Method and system for representing restricted driving maneuvers

[0002] The present invention relates to navigation systems and more particularly the present invention relates to a way to avoid prohibited driving maneuvers when using a navigation system to determine a route to a destination.

[0003] Navigation systems provide useful features, such as calculating a route to a desired destination and providing guidance for following the route. In order to provide these features, navigation systems use geographic data that include information about the locations of roads and intersections, estimated travel times along road segments, the speed limits along roads, etc. Using geographic data, programming algorithms used in navigation systems can find an optimal (e.g, fastest or shortest) route to a specified destination.

[0004] The geographic data used by navigation systems also include data about traffic restrictions, such as one-way streets, no-left-turns, etc., so that the navigation system can calculate a legal route (i.e., a route that conforms to applicable traffic laws and regulations). For example, FIG. 1 illustrates a simple intersection at which it is illegal to make a right turn from road “A” to road “B.” In the geographic data, a data record used to represent the intersection of road A and road B may include information about this turn restriction. Similarly, if a road is a one-way street, information about this direction of travel restriction is included in the one or more data records that represent the road.

[0005] In addition to traffic restrictions that involve only two road segments, there are types of traffic restrictions that involve more than two road segments. Two examples of traffic restrictions that involve several segments (three or more segments) are shown in FIGS. 2 and 3. FIG. 2 illustrates lanes in one direction of traffic on an expressway where traffic flows from segment 2 to 3 to 4. Segment 1 represents an entrance ramp on the left, and segment 5 represents an exit ramp on the right. If segment 3 is too short to safely allow a vehicle entering the expressway on segment 1 from exiting via segment 5, traffic authorities may prohibit such a maneuver.

[0006] In FIG. 3, roads X and Y represent major arteries, while segments 5, 6, and 7 represent local roads. In many cases, a municipality will restrict drivers from taking a short cut from road X to road Y by prohibiting the sequence 1-5-6-4 and require drivers to follow the sequence 1-2-3-4. Turns are permitted into and out of the neighborhood as long as the illegal sequence is not followed.

[0007] In a navigation system, several-segment (3 or more) restricted driving maneuvers are more difficult for routing algorithms to deal with than two-segment restricted driving maneuvers. Several-segment restricted driving maneuvers require that the database include information that flags each segment in the several-segment restricted driving maneuver. Routing algorithms check every segment examined for this flag and ensure that the expanded route does not follow an illegal sequence. This becomes more complex if the routing algorithm is a two-ended A* algorithm and the several-segment restricted driving maneuver occurs where the source and destination search trees meet. Due to the complexity of implementation and extra processing required, some database compilers drop this data. Other database compilers may include it, but the in-vehicle routing application ignores it. As a result, illegal routes may be generated even when the data exists to prevent such routes.

[0008] Accordingly, there is a need for an improved means to handle several-segment restricted driving maneuvers.

[0009] To address these and other objectives, the present invention comprises a method that facilitates complying with traffic restrictions that involve three or more connected road segments when using a navigation system to determine a route. The method includes forming multiple instances of data representing each intermediate road segment between an entrance segment and an exit segment and storing data defining restrictions that apply to only two connected road segments, such that a valid driving paths exists between the entrance segment and the intermediate segment and between the intermediate segment and the exit segment, but that no valid driving paths exist between the entrance segment and the exit segment.

[0010] The present invention also includes a geographic database that embodies the described method for representing restricted driving maneuvers that involve three or more connected road segments, wherein the geographic database is stored on a computer-readable medium.

[0011] FIG. 1 is an illustration of an intersection having a turn restriction.

[0012] FIG. 2 illustrates a location that has a several-segment restricted driving maneuver wherein a section of an expressway has an entrance ramp on the left closely followed by an exit ramp on the right.

[0013] FIG. 3 illustrates another location that has a several-segment restricted driving maneuver wherein minor roads provide a potential shortcut between an intersection of major roads.

[0014] FIG. 4 illustrates the location of FIG. 2 with the inclusion of additional data for representing the several-segment restricted driving maneuver.

[0015] FIG. 5 illustrates the location of FIG. 3 with the inclusion of additional data for representing the several-segment restricted driving maneuver.

[0016] A solution to the problem of handling several-segment restricted driving maneuvers can be achieved by creating multiple instances of segments between the first and last segment of a several-segment restricted driving maneuver. Then, simple turn-restrictions like the one in FIG. 1 can be defined to satisfy the several-segment restriction. Furthermore, no extra functionality in the routing algorithm is needed to check for several-segment restricted driving maneuvers. To illustrate, reference is made to FIG. 4 that shows the same portion of expressway as shown in FIG. 2. In FIG. 4, the piece of road represented in FIG. 2 by segment 3 is replaced by two nearly identical segments that differ only in the access restriction attributes. For the example of FIG. 4, the two instances of segment 3 are renamed “3A” and “3B.” Simple turn restrictions are then assigned as follows.

[0017] As a result, there is no way to get from segment 1 to segment 5.

[0018] The example of FIG. 3 can be treated similarly. FIG. 5 shows the same portion of expressway as shown in FIG. 3, except that there are two segments between the start and end segment of the restricted driving maneuver. In FIG. 5, two instances of segments 5 and 6 are created and the following simple turn restrictions are assigned.

[0019] Again, using this representation, there is no legal path from segment 1 to segment 4 via segments 5 and 6. Yet it is still possible to route from segment 5 to segment 4 for local traffic using segment 5B and segment 6B.

[0020] The present embodiment can be used with any type of routing algorithm including the A* algorithm. The present embodiment can also be used with one-ended searches, two-ended searches, etc. Because simple turn-restrictions are handled routinely by routing algorithms, there is no extra processing required and no negative effect on route performance. The only cost is the space necessary to store multiple copies of the same segment.

[0021] It is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is understood that the following claims including all equivalents are intended to define the scope of the invention.