Patent Publication Number: US-2023162603-A1

Title: Autonomous Transportation Network with Junction Control Method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of UK Patent Application number 2005607.3 filed on 17 Apr. 2020. The entire disclosure of the UK Patent Application 2005607.3 is hereby incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The invention relates to a method for controlling a plurality of autonomous vehicles entering a junction. 
     BACKGROUND TO THE INVENTION 
     The term “automated transit network” or “automated transportation network” (abbreviated to ATN) is a relatively new designation for a specific transit mode that falls under the larger umbrella term of “automated guideway transits” (AGT). Before 2010, the name “personal rapid transit (PRT)” was used to refer to the ATN concept. In Europe, the ATN has been referred to in the past as “podcars”. 
     Like all forms of AGT, ATN is composed of automated and autonomous vehicles that run on an infrastructure and are capable of carrying passengers from an origin to a destination. The autonomous vehicles are able to travel from the origin to the destination without any intermediate stops or transfers, such as are known on conventional transportation systems like buses, trams (streetcars) or trains. The ATN service is typically non-scheduled, like a taxi, and travelers are able to choose whether to travel alone in the vehicle or share the vehicle with companions. 
     The ATN concept is different from self-driving cars which are starting to be seen on public streets. The ATN concept has most often been conceived as a public transit mode similar to a train or bus rather than as an individually used consumer product such, as a car. Current design concepts of the ATN currently rely primarily on a central control management for controlling individually the operation of the autonomous vehicles on the ATN. 
     On the other hand, the self-driving cars are often described as being “autonomous”, but in practice, there are different classes or levels of vehicle autonomy. The degree of vehicle autonomy is typically divided in five levels, as set out by the On-Road Automated Driving (ORAD) committee of the Society of Automotive Engineers (SAE) in “Taxonomy and definitions for terms related to driving automation systems for on-road motor vehicles” published in Recommended Practice SAE J 3016 on 15 Jun. 2018. Level 0 refers to a vehicle that has no driving automation. The driver of the vehicle is fully in charge of operating the movement of the vehicle. Vehicles of Level 0 may include safety systems such as, for example, a collision avoidance alert. Level 1 refers to vehicles having at least one driving assistance feature such as an acceleration or braking assist system. The driver is responsible for the driving tasks but is supported by the driving assist system which is capable of affecting the movement of the vehicle. Level 2 describes vehicles having more than one assist system for actively affecting the movement of the vehicle. The driver, in Level 2, is still responsible for the driving tasks and must actively monitor the trajectory of the vehicle at all times. The driver is, however, actively supported by the assist systems. Level 3 describes a so-called “conditional automation” of the vehicle. The vehicle is capable of autonomously driving in certain situations and with limitations. The driver is not required to actively monitor the assist system but is, however, required to take control of a driving situation if requested by the assist system. Level 4 describes autonomously travelling vehicles which are capable of travelling specific routes under normal conditions without human supervision. The vehicles of Level 4 can therefore operate without a driver but might need remote human supervision in case of conflict situations, travelling in remote areas, or when travelling extreme weather conditions. Level 5 Automation describes fully autonomously driving vehicles. No human interaction is required at any time for the operation of the vehicles. 
     The reliance of the existing ATN networks on a central control management leads to a bottleneck in that each of the autonomous vehicles needs to be in almost continuous communication with the central control management. This can result in problems if the communications network is overloaded or there is a major incident somewhere in the ATN network that requires action from the central control management. Bottlenecks can also occur at junctions at which several autonomous vehicles arrive substantially simultaneously from different directions on different inward routes and may need to exit the junction using the same outward route. The central control management must decide which one(s) of the autonomous vehicles are to be given priority at the junction and manage the process of negotiating the autonomous vehicle through the junction, which can fail if the response time is not fast enough. This can lead to unnecessary waiting time at the junction with consequent waste of resources, such but not limited to energy or utilization of the autonomous vehicle. 
     An example of such as central control management is outlined in U.S. Pat. No. 10,345,805 (Seally, assigned to Podway Inc.) in which the central control management receives a request from an autonomous vehicle for a route from the origin to the destination. The central control management calculates the route and sends to the autonomous vehicle a journey instruction set to allow the autonomous vehicle to navigate from the origin to the desired destination along the calculated route. The central control management in this system needs to transmit large amounts of data from the autonomous vehicles and gather data from the autonomous vehicles on a continuous basis. This requires a large amount of hardware and data bandwidth and can cause a problem if an autonomous vehicle enters an area in which connectivity is poor. In the event of a breakdown of the central control management, then the autonomous vehicles will no longer be able to navigate or recalculate journeys. 
     Many current ATN concepts rely on guideways being built as part of the infrastructure. This may have its advantages when dedicated infrastructure separate from other traffic flows or pedestrians can be designed. The cost of the provision of the guideways is significant and this will delay the development of the ATN network. One example of such a guideway is the infrastructure that can be seen in London Heathrow airport&#39;s Terminal 5. 
     A report on “Automated Transit Networks (ATN): A Review of the State of the Industry and Prospects for the Future” published by the Mineta Transportation Institute, Report No 12-31 in September 2014 reported that at the date of writing no ATN having more than ten stations had been implemented in the world. Currently the ATN networks operate on the principle of mapping each of the origins to all of the destinations. This leads to a matrix with 20 entries even for a simple five-station system as there are four possible destinations from each of the five origins. A ten-station system would have 90 possible routes and it will be seen that as the number of origins and destinations increases, then an O/D matrix listing all of the possible routes will expand out of hand. 
     The addition of junctions into the mapping system further complicates the map as paths have to be created to take into account potential conflicts between the autonomous vehicles in the ATN at the junctions. 
     The current systems are therefore not scalable. 
     A further issue that has been identified in the ATN network is the handling of multiple vehicles and prioritizing of access for priority vehicles, such as paramedics or police. A solution is offered in U.S. Pat. No. 9,536,427 (Tonguz et al, assigned to Carnegie Mellon). The solution uses vehicle-to-vehicle communication to establish a priority zone as required. 
     Other patent documents are known for coordinating the movement of autonomous vehicles. For example, German Patent Application No DE 10 2017 007 814 A1 (Scania) teaches a method for coordinating the movement of autonomous vehicles to arrive a point at which a platoon or column of autonomous vehicles are put together. German Patent Application No DE 10 2017 215 564 (Bosch) teaches a method for calculating an optimal route to a point at which passengers can change vehicles. 
     One method for enabling autonomous vehicles to move through merging or branching junctions is shown in US Patent Application US 2019/196500 A1 (Harasaki, assigned to Murata Machinery). 
     US 2019/236948 A1 (Fujitsu) describes a system and method for intersection management for managing the passage of a plurality of the autonomous vehicles at an intersection or junction of two roads. An intersection manager is located at or near the intersection for managing the passage of the plurality of the autonomous vehicles and avoiding conflicts between the autonomous vehicles traversing the intersection. The autonomous vehicles wising to traverse the intersection send a traversing request to request a block of exclusive space-time resource of an intersection zone in order to traverse or cross through the intersection. The traversing request includes an earliest arrival time at the intersection zone, a position, a vehicle speed, an entry lane of an intersection, a departure lane of the intersection, and vehicle properties. The vehicle properties include a vehicle identity number, a width, a length, a maximum speed, a maximum acceleration, and a maximum deceleration. The method described allows the reservation of a trajectory or an exclusive block of space-time resource to satisfy the traversing request. If the reservation is approved by the intersection manager, the autonomous vehicle is informed that the autonomous vehicle is able to proceed through the intersection by receiving an approved reservation. The received approved reservation comprises information about a reserved trajectory including an entry time for the entry of the autonomous vehicle into the intersection, a traversing time for the autonomous vehicle to traverse through the intersection, and a traversing speed defined by the intersection manager for the traversing of the intersection. 
     US Patent Application US 2013/304279 A1 discloses a system and method for continuously allowing a plurality of autonomous vehicles to travel through an intersection. The travel through the intersection is done using synchronized and staggered timeslots for the crossing of the autonomous vehicles. The autonomous vehicles comprises a map database, a navigation system, and an autonomous vehicle controller. The system enables a number of time slot cells. Each time slot cell represents a location that a vehicle could be in at any particular point in time for a particular traffic flow pattern. The intersection has stop lines or inbound lanes. The stop lines represent a place where the autonomous vehicle traveling in a particular lane needs to stop so that the autonomous vehicle enters the intersection at the proper time to be in synchronization with other ones of the autonomous vehicles in the other lanes. In order to prevent the autonomous vehicles from colliding with each other, only one of the autonomous vehicles can be in a particular cell at a particular point in time. 
     The staggering of the entry of the vehicles into the intersection based on vacation of a particular time slot cell by one autonomous vehicle before the next autonomous vehicle enters that time slot cell. Depending on traffic volume and other factors, the autonomous vehicle controller controls the autonomous vehicles so that the autonomous vehicles arrive at the intersection in a staggered format or are stopped at the stop lines until the time for the particular autonomous vehicle to enter the intersection arrives. The size of the time slot cells is dependent on the speed of the autonomous vehicles and the size of the autonomous vehicles. 
     U.S. Pat. No. 10,437,256 B2 discloses a system, method, and apparatus for controlling autonomous or semi-autonomous vehicles at an intersection using an intersection manager. The apparatus for intersection management receives intersection crossing requests from one or more of the autonomous or semi-autonomous vehicles. The apparatus includes an analyzer for processing the received crossing request. Using the analyzer, the apparatus processes the intersection crossing requests and generates a command. The command comprises a crossing velocity for the autonomous vehicle, and a time at which to commence the crossing velocity. The command is transmitted, using an output interface, to the requesting one of the autonomous vehicles. 
     Methods for controlling the operation of an autonomous vehicle are shown in US Patent Application Publication No 2020/012295 (Kim, assigned to LG Electronics). The prior art documents teach the use of centralized intersection or junction management controllers to control the autonomous vehicles passing through the intersections or junctions. These single intersection or junction management controllers are liable to failure or to overloading, for example if there are a large number of vehicles in the autonomous vehicle network. There is therefore a need for providing a resilient method of controlling a plurality of autonomous vehicles entering the intersection or junction. 
     SUMMARY OF THE INVENTION 
     This document describes a method of controlling a plurality of autonomous vehicles entering a junction from a plurality of inward routes and leaving the junction in at least one outward route, wherein the controlling comprises coordinating of the autonomous vehicles. The method enables the control and coordination of the passage through the junction by a plurality of the autonomous vehicles to avoid conflicts. In one aspect, the method comprises calculating a first time slot for entering the junction on a first inward route for a first autonomous vehicles. The first time slot has a first entry time at which the first autonomous vehicle enters the junction and is communicated from a beacon to the first autonomous vehicle. The velocity of the first autonomous vehicle is then adjusted by an onboard processor such that the first autonomous vehicle arrives at the junction at the first entry time and is able to enter the reserved slot on the junction. 
     A second time slot for entering the junction for a second autonomous vehicle of the plurality of autonomous vehicles arriving on a second inward route different from the first inward route of the first autonomous vehicle. The second time slot has a second entry time at which the second autonomous vehicle enters the junction and wherein the second entry time is later than the first entry time such that the second autonomous vehicle does not impact the first autonomous vehicle. The second time slot data real including the second entry time is communicated from the beacon to the second autonomous vehicle and the second autonomous vehicle adjusts, using the onboard processor, its velocity to arrive at the second entry time, which will be after the first autonomous vehicle has left the junction. Thus, a conflict between the first autonomous vehicle and the second autonomous vehicle is avoided at the junction. 
     In a further aspect, a third time slot for entering the junction is set for a third autonomous vehicle of the plurality of autonomous vehicles. The third autonomous vehicle is travelling parallel to the first autonomous vehicle on a same one of the first inward route and the third time slot has a third entry time at which the third autonomous vehicle may enter the junction. The third time slot including the third entry time is communicated from the beacon to the third autonomous. The third entry time is later than the first entry time; and the velocity of the third autonomous vehicle is adjusted by the onboard processor so that the third autonomous vehicle arrives at the third entry time. 
     The durations of the first time slot, the second time slot and the third time slot is dependent on the type of the ones of the autonomous vehicles entering the junctions. 
     The autonomous vehicles can in another aspect exit the junction on a plurality of outward routes. 
     The method comprises transmitting to the beacon an identification of the autonomous vehicle when the autonomous vehicle is near the beacon. This enables the junction controller to confirm that the autonomous vehicle is expected. 
     This document also discloses a junction administration system for administering a flow of autonomous vehicles entering a junction on a plurality of inward routes and leaving the junction on at least one outward route. The junction administration system comprises a processor for calculating a plurality of adjacent time slots and allocating single of the time slots to ones of the autonomous vehicles desiring to enter the junction and a beacon for communicating the allocated one of the time slots to a corresponding one of the autonomous vehicles. 
     This document discloses a method for controlling an autonomous vehicle entering a junction comprises receiving from a beacon time slot data including a unique entry time for indicating the time of entry of the autonomous vehicle at the junction, calculating in an onboard processor required time from position of receipt of time slot data to the junction, and adjusting, by the onboard processor, the velocity of the autonomous vehicle to enable arrival at the junction at the unique entry time. 
     In one aspect, the autonomous vehicles include assist systems of Level 2 or Level 3, as described above. Using the onboard processor, the autonomous vehicles are capable of autonomously travelling in the transportation network. The autonomous vehicles, therefore, do not require a driver for driving of the autonomous vehicle. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG.  1    shows an overview of the ATN of this document. 
         FIGS.  2 A and  2 B  show an example of a junction. 
         FIG.  3    shows the method of operation. 
         FIG.  4    shows a junction with multiple outward routes. 
         FIG.  5    shows a junction with parallel arriving autonomous vehicles. 
         FIG.  6 A  shows a kinematic envelope in front of an autonomous vehicle. 
         FIG.  6 B  shows two autonomous vehicles on parallel tracks 
         FIG.  6 C  shows a larger autonomous vehicle and a smaller autonomous vehicle. 
         FIG.  6 D  shows a kinematic envelope for an autonomous vehicle which can change direction. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention. 
       FIG.  1    shows a first example of an autonomous transportation network  10  according to one aspect of this document. The autonomous transportation network has a plurality of autonomous vehicles  20  running on a plurality of tracks  15 . The tracks  15  form a network of tracks with junctions over which the autonomous vehicles  20  are able to run. It will be appreciated that the tracks  15  may include guide rails, such as steel rails or concrete guidance elements, but could also comprise separated roadways. It is envisaged that the tracks  15  could also be incorporated into regular roadways and streets as long as sufficient safety measures are incorporated. The tracks  15  are provided with a plurality of beacons  17  (similar to rail balises) which monitor the progress of the autonomous vehicles  20  and can also send signals to the autonomous vehicles  20  using a vehicle antenna  25  mounted on the autonomous vehicle  20 . 
     The autonomous vehicle  20  has not only the afore-mentioned vehicle antenna  25  and a vehicle memory  28  but will also include an onboard processor  27  which can control the autonomous vehicle  20  using the information in the vehicle memory  25  and any information received from the beacons  17 . The autonomous vehicle  20  is also equipped with brakes and may be equipped with object detectors. The object detectors are used to detect any objects, such as logs, stones, people, etc. that may be present on the track  15  in front of the autonomous vehicle  20 . The object detector, if present, will issue a signal to the autonomous vehicle  20  to apply the brakes if one or more of the objects are detected. 
     The autonomous vehicles  20  will be running on one or more of a plurality of routes  50  in the autonomous transportation network  10 . The routes  50  are connected together at junctions  56 , as shown in  FIG.  2   . The junctions  56  could be simple merge junctions  56  in which one of the routes joins another one of the routes, a roundabout (also called traffic circle or rotary), with several routes  50  entering and exiting the roundabout, or a more complicated arrangement with a plurality of inward routes and outward routes. The routes  50  could comprise a single pathway in which ones of the autonomous vehicles  20  are in a single file travelling at substantial the same velocity. The routes  50  could have parallel pathways in which two or more of the autonomous vehicles  20  can travel substantially parallel to each other, such as is typically the case on a limited access freeway (also called motorway). The autonomous vehicles  20  include assist systems of Level 2 or Level 3, as defined in the introduction. The autonomous vehicle  20  is capable of autonomously travelling in the transportation network  10  using the onboard processor  27 . The autonomous vehicles  20 , therefore, do not require a driver for driving of the autonomous vehicle  20 . A typical velocity in an urban environment for the autonomous vehicles  20  would be for example, 50 km/hour, but it will be appreciated that the method set out in this document is not limited by the speed of the autonomous vehicles  20 . 
     The time between the autonomous vehicles  20  travelling in the single file is set to be about 0.5 seconds to allow a sufficient safety margin to allow emergency braking. This leads to a distance of about 6 m between each one of the autonomous vehicles  20 . It will be appreciated that these values are not limiting of the invention. Slower and heavier autonomous vehicles  20  may require a smaller or larger distance between the autonomous vehicle  20  to provide an additional margin of safety. 
       FIGS.  2 A and  2 B  show an example of the management of autonomous vehicles  20  at the junction  56 . In this case, a simple junction  56  is shown which comprises two inward routes  60   a  and  60   b  merging and leading to an outward route  60   c.  A first autonomous vehicle  20 - 1  is travelling on the first one of the two inwards routes  60   a  and a second autonomous vehicle  20 - 2  is travelling on the second one of the two inwards routes  60   b.  Both of the autonomous vehicles  20 - 1  and  20 - 2  are travelling at the same velocity at a distance  70 - 1  and  70 - 2  from the junction  56 . The junction  56  is equipped with a junction controller  58  and beacons  17 - 1  and  17 - 2  which are in communication with the arriving autonomous vehicles  20 - 1  and  20 - 2  through an antenna and sending messages  19  in the form of signals to the onboard processors  27  of the autonomous vehicles  20  through their vehicle antennas  25 . Typically, the beacons  17 - 1  and  17 - 2  are around 50 m from the junction  56 , but this is not limiting of the invention. 
     The protocols used in the communication between the beacons  17 - 1  and  17 - 2  and the autonomous vehicles  20 - 1  and  20 - 2  are, for example, NFC (near-field communication) protocols, but this is not limiting of the invention. The NFC protocols are short-range wireless protocols which can transmit data over a short distance. The NFC protocols are secure and, because of their short range, more difficult to hack than a network-wide communication protocol. The beacons  17 - 1  and  17 - 2  are connected to the junction controller  58 . Only a limited amount of information needs to be transmitted from the autonomous vehicles  20 - 1  and  20 - 2  to the beacons  17 - 1  and  17 - 2 . In one aspect only an identification number of the autonomous vehicle  20 - 1  or  20 - 2  is transmitted and no further information will be transmitted. This limits the amount of communication traffic and enables reliability of the communication. 
     Suppose now that both of the autonomous vehicles  20 - 1  and  20 - 2  are approximately the same distance (e.g. 50 m) from the junction  56 , i.e. first distance  70 - 1  of the first autonomous vehicle  20 - 1  is approximately the same as the second distance  70 - 2  of the second autonomous vehicle  20 - 2  from the junction  56 . The junction controller  58  knows that the normal velocity of the autonomous vehicles  20 - 1  and  20 - 2  is 50 km/hour (as described above) and thus the junction controller  58  can calculate a time of arrival for both of the autonomous vehicles  20 - 1  and  20 - 2  by assuming that the autonomous vehicles  20 - 1  and  20 - 2  are travelling at this normal velocity. If both of the autonomous vehicles  20 - 1  and  20 - 2  were to continue at the same velocity, then the two autonomous vehicles  20 - 1  and  20 - 2  would conflict and possibly collide at the junction  56 . There is therefore the need for a junction control system to manage the approach of the autonomous vehicles  20 - 1  and  20 - 2  to the junction  56 . 
     The junction control system achieves this by defining time slots  80  as shown in  FIG.  2 B . Each time slot is sufficiently long that an autonomous vehicle  20  can enter the junction  56  at an entry time and exit the junction  56  at an exit time thus defining a set period of time for the exclusive passage of the autonomous vehicle  20  through the junction  56 . The next set period of time can then be allocated to the next autonomous vehicle  20  that wishes to enter the junction  56 . This is similar to a rotating door or barrier such as found in some buildings that allows only the passage of a single person through the rotating door at one time. 
     The length of the period of time will depend on the velocity of the autonomous vehicles through the junction  56  and also on the capacity of the outward route  60   c.  It was noted above that the autonomous vehicles  20  are travelling at 50 km/hour with a time of 0.5 s between each one of the autonomous vehicles  20 . This will therefore be typically the length of the period of time of the time slot  80 . It is possible in some aspects to change the length of the time slot  80  to cater for additional safety margins at the junction  56  of the need, for example at a roundabout, for the autonomous vehicle  20  to slow down for the comfort of the passengers in the autonomous vehicle  20  who would otherwise experience large side forces whilst going around the curved path of the roundabout. 
     It was noted in the Applicant&#39;s co-pending UK patent application No. 2003395.7, the contents of which are incorporated herein by reference, that a control management system for the autonomous transportation network  10  monitors the progress of the autonomous vehicles  20  through the autonomous transportation network  10 . Information about the progress is passed to the junction controller  58  and thus the junction controller  58  will know when one or more of the autonomous vehicles  20  is to be expected at the junction  56 . Thus, the data transmission from the autonomous vehicle  20  at one of the beacons  17  is used to confirm that the autonomous vehicle  20  is on time. It is possible that the autonomous vehicle  20  is delayed because of a defect or a bad track  15 , for example, and the junction controller  58  will therefore resolve potential conflicts at the junction  56  on detection of the arrival of the autonomous vehicle  20 . 
     In one aspect of the invention, there may be second beacons  18 - 1  and  18 - 2  set up on the inward routes  60   a  and  60   b.  The second beacons  18 - 1  and  18 - 2  receive also the vehicle identification and transmit the vehicle identification to the junction controller  58 . The second beacons  18 - 1  and  18 - 2  serve as a fallback safety device. If the junction controller  58  knows that there is still one of the autonomous vehicles  20  on the junction  56  when a second one of the autonomous vehicles  20  is about to enter the junction  56 , then the junction controller  58  can initiate an emergency stop. In an ideal world, such a conflict should never occur, but there may be problems such as a breakdown of the first one of the autonomous vehicles  20  at the junction  56 . 
       FIG.  3    shows how the workflow of the management of the autonomous vehicles at the junction  56  and starts at step  300 . In step  310  the approach of the autonomous vehicles  20  to the junction  56  is detected by the transmission of the identification of the autonomous vehicle  20  to one of the beacons  17   a  or  17   b  on the inward route  60   a  or  60   b.  The junction controller  58  calculates in step  320  the time slot  80  and allocates the time slot  80  for each of the autonomous vehicles  20  to pass through the junction  56 . The time slots  80  include an entry time at which the autonomous vehicle  20  should enter the junction  56  and an exit time at which the autonomous vehicle  20  should exit the junction  56 . The time slot  80  allocated is unique to the allocated one of the autonomous vehicle  20  and there are no overlapping time slots  80 . In other words, the time slots  80  are allocated so that only one of the autonomous vehicles  20  passes through the junction  56  at any one point in time and that therefore there should never be two autonomous vehicles  20  at the junction  56  at the same time. 
     The junction controller  58  knows the distance  70  of the autonomous vehicle  20  from the junction  56  and either assumes the velocity of the autonomous vehicle  20  (i.e. 50 km/hour, typically) and is therefore able to calculate the expect time of arrival at the junction  56  in step  320  from the velocity of the autonomous vehicle  20  and the distance  70 . The junction controller  58  sends time slot data  85  about the allocates time slot  80  with the calculated entry time and the exit time to the arriving autonomous vehicle  20  in step  330 . Passage of the autonomous vehicle  20  at the junction  56  is therefore reserved for this autonomous vehicle  20  receiving the time slot data  85  at the calculated times. 
     In many modes of operation and at many times of the day, the allocation of the time slot  80  to any one of the autonomous vehicles  20  is simple. There are no conflicts and no potentially overlapping time slots  80 . The autonomous vehicle  20  can pass through the junction  56  with no change of velocity in step  340   
     Suppose, however, that the junction controller  58  detects in step  310  that there are two autonomous vehicles  20 - 1  and  20 - 2  arriving at the junction  56  almost simultaneously or with a slight delay. The junction controller  58  will identify from the calculated time slots  80  in step  320  that there is a potential conflict and if no action is taken the two autonomous vehicles  20 - 1  and  20 - 2  could potentially meet and collide at the junction  56 . In this case, the junction controller  58  will allocate a first time slot  80 - 1  to a first one of the arriving autonomous vehicles  20 - 1  and send the allocated first time slot  80 - 1  to the first autonomous vehicle  20 - 1  as first time slot data. The junction controller  58  will then calculate a second time slot  80 - 2  for the second arriving one of the autonomous vehicles  20 - 2 . The second time slot  80 - 2  will not be contemporaneous with the first time slot. In other words, the second entry time for the second autonomous vehicle  20 - 2  will be later than the first exit time for the first autonomous vehicle  20 - 1 . The second time slot data with the second entry time will be sent to the second autonomous vehicle  20 - 2  (step  330 ). 
     The second autonomous vehicle  20 - 2  receives the second time slot data and processes the second time slot data in the onboard processor  27 . This onboard processor  27  will calculate that, at the current velocity, the second autonomous vehicles  20 - 2  will arrive too early at the junction  56  to pass through the junction  56 , i.e. before the second time slot  80 - 2  starts. The onboard processor  27  will then calculate the velocity required for the second autonomous vehicle  20 - 2  to arrive at the junction  56  at the second entry time and reduce the velocity of the second autonomous vehicle  20 - 2  to the optimal velocity so that the second autonomous vehicle  20 - 2  arrives at the junction  56  at the second entry time. The distance  70 - 2  from the junction  56  to the second autonomous vehicle  20 - 2  is generally such that only a small reduction in velocity is required. Suppose the velocity is 50 km/hour then typically a reduction of only 3-5 km/hour is required and this reduction in speed is unlikely to be noted by a passenger travelling in the second autonomous vehicle  20 - 2 . It will be noted that the reduction in velocity can also be dependent on the state of the track  15  at the junction  56  or the local weather conditions. For example, if there is known to be ice on the track  15 , then the velocity must be reduced in a different manner than if the track  15  is dry. 
     The onboard processor  27  of the first autonomous vehicle  20 - 1  generally knows the distance  70 - 1  between the first autonomous vehicle  20 - 1  and the junction  56 . The onboard processor  27  of the second autonomous vehicle  20 - 2  knows the distance  70 - 2  of the second autonomous vehicle  20 - 2  and the junction  56 . The onboard processor  27  of the first autonomous vehicle  20 - 1  also knows the velocity of the first autonomous vehicle  20 - 1 . The onboard processor  27  of the second autonomous vehicle  20 - 2  knows the velocity of the second autonomous vehicle  20 - 2 . The onboard processor  27  is also, for example, aware of the state of the track  15  at the junction  56  or the local weather conditions at the junction  56 . 
     The first time slot  80 - 1  including the entry time and the exit time for the first autonomous vehicle  20 - 1  are sent by the junction controller  58  to the first autonomous vehicle  20 - 1  (see step  330  below). Similarly, the second time slot  80 - 2  including the entry time and the exit time for the second autonomous vehicle  20 - 2  are sent by the junction controller  58  to the second autonomous vehicle  20 - 2 . The onboard processor  27  of the first autonomous vehicle  20 - 1  calculates and adjusts in step  340 , using the received first time slot  80 - 1 , the velocity of the first autonomous vehicle  20 - 1  for the passage of the first autonomous vehicle  20 - 1  through the intersection  56  in the first time slot  80 - 1 . The calculating and adjusting in step  340  is done by the onboard processor  27  of the first autonomous vehicle  20 - 1  independently from the junction controller  58 . 
     Similarly, the onboard processor  27  of the second autonomous vehicle  20 - 2  calculates and adjusts in step  340 , using the received second time slot  80 - 2 , the velocity of the second autonomous vehicle  20 - 2  for the passage of the second autonomous vehicle  20 - 2  through the intersection  56  in the second time slot  80 - 2 . The calculating and adjusting in step  340  of the second autonomous vehicle  20 - 2  is done by the onboard processor  27  of the second autonomous vehicle  20 - 2  independently from the junction controller  58 . 
     There is no need for the junction controller  58  to send commands for the velocity and/or the time at which to assume the velocity to the autonomous vehicles  20 . The onboard processors  27  of the first autonomous vehicle  20 - 1  and/or of the second autonomous vehicle  20 - 2  calculate and adjust the velocity of the respective first autonomous vehicle  20 - 1  and/or of the second autonomous vehicle  20 - 2  independently from the junction controller  58 . The autonomous vehicles  20  are capable of autonomously passing through the intersection  56  by using the assist systems of Level 2 or Level 3, as described above. 
     After the reduction in speed, for example, the second autonomous vehicle  20 - 2  arrives at the junction  56  at the second entry time without any conflict at the junction  56 . The second autonomous vehicle  20 - 2  can then accelerate to the regular velocity, i.e. 50 km/hour, and pass through the junction  56 . The second autonomous vehicle  20 - 2  may also, however, pass through the junction  56  at a lower or higher velocity than the regular velocity and accelerate or decelerate after passing through the junction  56 . The onboard processor  27  can accelerate or decelerate the autonomous vehicle  20  before and/or during the passage through the junction  56  depending on the state of the track  15  at the junction  56 , the local weather conditions, or for the comfort of the passengers. 
     The prioritizing of the first autonomous vehicle  20 - 1  or the second autonomous vehicle  20 - 2  at the junction  56  is generally based on detection of the presence of the first one of the arriving autonomous vehicles  20 - 1  or  20 - 2  in step  310  by the junction controller  58 . It would of course be possible to use other priority criteria. For example, one of the arriving autonomous vehicles  20 - 1  or  20 - 2  could be a slower moving autonomous vehicle  20  and would therefore receive the second time slot  80 - 2  even if the slower moving autonomous vehicle  20  were in fact the first autonomous vehicle  20 - 1  to indicate its presence to the junction controller  58 . Alternately one of the arriving autonomous vehicles  20 - 1  or  20 - 2  could in fact be a priority vehicle which receives priority at all of junctions  56  and is always allocated the first available time slot  80 - 1  on arrival at the junction  56 . 
     It will be noted that there is no need for the autonomous vehicles  20 - 1  or  20 - 2  departing on the outward routes  65 ,  65   a  or  65   b  to be managed. The effect of the allocation of the time slots at the junction  56  will mean that the autonomous vehicles  20  on the outward route  65  will be spaced appropriately apart from each other. 
     In the above simple example, it was assumed that the autonomous vehicle  20  do not slow down whilst passing through the junction  56 . This may be true for a simple junction  56  as shown in  FIG.  2   , but as noted above if the junction  56  is a roundabout then it is likely that the autonomous vehicle  20  will slow slightly for the comfort of the passengers in the vehicle. 
     The approach taken above can be adopted for more complicated junctions  56 .  FIG.  4    shows, for example, a junction  56  with two inward routes  60   a, b  and two outward routes  65   a, b.  The same principle of calculating in step  320  the time slots for the arriving autonomous vehicles  20  applies. However, the time slots might be slightly different in length so that the first autonomous vehicle  20 - 1  passing, for example, from the first inward route  60   a  to the second outward route  65   b  requires slightly more time than the second autonomous vehicle  20 - 2  because of the slightly larger distance through the junction  56 . The junction controller  58  receives the routing information by wireless transmission from the arriving autonomous vehicles  20 - 1  and  20 - 2  in step  310  and can make this calculation taking into account the slightly longer time required to pass through the junction  56 . 
     The principle can be adopted for autonomous vehicles  20  on multi-lane tracks  15  merging onto single-lane tracks  15 , as shown in  FIG.  5    in which on the first inward route  60   a  there are two autonomous vehicles  20 - 1  and  20 - 3  travelling essentially in parallel with each other and possibly at the same velocity for passing through the junction  56  and merging onto the single-lane track  15 . The junction controller  58  receives the information about the parallel arriving autonomous vehicles  20  and allocates different time slots for each of the arriving autonomous vehicles  20 - 1  and  20 - 3 . One of the arriving autonomous vehicles  20 - 1  and  20 - 3  will then be slowed slightly to avoid a conflict at the junction  56 . 
     The junction controller  58  allocates the first timeslot  80 - 1  to the first autonomous vehicle  20 - 1  and the second time slot  80 - 2  to the second autonomous vehicle  20 - 2 . The onboard processor  27  of the first autonomous vehicle  20 - 1  independently calculates and adjusts the velocity of the first autonomous vehicle  20 - 1  to arrive at the junction  56  at the assigned entry time of the first time slot  80 - 1 . The onboard processor  27  of the second autonomous vehicle  20 - 2  independently calculates and adjusts the velocity of the second autonomous vehicle  20 - 2  to arrive at the junction  56  at the assigned entry time of the second time slot  80 - 2 . In the example of  FIG.  5   , the first autonomous vehicle  20 - 1  and the second autonomous vehicle  20 - 2  merge lanes before or during the passage through the intersection  56 . 
     The idea can of course be applied to a junction  56  in which there are multiple routes through the junction  56 , such as a large gyratory system with multiple lanes. In this case, different non-conflicting and non-contemporaneous time slots can be allocated to the autonomous vehicles  20  wishing to pass through the junction  56 . 
     The concept behind this method can be generalized by considering  FIG.  6 A  which shows two autonomous vehicles  20 - 1  and  20 - 2  on the track  15 . A so-called “kinematic envelope”  600 - 1  and  600 - 2  is shown surrounding each of the autonomous vehicles  20 - 1  and  20 - 2  and extending in a space in front of the autonomous vehicles  20 - 1  and  20 - 2 . The kinematic envelope  600  shows the area of the track  15  which is occupied by one of the autonomous vehicles  20 - 1  or  20 - 2  in the next period of time. The kinematic envelope  600 - 1  and  600 - 2  is a rolling or moving envelope and moves with the autonomous vehicle  20 - 1  or  20 - 2 . The kinematic envelope  600 - 1  and  600 - 2  is used by the junction controller  58  to calculate the time slots  80  of the autonomous vehicles  20  for the passage through the junction  56 . 
     The purpose of the kinematic envelope  600 - 1  and  600 - 2  is to establish a zone or an area within which the autonomous vehicle  20 - 1  or  20 - 2  is free to move at its current velocity and there is no or little risk of a conflict with another one of the autonomous vehicles. The size of the kinematic envelope  600 - 1  and  600 - 2  depends therefore on, for example, the velocity of the autonomous vehicle  20 . The size of the kinematic envelope  600 - 1  and  600 - 2  can further depend on the size of the autonomous vehicle  20 , a weight and/or load of the autonomous vehicle  20 , the passenger/passengers of the autonomous vehicle  20 , and/or the maximum acceleration/deceleration of the autonomous vehicle  20 . The size of the kinematic envelope  600 - 1  and  600 - 2  may also depend on the local weather conditions at the junction  56 . For example, an autonomous vehicle travelling at 50 km/hour needs about a space of 0.5 seconds in front of the vehicle to avoid a conflict. This leads to a distance of just under 7 m. A conflict should be avoided if nothing enters the kinematic envelope  600 - 1  and  600 - 2  extending approximately 7 m in front of the autonomous vehicle  20 . 
     This concept can be used to ensure that the autonomous vehicles  20  are equally distributed along the track  15 . The rotating door concept is used to define slots through which the autonomous vehicles can pass at any position  610 . If we assume that the autonomous vehicles  20  should all be travelling at 50 km/hour (as noted above) then the rotating door (shown at the position  610  on  FIG.  6 A ) will have equally spaced time slots though which the autonomous vehicles can pass. Should one of the autonomous vehicles  20  arrive too early for its time slot to pass through the “rotating door”, then the autonomous vehicle  20  can be slowed down on its approach to the position  610  as explained above in connection with the approach to the junction  56 . The size of the time slot and the entry time at the position  610  will correspond to the kinematic envelope  600  of the autonomous vehicle  20 . 
     The rotating door concept does not involve an actual physical rotating door at the position  610  but is used to illustrate the concepts of time slots through which an autonomous vehicle  20  passes a particular position  610 . In the discussion above, this position  610  was the junction  56 , but the concept applies equally to other defined positions  610  along the track  15 . 
     In a further aspect of the method, there may be two or more parallel tracks  15 - 1  and  15 - 2  along which the autonomous vehicles  20  are running, as shown in  FIG.  6 B , which also shows the junction  56 . In this aspect, different time slots are calculated for different vehicles on different ones of the tracks  15 . In other words, there are two “rotating doors” operating in parallel to ensure that the autonomous vehicles  20  do not conflict on the different tracks  15 . 
     The above discussion assumes that the size of the autonomous vehicle  20  is constant. There may, however, be larger autonomous vehicles  20 ′ used, for example, for freight purposes. In this case, the kinematic envelope  600 ′ will be wider, as is shown in  FIG.  6 C  and indeed occupy the space of two tracks  15 - 1  and  15 - 2  on which a “normal” autonomous vehicle  20  would travel. Any other autonomous vehicles  20  travelling nearer the larger autonomous vehicles  20 ′ will need to ensure that their own kinematic envelope  600  does not overlap with that kinematic envelope  600 ′ of the larger autonomous vehicle  20 ′. The rotating door concept discussed above can be equally applied to this aspect. For the “normal” autonomous vehicles travelling independently on the two tracks  15  there are two, independently operating, rotating doors, whereas the same track  15  has a single rotating door enabling conflict-free passage of the larger autonomous vehicles  20 ′ in the appropriate time slot. It will be appreciated that it is possible for both large autonomous vehicles  20 ′ and smaller or regular autonomous vehicles  20  to share the tracks  15 . The rotating door concept discussed above will be adapted depending on whether two regular autonomous vehicles  20  or one large autonomous vehicle  20 ′ wish to pass the junction  56 . The junction controller  58  makes the appropriate adaptation to ensure that there are no conflicts. 
     The discussion above has assumed that the autonomous vehicles  20  move in straight lines. It is possible that on a wider track  15 , that the autonomous vehicles  20  can change direction and almost move to one side or another to take advantage of the available space on the track  15 . This is shown in  FIG.  6 D  which shows the kinematic envelope  600  as a circular sector extending in front of the autonomous vehicle  20 . The autonomous vehicle  20  receives the messages  19  from the beacons  17  at the side of the track  15  to change direction as well as the velocity. 
     The size of the kinematic envelope  600  will depend on the velocity of the autonomous vehicle  20 . It is likely that the usual velocity of a freight-carry autonomous vehicle  20  would be less than 50 km/hour. However, the method discussed above would be equally applicable to such slower autonomous vehicles  20 . 
     REFERENCE NUMERALS 
     
         
           10  Autonomous transportation network 
           15  Tracks 
           17  Beacons 
           18  Second beacons 
           19  Messages 
           20  Autonomous vehicles 
           25  Vehicle antenna 
           27  Onboard processor 
           28  Vehicle memory 
           50  Route 
           56  Junction 
           58  Junction controller 
           60   a, b  Inward route 
           60   c  Outward route 
           65  Outward route 
           70 - 1 , 2  Distance 
           80  Time slots 
           85  Time slot data 
           600  Kinematic envelope 
           610  Position