Abstract:
A guideway transit system which can reduce a scale of an infrastructure while maintaining ride comfort for passengers of a vehicle is provided. The guideway transit system includes a noncontact vehicle guiding system and a contact vehicle guiding system. The noncontact vehicle guiding system detects information relating to a lateral position of a vehicle on a road and steers the vehicle to move along a predetermined path on the road based on the detected information. The contact vehicle guiding system which restricts a lateral position of the vehicle by a contact between a guide wheel which laterally projects from the vehicle and a guide wall provided on a side of the road. The guideway transit system further includes a controller which prohibits steering of the vehicle by the noncontact vehicle guiding system when a lateral position of the vehicle is restricted by the contact vehicle guiding system. An automated vehicle which is used in the guideway transit system is also provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a guideway transit system which guides a vehicle by holding a guide wheel provided on the vehicle in contact with a guide wall provided on a side of a road, and to an automated vehicle used in such a guideway transit system 
     2. Description of the Related Art 
     Conventionally, as shown in FIG. 1, there is known a guideway transit system which guides a vehicle by constraining guide wheels which laterally project from both sides of the vehicle between guide walls provided on both sides of a road (“Computer Simulation of Lateral Guidance System for Automated Guideway Transit Vehicles”, Tsunashima and Fukumoto, KOBE STEEL ENGINEERING REPORTS, Vol. 37, No. 4 (1987)). 
     In this system, guide wheels  21   a ,  21   b , which are connected to each other by a shaft, are provided on a front part of a vehicle  10 . The guide wheels  21   a ,  21   b  laterally project from both sides of the vehicle  10  and are constrained between guide walls (not shown) which are provided on both sides of a road R. The shaft connecting the guide wheels  21   a ,  21   b  is connected to front wheels  11   a ,  11   b , which are steered wheels, of the vehicle  10  via a link mechanism  20 . In this system, rear wheels  12   a ,  12   b  are not connected to the guide wheels  21   a ,  21   b.    
     When the guide wheels  21   a ,  21   b , which are in contact with the guide walls, move with the shaft in accordance with a shape of the road R, a relative position of the guide wheels  21   a ,  21   b  and the vehicle  10  changes. In this case, the link mechanism functions to steer the front wheels  11   a ,  11   b  in accordance with the change in the relative position. Thus, the vehicle  10  can always run along a predetermined path defined on the road R. 
     In the above-mentioned conventional guideway transit system, since the vehicle is steered by always holding the guide wheels in contact with the guide walls, the guide walls must be provided with relatively high positional accuracy over a whole part of the road on which the vehicle should run. As a length of the road on which the vehicle should run increases, a larger cost is required to construct an infrastructure since it becomes more difficult to provide the guide walls with relatively high accuracy over a whole part of the road. 
     Additionally, since the vehicle runs with the guide wheels being in contact with the guide walls provided on both sides of the road, vibrations are transmitted from the guide walls to the vehicle via the guide wheels, resulting in ride discomfort for passengers of the vehicle. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide a guideway transit system which can reduce a scale of an infrastructure while maintaining ride comfort for passengers of a vehicle. 
     It is a second object of the present invention to provide an automated vehicle which is used in such a guideway transit system. 
     The first object of the present invention can be achieved by a guideway transit system comprising: 
     a noncontact vehicle guiding system which detects information relating to a lateral position of a vehicle on a road and steers the vehicle to move along a predetermined path on the road based on the detected information; 
     a contact vehicle guiding system which restricts a lateral position of the vehicle by a contact between a guide wheel which laterally projects from the vehicle and a guide wall provided on a side of the road; and 
     a controller which prohibits the steering of the vehicle by the noncontact vehicle guiding system when a lateral position of the vehicle is restricted by the contact vehicle guiding system. 
     In such a guideway transit system, in an area of the road where the noncontact vehicle guiding system operates, the vehicle is steered so as to run along the predetermined path based on the detected information relating to a lateral position of the vehicle without using the guide wheel provided on the vehicle. On the other hand, in an area of the road where the contact vehicle guiding system operates, a lateral position of the vehicle is restricted by the guide wheel, which laterally projects from the vehicle, being in contact with the guide wall provided on a side of the road, and steering of the vehicle by the noncontact vehicle guide system is prohibited. In this case, the vehicle is steered to maintain the lateral position restricted by the contact vehicle guiding system. 
     The area where the contact vehicle guiding system should operate may be set to be an area where a lateral position of the vehicle should be accurately controlled. 
     The area where the noncontact vehicle guiding system should operate is set to be an area where the vehicle regularly runs. Thus, vibrations can be prevented from being transmitted to the vehicle from the guide wall via the guide wheel in the regular situation. 
     Additionally, the contact vehicle guiding system may also operate when the vehicle deviates from the predetermined path due to a trouble in a steering control of the vehicle by the noncontact vehicle guiding system. In this case, the steering control of the vehicle by the noncontact vehicle guide system is prohibited, and, when the vehicle deviates from the predetermined path until the guide wheel comes into contact with the guide wall, a lateral position of the vehicle is restricted by a contact of the guide wheel and the guide wall. When a lateral position of the vehicle is restricted in this way, the vehicle is preferably braked by an emergency braking. 
     Considering the fact that the contact vehicle guiding system operates when the noncontact vehicle guiding system cannot normally steer the vehicle, it is necessary to provide the guide wall in the area where the noncontact vehicle guiding system should operate. Since the guide wall provided in the area where the noncontact vehicle guiding system should operate has a function of limiting a lateral position of the vehicle within a predetermined range, positional accuracy of the guide walls may be lower than that of the guide walls provided in the area where the contact vehicle guiding system should operate. 
     As mentioned above, since the noncontact vehicle guiding system regularly steers the vehicle and the contact vehicle guiding system operates only in an area where a lateral position of the vehicle should be accurately controlled, ride comfort for passengers of the vehicle can be maintained in the regular situation. Additionally, since the contact vehicle guiding system operates only when the vehicle cannot be guided along the path by the noncontact vehicle guiding system, accuracy of the guide wall need not be high. Thus, a scale of the infrastructure can be reduced. 
     The above-mentioned second object of the present invention can be achieved by an automated vehicle, comprising: 
     a lateral position detector which detects a lateral position of the vehicle on a road; 
     an automatic steering mechanism which steers the vehicle based on the position detected by the lateral position detector so that the vehicle moves along a predetermined path on the road; 
     a guide wheel which laterally projects from a vehicle body; and 
     an automatic steering prohibiting part which prohibits the automatic steering by the automatic steering mechanism when the vehicle is laterally constrained by the guide wheel being in contact with a guide wall which is provided on a side of the road. 
     In the guideway transit system, the guide wall may be provided on each side of the road and the guide wheel may be provided on each side of the vehicle. 
     In such a guideway transit system, since the guide wheels can be held between the guide walls, a lateral position of the vehicle is effectively restricted by the contact vehicle guiding system. In this case, a space between the guide walls in the area where the noncontact vehicle guiding system should operate may be set to be so large that the guide wheels of the vehicle are prevented from coming into contact with the guide walls. 
     In order that the vehicle can be easily steered by restricting a lateral position of the vehicle by the contact vehicle guiding system, the controller may comprise a constraint-canceling mechanism which can cancel constraint of a steered wheel by a steering mechanism which is controlled by the noncontact vehicle guiding system. 
     According to such a guideway transit system, since constraint of the steered wheel by the steering mechanism is canceled when the contact vehicle guiding system restricts a lateral position of the vehicle, a load of the steered wheel is decreased. As a result, a force required to restrict a lateral position of the vehicle becomes smaller, and thus the vehicle can be smoothly steered by the contact vehicle guiding system. 
     Additionally, in view of simplifying a structure of the contact vehicle guiding system, the guide wheel and a steered wheel steered by a steering mechanism which is controlled by the noncontact vehicle guiding system are mechanically disconnected from each other. 
     According to this guideway transit system, when a lateral position of the vehicle is restricted by a contact between the guide wall and the guide wheel in a state where a steering control of the vehicle by the noncontact vehicle guiding system is prohibited, a lateral force is exerted on the vehicle from the guide wall via the guide wheel. Due to this lateral force, the steered wheel which is mechanically disconnected from the guide wheel can be steered in a neutral direction (for example, a straight direction) by a self aligning force, without being excessively steered as compared to a case where the guide wheel and the steered wheel (front wheel, for example) are connected to each other by a link mechanism as shown in FIG.  1 . In this way, the steered wheel can be naturally steered in a straight direction without a connection between the guide wheel and the steered wheel by a link mechanism. 
     Considering a fact that the vehicle stops at a station where passengers get on and off the vehicle, the contact vehicle guiding system may be provided in a predetermined area including a position at which the vehicle should be stopped. 
     In such a guideway transit system, when the vehicle enters the predetermined area including a position such as a station at which the vehicle should be stopped, a lateral position of the vehicle is restricted by the contact vehicle guiding system. Thus, it is possible to stop the vehicle at the station while accurately controlling a relative position of the vehicle and other structures such as a platform. 
     In order to more accurately control a lateral position of the vehicle by the contact vehicle guiding system in which the guide wheel is provided on each side of the vehicle, each of the guide wheels may be supported by a damper mechanism which generates a reaction force against a compression in a lateral direction of the vehicle. 
     According to such a guideway transit system, when the guide wheels laterally projecting from both sides of the vehicle are constrained between the guide walls, the damper mechanism is compressed. The damper mechanism generates a force against the compression, and this force is exerted on the vehicle from both sides thereof. Thus, a position of the vehicle can be controlled with higher accuracy. 
     In this case, a space between the guide walls may gradually decrease to a minimum value in a running direction of the vehicle. 
     In such a guideway transit system, when the vehicle is in a position where a space between the guide walls is the minimum value, a force generated by the damper mechanism is maximum since an extent of compression thereof is maximum. In this state, a lateral position of the vehicle is most accurately controlled. Since the space between the guide walls gradually decreases toward the position where the space is the minimum value in the running direction of the vehicle, an extent of compression of the damper mechanism gradually increases as the vehicle advances. Thus, the vehicle can smoothly enter the area where a lateral position thereof can be most accurately controlled, with an increasing lateral force exerted on the vehicle by the damper mechanism. 
     In order that the vehicle, which has stopped with the guide wheels being constrained between the guide walls, can smoothly start running in the guideway transit system in which the guide wheels are supported by the damper mechanisms, the guideway transit system may further comprise a damper-force changing mechanism which decreases the force generated by the damper mechanism when the vehicle, which has stopped with the guide wheels being constrained between the guide walls, starts running. 
     In such a guideway transit system, since the force laterally exerted on the vehicle by the damper mechanism is decreased when the vehicle starts running, the vehicle can smoothly start running. 
     In order to prevent a rapid change in a direction of the steered wheel when steering of the vehicle by the noncontact vehicle guiding system is prohibited and the vehicle starts being steered by the contact vehicle guiding system, a steering mechanism of the vehicle may comprise a steering damper mechanism which generates a force against a steering movement of a steered wheel of the vehicle, and the guideway transit system may further comprise a damper force adjuster which adjusts the force generated by the steering damper mechanism based on at least a steering angle of the steered wheel when the steering control by the noncontact vehicle guide system is prohibited. 
     In such a guideway transit system, when the steering control of the vehicle by the noncontact vehicle guiding system is prohibited and the vehicle starts being steered by the contact vehicle guiding system, a movement of the steered wheel is damped by the force generated by the steering damper mechanism against the movement. For example, if the steering control of the vehicle by the noncontact vehicle guiding system is prohibited when the vehicle is running on a curved road, a relatively large force is generated by the steering damper since a steering angle at that time is relatively large. As a result, a rapid change in a direction of the steered wheel from that large steering angle can be prevented, and thus the vehicle can run more stably. 
     The damper force adjuster adjusts the force generated by the steering damper mechanism at least based on the steering angle, as mentioned above. However, the damper force adjuster may adjust the force based on a running state such as a vehicle speed and an acceleration/deceleration, in addition to the steering angle. For example, the force generated by the steering damper mechanism may be adjusted to be larger for a higher vehicle speed if the steering angle is the same. 
     In order that the damper force adjuster can switch the force generated by the steering damper mechanism between two levels, the damper force adjuster may comprise: 
     a determining part which determines whether or not the force generated by the steering damper mechanism should be increased based on a criterion determined in accordance with at least the steering angle; and 
     a force controller which increases the force generated by the steering damper mechanism when the determining part determines that the force generated by the steering damper mechanism should be increased. 
     The criterion which is used in the determining part is preferably determined based on whether or not the vehicle can stably run with a rate of change in a direction of the steered wheel steered by the contact vehicle guiding system against the force currently generated by the steering damper mechanism. 
     In order to reduce vibrations which are transmitted to the vehicle from the guide wall via the guide wheel, the guide wall may comprise a shock-absorbing member having a shock-absorbing function in a lateral direction of the road. 
     In such a guideway transit system, a shock generated by an impact between the guide wheel and the guide wall can be damped by the shock-absorbing function of the shock-absorbing member which constitutes the guide wall. Thus, vibrations transmitted to the vehicle from the guide wall via the guide wheel can be reduced. 
     In order to simply construct such a guide wall, the shock-absorbing member may comprise a belt-like member which moves in a direction in which the road extends. 
     In order that the vehicle can enter one of two branch roads in accordance with a steering control by the noncontact vehicle guiding system while being positively guided into that branch road if the vehicle laterally shifts toward the other branch road, the contact vehicle guiding system may include a branch-road guiding system which guides the vehicle into one of two branch roads by guiding a branch-road guide member provided ahead of front wheels on the vehicle along a branch wall provided at a border between the two branch roads. 
     In such a guideway transit system, the branch-road guide member of the vehicle may come into contact with the branch wall provided at the border between the two branch roads if the vehicle shifts toward the other branch road. In this case, a lateral force is exerted on the vehicle from the branch wall via the branch-road guide member. Thus, the vehicle can be guided into the desired branch road by the branch-road guide member being guided along the branch wall. 
     In order to maintain a wide vision area at a junction of the branch road, the branch wall may have a height which is smaller than a height of the guide wall. 
     In order that the vehicle can be smoothly guided into any one of the branch roads, the branch-road guide member may comprise a substantially U-shaped plate-like member having a convex shape at a front end part thereof. 
     In such a guideway transit system, when the vehicle enters a branch road branching to the right, a left side surface of the U-shaped plate-like member is guided along the branch wall. On the other hand, when the vehicle enters a branch road branching to the left, a right side surface of the U-shaped plate-like member is guided along the branch wall. 
     In order that the branch-road guide member can be smoothly guided along the branch wall, a strength of the branch-road guide member in a direction of contact with the branch wall may gradually increase toward the rear. 
     In such a guideway transit system, the vehicle is guided into one of the branch roads with the branch-road guide member sliding on the branch wall from a front end part toward the rear. If the front end part of the branch-road guide member impacts on the branch wall with a high speed, the impact part of branch-road guide member may be destroyed. In this case, as the branch-road guide member moves forward while sliding on the branch wall, an extent of the destruction becomes smaller due to the above-mentioned strength distribution. A force exerted on the vehicle body from the branch wall via the branch-road guide member becomes smaller in accordance with an increase in the extent of the destruction since the force is absorbed by the destruction of the branch-road guide member. Thus, according to the above-mentioned behavior of the branch-road guide member, the force exerted on the vehicle from the branch wall gradually increases as the vehicle advances so that the vehicle can be smoothly guided into one of the branch roads. 
     In order to simply construct the branch-road guide member having the above-mentioned strength distribution, the branch-road guide member may comprise: 
     a plate-like base body; and 
     a plurality of force-adjusting plates layered on the base body with end parts of the force-adjusting plates being shifted one after another. 
     In such a guideway transit system, the number of the layered force-adjusting plates increases toward the rear side of the branch-road guide member. Thus, the strength of the branch-road guide member in a direction of contact with the branch wall gradually increases toward the rear. 
     In this case, the base body may have a honeycomb structure which has a relatively low strength in a direction of contact with the branch wall. 
     In order to prevent the vehicle from going over the branch wall if the branch wall is constructed to be low, contact surfaces of the branch wall and the branch-road guide member may be inclined so that the contact surface of the branch wall is above the contact surface of the branch-road guide member. 
     In such a guideway transit system, the branch-road guide member comes into contact with the branch wall from a lower side. In this case, the branch-road guide member fixed to the vehicle is pushed down by the branch wall. Thus, it is possible to prevent the vehicle from going over the branch wall if the branch wall is constructed to be low. 
     In order that the branch-road guide member can be stably guided along the branch wall if the vehicle body rolls when the vehicle enters a branch road, an inclination angle of the contact surface of the branch-road guide member may be set to be larger than an inclination angle of the contact surface of the branch wall. 
     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing an example of a conventional guideway transit system; 
     FIG. 2 is a diagram showing an example of a structure used in a guideway transit system according to an embodiment of the present invention; 
     FIG. 3 is a diagram showing an example of a contact vehicle guiding system; 
     FIG. 4 is a diagram showing an example of a support structure of guide wheels in the contact vehicle guiding system; 
     FIG. 5 is a diagram showing a state of the support structure in which the guide wheel is housed in a vehicle body; 
     FIG. 6 is a block diagram showing an example of a control system of a noncontact vehicle guiding system; 
     FIG. 7 is a flowchart of a process performed by a control unit shown in FIG. 6; 
     FIG. 8 is a flowchart of a process performed by an automated driving control unit shown in FIG. 6; 
     FIG. 9 is a diagram showing another example of a contact vehicle guiding system; 
     FIG. 10 is a diagram showing a further example of a contact vehicle guiding system; 
     FIG. 11 is a diagram showing a still further example of a contact vehicle guiding system; 
     FIGS. 12A and 12B are diagrams showing an example of branch roads in the guideway transit system; 
     FIG. 13 is a diagram showing another example of a structure of the vehicle in the contact vehicle guiding system; 
     FIG. 14 is a diagram showing a mount structure of a branch-road guide member shown in FIG. 13; 
     FIG. 15 is a diagram showing a top view of the branch-road member; 
     FIG. 16 is a diagram showing a cross section of the branch-road member; 
     FIG. 17 is a diagram showing a state in which the branch-road guide member is in contact with a branch wall when the vehicle is guided into a branch road; 
     FIG. 18 is a diagram showing an example of a structure of contact surfaces of the branch-road guide member and the branch wall; and 
     FIG. 19 is a diagram showing another example of a structure of contact surfaces of the branch-road guide member and the branch wall. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 shows a guideway transit system according to an embodiment of the present invention. As shown in FIG. 2, guide walls  100   a ,  100   b  are provided on both sides of a road R. Each of the guide walls  100   a ,  100   b  has a height of approximately 60 centimeters, for example. The road R provided with the guide walls  100   a ,  100   b  comprises a general road part R 1 , an entrance part R 2  and a stop part R 3 . 
     In the general road part R 1 , the guide walls  100   a ,  100   b  are provided in parallel with each other with a space W 1 . An automated vehicle (hereinafter simply referred to as a vehicle)  10  runs on a predetermined path between the guide walls  100   a ,  100   b , as will be described later. 
     The stop part R 3  is provided with a station (not shown) at which the vehicle  10  should stop. In the stop part R 3 , the guide walls  100   a ,  100   b  are provided in parallel with each other with a space W 2  which is smaller than the space W 1 . 
     The vehicle  10  is controlled to stop at a predetermined position in the stop part R 3 . 
     The entrance part R 2  connects the general road part R 1  and the stop part R 3 . In the entrance part R 2 , a space between the guide walls  100   a ,  100   b  linearly changes from W 1  at a side of the general road part R 1  to W 2  at a side of the stop part R 3 . 
     Although FIG. 2 shows only a part of the road R, the road R is actually constructed as a combination of a number of the general road parts R 1 , the entrance parts R 2  and the stop parts R 3 . In this case, an exit side of the stop part R 3  may be connected to a general road part R 1  via a part like the entrance part R 2  where a space between the guide walls  100   a ,  100   b  gradually increases, or may be directly connected to a general road part R 1  without providing such a part where a space between the guide walls  100   a ,  100   b  gradually increases. 
     Magnetic markers, for example, which can be magnetically detected are provided at a predetermined lateral position (a center position, for example) of the road R at predetermined intervals (every one meter, for example). An arrangement of the magnetic markers corresponds to a path along which the vehicle  10  should run. Additionally, specific magnetic markers are provided at a boundary position between the general road part R 1  and the entrance part R 2 , a position of the entrance part R 2  at a predetermined distance before the stop part R 3  (a station entrance mark), a position of the stop part R 3  at which the vehicle  10  should stop (a stop mark) and a position at which the vehicle  10  leaves the stop part R 3  (a station exit mark). These specific magnetic markers may be formed by combinations of N and S poles, for example, so that the respective positions can be identified. 
     As shown in FIGS. 2 and 3, the vehicle  10  is provided with front guide wheels  31   a ,  31   b  and rear guide wheels  32   a ,  32   b . The front guide wheels  31   a ,  31   b  laterally project from both sides of a front part FR of the vehicle  10  ahead of front wheels  11   a ,  11   b , and the rear guide wheels  32   a ,  32   b  laterally project from both sides of the vehicle  10  behind rear wheels  12   a ,  12   b . Heights of the front guide wheels  31   a ,  31   b  and the rear guide wheels  32   a ,  32   b  above ground are set to be lower than heights of the guide walls  100   a ,  100   b . According to such a relationship in height, when the vehicle  10  moves closer to the guide wall  100   a , the front guide wheel  31   a  and the rear guide wheel  32   a  come into contact with the guide wall  100   a , and when the vehicle  10  moves closer to the guide wall  100   b , the front guide wheel  31   b  and the rear guide wheel  32   b  come into contact with the guide wall  100   b.    
     The road R shown in FIG. 2 is an exclusive road for the vehicle  10 . In order to enable the vehicle  10  which runs on such an exclusive road to run on general roads, the guide wheels  31   a ,  31   b ,  32   a ,  32   b  must be housed in a vehicle body of the vehicle  10 . FIGS. 4 and 5 show a support structure which includes a mechanism for housing the front wheels  31   a ,  31   b  in the vehicle body. 
     As shown in FIG. 4, a lateral frame  63  which extends in a lateral direction of a vehicle body  10   a  is fixed to a front end part of longitudinal frames  61 ,  62  which extend in a longitudinal direction of the vehicle body  10   a . One end of a support bar  41  is pivotably supported at an end of the lateral frame  63 . The front guide wheel  31   a  is rotatably supported at the other end of the support bar  41 . An end of a piston of a guide-wheel damper (an air cylinder)  42  is pivotably connected to the end of the support bar  41  which supports the front guide wheel  31 . An end of a link bar  43  is pivotably connected to the lateral frame  63 , and the other end of the link bar  43  is pivotably connected to an end of a cylinder of the guide-wheel damper  42 . Lengths of the support bar  41  and the link bar  43  connected to both ends of the guide-wheel damper  42  are set so that the guide-wheel damper  42  is positioned substantially in parallel with a lateral direction of the vehicle body  10   a . Thus, the guide-wheel damper  42  can effectively damp a lateral force which is exerted thereon via the guide wheel  31   a.    
     The end of the link bar  43  connecting to the guide-wheel damper  42  is pivotably connected to one end of a link bar  44 . Additionally, a stopper  45  is fixed to the lateral frame  63  so that the stopper  45  abuts on a side face of the link bar  43  facing outside of the vehicle body  10   a  via a cushion member  48 . 
     A support bar  51 , a guide-wheel damper  52 , link bars  53 ,  54  and a stopper  55  are provided inside a front-left part of the vehicle body  10   a  in a symmetrical manner to the support bar  41 , the guide-wheel damper  42 , the link bars  43 ,  44  and the stopper  45  provided inside a front-right part of the vehicle body  10   a . The front guide wheel  31   b  is rotatably supported at an end of the support bar  51 . The guide-wheel damper  52  can effectively damp a lateral force which is exerted thereon via the front guide wheel  31   b  in the same manner as the guide wheel-damper  42 . Similar to a case of the stopper  45  and the link bar  43 , a cushion member  58  is interposed between the stopper  55  and the link bar  53 . 
     The link bar  44  on the right side and the link bar  54  on the left side are pivotably connected to each other so that the link bars  44 ,  54  are substantially directed in a lateral direction of the vehicle body  10   a . A movement of the connecting part between the link bars  44 ,  54  is restricted by a guide plate  46 . The guide plate  46  is fixed to the lateral frame  63  and extends substantially in a longitudinal direction of the vehicle body  10   a . The guide plate  46  is formed with a slit  46   a . The connecting part between the link bars  44 ,  54  is guided in the slit  46   a  so that the connecting part can move in a longitudinal direction of the vehicle body  10   a . The guide plate  46  is provided with a lock mechanism  47  which can lock (fix) the connecting part between the link bars  44 ,  54  at either end of the slit  46   a.    
     A guide-wheel housing actuator (air cylinder)  50  is provided between the lateral frame  63  and the link bar  53 . Specifically, an end of a cylinder of the guide-wheel housing actuator  50  is pivotably connected to the lateral frame  63  and an end of a piston of the guide-wheel housing actuator  50  is pivotably connected to the link bar  53 . Thus, the link bar  53  swings around a supporting point on the lateral frame  53  when the piston of the guide-wheel housing actuator  50  axially moves. 
     According to the above-mentioned support structure of the front guide wheels  31   a ,  31   b , when the vehicle  10  moves closer to the guide wall  100   a  until the front guide wheel  31   a  comes into contact with the guide wall  100   a , the front guide wheel  31   a  moves toward the inside of the vehicle body  10   a  due to a contraction of the guide-wheel damper  42  caused by a lateral force exerted thereon from the guide wall  100   a  via the front guide wheel  31   a . In this case, the lateral force exerted on the guide-wheel damper  42  is received by the stopper  55  via the link bars  44 ,  54 ,  53  and the cushion member  58 . Similarly, when the front guide wheel  31   b  comes into contact with the guide wall  100   b , the front guide wheel  31   b  moves toward inside of the vehicle body  10  due to a contraction of the guide-wheel damper  52  caused by a lateral force exerted thereon from the guide wall  100   b  via the front guide wheel  31   b , and this lateral force is received by the stopper  45  via the link bars  54 ,  44 ,  43  and the cushion member  48 . 
     Additionally, when both the front guide wheels  31   a ,  31   b  are housed into the vehicle body  10   a , the guide-wheel housing actuator  50  is actuated after the lock mechanism  47  of the guide plate  46  is unlocked. In this case, the link bar  53  swings toward the inside of the vehicle body  10   a  around a supporting point on the lateral frame  63  since the piston of the guide-wheel housing actuator  50  is retracted into the cylinder, pulling the link bar  53 . In association with such a movement of the link bar  53 , the connecting point between the link bars  54 ,  44  moves along the slit  46   a  of the guide plate  46  toward the lateral frame  63 . In this case, the guide-wheel damper  52  moves toward the inside of the vehicle body  10   a  following the movement of the link bar  53 . As a result, the support bar  51  swings toward the inside of the vehicle body  10   a  around the supporting point on the lateral frame  63  so that the front guide wheel  31   b  is housed into the vehicle body  10   a.    
     The link bar  44  moves in a manner similar to the link bar  54  in association with the movement of the connecting part between the link bars  54 ,  44  along the guide plate  46 . The guide-wheel damper  42  moves toward the inside of the vehicle body  10   a  following the movement of the link bar  44 . Thus, the support bar  41  swings toward inside of the vehicle body  10   a  around the supporting point on the lateral frame  63  so that the front guide wheel  31   a  is housed in the vehicle body  10   a.    
     FIG. 5 shows a state of the support structure of FIG. 4 in which the front guide wheels  31   a ,  31   b  are housed in a front part of the vehicle body  10   a  as mentioned above. In this state, a damper  49 , which was under the link bars  44 ,  54  and not shown in FIG. 4, is compressed between a connecting part of the guide-wheel damper  52  and the link bars  53 ,  54  and a connecting part of the guide-wheel damper  42  and the link bars  43 ,  44 . By locking the lock mechanism  47  in such a state so that a movement of the connecting part between the link bars  54 ,  44  is prohibited, the state shown in FIG. 5 in which the front guide wheels  31   a ,  31   b  are housed in the vehicle body  10   a  can be maintained. 
     When the lock mechanism  47  is unlocked and the guide-wheel housing actuator  50  is actuated so that the piston thereof advances, the link bar  53  swings away from the lateral frame  63  around the supporting point on the lateral frame  63 . In association with such a movement of the link bar  53 , the damper  49  extends and the connecting part between the link bars  44 ,  54  moves away from the lateral frame  63  along the slit  46   a  of the guide plate  46 . Thus, the link bar  43  swings away from the lateral frame  63  around the supporting point on the lateral frame  63 . As a result, the guide-wheel dampers  52 ,  42  are pushed outwardly so that the respective support bars  51 ,  41  swing toward the outside of the vehicle body  10   a  around the respective supporting points, and thus the respective front guide wheels  31   a ,  31   b  are pushed out from the vehicle body  10   a.    
     It should be noted that a support structure of the rear guide wheels  32   a ,  32   b  (shown in FIG. 3) has substantially the same construction as shown in FIGS. 4 and 5. 
     FIG. 6 shows an example of a control system provided in the vehicle  10 . In FIG. 6, a vehicle speed sensor  71  outputs a pulse signal in accordance with a vehicle speed, and a marker sensor  72  outputs a signal in accordance with a magnetic field generated by the magnetic markers provided on the road R. The output signals of the vehicle speed sensor  71  and the marker sensor  72  are supplied to each of a control unit  70  and an automated driving control unit  80 . Additionally, an operating signal from a switch  73  is supplied to the control unit  70 . The switch  73  is operated by an operator for retracting and extracting the front guide wheels  31   a ,  31   b  and the rear guide wheels  32   a ,  32   b.    
     The automated driving control unit  80  controls a steering actuator  81 , a brake actuator  82  and an accelerator actuator  83  based on the output signals of the vehicle speed sensor  71  and the marker sensor  72  so that the vehicle  10  runs along a path defined on the road R (see FIG. 2) in accordance with a predetermined velocity pattern. The steering actuator  81  (a motor, for example) constitutes a part of a steering mechanism of the front wheels  11   a ,  11   b  (steered wheels) and is connected to the front wheels  11   a ,  11   b  via, for example, a clutch mechanism  84  as shown FIG.  3 . 
     The brake actuator  82  (a solenoid valve, for example) controls a fluid pressure which is supplied to wheel cylinders provided to the front wheels  11   a ,  11   b  and the rear wheels  12   a ,  12   b , respectively. Additionally, the accelerator actuator  83  (a motor, for example) controls an opening of a throttle valve. 
     The control unit  70  controls switching of damper orifices inside the guide-wheel dampers  42 ,  52  and a steering damper  85  based on the output signals of the vehicle speed sensor  71  and the marker sensor  72 . Additionally, the control unit  70  controls actuation of the guide-wheel housing actuator  50  based on the operating signal supplied from the switch  73 . Further, the control unit  70  supplies the automated driving control unit  80  with instructions to invalidate and validate a steering control (hereinafter referred to as a steering-free instruction and a steering-free canceling instruction, respectively). 
     When the vehicle  10  runs on the road R in a state where the front guide wheels  31   a ,  31   b  and the rear guide wheels  32   a ,  32   b  are extracted from the vehicle body  10   a  (see FIGS.  3  and  4 ), the control unit  70  and the automated driving control unit  80  perform processes in accordance with, for example, flowcharts shown in FIGS. 7 and 8, respectively. 
     In FIG. 7, the control unit  70  calculates a lateral position of the vehicle  10  on the road R based on the output signal of the marker sensor  72  (a running determination process: P 100 ). Then, it is determined whether or not the calculated lateral position on the road R is abnormal based on, for example, whether or not the vehicle  10  has deviated from the predetermined path to such an extent that the guide wheels  31   a ,  32   a  or  31   b ,  32   b  are in contact with the guide wall  100   a  or  100   b  (S 11 ). If the lateral position is not abnormal, then it is determined whether or not the magnetic marker (the station entrance marker) provided on the entrance part R 2  of the road R at a predetermined distance before the stop part R 3  is detected (S 12 ). While the vehicle  10  is normally running on the general road part R 1 , the running determination process P 100  and the processes of steps S 11 , S 12  are repeatedly performed. 
     In this case, as shown in FIG. 8, the automated driving control unit  80  repeatedly performs an automated driving control (P 200 ) in which the steering actuator  81 , the brake actuator  82  and the accelerator actuator  83  are controlled in accordance with the output signals of the vehicle speed sensor  71  and the marker sensor  72 , while determining whether or not the steering-free instruction is supplied from the control unit  70  in step S 31  (an automated driving mode). 
     If the vehicle  10  enters the entrance part R 2  and the station entrance mark is detected (YES in S 12  of FIG. 7) while the vehicle  10  is running on the general road part R 1  in the automated driving mode, as mentioned above, the control unit  70  supplies the steering-free instruction to the automated driving control unit  80  (S 13 ). Thereafter, the control unit  70  repeatedly determines whether or not an instruction to start the vehicle  10  (a departure instruction) is generated (S 14 ). 
     In such a state, if the automated driving control unit  80  determines that the steering-free instruction is supplied from the control unit  70  (YES in S 31  of FIG.  8 ), the automated driving control unit  80  turns off the steering actuator  81  and performs a steering-free control (S 32 ). Specifically, in the steering-free control, the automated driving control unit  80  operates the clutch mechanism  84  connecting the steering actuator  81  and the steered wheels (front wheels  11   a ,  11   b ) so that the steered wheels are released from constraint by the steering mechanism. Then, the automated driving control unit  80  determines whether or not the station entrance mark is detected (S 33 ). Since the station entrance mark has been detected before the steering free instruction is supplied (see S 12 , S 13  in FIG.  7 ), it is affirmatively determined in S 33 . Thus, the automated driving control unit  80  performs an automatic braking control (S 34 ) so that the vehicle  10  is decelerated in accordance with a predetermined velocity pattern corresponding to a case of stopping until the stop mark provided in the stop part R 3  is detected. When the stop mark is detected, the brake actuator  82  is controlled to generate a maximum braking force so as to positively stop the vehicle  10  (S 36 ). As a result, the vehicle  10  stops at the station provided in the stop part R 3 . Thereafter, the automated driving control unit  80  repeatedly determines whether or not the departure instruction is generated (S 37 ). 
     According to the above-mentioned processes performed by the control unit  70  and the automated driving control unit  80 , the steered wheels (front wheels  11   a ,  11   b ) are released from constraint by the steering mechanism including the steering actuator  81  when the vehicle  10  reaches a position at the predetermined distance before the stop part R 3 . This timing at which the steered wheels are released from constraint by the steering mechanism corresponds to a timing immediately before the front guide wheels  31   a ,  31   b  come into contact with the guide walls  100   a ,  100   b , a space of which gradually decreases. When at least one of the front guide wheels  31   a ,  31   b  comes into contact with the corresponding guide walls  100   a  or  100   b  in a state where the steered wheels can be freely steered (hereinafter, this state is referred to as a steering-free state), the steered wheels are directed in a straight (neutral) direction of the vehicle  10  by a lateral force exerted on the vehicle  10  from the guide wall  100   a  or  100   b  via the front guide wheel  31   a  or  31   b . Further, when both the front guide walls  31   a ,  31   b  are in contact with the guide wheels  100   a ,  100   b , respectively, a lateral position of the vehicle  10  is restricted to a substantially central position of the road R. 
     When the vehicle  10  continues to run in such a state, lateral forces exerted on the front guide wheels  31   a ,  31   b  gradually increase in association with a decrease in a space between the guide walls  100   a ,  100   b . Thus, the front guide wheels  31   a ,  31   b  are moved toward the inside of the vehicle body  10   a  in association with contraction of the guide-wheel dampers  42 ,  52  which support the front guide wheels  31   a ,  31   b . In this case, forces which restrict a lateral position of the vehicle  10  from both sides thereof gradually increase due to an increase in reaction forces generated by the guide-wheels dampers  42 ,  52 . After both the front guide wheels  31   a ,  31   b  have come into contact with the guide walls  100   a ,  100   b , the rear guide wheels  32   a ,  32   b  come into contact with the guide walls  100   a ,  100   b , and thereafter, the vehicle  10  reaches the stop part R 3  where a space between the guide walls  100   a ,  100   b  is the minimum value W 2 . In this stop part R 3 , since the lateral forces exerted on the vehicle  10  become maximum, a lateral position of the vehicle  10  can be positively restricted to a substantially central position of the road R. The vehicle  10  stops at the station in such a state. 
     When the control unit  70  detects the departure instruction after the vehicle  10  has stopped at the station of the stop part R 3  and passengers have finished getting on and off the vehicle  10  (YES in S 14  of FIG.  7 ), the control unit  70  decreases damping pressures of the guide-wheel dampers  42 ,  52  (S 15 ). Thus, the lateral forces exerted on the vehicle  10  which restrict a lateral position of the vehicle  10  is decreased. Thereafter, the control unit  70  repeatedly determines whether or not the station exit mark is detected (S 16 ). The departure instruction may be generated by another control system in the vehicle  10  which can monitor passengers getting on and off the vehicle  10  or by a monitor system provided on the station. 
     On the other hand, when the automated driving control unit  80  detects the departure instruction generated as mentioned above (YES in S 37  of FIG.  8 ), the automated driving control unit  80  operates the brake actuator  82  so as to cancel the generation of the maximum braking force by the automatic braking control (S 38 ). Then, the automated driving control unit  80  operates the accelerator actuator so as to perform an automatic acceleration control in accordance with a predetermined acceleration control pattern corresponding to a case of starting the vehicle  10  (S 39 ). 
     Since the automatic acceleration control is performed in a state where the lateral forces which restrict a lateral position of the vehicle  10  are decreased as mentioned above, the vehicle  10  can smoothly depart from the station. 
     When the control unit  70  detects the station exit mark while the vehicle  10  is running in the stop part R 3  (YES in S 16  of FIG.  7 ), the control unit  70  returns the damping pressures of the guide-wheel dampers  42 ,  52  to a regular value (S 17 ) and supplies the steering-free canceling instruction to the automated driving control unit (S 18 ). Thereafter, the control unit  70  repeatedly performs the running determination process (P 100 ), the process of determining abnormality of a lateral position of the vehicle  10  (S 11 ) and the process of determining a detection of the station entrance mark (S 12 ), as mentioned above. 
     On the other hand, if the automated driving control unit  80  determines a detection of the station exit mark (YES in S 40  of FIG.  8 ), the automated driving control unit  80  further determines whether or not the steering-free canceling instruction is supplied from the control unit  70  (S 41 ). When the steering-free canceling instruction is supplied from the control unit  70  as mentioned above (YES in S 41 ), the steering actuator  81  is turned on and the actuation of the clutch mechanism  84  connecting the steering actuator  81  and the steered wheels is stopped so as to cancel the steering-free state (S 42 ). Thereafter, the automated driving control unit  80  controls the steering actuator  81 , the brake actuator  82  and the accelerator actuator  83  based on the output signals of the vehicle speed sensor  71  and the marker sensor  72  so that the vehicle  10  runs on the predetermined path with the predetermined velocity pattern (the automated driving mode: P 200 ), while determining whether or not the steering-free instruction is supplied from the control unit  70 . 
     As mentioned above, in a regular situation, when the vehicle  10  is running in the general road part R 1 , the vehicle  10  is controlled to run along the predetermined path in the automated driving mode. On the other hand, when the vehicle  10  moves from the entrance part R 2  to the stop part R 3  or from the stop part R 3  to the general road part R 1 , the vehicle  10  is steered by restricting a lateral position thereof with the front guide wheels  31   a ,  31   b  and the rear guide wheels  32   a ,  32   b  being constrained between the guide walls  100   a ,  100   b  in a state where the steered wheels (front wheels  11   a ,  11   b ) can be freely steered, instead of by controlling the vehicle  10  in the automated driving mode. 
     In the above-mentioned processes of the driving control, if a lateral position of the vehicle  10  has deviated from the predetermined path until the guide wheels  31   a ,  32   a  or  31   b ,  32   b  come into contact with the corresponding guide wall  100   a  or  100   b  due to a burst of a tire, a slip, or a failure of a sensor of the vehicle  10  while the vehicle  10  is running in the general road part R 1 , the control unit  70  determines an abnormality of a lateral position of the vehicle  10  based on the output signal of the marker sensor  72  (YES in S 11  of FIG.  7 ). When it is determined that the lateral position of the vehicle  10  is abnormal in this way, the control unit  70  further determines whether or not it is necessary to increase a damping pressure of the steering damper  85  (S 19 ). A description regarding the necessity of increasing the damping pressure of the steering damper  85  will be given later. 
     If it is determined that the damping pressure of the steering damper  85  need not be increased, the control unit  70  supplies the steering-free instruction to the automated driving control unit  80  (S 21 ). Thereafter, the control unit  70  repeatedly determines whether or not the vehicle  10  has stopped (S 22 ). 
     On the other hand, when the automated driving control unit  80  receives the steering-free instruction from the control unit  70  (YES in S 31  of FIG.  8 ), the automated driving control unit  80  turns off the steering actuator  81  and actuates the clutch mechanism  84  which connects the steering actuator  81  and the steered wheels (front wheels  11   a ,  11   b ) (S 32 ). Thus, the steered wheels are released from constraint by the steering mechanism. In this case, since the vehicle  10  is running in the general road part R 1 , the station entrance mark is not detected (NO in S 33 ). Thus, the automated driving control unit  80  operates the brake actuator  82  so as to perform a forcible braking control which forcibly generates a braking force (S 43 ) while determining whether or not the vehicle  10  has stopped (S 44 ). 
     According to the above-mentioned processes performed by the control unit  70  and the automated driving control unit  80 , the guide wheels  31   a ,  32   a  (or  31   b ,  32   b ) come into contact with the guide wall  100   a  (or  100   b  ) in the steering-free state. Thus, a lateral position of the vehicle  10  is restricted by the guide wall  100   a  (or  100   b ). In this case, a lateral force is exerted on the vehicle  10  from the guide wall  100   a  (or  100   b ) via the guide wheels  31   a ,  32   a  (or  31   b ,  32   b ) supported by the guide-wheel damper  42  (or  52 ). When the lateral force exerted on the vehicle  10  exceeds a restoring force of the steered wheels (front wheels  11   a ,  11   b ), the steered wheels are naturally steered in a neutral (straight) direction (indirect steering). As a result, the vehicle  10  is decelerated to be stopped by the forcible braking control with the guide wheels moving along the guide wall. 
     When the steered wheels are indirectly steered by a lateral force exerted on the vehicle  10 , as mentioned above, it may be desirable to adjust a damping force of the steering damper  85  which governs the restoring force of the steered wheels, in view of improving a stability of the vehicle  10 . That is, the determination of a necessity of increasing the damping pressure of the steering damper  85  in step S 19  is performed in the following manner. 
     First, a curvature of the road R on which the vehicle  10  is running is calculated based on detected vehicle speed and lateral acceleration (a lateral-acceleration sensor is not shown in the figures). If the calculated curvature is larger than or equal to a predetermined value (that is, if the road R curves sharply), it is determined whether or not the detected vehicle speed is larger than or equal to a reference vehicle speed predetermined in accordance with a curvature of the road. If the detected vehicle speed is larger than or equal to the reference vehicle speed, it is determined that the damping force of the steering damper  85  should be increased. That is, as a curvature of the road becomes larger and as a vehicle speed becomes higher, the damping force of the steering damper  85  should be increased because the steered wheels should be more slowly returned to be in the neutral direction. 
     The above-mentioned predetermined value for the curvature of the road and the reference vehicle speed are, for example, experimentally determined as values with which the vehicle  10  can stably run in a state where the steered wheels can be freely steered. 
     If it is determined that the damping pressure of the steering damper  85  should be increased in the above-mentioned manner (YES in S 19 ), the control unit  70  operates an electromagnetic actuator for switching a diameter of the damper orifice inside the steering damper  85  so that the orifice diameter is switched to a smaller value. As a result, the damping pressure of the steering damper  85  is increased (S 20 ). 
     When the vehicle  10  has been stopped by the forcible braking control performed by the automated driving control unit  80 , the control unit  70  determines that the vehicle  10  has stopped (YES in S 22  of FIG.  7 ). In this case, the control unit  70  returns the damping pressure of the steering damper  85  to the regular value by operating the above-mentioned electromagnetic actuator (S 23 ). On the other hand, if the automated driving control unit  80  determines that the vehicle  10  has stopped (YES in S 44  of FIG.  38 ), the processes shown in FIG. 8 are finished. 
     As mentioned above, when the vehicle  10  has deviated from the path due to a burst of a tire, a slip or a failure of a sensor, the steered wheels (front wheels  11   a ,  11   b ) are set in the steering-free state since the automated driving mode should not be maintained. In this case, since the vehicle  10  runs with the guide wheels  31   a ,  32   a  (or  31   b ,  32   b ) being in contact with the corresponding guide wall  100   a  (or  100   b ), the steered wheels are naturally steered to be in the neutral direction by a lateral force exerted on the vehicle  10  from the guide wall via the guide wheels (indirect steering). Thus, the vehicle  10  can be stably steered. Additionally, the vehicle  10  can be safely stopped by the forcible braking control. 
     In the above-mentioned embodiment, descriptions are given for a case where the vehicle  10  has deviated from the path due to a burst of a tire, a slip or a failure of a sensor. However, the above-mentioned control can be applied to a case where the vehicle  10  has deviated from the path due to a strong crosswind, for example. 
     That is, when the vehicle  10  is steered in the automated driving mode, the vehicle  10  may be moved in a lateral direction until the guide wheels  31   a ,  32   a  (or  31   b ,  32   b ) come into contact with the guide wall  100   a  (or  100   b ) due to a strong crosswind. In this case, a reaction force of the guide-wheel damper  42  (or  52 ) supporting the guide wheels  31   a ,  32   a  (or  31   b ,  32   b ) is exerted on the vehicle  10  as a force which pushes the vehicle  10  toward the center of the road  10 . If the vehicle  10  is returned to the predetermined path by this force, the automated driving mode can be maintained. 
     On the other hand, if the vehicle is not returned to the predetermined path by the above-mentioned force, the automated driving mode is interrupted and the steered wheels are set in the steering-free state, as a case of the above-mentioned embodiment. Thus, the vehicle  10  is decelerated to be stopped by the forcible braking control with the steered wheels being indirectly steered by the lateral force exerted on the vehicle  10  from the guide wall via the guide wheels. 
     Considering the above-mentioned case where the vehicle  10  is laterally moved by a crosswind, it may be determined that a lateral position of the vehicle  10  is abnormal in step S 11  of FIG. 7 when, for example, a state in which the vehicle  10  has deviated from the path and the guide wheels are in contact with the guide wall is maintained for a predetermined time. 
     In the above-mentioned embodiment, the front guide wheels  31   a ,  31   b  ahead of the front wheels  11   a ,  11   b  and the rear guide wheels  32   a ,  32   b  behind the rear wheels  12   a ,  12   b  laterally project from the vehicle  10 . However, it is also possible to achieve the same function as the above-mentioned embodiment by providing only the front guide wheels  31   a ,  31   b  ahead of the front wheels  11   a ,  11   b (steered wheels), as shown in FIG.  9 . 
     Additionally, the guide wheels  31   a ,  31   b ,  32   a ,  32   b  may be supported by a laterally rigid frame instead of the guide-wheel dampers  42 ,  52 . In such a structure, the guide wheels  31   a ,  31   b ,  32   a ,  32   b  preferably have a high lateral elasticity by being made of, for example, polyurethane foam rubber. In this case, a space between the guide walls  100   a ,  100   b  may be set to be slightly larger than a width of the vehicle body  10   a , as shown in FIG. 10, so that a lateral position of the vehicle  10  can be restricted by a resilient force of the guide wheels  31   a ,  31   b ,  32   a ,  32   b  generated in accordance with the lateral elasticity thereof. 
     Further, one of the guide walls  100   a ,  100   b  in the entrance part R 2  may be constructed as a belt which has a shock-absorbing function in the lateral direction, as shown in FIG.  11 . In the structure shown in FIG. 11, a shock-absorbing guide wall  200  comprises a driving pulley  202 , driven pulleys  203 ,  204  and a rubber belt  201  which is engaged around the pulleys  202 ,  203 ,  204  with a predetermined tension. The driving pulley  202  is rotated so that the belt  201  moves in a direction shown by an arrow in FIG.  11 . The shock-absorbing guide wall  200  having such a structure is provided in the entrance part R 2  instead of the guide wall  100   a.    
     When the vehicle  10  enters the entrance part R 2  provided with the shock-absorbing guide wall  200 , the steered wheels in the steering-free state are steered by a lateral force exerted on the vehicle  10  each time when the front guide wheel  31   b  and the rear guide wheel  32   b  on the left side come into contact with the guide wall  100   b  or the front guide wheel  31   a  on the right side comes into contact with the belt  201 . Thus, a lateral position of the vehicle  10  gradually converges toward a center of the road R. When the front guide wheels  31   a ,  31   b  are constrained between the guide wall  100   b  and the belt  201 , the lateral position is substantially restricted to the center of the road R. The vehicle  10  enters the subsequent stop part R 3  in such a state. 
     In this case, vibrations transmitted to the vehicle  10  are reduced by the shock-absorbing function of the belt  201 . 
     The shock-absorbing guide wall  200  comprising the belt  201  may be used as each guide wall in the stop part R 3  where the station is provided or as a guide wall on a downwind side of the general road part R 1  where a strong crosswind frequently blows. Additionally, the shock-absorbing guide wall  200  may be provided on a junction of the road R where the road R branches into two lanes. 
     When a road R 1  branches into two branch roads R 2 , R 3  as shown in FIG. 12A, for example, a branch wall  100   c  is provided at a junction of the branch roads R 2  and R 3 , as shown in FIG.  12 B. FIG. 12B shows a cross section along a line A—A in FIG.  12 A. 
     As shown in FIGS. 12A and 12B, the guide wall  100   a  which is provided on a right side of the road R 1  extends into the guide wall  100   a  which is provided on a right side of the branch road R 2 . Similarly, the guide wall  100   b  which is provided on a left side of the road R 1  extends into the guide wall  100   b  which is provided on a left side of the branch road R 3 . In addition, the branch wall  100   c  is provided at a border between the branch roads R 2  and R 3 . The branch wall  100   c  has a convex shape projecting into the road R 1 . Side faces of the branch wall  100   c  extend along a left side of the branch road R 2  and a right side of the branch road R 2 , respectively. A height of the branch wall  100   c  is smaller than a height of each of the guide walls  100   a ,  100   b  and is designed to be approximately 20 centimeters, for example. 
     When the vehicle  10  passes through the junction provided with the branch wall  100   c , the vehicle  10  runs along one of the branch roads R 2 , R 3  which branch from the road R 1  in the automated driving mode. However, a lateral position of the vehicle  10  may be shifted toward the branch wall  100   c  between the branch roads R 2 , R 3  due to some trouble in driving control of the automated driving mode when the vehicle  10  enters one of the branch roads R 2 , R 3 . In this case, the lateral position of the vehicle  10  is restricted by a branch-road guide member  90  provided on the vehicle  10  being in contact with the branch wall  100   c.    
     In such a guideway transit system, the branch-road guide member  90  is provided ahead of the front wheels of the vehicle  10 , together with the guide wheels  31   a ,  31   b  laterally projecting from the vehicle  10 , as shown in FIGS. 13 and 14. 
     As shown in FIG. 13, the longitudinal frames  61 ,  62  and the lateral frame  63  are connected to each other inside the vehicle body  10   a  in the same manner as shown in FIGS. 4 and 5. The front guide wheel  31   a  is rotatably supported at one end of the support bar  41 , and the other end of the support bar  41  is pivotably connected to the lateral frame  63  on a right part of the vehicle body  10   a . Additionally, the end of the support bar  41  supporting the front guide wheel  31   a  is connected to an end of the piston of the guide-wheel damper  42 . Similarly, the support bar  51  and the guide-wheel damper  52  are provided in a left part inside the vehicle body  10   a . Ends of the cylinders of the guide-wheel dampers  42 ,  52  are supported by the link mechanism constituted by the link bars  56 ,  57 ,  59 . 
     According to the above-mentioned structure, when the front guide wheel  31   a  is pressed against the guide wall  100   a , a lateral position of the vehicle  10  is restricted and the guide-wheel damper  42  is compressed so that a reaction force of the guide-wheel damper  42  is exerted on the vehicle body  10   a , as in the case of the above-mentioned embodiment shown in FIGS. 4 and 5. Similarly, when the front guide wheel  31   b  is pressed against the guide wall  100   b , a lateral position of the vehicle  10  is restricted and a lateral force is exerted on the vehicle body  10   a . Thus, the steered wheel in the steering-free state is steered in the neutral direction by the lateral forces exerted from the guide walls  100   a ,  100   b.    
     The branch-road guide member  90  is provided below the support mechanism of the front guide wheels  31   a ,  31   b  and the frames  61 ,  62 ,  63 . The branch-road guide member  90  is a U-shaped plate-like member having a convex shape at a front end thereof. A reinforcing frame  65  is fixed to an upper surface of the branch-road guide member  90  via a flange part by means of bolts or adhesive. 
     FIG. 14 is a side view of the vehicle body  10   a  seen from the left in FIG.  13 . In FIG. 14, a structure for mounting the branch-road guide member  90  is mainly shown and other members are omitted. 
     As shown in FIG. 14, a plurality of slide bars  66  which extend vertically are provided integrally with the lateral frame  63 , and a plurality of slide bars  67  which extends vertically are provided integrally with the longitudinal frames  61 ,  62 . Support bars  68  are slidably mounted on the respective slide bars  66 . Similarly, support bars  69  are slidably mounted on the respective slide bars  67 . The branch-road guide body  90  is fixed to lower ends of the support bars  68 ,  69  so as to be in parallel with a road surface. 
     When the vehicle  10  is used as a vehicle of the guideway transit system shown in FIG. 2, a height of the branch-road guide member  90  is adjusted so that the branch-road guide member  80  can be in contact with the branch wall  100   c . On the other hand, when the vehicle  10  runs on a general road, the branch-road guide member  90  is held in a position which is higher than a minimum height of the vehicle  10  by lifting the support bars  68 ,  69  along the slide bars  66 ,  67  by means of a lifter mechanism (not shown). 
     FIGS. 15 and 16 show a detailed structure of the branch-road guide member  90 . As seen from FIGS. 15 and 16, thin plates  92   a ,  93   a ,  94   a ,  95   a ,  96   a  which are reinforced by carbon fibers are provided on an upper surface of a base plate  91  with ends of the plates  92   a  to  96   a  being shifted one after another. Similarly, thin plates  92   b ,  93   b ,  94   b ,  95   b ,  96   b  which are reinforced by carbon fibers are provided on a lower surface of the base plate  91  with ends of the plates  92   b  to  96   b  being shifted one after another. 
     The base plate  91  is made of thermosetting resin such as polycarbonate or polypropylene, and has a honeycomb structure which has a relatively low strength under a force acting obliquely from the front, that is, a force acting in a direction of contact with the branch wall  100   c . The base plate  91  and the thin plates  92   a ,  92   b ,  93   a ,  93   b ,  94   a ,  94   b ,  95   a ,  95   b ,  96   a ,  96   b  are fixed together by thermosetting adhesive. 
     According to the above-mentioned structure of the branch-road guide body  90 , a strength of the branch-road guide body  90  in a direction of contact with the branch wall  100   c  gradually increases from the front toward the rear. A distribution of the strength can be adjusted by changing an amount of the shift between thin plates or a number of the thin plates layered on the base plate  91 . 
     Consider a case where the vehicle  10 , which is provided with the branch-road guide body  90  in a front part thereof, enters the branch road R 2  from the road R 1  (see FIG.  12 ). In this case, if the vehicle  10  deviates from a path toward the branch wall  100   c , a front end part of the branch-road guide member  90  comes into contact with the branch wall  100   c  at first, as shown in FIG.  17 . When the vehicle  10  continues to run in this state, the branch-road guide member  90  is laterally pressed against the branch wall  100   c . Thus, the vehicle  10  is guided into the branch road R 2  by a lateral force exerted on the branch-road guide member  90  from the branch wall  100   c.    
     When the branch-road guide member  90  moves while being pressed against the branch wall  100   c  as mentioned above, the branch-road guide member  90  is destroyed by a force exerted from the branch wall  100  as shown by a hatched part in FIG.  17 . Since a strength of the destroyed part of the branch-road guide member  90  gradually increases from the front end to the rear, the lateral force exerted on the vehicle  10  gradually increases as the vehicle  10  advances. Thus, the vehicle  10  can be smoothly guided into the branch road R 2 . 
     The control unit  70  and the automated driving control unit  80  of the vehicle  10  guided into the branch road R 2  perform the above-mentioned processes shown in FIGS. 7 and 8, respectively. During these processes, if the vehicle  10  can be returned to the predetermined path by the lateral force exerted thereon from the branch wall  100   c  via the branch-road guide member  90 , the vehicle  10  continues to be controlled in the automated driving mode. On the other hand, if the vehicle  10  cannot be returned to the predetermined path within a predetermined time, it is determined that a lateral position of the vehicle  10  is abnormal (YES in S 11  of FIG.  7 ). In this case, the steered wheels (front wheels  11   a ,  11   b ) are set in the steering-free state, and the vehicle  10  is decelerated to be stopped by the forcible braking control with the steered wheels being steered in the neutral direction by the indirect steering. 
     Contact surfaces of the branch-road guide member  90  and the branch wall  100   c  may be constituted as shown in FIG. 18, for example. In this example, a contact surface  100   cc  of the branch wall  100   c  and a contact surface  90   c  of the branch-road guide member  90  are inclined so that the contact surface  100   cc  faces the contact surface  90   c  from above. 
     According to this structure, when the branch-road guide member  90  moves while being pressed against the branch wall  100   c , a force which pushes down the branch-road guide member  90  is exerted thereon from the branch wall  100   c . Thus, it is possible to prevent the vehicle  10  from moving over the relatively low branch wall  100   c.    
     Additionally, when the vehicle  10  moves from the road R 1  to, for example, the branch road R 2  (see FIG.  12 ), the vehicle body  10   a  rolls in an outward direction of turning due to a centrifugal force. That is, a side of the vehicle body  10   a  facing the branch wall  100   c  sinks. In order to achieve a stable movement of the branch-road guide member  90  along the branch wall  100   c  when the branch-road guide member  90  comes into contact with the branch wall  100   c  in such a state, it is preferable to set inclination angles of the contact surfaces  100   cc  and  90   c  as shown in FIG.  19 . 
     As shown in FIG. 19, an inclination angle B of the contact surface  90   c  of the branch-road guide member  90  with respect to a vertical direction is set to be larger than an inclination angle A of the contact surface  100   cc  of the branch wall  100   c  with respect to a vertical direction, in accordance with an inequality B≧(A+α), for example. In this inequality, α is an expected roll angle of the vehicle body  10   a  when the vehicle  10  enters one of branch roads. This roll angle α is determined based on a vehicle speed when the vehicle  10  enters the branch road, a turning radius, a weight of the vehicle  10  (including a weight of an expected number of passengers), an elasticity of a suspension, and so on. For example, when the inclination angle A of the contact surface  100   cc  of the branch wall  100   c  is set to be 8° and the expected roll angle α is set to be 4°, the inclination angle B of the contact surface  90   c  of the branch-road guide member  90  is set to be equal to or slightly larger than 12°. 
     If the inclination angle A of the contact surface  100   cc  of the branch wall  100   c  is set to be smaller than the inclination angle B of the contact surface  90   c  of the branch-road guide member  90  as mentioned above, an end part of the contact surface  90   c  comes into contact with the branch wall  100   c  at first when the vehicle  10  enters the branch road. Then, when the branch-road guide member  90  swings in a direction indicated by an arrow C in FIG. 19 in association with a roll of the vehicle body  10   a , a whole part of the contact surface  90   c  of the branch-road guide member  90  comes into contact with the contact surface  100   cc  of the branch wall  100   c . Thus, the branch-road guide part  90  can be stably guided along the branch wall  100   c.    
     A sensor may be provided on an end part of the contact surface  90   c  of the branch-road guide part  90  for detecting a contact with the branch wall  100   c . Since an end part of the contact surface  90   c  comes into contact with the branch wall  100   c  at first, the sensor can immediately detect the contact between the branch-road guide member  90  and the branch wall  100   c . Thus, the information detected by the sensor can be used, for example, as a trigger to start an emergency braking of the vehicle  10  or generation of a warning. 
     The present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority applications No. 10-276014 filed on Sep. 29, 1998 and No. 11-165027 filed on Jun. 11, 1999, the entire contents of which are hereby incorporated by reference.