Patent Publication Number: US-2007106460-A1

Title: Route guidance system, methods and programs

Description:
INCORPORATION BY REFERENCE  
      The disclosure of Japanese Patent Application No. 2005-317769 filed on Oct. 31, 2005, including the specification, drawings and abstract is incorporated herein by reference in its entirety.  
     BACKGROUND  
      Related technical fields include navigation guidance systems, methods and programs.  
      In prior navigation system devices, an arrangement has been made wherein the current position of a vehicle that is a host vehicle is detected by a Global Positioning System (GPS) device. Map data is read out from a data storage portion, and a map screen is formed on a display unit. The map of the area surrounding the vehicle position, and the like are displayed on the map screen. Therefore, a driver can drive the vehicle according to the vehicle position displayed on the map screen.  
      Upon the driver inputting a destination and setting search conditions, route searching is executed based on the search conditions, and a route to the destination from the current position is sought according to the map data. A route that is specified is displayed on the map screen together with the vehicle position and guidance along the specified route is executed. Therefore, the driver can drive the vehicle along the displayed route.  
      During route guidance, when there is a prescribed point where the vehicle must turn, route guidance is executed, such as by voice output before the vehicle arrives at the turn. That is, the guidance intersection that serves as a guidance point. In order for route guidance to be executed, a plurality of route guidance points are set at locations at set distances before the guidance intersection along the specified route. When the vehicle arrives at the route guidance points, route guidance with a content that is set in advance for each of the route guidance points is output by voice. (Refer to Japanese Patent Application Publication No. JP-A-7-98223, for example.)  
       FIG. 2  is a diagram showing an example of route guidance according to a conventional navigation system.  
      In  FIG. 2 , the reference numerals r 1  to r 4  denote roads, the reference numeral cr 1  denotes an intersection of the roads r 1  and r 4 , and the reference numeral c 1  denotes a guidance intersection where the roads r 1  and r 2  intersect and the roads r 2  and r 3  intersect. The guidance intersection c 1  includes successive intersections ca and cb. The roads r 1  and r 2  intersect at the intersection ca, and the roads r 2  and r 3  intersect at the intersection cb. The reference numeral Rt 1  denotes the specified route. The specified route Rt 1  is configured such that it passes along the roads r 1  to r 3  in that order and, at the guidance intersection c 1 , turns right at the intersection ca, then immediately turns left at the intersection cb.  
      Progressing along the specified route Rt 1 , route guidance points h 1  to h 4  are set at locations 700 meters, 300 meters, 100 meters, and 30 meters before the guidance intersection c 1 , and route guidance points h 5  and h 6  are set between the intersections ca and cb on the road r 2 .  
      During travel on the road r 1 , a message such as “Turn right 700 meters ahead at XXXX,” or the like is output by voice at the route guidance point h 1 . A message such as “Turn right 300 meters ahead at XXXX,” or the like is output by voice at the route guidance point h 2 . A message such as “Turn right just ahead, then turn left 200 meters after that at YYYY,” or the like is output by voice at the route guidance point h 3 . At the route guidance point h 4 , a notification sound (two beeps) is output to indicate that the vehicle is about to enter the guidance intersection c 1 .  
      Next, after the vehicle enters the guidance intersection c 1 , a message such as “Turn left just ahead” or the like is output by voice at the route guidance point h 5 . At the route guidance point h 6 , a notification sound (two beeps) is output to indicate that the vehicle is about to enter the intersection cb.  
      In a navigation system that is capable of providing route guidance on a lane-by-lane basis, a prescribed lane is recommended as a preferable lane for driving. That is, the vehicle is guided from the lane in which it is currently driving to the recommended lane.  
     SUMMARY  
      In a case where the recommended lane changes when the road circumstances change before the vehicle arrives at the guidance intersection c 1 , such as when there is a right turn-only lane or left turn-only lane before the intersection cr 1 , or if the number of lanes changes, the conventional navigation system described above recommends a lane change after the vehicle has passed the point where the recommended lane changes, that is, the recommended lane change point. This confuses the driver.  
      Accordingly, exemplary implementations of the broad principles described herein reduce driver confusion.  
      Exemplary implementations provide route guidance systems, methods and programs that may detect a current position of a host vehicle and search for a specified route to a destination based on the current position of the vehicle. The systems, methods and programs may set a guidance intersection based on a specified route, and may compute a recommended lane on each road along the specified route. The systems, methods and programs may detect a recommended lane change point where a recommended lane changes between the current position of the vehicle and the guidance intersection. The systems, methods and programs may notify the driver that the recommended lane will change before the host vehicle arrives at the recommended lane change point.  
      According to the an exemplary implementation, the recommended lane change point, where the recommended lane changes, is detected between the current position and the guidance intersection, and the driver is notified, before the host vehicle arrives at the recommended lane change point, that the recommended lane will change. Therefore, the driver confusion may be reduced when being guided to drive the host vehicle in the recommended lane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Exemplary implementations will now be described with reference to the accompanying drawings, wherein:  
       FIG. 1  is a diagram showing an exemplary navigation system;  
       FIG. 2  is a diagram showing exemplary route guidance;  
       FIG. 3  is a flowchart showing an exemplary route guidance method;  
       FIG. 4  is a schematic diagram showing an exemplary guidance intersection;  
       FIG. 5  is a detailed drawing of an exemplary guidance intersection; and  
       FIG. 6  is a diagram showing exemplary lane guidance for the guidance intersection. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY IMPLEMENTATIONS  
       FIG. 1  is a diagram showing an exemplary navigation system. In  FIG. 1 , the reference numeral  10  denotes, for example, an automatic transmission control portion that serves as a power train control portion. The automatic transmission control portion  10  controls, for example, a power train that shifts gears at a prescribed gear ratio, such as a continuously variable transmission (CVT) that serves as an automatic transmission, a stepped transmission (automatic transmission), an electric drive unit, or the like.  
      The reference numeral  14  denotes, for example, a navigation unit that serves as an information terminal, such as an on-board unit that is mounted in a vehicle. The reference numeral  63  denotes, for example, a network, and the reference numeral  51  may denote an inform center that serves as an information provider. A navigation system may be made up, for example, of the automatic transmission control portion  10 , the navigation unit  14 , the network  63 , the information center  51 , and the like.  
      The navigation unit  14  includes, for example, a Global Positioning System (GPS) sensor  15 , a memory (e.g., a data storage portion  16 ), a controller (e.g., a navigation processing portion  17 ), a direction sensor  18 , an operation portion  34 , a display portion  35 , a voice input portion  36 , a voice output portion  37 , and a communications portion  38 . The GPS sensor  15  serves, for example, as a current position detection portion that detects the current position of the vehicle. The data storage portion  16  serves, for example, as an information storage portion where map data and various other types of data are stored. The navigation processing portion  17  may carry out, for example, various types of computations, such as navigation computations and the like, based on information that is input. The direction sensor  18  serves, for example, as a direction detection portion that detects the vehicle&#39;s direction. The operation portion  34  serves, for example, as a first input portion, by operating which the driver, who is the operator, makes a prescribed input. The display portion  35  serves, for example, as a first output portion that uses images displayed on a screen not shown in  FIG. 1  to express various types of information and notify the driver. The voice input portion  36  serves, for example, as a second input portion for making a prescribed input by voice. The voice output portion  37  serves, for example, as an output portion that uses voice to express various types of information and notify the driver. The communications portion  38  serves, for example, as a transmitting and receiving portion that functions as a communications terminal. The GPS sensor  15 , the data storage portion  16 , the direction sensor  18 , the operation portion  34 , the display portion  35 , the voice input portion  36 , the voice output portion  37 , and the communications portion  38  may be, for example, connected to the navigation processing portion  17 .  
      Also connected to the navigation processing portion  17  may be, for example, the automatic transmission control portion  10 , a forward monitoring unit  48 , a rear view camera (rear monitoring camera)  49 , an accelerator sensor  42 , a brake sensor  43 , a vehicle speed sensor  44 , and the like. The forward monitoring unit  48  may be installed at a prescribed location on the front end of the vehicle and monitors the area in front of the vehicle. The rear view camera  49  may be installed at a prescribed location on the rear end of the vehicle and may serve as a photography unit that captures images of the area behind the vehicle and as a rear monitoring unit. The accelerator sensor  42  serves, for example, as an engine load detection portion that detects the driver&#39;s operation of the accelerator pedal based on the accelerator angle. The brake sensor  43  serves, for example, as a braking detection portion that detects the driver&#39;s operation of the brake pedal based on the amount by which the pedal is depressed. The vehicle speed sensor  44  may serve as a vehicle speed detection portion that detects the vehicle speed. Note that the accelerator sensor  42 , the brake sensor  43 , and the like may, for example, make up an operation information detection portion that detects information on the operation of the vehicle by the driver.  
      The GPS sensor  15  may detect the vehicle&#39;s current position on the Earth, as well as the time, by receiving radio waves generated by a satellite. In an exemplary implementation, the GPS sensor  15  is, for example, used as the current position detection portion, but a distance sensor, a steering sensor, an altimeter, or the like can also be used individually or in combination instead of the GPS sensor  15 . A gyroscopic sensor, a geomagnetic sensor, or the like can be used as the direction sensor  18 . In an exemplary implementation, the direction sensor  18 , the vehicle speed sensor  44 , and the like are installed, but where a GPS sensor having functions to detect the host vehicle direction, the vehicle speed, and the like is used, the direction sensor  18 , the vehicle speed sensor  44 , and the like may not be necessary.  
      The data storage portion  16  may be, for example, provided with a map database made up of map data files, and map data is stored in the map database. The map data may include, for example, intersection data pertaining to intersections (branching points), node data pertaining to nodes, road data pertaining to road links, search data that is processed for searching, facilities data pertaining to facilities, and the like, as well as local feature data pertaining to local features.  
      As used herein, the term “link” refers to, for example, a road or portion of a road. For example, according to one type of road data, each road may consist of a plurality of componential units called links. Each link may be separated and defined by, for example, an intersection, an intersection having more than three roads, a curve, and/or a point at which the road type changes. As used herein the term “node” refers to a point connecting two links. A node may be, for example, an intersection, an intersection having more than three roads, a curve, and/or a point at which the road type changes.  
      The local features may be made up of displays installed or formed on the road to provide various kinds of driving-related information and guidance to drivers. These displays may include marking lines, indicators, pedestrian crosswalks, manholes, traffic signals, and the like. Marking lines may include stop lines to stop vehicles, lane demarcation lines that delineate the boundaries of lanes, demarcation lines that delineate parking spaces, and the like. Indicators include, for example, lane differentiation indicators in the form of arrows in each lane to indicate the direction of travel, and guidance indicators, such as the word “Stop” and the like, that warn of an approaching location where the vehicle must stop momentarily. The local feature data may include position information, which describes the position of each feature in terms of coordinates and the like, and image information, which shows an image of each feature. Note that for locations where the vehicle must stop momentarily, the information may include places where vehicles enter main roads from side roads, crossings, intersections with flashing red lights, and so on.  
      The road data pertaining to the lanes includes, for example, lane data that may serve as lane information, including the number of lanes, lane numbers that are assigned to each lane on a road, lane positions, traffic categories that express the direction of travel in each lane, and the like. Data may also be stored in the data storage portion  16  in order for the voice output portion  37  to output prescribed information.  
      A statistical database made up of statistical data files and a driving history database made up of driving history data files may also be stored in the data storage portion  16 . The statistical data in the statistical data files and the driving history data in the driving history data files are, for example, stored as actual results data.  
      The statistical data may include actual traffic information provided in the past, that is, historical information that describes a history. Traffic information provided in the past by traffic information centers and the like as information providers, such as the Vehicle Information and Communication System (VICS) center and the like, traffic census information, which is data on traffic volumes from traffic censuses provided by the Ministry of Land Infrastructure and Transport, and road timetable information and the like, also provided by the Ministry of Land Infrastructure and Transport, may also be used individually or in combination. The statistical data may be created by refining the information as necessary, then carrying out statistical analysis. Note that congestion forecasting information and the like for forecasting congestion and other purposes can be added. In that case, when the statistical data is created, detailed conditions may be added to the historical information, such as information on dates and times, days of the week, weather, various types of events, seasons of the year, facilities (the presence or absence of department stores, supermarkets, and the like), and the like.  
      The data items in the statistical data are, for example, made up of link numbers for various road links, direction flags to indicate the direction of travel, information classifiers that show the type of information, degrees of congestion at specific times, link required times that describe the times required to travel on various road links at specific times, data on link required times averaged for each day of the week (for example, average time for Wednesday), and the like.  
      The driving history data is, for example, made up of information collected by the information center  51  from a plurality of vehicles, i.e., the host vehicle and other vehicles, and represents actual driving records of vehicles traveling on roads where each vehicle has traveled. That is, it may be actual history information that describes driving records, and based on the driving data, probe data may be computed and accumulated.  
      The data items in the driving history data may be made up of link required times at specific times when vehicles traveled on each road link, degrees of congestion at specific times when vehicles traveled on each road link, and the like. Note that the driving history data can be added to the statistical data. In an exemplary implementation, the degree of congestion is used as a congestion indicator that expresses the scale of congestion. Congestion, crowding, and non-congestion may be expressed separately.  
      In order to store the various types of data, the data storage portion  16  may include, for example, a disk not shown in  FIG. 1 , such as a hard disk, a CD, a DVD, an optical disk, or the like. The data storage portion  16  may also include a read/write head or the like for reading and writing various types of data. It is also possible to use a memory card or the like for the data storage portion  16 . Note that an external storage device may be formed by the various disks, the memory card, or the like.  
      The map database, the statistical database, the driving history database, and the like may be installed in the data storage portion  16 , but the map database, the statistical database, the driving history database, and the like can also be installed in the information center  51 .  
      The navigation processing portion  17  may include a CPU  31 , a RAM  32 , a ROM  33 , and a flash memory that is not shown in  FIG. 1 . The CPU  31  may serve as a control device that controls the entire navigation unit  14  and/or as a computation device. The RAM  32  is, for example, used as working memory when the CPU  31  performs various types of computations. The ROM  33  may contain a control program, as well as various types of programs that search for routes to destinations, execute route guidance, and so on. The flash memory is used to store various types of data, programs, and the like. Note that an internal storage device may be formed by the RAM  32 , the ROM  33 , the flash memory, or the like.  
      Various types of programs may be stored in the ROM  33 , and various types of data can be stored in the data storage portion  16 , but programs, data, and the like can also be stored on a disk or the like. In that case, programs, data, and the like that are read from the disk or the like can be written to the flash memory. The programs, data, and the like can therefore be updated by replacing the disk or the like. The control programs, data, and the like of the automatic transmission control portion  10  can also be stored on the disk or the like. The programs, data, and the like can be received through the communications portion  38  and written to the flash memory in the navigation processing portion  17 .  
      The operation portion  34  may execute such tasks, for example, as correcting the current position when the vehicle starts to move, inputting a departure point and a destination, inputting points to be passed, and operating the communications portion  38 , all according to the driver&#39;s operations. The operation portion  34  can use a keyboard, mouse, or the like that may be installed independently of the display portion  35 . The operation portion  34  can also use a touch panel that is capable of executing prescribed input operations that are done by touching or clicking on an image operation portion, such as various types of keys, switches, buttons, and the like that are displayed as images on a screen that is formed by the display portion  35 .  
      The display portion  35  may be used as a display. The various screens that are formed on the display portion  35  can, for example, display the vehicle&#39;s current position; the vehicle&#39;s direction; maps, the specified route, guidance information along the specified route, traffic information, and the like; the distance to the next intersection on the specified route and the direction of travel at the next intersection. The screens may also display operation guidance, operation menus, and key guidance for the image operation portion, the operation portion  34 , the voice input portion  36 , and the like. The screens can also display programs and the like that are broadcast by FM multiplex.  
      The voice input portion  36  may include a microphone and can input required information by voice. The voice output portion  37  may include a voice synthesizing unit and a speaker. The voice output portion  37  may output the specified route, the guidance information, the traffic information, and the like by a voice that is, for example, synthesized by the voice synthesizing unit, for example.  
      The communications portion  38  may include a beacon receiver and an FM receiver for receiving various types of information, such as current traffic information transmitted from the traffic information center, general information, or the like. The beacon receiver may receive, for example, the information as radio wave signals or optical signals via radio wave beacons or optical beacons installed along the road. The FM receiver may receive the information as FM multiplex broadcasts via an FM broadcast station. Note that the traffic information may include congestion information, regulatory information, parking space information, traffic accident information, service area congestion status information, and the like. The general information may include news, weather forecasts, and the like. The beacon receiver and the FM receiver are combined in a single VICS receiver, but they can also be installed separately.  
      The traffic information may contain, for example, an information classification that may define the type of information, a mesh number that specifies a mesh, a link number that specifies a road link connecting two points (e.g., two intersections) and also distinguishes between inbound and outbound halves of the road, and link information that constitutes the content of the information that is provided for the corresponding link number. For example, if the traffic information may be congestion information, the link information may be made up of congestion leading edge data, which tells the distance from the start of the road link to the leading edge of the congestion; the degree of congestion; a congestion length, which tells the distance from the leading edge of the congestion to its trailing edge; the link required time, which tells the time required to travel the road link; and so on.  
      The communications portion  38  can also, for example, receive map data, statistical data, driving history data, and the like, as well as various types of the information such as traffic information, general information, and the like, via the network  63 .  
      For that reason, the information center  51  may include a controller (e.g., a server  53 ), a communications portion  57  connected to the server  53 , a database  58  that serves as an information storage portion, and so on. The server  53  may include a CPU  54 , a RAM  55 , and a ROM  56 . The CPU  54  may serve as a control device and/or a computation device. The database  58  may store the same sort of data that is stored in the data storage portion  16 , such as map data statistical data, and driving history data, for example. The information center  51  can also, for example, provide in real time various types of the information, such as current traffic information that is transmitted from the traffic information center, general information, and the like, as well as driving history data that is collected from a plurality of vehicles (the host vehicle and other vehicles).  
      The forward monitoring unit  48  may be made up of a radar, such as a laser radar, a millimeter-wave radar, or the like, or an ultrasonic sensor or the like, or a combination of a radar or the like and an ultrasonic sensor or the like. The forward monitoring unit  48  may monitor a vehicle that is traveling ahead of the host vehicle, that is, a vehicle ahead, and may also monitor momentary stopping points, obstacles, and the like. The forward monitoring unit  48  may also detect the relative speed, which is the vehicle speed relative to the vehicle ahead, the approach speed in relation to momentary stopping points, the approach speed in relation to obstacles, the distance to the vehicle ahead, the time to the vehicle ahead, and the like, all as information about the area around the host vehicle.  
      The rear view camera  49  may be made up of a CCD device, for example, and may be mounted so that its optical axis tilts downward in order to monitor the area behind the vehicle. In addition to local features, the subjects for image capture may include a vehicle traveling behind the host vehicle, that is, a vehicle behind, buildings and other structures on the roadside, and the like. The rear view camera  49  may generate image data of the photographed subjects and may send the data to the CPU  31 . The CPU  31  may, for example, read the image data to recognize individual photographed subjects as recognized objects. In an exemplary implementation, a CCD device is used as the rear view camera  49 , but a C-MOS device or the like can be used.  
      Note that the navigation system, the control portion  10 , the navigation processing portion  17 , the CPUs  31 ,  54 , the server  53 , and the like may, for example, function as computers, independently or in combinations of two or more, and execute computations based on various types of programs, data, and the like. Also, storage media may be made up of the data storage portion  16 , the RAMs  32 ,  55 , the ROMs  33 ,  56 , the database  58 , the flash memories, and the like. Also, microprocessors or the like can be used as computation devices in place of the CPUs  31 ,  54 .  
      Next, the basic operation of an exemplary navigation system described above will be explained.  
      First, when the driver operates the operation portion  34  and the navigation unit  14  starts up, the CPU  31  may read the current position of the host vehicle detected by the GPS sensor  15 , read the host vehicle direction detected by the direction sensor  18 , and may initialize various types of data. Next, the CPU  31  may specify the current position by judging on which road link the current position lies, based on the track of the current position that was read, the shapes and arrangement of the various road links that make up the roads in the vicinity of the current position, and so on.  
      Also, in an exemplary implementation, the CPU  31  may further specify the current position based on the positions of various local features that are photographed subjects photographed by the rear view camera  49 , for example.  
      For that purpose, the CPU  31 , may read in image data from the rear view camera  49  and recognize a local feature in an image formed from the image data. Also, the CPU  31 , may compute a distance La from the camera  49  to the actual local feature, based on the position of the local feature in the image. The CPU  31  may read in the distance La and read local feature data from the data storage portion  16  to obtain the coordinates of the local feature, then specify the current position based on the coordinates and the distance La.  
      The CPU  31 , may detect the lane in which the host vehicle is currently driving by checking a local feature that was recognized based on the image data against the local feature data that are read from the data storage portion  16 .  
      CPU  31  may also detect the current driving lane by reading the sensor output from the geomagnetic sensor, judging whether or not a detected object consisting of a strongly magnetic object such as a manhole cover or the like is present in a given lane on the road, based on the sensor output, and then detect the driving lane based on that judgment. The CPU  31  may also detect the current driving lane by using the highly accurate GPS sensor  15  to detect the current position with high accuracy, then detect the lane based on the current position detection result. As necessary, the CPU  31  may also detect the current driving lane by combining the geomagnetic sensor output, the current position, and the like at the same time that it analyzes image data from marking lines.  
      The CPU  31  may obtain map data from the data storage portion  16  or receive map data from the information center  51  or the like via the communications portion  38 . Note that when map data is obtained from the information center  51  or the like, the CPU  31  may write the received data to the flash memory.  
      The CPU  31  may form various types of screens on the display portion  35 . For example, The CPU  31  may form a map display screen on the display portion  35  that displays the current position as the host vehicle position and the vehicle direction as the host vehicle direction, while also displaying maps of the areas surrounding the map screen.  
      Therefore, the driver is able to drive the vehicle according to the map, the host vehicle position, and/or the host vehicle direction.  
      When the driver operates the operation portion  34  to input a destination, the CPU  31  may set the destination. Note that the departure point may also be input and set as necessary. It is also possible to register a given location in advance, then set the registered location as the destination. When the driver operates the operation portion  34  to input a search condition the CPU  31  may execute set the search condition.  
      When the destination and search condition are set in this manner, the CPU  31  may execute route searching wherein the CPU  31  reads the current position, the destination, the search condition, and the like, and reads search data and the like from the data storage portion  16 . Based on the current position, the destination, and the search data, the CPU  31  searches for a route from the departure point, expressed as the current position, to the destination, according to the search condition. The CPU  31  may output route data that describes the specified route. The specified route may be the route for which the total of the link costs assigned to each road link is the lowest.  
      Note that route searching can be executed at the information center  51 . In that case, the CPU  31  may transmit the current position, the destination, the search condition, and the like to the information center  51  via the network  63 . When the information center  51  may receive the current position, the destination, the search condition, and the like, the CPU  54  may execute route searching in the same manner as CPU  31 . The CPU  31  may read search data from the database  58  and based on the current position, the destination, and the search data, search for a route from the departure point to the destination, according to the search condition. The CPU  31  may output route data that describe the specified route. Next, the CPU  54 , not shown in  FIG. 1 , may, transmit the route data to the navigation unit  14  via the network  63 .  
      Next, the CPU  31  may provide route guidance. For this purpose, the CPU  31  may read the route data and display the specified route on the map screen according to the route data.  
      Incidentally, when the vehicle must turn right or left at a prescribed intersection, the intersection is set as a guidance point and as a guidance intersection for route guidance. For that purpose the CPU  31  may execute guidance intersection setting, wherein the CPU  31  determines, according to the route data, that is, based on the specified route, whether or not there is an intersection where the vehicle must turn right or left. If there is an intersection where the vehicle must turn right or left, the intersection is set as a guidance intersection.  
      Next, the CPU  31  may form an enlarged guidance map before the vehicle arrives at the guidance intersection, and CPU  31  may form an enlarged map of the guidance intersection, that is, an enlarged intersection map, as an enlarged guidance point map in a specified area of the map screen and use the enlarged intersection map to provide route guidance. In order for route guidance to be provided, an enlarged guidance point map display point is set at a location that is a set distance before the guidance intersection (closer than the guidance intersection to the current position) along the specified route. When the vehicle arrives at the enlarged guidance point map display point, the enlarged guidance point map may be displayed.  
      In this case, a map of the area surrounding the guidance intersection, the specified route, and landmarks such as facilities and the like that serve as markers at the guidance intersection may be displayed on the enlarged intersection map. Note that on an automobile-only toll road, such as an expressway, metropolitan expressway, toll road, or the like, intersections such as junctions and the like, where traffic merges or diverges, may also beset as guidance intersections.  
      Incidentally, in a case where the specified route includes a road in which a plurality of lanes are formed, lane guidance can be provided. For that purpose, the CPU  31  may read the specified route, as well as intersection data, lane information, and the like, then compute a recommended lane on each road on the specified route, based on the specified route, the intersection data, the lane information, and the like. Also the CPU  31  may form a lane guidance map in a specified area of the map screen, displaying the recommended lane in the lane guidance map, and guiding the vehicle from its current driving lane to the recommended lane.  
      In a case where a plurality of lanes are formed in a road that enters a guidance intersection (hereinafter referred to as an entrance road) or in a road that exits a guidance intersection (hereinafter referred to as an exit road), the CPU  31  may display the recommended lane on the enlarged intersection map.  
      Incidentally, during the interval that lane guidance is being provided for the guidance intersection, it may sometimes happen that the recommended lane changes before the vehicle arrives at the guidance intersection. This may occur, for example, because the road circumstances change, such as when there is a right turn-only lane or left turn-only lane before the guidance intersection, or the number of lanes decreases. In that case, if the system recommends a lane change after the vehicle has passed the point where the recommended lane changes (the recommended lane change point), it may become difficult or impossible to change lanes as recommended, thus, the driver may become confused.  
      Accordingly, in an exemplary implementation, the CPU  31  may recommend lane information by first judging whether the recommended lane will change during the interval from the current position to the guidance intersection (that is, during the interval when lane guidance is provided). If the recommended lane will change, the CPU  31  may detect recommended lane change point. The CPU  31  may then read the recommended lane change point and notify the driver that the lane will change before the vehicle arrives at the recommended lane change point, that the recommended lane will change. For that purpose the CPU  31 , sets a point at a specified distance before the recommended lane change point as the point for notifying the driver, as the recommended lane change point notification point. The CPU  31  may output voice, such that when the vehicle arrives at the recommended lane change notification point, the system notifies the driver by voice output from the voice output portion  37 , that the recommended lane will change at the recommended lane change point.  
      The CPU  31  may set one or more route guidance points, such as a plurality of route guidance points, at locations at set distances before the guidance intersection on the specified route. When the vehicle arrives at a route guidance point, CPU  31  may output voice from the voice output portion  37  for the guidance intersection with content that is set in advance for each of the route guidance points. Note that the enlarged guidance point map display point at which the enlarged guidance point map is displayed and one of the route guidance points, such as the first route guidance point, for example, can be set to the same point.  
      In this case, if there is a recommended lane change point on the specified route to the guidance intersection, if the timing of the start of route guidance for the guidance intersection is not the optimum timing, it may not be possible to make the vehicle change reliably to the new recommended lane at the recommended lane change point.  
      Accordingly, in order for it to be possible to make the vehicle change reliably to the new recommended lane at the recommended lane change point, the recommended lane change point may be used as a reference point for computing the timing of the start of route guidance for the guidance intersection, that is, the guidance start timing, and for setting the first route guidance point.  
      Next, the system may judge whether or not the vehicle has passed the recommended lane change point. When the vehicle passes the recommended lane change point the CPU  31  may set a point at a specified distance beyond the recommended lane change point as a recommended lane change point passing guidance point. When the vehicle arrives at the recommended lane change point passing guidance point, the system may notify the driver that the vehicle has passed the recommended lane change point by providing guidance to the new recommended lane.  
      In  FIG. 4 , the reference numerals r 1  to r 4  denote roads, the reference numeral cr 1  denotes an intersection of the roads r 1  and r 4 , and the reference numeral c 1  denotes a guidance intersection where the roads r 1  and r 2  intersect and the roads r 2  and r 3  intersect. The guidance intersection c 1  includes successive intersections ca and cb. The roads r 1  and r 2  intersect at the intersection ca, and the roads r 2  and r 3  intersect at the intersection cb. The reference numeral Pr denotes the current position, and the reference numeral Rt 1  denotes the specified route. The specified route Rt 1  is configured such that it passes along the roads r 1  to r 3  in that order and, at the guidance intersection c 1 , turns right at the intersection ca, then immediately turns left at the intersection cb.  
      As shown in  FIG. 5 , lanes k 1  to k 3  are formed on the road r 1 , and lanes k 11  to k 15  are formed on the road r 2 . The lane k 1  is a left turn-only lane before the intersection cr 1 , but before the intersection ca of the guidance intersection c 1 , the lane k 1  is a lane where both right and left turns are possible. The lanes k 2  and k 3  are right turn-only lanes before the intersection ca of the guidance intersection c 1 .  
      When the vehicle travels along the specified route Rt 1 , the vehicle passes the intersection cr 1 , then at the guidance intersection c 1 , turns right at the intersection ca, entering the road r 2 , and then turns left at the intersection cb.  
      At this time, on the road r 1 , the lane k 1  is a left turn-only lane before the intersection cr 1 , so the CPU  31  makes the lane k 2  the recommended lane in the lane guidance from the current position Pr to the intersection cr 1 .  
      Before the guidance intersection c 1 , the lane k 1  is a lane where a right turn is possible, and the lanes k 2  and k 3  are right turn-only lanes, but because the vehicle will turn left at the intersection cb, the CPU  31  makes the lane k 1  the recommended lane in the lane guidance from the intersection cr 1  up to the intersection ca and makes the lane k 11  the recommended lane in the lane guidance from the intersection ca to the intersection cb.  
      The CPU  31  reads the recommended lane information and detects the recommended lane change point on the specified route Rt 1  to the intersection cb. On the specified route Rt 1 , the recommended lane changes from the lane k 2  to the lane k 1  at the intersection cr 1 , so the intersection cr 1  is detected as the recommended lane change point. Note that it is actually not desirable for the lane to be changed within the intersection cr 1 , so the far-side edge of the intersection cr 1  is set as the recommended lane change point. The near-side edge of the intersection cr 1  can also be set as the recommended lane change point.  
      Then, as shown in  FIG. 6 , the CPU  31  sets a point at a specified distance before the intersection cr 1  as a recommended lane change point notification point ha. When the vehicle arrives at the recommended lane change point notification point ha, which may be set at a location 400 meters before the intersection cr 1 , the CPU  31  may notify the driver by voice output from the voice output portion  37  that the recommended lane will change from the lane k 2  to the lane k 1  at the intersection cr 1 .  
      The CPU  31  may set route guidance points h 11  to h 14  on the specified route Rt 1  at locations 800 meters, 300 meters, 100 meters, and 30 meters before the guidance intersection c 1 , and sets route guidance points h 15  and h 16  between the intersections ca and cb on the road r 2 .  
      Next, when the vehicle arrives at each of the route guidance points h 11  to h 16 , the CPU  31  may output voice from the voice output portion  37  for route guidance through intersection c 1  with content that is set in advance for each of the route guidance points h 11  to h 16 .  
      In this case, the intersection cr 1  is set as a recommended lane change point on the specified route Rt 1  to the guidance intersection c 1 , so the intersection cr 1  is used as a reference point for computing the guidance start timing for the guidance intersection c 1 , and for setting the first route guidance point h 11  at 800 meters before the guidance intersection c 1 , so that the vehicle will be able to change to the new recommended lane k 1  at the intersection cr 1 .  
      Next, the system may judge whether or not the vehicle has passed the intersection cr 1 . When the vehicle passes the intersection cr 1 , the CPU  31  may provide guidance to the new recommended lane at a recommended lane change point passing guidance point hb that is set on the guidance intersection c 1  side of the intersection cr 1 .  
      Next, an example of lane guidance will be explained.  
      When the vehicle is in transit on the road r 1 , a message such as “Turn right 800 meters ahead. The middle lane is the recommended lane,” or the like may be output by voice at the route guidance point h 11 . A message such as “After the intersection, the recommended lane shifts one lane to the left,” or the like may be output by voice at the recommended lane change point notification point ha. A message such as “The recommended lane is one lane to the left,” or the like may be output by voice at the recommended lane change point passing guidance point hb, after the vehicle has passed the intersection cr 1 . A message such as “Turn right 300 meters ahead at XXXX,” or the like may be output by voice at the route guidance point h 12 . A message such as “Turn right just ahead, then turn left 200 meters after that at YYYY,” or the like may be output by voice at the route guidance point h 13 . At the route guidance point h 14 , a notification sound (two beeps) may be output to indicate that the vehicle is about to enter the guidance intersection c 1 .  
      Also, when the vehicle passes the intersection ca, a message such as “Turn left just ahead,” or the like may be output by voice at the route guidance point h 15 . At the route guidance point h 16 , a notification sound (two beeps) may be output to indicate that the vehicle is about to enter the intersection cb.  
      Because the driver is thus notified that the recommended lane will change, before the vehicle arrives at the recommended lane change point, the driver does not become confused. Also, because the driver can know the recommended lane change point and the new recommended lane as a result of the notification, it is not necessary for the driver to change lanes suddenly. Therefore, it is possible for the driver to drive the vehicle safely and smoothly.  
      Also, because the guidance start timing for the guidance intersection is computed and the first route guidance point h 11  may be set using the recommended lane change point as a reference, the timing of the start of route guidance for the guidance intersection can be optimized. Therefore, sufficient distance can be ensured from the current position to the recommended lane change point, so it is possible for the vehicle to change reliably to the new recommended lane at the recommended lane change point.  
      The above-described method is summarized below with respect to  FIG. 3 .  FIG. 3  is a flowchart showing an exemplary route guidance method. The exemplary method may be implemented, for example, by one or more components of the above-described navigation system. However, even though the exemplary structure of the above-described navigation system may be referenced in the description, it should be appreciated that the structure is exemplary and the exemplary method need not be limited by any of the above-described exemplary structure.  
      At step S 1 , the system judges whether or not there is a recommended lane change point on the specified route. If there is a recommended lane change point, the CPU  13  advances to step S 2 . If there is no recommended lane change point, flow ends.  
      At step S 2 , the system waits until the vehicle approaches the recommended lane change point. When the vehicle approaches, the CPU  13  advances to step S 3 .  
      At step S 3 , guidance is provided for the recommended lane change point and the new recommended lane.  
      At step S 4 , the system waits until the vehicle passes the recommended lane change point. When the vehicle passes the recommended lane change point, the CPU  31  advances to step S 5 .  
      At step S 5 , guidance is provided for the new recommended lane, and control is returned to the beginning of the flow.  
      While various features have been described in conjunction with the examples outlined above, various alternatives, modifications, variations, and/or improvements of those features and/or examples may be possible. Accordingly, the examples, as set forth above, are intended to be illustrative. Various changes may be made without departing from the broad spirit and scope of the underlying principles.