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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle guidance system capable of
showing a recommendable route between the present position of the vehicle
and a destination on a map.
2. Description of the Prior Art
FIG. 1 is a block diagram showing the configuration of a vehicle guidance
system disclosed in Japanese Patent Laid-open (Kokai) No. 2-28800.
Referring to FIG. 1, the vehicle guidance system comprises a data
processing unit which executes control programs for guiding a vehicle, a
traffic information receiving unit 2 for receiving traffic information
transmitted by a traffic information center through transmitters installed
on road signboards, the posts of traffic signals and the like, a compact
disk player 3 serving as an external read-only storage device for reading
road map data stored on a compact disk, a CRT display (cathode-ray tube
display) 4 for displaying pictures represented by signals provided by the
data processing unit 1, an operating unit 5 comprising input devices, such
as key switches and a light pen, a self-supported position sensor 6. The
data processing unit 1 comprises a CPU 11, a ROM 12, a RAM 13 and an I/O
interface 14. These components of the data processing unit 1 are
interconnected by a bus 15.
In operation for finding an optimum route to the destination, the user
specifies the destination with the light pen or the like of the operating
unit 5 on a road map represented by road map data read by the compact disk
player 3 and displayed on the CRT display 4. Then, the data processing
unit 1 decides a recommendable route between the present position and the
destination through sequential steps of finding a recommendble route
between the present position detected by the self-supported position
sensor 6 and the destination, selecting routes meeting predetermined
restrictive conditions from among the possible routes, and selecting a
recommendable route from among the routes selected in the second step and
meeting the predetermined restrictive conditions on the basis of traffic
information received by the traffic information receiving unit 2 and
predetermined routing conditions. Then, the data processing unit 1
displays the recommendable route on the road map displayed on the CRT
display 4.
Inventions relating to such a known vehicle guidance system are disclosed,
for example, in Japanese Patent Laid-open (Kokai) Nos. 63-148115,
63-171377, 1-161111 and 2-224200.
The known vehicle guidance system thus constructed is not provided with any
means for coping with traffic congestion. If the vehicle is involved in
traffic congestion at a place unknown to the passengers and where traffic
information is unavailable while traveling by the recommended route, it is
impossible to estimate the length of a congested section on the route.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems and it
is therefore an object of the present invention to provide a vehicle
guidance system capable of estimating the length of a congested section on
a recommended route when involved in traffic congestion while traveling by
the recommended route.
A vehicle guidance system in a first aspect of the present invention
comprises a road data storage means storing road data, i.e., information
about roads, a present position detecting means for detecting the present
position of the vehicle, a destination specifying means for specifying a
destination, a routing means for finding a recommendable route between the
present position and the destination on the basis of the road data, and a
traffic congestion estimating means for estimating congested roads on the
recommendable route on the basis of the road data when the vehicle is
involved in traffic congestion. This vehicle guidance system is capable of
estimating congested roads even if the vehicle is involved in traffic
congestion at a place where external traffic information is unavailable.
A vehicle guidance system in a second aspect of the present invention
comprises a road data storage means storing road data, i.e., information
about roads, a present position detecting means for detecting the present
position of the vehicle, a destination specifying means for specifying a
destination; a routing means for finding a recommendable route between the
present position and the destination on the basis of the road data, a
traffic condition detecting means for detecting the condition of traffic
congestion on the basis of the traveling condition of the vehicle, and a
congested road estimating means for estimating congested roads on the
recommended road on the basis of the road data when the traffic condition
detecting means decides that the vehicle is involved in traffic
congestion. This vehicle guidance system is capable of detecting traffic
congestion independently when external traffic information is unavailable
and of estimating congested roads on the recommended route.
The vehicle guidance system is capable of weighting the road data of
presumably congested roads and finding another recommendable route on the
basis of the weighted data of the presumably congested roads and of
showing the new recommendable route by which the vehicle is able to reach
the destination, evading traffic congestion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a known vehicle guidance system;
FIG. 2 is a block diagram of assistance in explaining the functional
configuration of a vehicle guidance system in accordance with the present
invention;
FIG. 3 is a block diagram of a vehicle guidance system in accordance with
the present invention;
FIG. 4 is a diagrammatic view of an example of road data stored in a road
data storage device;
FIG. 5 is flow chart of assistance in explaining the operation of a vehicle
guidance system in a first embodiment according to the present invention;
FIG. 6 is a diagrammatic view of assistance in explaining a procedure of
finding a recommendable route;
FIG. 7 is a diagrammatic view of assistance in explaining a procedure of
finding another recommendable route evading traffic congestion;
FIG. 8 is a view of an example of a picture showing information about
traffic congestion;
FIG. 9 is a flow chart of a traffic congestion detecting procedure to be
executed by the vehicle guidance system in the first embodiment;
FIG. 10 is a flow chart of a congested place estimating procedure to be
executed by the vehicle guidance system in the first embodiment;
FIG. 11 is a congestion factor table, which shows factors assigned
respectively to types of junctions;
FIG. 12 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in a second embodiment according to the
present invention;
FIG. 13 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in a third embodiment according to the
present invention;
FIG. 14 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in a fourth embodiment according to the
present invention;
FIG. 15 is another congestion factor table;
FIG. 16 is a third congestion factor table;
FIG. 17 is a fourth congestion factor table;
FIG. 18 is a fifth congestion factor table;
FIG. 19 is a flow chart of a road data weighting procedure to be executed
by a vehicle guidance system in a fifth embodiment according to the
present invention;
FIG. 20 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in a sixth embodiment according to the
present invention;
FIG. 21 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in a seventh embodiment according to the
present invention;
FIG. 22 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in an eighth embodiment according to the
present invention;
FIG. 23 is a flow chart of a congestion detecting procedure to be executed
by a vehicle guidance system in a ninth embodiment according to the
present invention;
FIG. 24 is graph showing the relation between mean traveling speed and the
length of a congested section;
FIG. 25 is a flow chart of a congested place estimating procedure to be
executed by a vehicle guidance system in a tenth embodiment according to
the present invention;
FIG. 26 is a flow chart of a congested place estimating procedure to be
executed by a vehicle guidance system in an eleventh embodiment according
to the present invention;
FIG. 27 is a block diagram of a congested place estimating unit included in
the vehicle guidance system in the eleventh embodiment;
FIG. 28 is a table showing statistically estimated data of traffic
congestion by way of example;
FIG. 29 is a table showing statistically estimated data of traffic
congestion to be used by a vehicle guidance system in a twelfth embodiment
according to the present invention;
FIG. 30 is a flow chart of a congested place estimating procedure to be
executed by a vehicle guidance system in a thirteenth embodiment according
to the present invention;
FIG. 31 is a block diagram of a congested place estimating unit included in
the vehicle guidance system in the thirteenth embodiment; and
FIG. 32 is a table showing statistically estimated data of congestion by
way of example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described
hereinafter with reference to the accompanying drawings.
First Embodiment
Referring to FIG. 2 showing the functional configuration of a vehicle
guidance system in a first embodiment according to the present invention,
there are shown a present position detecting means 21 for detecting the
present position of the vehicle, a destination specifying means 22 for
specifying a destination of the vehicle, a traffic congestion detecting
means 23 for detecting traffic condition, a routing means 24 for finding a
recommendable route between the present position and the destination, a
road data weighting means 25 for weighting the road data of congested
roads, a congested place estimating means 26 for estimating congested
roads on a recommended route, a presentation means 27 for displaying a
recommended route and congested roads, a road data storage means 28
storing road data and information about the road data, and a congestion
length calculating means 29 for calculating the length of a congested
section.
Referring to FIG. 3, the vehicle guidance system has a control unit 31
which controls the general operation of the vehicle guidance system to
realize the traffic congestion detecting means 23, the routing means 24,
the road data weighting means 25, the congested place estimating means 26
and the congestion length calculating means 29. The control unit 31 is a
microcomputer comprising, for example, a memory unit 41 including a ROM
and a RAM, an input circuit 42, an output circuit 43, and a CPU 44
connected to the foregoing components.
A GPS receiver 32 connected to the control unit 31 receives radio waves
transmitted by artificial satellites of the global positioning system
(GPS) and sends the received information to the control unit 31. An
operating unit 33 has input devices, such as key switches, a light pen and
infrared touch switches, for entering information to send control signals
to the control unit 31. A map data storage unit 34 is, for example, a ROM.
Road data and information about the road data are stored in the map data
storage unit 34. A display 35, such as a CRT display, displays pictures
represented by image signals provided by the control unit 31. A braking
mode sensor 36 detects a braking mode while the vehicle is traveling. A
gear ratio sensor 37 detects the selected gear of the transmission. A
traveling speed sensor 38 detects the traveling speed of the vehicle.
The present position detecting means 21 shown in FIG. 2 may be a position
detecting means of any type, provided that the present position detecting
means is capable of detecting the present position and direction of the
vehicle at fixed intervals, for example, at intervals of 1 sec. The
present position detecting means 21 may be, for example, a means that uses
signals provided by the GPS receiver 32 of FIG. 3, a means capable of
detecting the position of the vehicle on the basis of the output signals
of a distance sensor and a direction sensor, and the map data, a means
that uses signals provided by a beacon receiver or a means that uses
signals provided by a loran C receiver.
The destination specifying means 22 may be a position specifying means of
any type, provided that the position specifying means is capable of giving
information about a destination specified by the operator to the routing
means 24. The destination specifying means 22 may be, for example, a means
employing an operating set to be operated by the operator for setting a
destination, such as the operating unit 33 of FIG. 3, a means that
specifies a destination by the name of a place or a means that specifies a
place by the latitude and the longitude.
The traffic congestion detecting means 23 calculates the traveling speed of
the vehicle on the basis of the present position varying every moment
provided by the present position detecting means 21, and determines
whether or not the vehicle is involved in traffic congestion. The routing
means 24 uses a junction nearest to the present position as a starting
junction, and a junction nearest to the destination specified by the
destination specifying means 22 as a goal junction, and searches the map
with reference to the road data for an optimum, recommendable route
between the starting junction and the goal junction, having the shortest
distance to travel or requiring the shortest time to travel.
The road data weighting means 25 weights the road data of congested roads
estimated by the congested place estimating means 26. When the traffic
congestion detecting means 23 decides that the roads are "Congested", the
congested place estimating means 26 estimates a junction causing traffic
congestion on the recommended route on the basis of the forms of roads,
and gives estimated congestion information about the estimated congested
roads to the road data weighting means 25 and the congestion length
calculating means 29. The presentation means 27 displays the present
position and direction of the vehicle detected by the present position
detecting means 21, road data provided by the road data storage means 28,
the recommended route recommended by the routing means 24, and congestion
information provided by the congestion length calculating means 29. For
example, the display means 27 consists of the display unit 35 of FIG. 3
and a display control circuit, and is capable of displaying a road map on
an enlarged scale, a road map on a reduced scale, the route on a road map,
directory of road maps for use when specifying a destination, a specified
destination, the present position of the vehicle on a road map, the
direction of the vehicle on a road map and such.
The road data storage means 28, which corresponds to the map data storage
unit 34 of FIG. 3, stores road data and information about the road data.
Data as shown in FIG. 4 by way of example is stored in the road data
storage means 28. In FIG. 4, circles indicate junctions Nos. 101 to 116,
straight lines between the circles are roads between the junctions,
numerals on the straight lines are distances (km) between the junctions,
numerals in parentheses are mean traveling speeds (km/hr) respectively on
the roads, numerals in brackets indicate the respective classes of the
roads ([1]: Express way, [2]: National highway, [3]: Prefectural road,
[4]: Principal local road, [5]: Local road) and numerals in circles are
the respective widths of the roads (1: 13.0 m or above, 2: 5.5 m or above
and less than 13.0 m, 3: 3.0 m or above and less than 5.5 m, 4: less than
3.0 m). A remark " Tunnel" indicates that the road has a tunnel or
tunnels, and a remark "Bridge" indicates that the road has a bridge or
bridges.
The congestion length calculating means 29 calculates the length of the
congested section on the basis of the estimated congestion information
provided by the congested place estimating means 26 and gives signals
representing the estimated congestion information and the calculated
length of the congested section to the presentation means 27.
The operation of the vehicle guidance system for finding a recommendable
route between the present position and the destination, automatically
finding another route to evade traffic congestion when the vehicle is
involved in traffic congestion on the recommended route, calculating the
length of the congested section and displaying congested roads, the
lengths of the congested roads and another route evading the congested
roads will be described hereinafter with reference to a flow chart shown
in FIG. 5.
In step ST1, a desired destination is specified by means of the destination
specifying means 22. The routing means 24 realized by the control unit 31
receives "Present position", i.e., a signal representing the present
position of the vehicle, from the present position detecting means 21 in
step ST2 and reads road data from the road data storage means 28 in step
ST3. The routing means 24 selects a junction nearest to the present
position as a starting junction, and a junction nearest to the destination
as a goal junction, and then finds a recommendable route between the
starting junction and the goal junction in step ST4. FIG. 6 shows, by way
of example, the road data read by the routing means 24 from the road data
storage means 28. In FIG. 6, the destination specified in step ST1 is
denoted by "Destination" and "Present position" representing the present
position of the vehicle received from the present position detecting means
21 in step ST2 is denoted by "Present position A". Accordingly, a junction
107 is the goal junction, and a junction 101 is the starting junction. The
routing means 24 selects a route having the shortest distance to travel
and requiring the shortest time to travel as a recommendable route. In
this case the recommendable route passes junctions 101, 102, 103, 104,
105, 106 and 107 sequentially as indicated by broad lines in FIG. 6.
In step ST5, the recommendable route determined in step ST4 is displayed on
the presentation means 27 together with the road data read from the road
data storage means 28, the data representing the present position and
direction of the vehicle provided by the present position detecting means
21. Then, in step ST6, the control unit 31 receives "Present position"
representing the present position of the vehicle varying every moment from
the present position detecting means 21 and stops its operation upon the
coincidence of the present position of the vehicle with the destination.
If the present position of the vehicle is not in coincidence with the
destination, the control unit 31 executes a traffic congestion detecting
procedure in step ST7. In step ST8, the traffic congestion detecting means
23 decides whether or not the vehicle is involved in traffic congestion on
the basis of data representing the traveling condition of the vehicle,
such as the traveling speed of the vehicle. If it is decided in step ST9
that the roads are "Congested", a congested place estimating procedure is
executed. If it is decided in step ST9 that the traffic is "not
congested", the routine returns to step ST5. In step ST10, the congested
place estimating means 26 estimates a congested road, and gives estimated
congestion information about the estimated congested road to the
congestion length calculating means 29 and the road data weighting means
25. The estimated congestion information, which will be described in
detail later, is information about the condition of roads between the
junction expected to have caused traffic congestion and the junction
nearest to the present position.
The congestion length calculating means 29 calculates the length of a
congested section in step ST11. The calculated length of the congested
section, and the estimated congestion information given to the congestion
length calculating means 29 in step ST10 are given to the presentation
means 27. Then, the presentation means 27 displays those pieces of
information in step ST12. For example, when the estimated congestion
information includes the junctions 103, 104, 105 and 106 shown in FIG. 6,
the length of the congested section corresponds to the sum of the
respective lengths of the roads connecting the junctions 103, 104, 105 and
106, namely, as shown in FIG. 5, 0.8+0.8+0.8=2.4. Thus, the length of the
congested section is about 2.4 km.
In step ST13, the road data weighting means 25 weights the road data on the
basis of the estimated congestion information provided by the congested
place estimating means 26. For example, the length of each congested road
is multiplied by 5 or the traveling speed on each congested road is
multiplied by 1/5. The congested road is such a road as specified by the
estimated congestion information. Then, the routine returns to step ST4.
After receiving "Present position" from the present position detecting
means 21, the routing means 24 selects a junction nearest to the present
position as a starting junction, and a junction nearest to the destination
as a goal junction, and executes step ST4 to find a new, recommendable
route by using the weighted road data of the congested roads and gives
information about the new, recommendable route to the presentation means
27.
In FIG. 7 showing road data of the new, recommendable route including roads
represented by weighted road data, the present position B marked with a
cross (x) is a position where the traffic congestion detecting means 23
decided that the roads ahead of the position are congested. When the
estimated congestion information indicates that the roads passing the
junctions 103, 104, 105 and 106 are congested, for example, the length of
each of the roads is multiplied by 5 or the traveling speed on the road is
multiplied by 1/5 for weighting. Then, the routing means 24 executes a
routing operation on the basis of the weighted road data to find a
recommendable route from the junction 103 nearest to the present position
B to the goal junction 107 nearest to the destination specified in step
ST1. In the case shown in FIG. 7, the recommendable route, which has the
shortest distance to travel and requires the shortest time to travel,
determined by the routing means 24 starts from the junction 103, passes
the junctions 108, 109, 110 and 111, and terminates at the junction 107 as
indicted by broad lines in FIG. 7.
The presentation means 27 displays the new, recommendable route in step
ST5. FIG. 8 shows a picture of the new, recommendable route by way of
example; that is the road data, the present position and direction of the
vehicle, the length of the congested section, the estimated congestion
information and the recommended route are displayed on the screen of the
display unit 35. In FIG. 8, the present position of the vehicle is marked
with a cross, the congested roads are marked with diamonds, the length of
the congested section is displayed in the lower portion of the screen, and
the recommended route evading the congested section is indicated by broad
lines.
A congestion detecting procedure to be executed in step ST8 will be
described hereinafter with reference to a flow chart shown in FIG. 9.
Referring to FIG. 9, "Place 1", "Place 2" and "Detection starting
position" are variables. The present position detected by the present
position detecting means 21 is given to the congestion detecting means 23
in step ST21. Then, the congestion detecting means 23 sets "Place 2" as
"Present position" in step ST22, clears a counter to "0" in step ST23, and
clears "Detection starting position" in step ST24. Then, the congestion
detecting means 23 receives "Present position" from the present position
detecting means 21 in step ST25 and sets "Place 1" as "Present position"
in step ST26. The present position detecting means 21 detects the present
invention periodically at intervals of, for example, 1 sec. therefore, the
congestion detecting means 23 is able to determine the traveling speed
(km/hr) by dividing the distance between the "Place 1" and "Place 2" by,
for example, 1/3600 hours in step ST27. For example, when "Place 1" is
indicated by coordinates (x1, y1) and "Place 2" is indicated by
coordinates (x2, y2), the traveling speed of the vehicle can be calculated
by:
##EQU1##
The congestion detecting means 23 compares the calculated traveling speed
with a predetermined threshold speed v, for example, 20 km/hr, in step
ST28. The routine returns to step ST23 if the calculated traveling speed
is higher than the threshold speed v or the congestion deciding procedure
is started if the calculated traveling speed is not higher than the
threshold speed v.
The congestion detecting means 23 makes a query in step ST29 to see if the
count of the counter is zero. If the response in step ST29 is affirmative,
the congestion detecting means 23 sets the present position detected at
the time when the congestion deciding operation was started as a
"detection starting position" in step ST30, increments the count of the
counter by one in step ST31, and then the place set as "Place 1" is set as
"Place 2" in step ST32. If the count of the counter is less than a
predetermined count n, such as 600, the routine returns to step ST25 for
the subsequent detection of the reduction of the traveling speed. The
count of the counter equal to or greater than the predetermined count n
indicates that the reduction of the traveling speed has continued for a
time period corresponding to a time period in which the predetermined
count n is counted. Accordingly, the congestion detecting means 23 decides
in step ST33 that the vehicle is involved in traffic congestion or the
vehicle is stopped and goes to step ST34. When the traveling speed
increases beyond the threshold speed v before the count of the counter
reaches the predetermined count n, the congestion detecting means 23 exits
the congestion deciding loop in step ST28 and clears the counter in step
ST23.
When it is decided that the vehicle is involved in traffic congestion or
stopped, the congestion detecting means 23 compares "Place 1" set as
"Present position" with "Detection starting position" in step ST34. If
"Place 1" and "Detection starting position" are the same position, it is
decided that the vehicle is stopping, and the routine returns to step
ST23. If the "Place 1" and the "Detection starting position" are different
from each other, the congestion detecting means 23 decides that the roads
are "Congested" and gives a signal to the congested place estimating means
26 to that effect in step ST35.
A congested place estimating procedure to be executed in step ST10 will be
described hereinafter with reference to a flow chart shown in FIG. 10. In
step ST41, the congested place estimating means 26 samples a predetermined
number m of junctions, for example, ten junctions, ahead of the present
position where the congestion detecting means 23 has decided that the
roads are "Congested" on the recommended route. If the number of junctions
on the recommended route from the present position to the destination is
smaller than the predetermined number m, the congested place estimating
means 26 samples all the junctions. For example, when the present position
detecting means 21 provides "Present position B" marked with a cross in
FIG. 6 and the congestion detecting means 23 provides a signal
representing "Congested" the junctions 103, 104, 105, 106 and 107 are
sampled.
Then, the congested place detecting means 26 finds the respective classes
of the roads meeting at each of the junctions sampled in step ST41, making
reference to the road data read from the road data storage means 28. Then,
in step ST42, the congested place estimating means 26 attaches congestion
estimation factors shown in the table of congestion estimation factors
(FIG. 11) to the junctions.
The table of congestion estimation factors shows the classes of roads
meeting at the junctions and corresponding factors indicating
probabilities of occurrence of congestion. In FIG. 11, [1] to [5]
indicates the classes of roads; for example, [1] indicates an express way,
[2] indicates a national highway, [3] indicates a prefectural road, [4]
indicates a principal local road and [5] indicates a local road. The
junction where an express way and a national highway meet has many causes
of congestion, such as an interchange and heavy traffic, and hence a large
congestion estimation factor is assigned to such a junction. Since
principal local roads and local roads have only a few causes of
congestion, small congestion estimation factors are assigned to those
roads. In this case, the congestion estimation factors 3.0, 4.0, 3.0, 5.0
and 3.0 are assigned to the junctions 103, 104, 105, 106 and 107,
respectively.
Then, in step ST42, the congested place estimating means 26 selects the
junction to which the largest congestion estimation factor was attached
from among the sampled junctions. If there are a plurality of junctions to
which the largest congestion estimation factor was attached, the junction
farthest from the present position of the vehicle is selected in step
ST43. In the case shown in FIG. 6, the junction 106 to which a congestion
estimation factor 5.0 is attached is selected from among the junctions
103, 104, 105, 106 and 107.
Then, in step ST44, the junctions between the present position of the
vehicle and the junction to which the largest congestion estimation factor
was attached are sampled to use the junctions as estimated congestion
information, and then the estimated congestion information is given to the
road data weighting means 25 and the congestion length calculating means
29 in step ST45. In this case shown in FIG. 6, since the junction 106 was
selected in step ST43, and the present position of the vehicle is at
"Present position B" marked with a cross, a string of the junctions 103,
104, 105 and 106 is the estimated congestion information.
Although a decision as to whether or not the road is congested is made on
the basis of the traveling condition of the vehicle, such as the traveling
speed of the vehicle, in this embodiment, it is also possible for the
operator to decide that the vehicle is involved in traffic congestion and
to give a signal to the vehicle guidance system to that effect by
operating the operating unit 33. The traveling speed may be detected by
the traveling speed sensor 38 provided on the vehicle.
Second Embodiment
The first embodiment decides that the vehicle is involved in traffic
congestion when traveling speeds not higher than the threshold speed v is
detected n times successively. However, it may be decided that the vehicle
is involved in traffic congestion when traveling speeds not higher than
the threshold speed v are detected successively in a predetermined
decision time t. A vehicle guidance system in a second embodiment
according to the present invention employs the latter method for deciding
that the vehicle is involved in traffic congestion.
The second embodiment will be described hereinafter on a assumption that
the threshold speed v=20 km/hr and the decision time t=5 min. The
functional configuration of the vehicle guidance system in the second
embodiment is the same as that shown in FIG. 2, and the arrangement of the
concrete components of the same is the same as that shown in FIG. 3. The
general operation of the vehicle guidance system in the second embodiment
is the same as that represented by the flow chart shown in FIG. 5, except
that the vehicle guidance system in the second embodiment executes a
procedure represented by a flow chart in FIG. 12 in step ST8.
In operation, a congestion detecting means 23 receives "Present position"
from a present position detecting means 21 in step ST51 and sets "Present
position" as "Place 2" in step ST52. A congestion detecting interval timer
TM is reset in step ST53 and "Detection starting position" is cleared in
step ST54.
The congestion detecting means 23 receives "Present position" again from
the present position detecting means 21 | | |
