the next intersection. Using this information and some guidelines that are preferably programmed into the computer 245, the computer determines and displays, visually and/or audibly, the next intersection in VC format, using the considerations developed in the preceding discussion. If the next intersection requires no special vehicle manoeuvre (e.g., pass'age straight through, with no turns or lane changes), the computer optionally does not display the next intersection. Preferably, the computer displays the next intersection in VC format, if at all, at least 5-60 seconds before the vehicle will reach an outer boundary of this intersection.

Claims: - 53 - Claims 1. A method for representation of an intersection in a vehicle route, the method being characterised by the steps of: receiving an indicium indicating a selected intersection in a network of road segments and a road segment for approach to, and a road segment for departure from, the selected intersection; retrieving from a computer database information that describes the selected intersection and road segments that contribute to the intersection; and visually displaying the selected intersection in a visually collapsed representation in which (1) the contributing segments that are displayed depend upon at least one of the approach road segment, the departure road segment, and a vehicle manoeuvre required to pass through the selected intersection and (2) road segments that intersect at least one of the approach road segment and the departure road segment that are located greater than a selected distance from the selected intersection, are not displayed. 2. A method as claimed in claim 1, wherein said step of receiving said indicium indicating said selected intersection is further characterised by the steps of: ■ tracking the location of a vehicle moving along said network of road segments; and selecting an indicium that corresponds to an intersection that the vehicle will encounter if the vehicle continues to move along said network of roads in a present direction of vehicle movement. 3. A method as claimed in claim 1, further characterised by the step of selecting said intersection from a class of intersections consisting of: an N-way node (N>3) with at least one straight or curvilinear right turn - 54 - road segment connecting two road segments that intersect at the node; an N-way node without a right turn road segment; an N-way node and a three-way node, spaced apart; two spaced apart three-way nodes; a three-way node located on a curving road; a three-way node and a four-way node, spaced apart; at least three tree-way nodes, spaced apart, along a road segment; an N-way node and first and second three-way, angularly oriented nodes, spaced apart; an N-way node and first and second three-way, angularly oriented nodes, spaced apart, with a straight or curvilinear road segment joining the first and second nodes; an N-way node and first and second four-way, angularly oriented nodes, spaced apart; an M-way node (M>4), with at least two approach roads oriented at an acute angle relative to each other; and an N-way node with at least two opposed approach roads laterally displaced from each other; and at least three three-way nodes, spaced apart 4. A method as claimed in claim 1, further characterised by the step of selecting said intersection from a class of intersections consisting of: a diverging Y- intersection; a converging Y-intersection; a diverging Y- intersection with at least one crossing road segment; a converging Y-intersection with at least one crossing road segment; a diverging Y-junction with at least one priority direction; and a converging Y-junction with at least one priority direction. 5. A method as claimed in claim 1, further characterised by the step of selecting said intersection from a class of intersections consisting of: a left turn crossover with approximately a quarter loop turn; and a left turn crossover with approximately a three-quarter loop turn. 6. A method as claimed in claim 1, further characterised by the step of selecting said intersection from a class of intersections consisting of: a partial- - 55 - circle roundabout, with at least one access road; a circular roundabout, with at least one access road; a partial-circle roundabout, having at least one access road with a Y- intersection where the access road joins the roundabout; and a circular roundabout, having at least one access road with a Y-intersection where the access road joins the roundabout. 7. A method as claimed in claim 1, further characterised by the step of selecting said intersection from a class of intersections consisting of: a polygon- shaped roundabout, with at least one access road; and a polygon-shaped roundabout, having at least one access road with a Y-intersection where the access road joins the roundabout . 8. A method as claimed in claim 1, further characterised by the step of selecting said intersection to include at least one road segment having at least one left turn lane or right turn lane . 9. Apparatus for representation of an intersection in a vehicle route, the apparatus being characterised by: a location determination (LD) unit that receives signals from one or more LD signal sources and estimates the location of the LD unit; and a computer that is programmed to: receive an indicium indicating a selected intersection in a network of road segments and a direction of approach to, and direction of departure from, the intersection; retrieve from a computer database information that describes the selected intersection and road segments that contribute to the intersection; and display the selected intersection in a visually collapsed representation in which (1) the contributing segments that are displayed depend upon at least one of the approach road segment, the departure road segment, and a vehicle manoeuvre required to pass through the selected - 5 6 - intersection and (2) road segments that intersect at least one of the approach road segment and the departure road segment that are located greater than a selected distance from the selected intersection, are not displayed. 10. An apparatus as claimed in claim 9, wherein said computer is further programmed to: track the location of a vehicle moving along said network of road segments; and select an indicium that corresponds to an intersection that the vehicle will encounter if the vehicle continues to move along said network of roads in a present direction of vehicle movement. 11. An apparatus as claimed in claim 9, wherein said intersection is drawn from a class of intersections consisting of: an N-way node (N>3) with at least one straight or curvilinear fight turn road segment connecting two road segments that intersect at the node; an N-way node without a fight turn road segment; an N-way node and a three-way node, spaced apart; two spaced apart three-way nodes; a three-way node located on a curving road; a three- way node and a four-way node, spaced apart; at least three three-way nodes, spaced apart, along a road segment; an N- way node and first and second three-way, angularly oriented nodes, spaced apart; an N-way node and first and second three-way, angularly oriented nodes, spaced apart, with a straight or curvilinear road segment joining the first and second nodes; an N-way node and first and second four-way, angularly oriented nodes, spaced apart; an M-way node (M>4), with at least two approach roads oriented at an acute angle relative to each other; and an N-way node with at least two opposed approach roads laterally displaced from each other; and at least three three-way nodes, spaced apart 12. An apparatus as claimed in claim 9, wherein said intersection is drawn from a class of intersections - 57 - consisting of: a diverging Y-intersection; a converging Y- intersection; a diverging Y-intersection with at least one crossing road segment; a converging Y-intersection with at least one crossing road segment; a diverging Y-junction with at least one priority direction; and a converging Y-junction with at least one priority direction. 13. An apparatus as claimed in claim 9, wherein said intersection is drawn from a class of intersections consisting of: a left turn crossover with approximately a quarter loop turn; and a left turn crossover with approximately a three-quarter loop turn. 14. An apparatus as claimed in claim 9, wherein said intersection is drawn from a class of intersections consisting of: a partial-circle roundabout, with at least one access road; a circular roundabout, with at least one access road; a partial-circle roundabout, having at least one access road with a Y-intersection where the access road joins the roundabout; and a circular roundabout, having at least one access road with a Y-intersection where the access road joins the roundabout. 15. An apparatus as claimed in claim 9, wherein said intersection is drawn from a class of intersections consisting of: a polygon-shaped roundabout, with at least one access road; and a polygon-shaped roundabout, having at least one access road with a Y-intersection where the access road joins the roundabout 16. An apparatus as claimed in claim 9, wherein said intersection is drawn from a class of intersections that include at least one road segment having at least one left turn lane or right turn lane.

Inventors: DESAI SIMON, SEKINE MASAYUKI, DESAI, SIMON, SEKINE, MASAYUKI
Applicants: MESSULAM ALEC MOSES, VISTEON TECH LLC, MESSULAM, ALEC, MOSES, VISTEON TECHNOLOGIES, LLC
Application year: 1999
Main classification: G01C21
IPC codes: G01C21, G08G1, G09B29