High speed transit system

• US 4,148,260 A
• Filed: 04/30/1976
• Issued: 04/10/1979
• Est. Priority Date: 01/31/1974
• Status: Expired due to Term

• Current Assignee: Michael A. Minovitch
• Original Assignee: Michael A. Minovitch
• Inventors: Minovitch, Michael A.
• Primary Examiner(s): Husar, Francis S.
• Assistant Examiner(s): Reese, Randolph A.
• Application Number:
  US05/682,085
• Time in Patent Office: 1,075 Days
• Field of Search: 104/138 R, 104/148 MS, 104/148 LM, 105/150, 105/365, 310/67 R, 310/74, 310/113, 244/161, 244/137 P, 49/68, 49/482, 61/69 R, 61/83, 114/16.6, 138/107
• US Class Current: 104/138.1
• CPC Class Codes: B60L 13/006 Electric propulsion adapted for monorail vehicles, suspension vehicles or rack railways B60L13/03 takes precedence
• CPC Class Codes: B60L 13/04 Magnetic suspension or levitation for vehicles
• CPC Class Codes: B60L 2200/26 Rail vehicles
• CPC Class Codes: B61B 13/10 Tunnel systems pneumatic tubes conveyors B65G ; B61C15/045 takes precedence
• CPC Class Codes: H01F 7/0236 Magnetic suspension or levitation for vehicles B60L13/04; magnetic bearings F16C39/063
• CPC Class Codes: H02K 41/00 Propulsion systems in which a rigid body is moved along a path due to dynamo-electric interaction between the body and a magnetic field travelling along the path electromagnetic launchers F41B6/00
• CPC Class Codes: Y02T 30/00 Transportation of goods or passengers via railways, e.g. energy recovery or reducing air resistance
• CPC Class Codes: Y10S 505/905 Motor structure
• CPC Class Codes: Y10S 505/908 Method of operation

Abstract

A high speed ground transportation system, is suspended in an underground vacuum tube by a frictionless magnetic suspension system and propelled by gravity. The tubes are suspended inside deep underground tunnels from anchor points near each adjacent station and follow smooth catenary curves similar to the main suspension cables of a suspension bridge. Gravity propulsion is accomplished by allowing the vehicle to coast down the descending arc of the tube, during which time it is accelerated by gravity, and decelerating by gravitational braking while coasting up the tube'"'"'s ascending arc. Thus, the trip is accomplished by transforming the vehicle'"'"'s gravitational potential energy at one station into kinetic energy and back into gravitational potential energy at the next station. Excess kinetic energy arising from coasting between stations having different elevations is supplied or absorbed by on-board linear motor/generators that provide supplementary propulsion or regenerative braking. These linear motor/generators draw and return energy to an on-board flywheel kinetic energy storage system. Passenger and cargo transfer between the vehicle'"'"'s interior and station is made without removing the vacuum environment of the vehicle, by providing air-locks through the tube walls at the station.

Claims

1. A rapid transit system comprising:

a plurality of stations;

an underground tube which slopes downwardly along a smooth curve between a pair of adjacent stations of said system;

means for evacuating and maintaining vacuum in the tube;

a vehicle in the tube;

means for levitating said vehicle by a magnetic suspension system such that said vehicle is propelled essentially entirely by gravity when moving from one station to another station at equal elevations wherein acceleration propulsion is obtained by coasting down the descending arc of the vacuum tube, thereby generating vehicle kinetic energy substantially entirely from gravitational potential energy, and wherein deceleration is obtained by coasting up the ascending arc of the vacuum tube, thereby converting substantially all of the vehicle'"'"'s kinetic energy back into gravitational potential energy to be used for making the next trip;

means for starting and stopping said vehicle in the immediate vicinity of each station; and

means for allowing passengers to pass between the said vehicle'"'"'s interior and said station without removing the vehicle from the vacuum environment of the tube or without having to pressurize the tube.

2. A rapid transit system as set forth in claim 1 wherein said vehicle is suspended in said tube by magnetic forces.

3. A rapid transit system as set forth in claim 2 wherein said magnetic suspension of said vehicle comprises:

a plurality of magnetic rails composed of permanent magnets of high coercivity extending lengthwise along the tube between adjacent stations; and

a plurality of self-centering magnetic suspension rails composed of permanent magnets of high coercivity extending lengthwise on the vehicle for levitating the vehicle above the tube'"'"'s magnetic rails by magnetic repulsion so that no part of the vehicle is in physical contact with any part of the tube;

said magnetic suspension rails being partitioned lengthwise into several self-centering sections that are free to move independently of each other a limited distance such that each section remains properly aligned over the tube magnetic rails when the vehicle passes over curves in the vertical or horizontal planes.

4. A rapid transit system as set forth in claim 3 further comprising:

skid rails mounted along the tube;

stand-off skids mounted on the vehicle that ride adjacent said skid rails to prevent accidental contact between the levitating magnets.

5. A rapid transit system as set forth in claim 3 wherein said permanent magnet levitation system comprises a number of substantially rigid but independent vehicle suspension units that are free to move slightly in transverse and vertical planes so that said vehicle can negotiate curves of relatively small radius of curvature while each independent suspension unit remains properly positioned over the tube magnetic rails.

6. A rapid transit system as set forth in claim 2 further comprising:

a plurality of tracks in the tube in the immediate vicinity of said station; and

a plurality of wheels on said vehicle for supporting the vehicle on said tracks in the immediate vicinity of said station;

the beginning section of said tracks being mounted in said tube such that as the vehicle approaches said station, its levitation is gradually shifted from non-contacting magnetic forces to said wheels contacting said tracks; and

the end section of said tracks being mounted in said tube such that as the vehicle leaves said station its levitation is gradually shifted from said wheels contacting said tracks to non-contacting magnetic forces.

7. A rapid transit system as set forth in claim 6 wherein said means for stopping and starting said vehicle at said station comprises:

regenerative electric motor/generators connected to said wheels for regenerative braking and propulsion; and

energy storage means located on-board said vehicle for storing incoming electrical energy generated from regenerative braking and using this stored energy to power said motor/generators for starting said vehicle on its way to the next station.

8. A rapid transit system as set forth in claim 7 wherein said means for storing energy on-board vehicle comprises:

flywheel motor/alternator kinetic energy storage units wherein incoming electrical energy is used to activate said motor which speeds up a flywheel thereby storing inertial energy and whereby energy is extracted from said flywheel by converting flywheel inertial energy into electrical energy by said alternator.

9. A rapid transit system as set forth in claim 6 further comprising means for switching the vehicle into various branches of tube intersections in the immediate vicinity of a station by conventional wheel and track switching systems.

10. A rapid transit system as set forth in claim 1 wherein the vehicle comprises a train of detachably coupled pressurized cars having pressure-tight doors, and means for coupling each car in the train so that a nearly constant car separation distance is maintained;

and said means for allowing passengers to pass between the interior of the vehicle and a station without removing the vehicle from the vacuum environment of the tube comprises;

a plurality of pressure-tight doors through the wall of the vacuum tube at each station with predetermined separation distances such that when a train stops at a predetermined location in the station, all the car doors are opposite station doors;

air-tight retractable flanges built into the tube walls adjacent each tube door;

means for extending such a flange toward the car and inserting one end into sealing engagement with a slot completely surrounding the periphery of the car door such that the chamber bounded by the flange, tube door and car door becomes an air-lock;

means for pressurizing the air-lock to atmospheric pressure;

means for opening the car door and tube door after the air-lock has been pressurized to atmospheric pressure, thereby allowing passenger transfer; and

means for closing the car door and tube door and evacuating the air-lock before retracting said flange.

11. A rapid transit system as set forth in claim 10 wherein said pressurization of such an air-lock comprises:

an air conduit leading from said air-lock to the interior of said station;

a valve connected to said conduit such that when opened, air is admitted into said air-lock from said station such that the atmospheric pressure in said air-lock becomes equal to atmospheric pressure in said station;

a vacuum pump;

a vacuum conduit leading from said air-lock to said vacuum pump;

a valve on saaid vacuum conduit such that when said valve is opened, said air-lock is partially evacuated;

a high vacuum storage tank having a working pressure significantly lower than that of said tube;

a high vacuum conduit leading from said air-lock to said vacuum storage tank; and

a valve on said high vacuum conduit such that when said valve is opened, said air-lock is further evacuated by allowing residual air to pass from said air-lock into said vacuum storage tank.

12. A rapid transit system as set forth in claim 10 comprising a vehicle positioning system at each station so that said vehicle is properly aligned to receive said flanges when said vehicle stops at said station.

13. A rapid transit system as set forth in claim 12 wherein said vehicle alignment system comprises:

a plurality of grooved guide wheels mounted on the upper and lower portions of said vehicle;

a plurality of flanged guide rails mounted in the tube in the immediate vicinity of the station such that as the vehicle approaches the station, the guide rails above the vehicle contact the vehicle'"'"'s upper guide wheels and press the vehicle slightly downward onto the lower guide rails;

said upper guide wheels rolling on said upper guide rails and said lower guide wheels rolling on said lower guide rails such that said rail flanges fit into said wheel grooves so that the vehicle is held in predetermined transverse and vertical alignment while it is approaching and stopped in said tube adjacent said station;

means at each station for engaging and positioning the train so that each car door is positioned opposite a tube door and properly aligned to receive said air-lock flanges; and

means for making electrical connections to the train to conduct electrical current while the train is stopped at the station.

14. A rapid transit system as set forth in claim 1 further comprising a wheel and rail suspension system for levitating said vehicle when said vehicle is in the immediate vicinity of a station.

15. A rapid transit system as set forth in claim 1 further comprising means for suspending said vacuum tube between a pair of stations at a pair of anchor structures located near each station, respectively, such that the path of the tube between the anchor structures is a catenary curve.

16. A rapid transit system as set forth in claim 15 wherein said means for suspending said vacuum tube between anchor structures comprising:

a tunnel in which said vacuum tube is suspended;

a plurality of main suspension cables extending along the inside of said tunnel, attached to the outside walls of said tube and anchored at the anchor structures;

a plurality of support cables attached to the upper portions of said tunnel which partially support said tube; and

means for adjusting said support cables and main suspension cables for aligning said tube as required;

said main suspension cables having substantial longitudinal stress so that the tube is not deflected downward appreciably by the weight of a passing vehicle.

17. A rapid transit system as set forth in claim 16 wherein an alignment monitoring system is provided to monitor the tube alignment between stations.

18. A rapid transit system as set forth in claim 17 wherein said alignment system between said anchor structures comprises:

a plurality of electrically energized conducting cables suspended freely between adjacent anchor structures to trace out smooth catenary paths parallel to the catenary path of said vacuum tube guideway; and

a plurality of spaced-apart conducting sensor rings attached to said tube and wherein said conducting cables pass through said conducting rings;

said conducting rings each having an inside diameter slightly greater than the outer diameter of said conducting cables so that no ring is in physical contact with said cable when said tube is in proper alignment and contacting said cables at misaligned tube sections thereby causing electrical current to flow between said rings and cable.

19. A rapid transit system as set forth in claim 17 wherein two vacuum tubes are independently suspended in a single tunnel between two stations to allow two-way traffic;

each of said tubes having its own independent suspension cables and alignment monitoring system.

20. a rapid transit system as set forth in claim 16 wherein said vacuum tube has a circular cross-section and further comprising:

support partition means extending longitudinally along the tube'"'"'s interior essentially through its horizontal diameter so as to form two corridors with vehicles moving in opposite directions in each corridor at the same time to permit two-way traffic in the same vacuum tube.

21. A rapid transit system as set forth in claim 20 wherein each of said vehicles moving on upper level and lower level vacuum tube corridors is equipped with an escape system means by which passengers stranded between stations in a disabled vehicle can be safely rescued from it without having to pressurize the tube or without having to tow the train to the next station, said means comprising:

a plurality of air-tight escape hatches mounted on the floor of each upper level vehicle and on the ceiling of each lower level vehicle and spaced apart so that when a lower level vehicle is directly below an upper level vehicle, the escape hatches on each side of the partition in each vehicle are opposite each other;

a retractable, flexible tube mounted around each escape hatch for manual extension to engage and completely surround an opposite escape hatch to form an air-lock;

means for allowing air into said air-lock for pressurizing it to atmospheric pressure; and

means for opening each escape hatch after the air-lock is pressurized from either vehicle so that passengers can be evacuated, whereby every upper level vehicle can be used to rescue passengers stranded in a disabled lower level vehicle and every lower level vehicle can be used to rescue passengers stranded in a disabled upper level vehicle anywhere in the tube.

22. A rapid transit system as set forth in claim 16 wherein said anchor structure comprises:

a cylindrical reinforced concrete foundation with inner diameter approximately equal to the diameter of said tunnel;

a cylindrical steel suspension sleeve mounted inside said concrete foundation and anchored to it by a plurality of adjustable length stand-off rods with said vacuum tube passing through said sleeve; and

means for anchoring said tube suspension cables to said suspension sleeve.

23. A rapid transit system as set forth in claim 15 wherein the tube path between adjacent anchor structures on each side of the station follow smooth transition curves such that the radius of curvature of the tube path from one station to the next station is a smooth, continuous and slowly varying function of distance along the tube.

24. A rapid transit system as set forth in claim 1 wherein said vehicle is composed of a train of detachably coupled cars;

means for allowing said train to negotiate curves in both horizontal and vertical planes;

means for pressurizing each car independently of all other cars in said train; and

means for transferring passengers from one car to an adjacent car and sealing off each car from the remaining cars of said train without having to stop the train or without having to re-pressurize the vacuum tube.

25. A rapid transit system as set forth in claim 24 wherein a means for evacuating an entire train stranded between stations is provided by transferring its passengers into the train immediately ahead or behind the stranded train without having to re-pressurize the vacuum tube or without having to perform the evacuation by a special rescue vehicle.

26. A rapid transit system as set forth in claim 24 wherein said means for independently pressuring each car in said train comprises:

a car coupling system that comprises an air-tight coupling seal around the end periphery of each car;

air-tight bulkheads located near each end of each car such that the chamber formed by the bulkheads at the ends of a pair of coupled cars and the car hulls on each side of the air-tight coupling seal forms an air-lock between each pair of coupled cars;

means for pressurizing or evacuating said air-lock independently of each adjacent car without disturbing the pressure environment in the interior of each adjacent car in the pair; and

an air-tight pressure door in each bulkhead to allow passengers to enter or exit the air-lock from the interior of adjacent cars.

27. A rapid transit system as set forth in claim 26 wherein the pressure hull near each end of each car is composed of a slightly flexible material so that said air-tight coupling between adjacent cars forms an air-tight articulated section that allows said train of coupled cars to negotiate curves in both horizontal and vertical planes.

28. A rapid transit system as set forth in claim 1 further comprising means on the vehicle for recovering and storing excess potential energy when moving from one station at a higher elevation to another station at a lower elevation;

and

means for using the stored energy later in propelling the vehicle from a station at a lower elevation to a station at a higher elevation.

29. A rapid transit system as set forth in claim 28 wherein said means for recovering, storing and using excess kinetic energy derived from moving between stations of different elevations comprises:

a reaction rail extending along the tube;

a regenerative linear motor on the vehicle for regenerative braking and propulsion without physically contacting the reaction rail; and

flywheel motor-alternator energy storage units located on-board said vehicle for transforming incoming electrical energy derived from regenerative vehicle braking into flywheel inertial energy for storage and for transforming stored flywheel inertial energy into electrical energy to power said linear motors.

30. A rapid transit system as set forth in claim 29 wherein an auxiliary lateral guidance system is provided for said linear motor and said vehicle such that the gap between said linear motor and said reaction rail can be significantly reduced, and comprising:

a row of high coercivity permanent magnets extending along the length of said reaction rail with north and south poles oriented along parallel lines perpendicular to the surface of said reaction rail; and

a plurality of U-shaped mild-steel channels mounted on said vehicle and aligned along a straight line and containing a plurality of high coercivity permanent magnets with north and south poles oriented parallel to those on said reaction rail such that the mild-steel channel conducts the magnetic flux of the magnets mounted therein to pole pieces so as to form a horizontal flux gap;

said U-shaped channels mounted on said vehicle such that said row of permanent magnets on the reaction rail passes inside said flux gaps of said mild-steel U-shaped channels;

the repulsion forces across the gaps keeping the linear motor and vehicle properly aligned laterally;

said channels being free to move slightly relative to each other in order to allow the vehicle to move smoothly along curves in both horizontal and vertical planes.

31. A rapid transit system as set forth in claim 30 wherein said permanent magnet lateral guidance means include means for controlling and dampening out horizontal oscillations comprising:

servo-controlled electromagnets fitted to some of said vehicle'"'"'s guidance magnets; and

inertial oscillation sensors on-board said vehicle that sense horizontal oscillations that control current feeding said electromagnets so as to dampen out possible horizontal oscillations.

32. A rapid transit system as set forth in claim 1 wherein the path of at least a portion of said tubes between adjacent stations comprises two continuously curving arcs sloping downwardly from each station separated by a straight horizontal path located at the maximum depth such that the entire path lies essentially in the vertical plane passing through the adjacent stations.

33. A rapid transit system as set forth in claim 1 further comprising means for increasing the vehicle'"'"'s speed by using additional energy;

and

regenerative braking means for later recovering said energy during deceleration.

34. A rapid transit system as set forth in claim 1 wherein the means for evacuating and maintaining vacuum in said vacuum tube comprises high capacity continually operating vacuum pumps located near said stations.

35. A rapid transit system as set forth in claim 1 wherein the vehicle comprises a train of detachably coupled cars;

and further comprising;

flywheel alternator-motor energy storage units on each car for supplying electrical power needed to operate all systems in the car while it is moving between stations;

means on each car for receiving electrical power to recharge said flywheel energy storage units from each station; and

umbilical lines that connect adjacent cars so that electrical current and air can be circulated throughout the entire train or concentrated to a particular car if needed.

36. A method of operating a rapid transit system having an underground tube which slopes downwardly between a pair of stations comprising the steps of:

maintaining a vacuum in the tube;

suspending a vehicle in the tube by a magnetic suspension system;

gravitationally accelerating the suspended vehicle down the descending portion of the tube whereby substantially all of the vehicle'"'"'s gravitational potential energy is converted to vehicle kinetic energy;

gravitationally decelerating the vehicle in the ascending portion of the tube whereby substantially all of the vehicle'"'"'s kinetic energy is converted back into gravitational potential energy; and

transferring passengers between a station and the interior of the vehicle when stopped at the station without removing the vehicle from the vacuum environment of the tube without pressurizing the tube.

37. A method of operating a rapid transit system as defined in claim 36 wherein said accelerating and decelerating steps comprise moving the vehicle through an underground tube that follows a continuous smooth curve lying essentially in the vertical plane passing through the stations.

38. A method of operating a rapid transit system as defined in claim 36 wherein said accelerating and decelerating steps comprise moving the vehicle through an underground tube that has two continuously curving arcs sloping downwardly from each station separated by a straight horizontal section located at the maximum depth such that the entire path lies essentially in the vertical plane passing through the stations.

39. A method of operating a rapid transit system as defined in claim 36 wherein said accelerating and decelerating steps comprise moving the vehicle through an underground tube that has two continuously curving arcs sloping downwardly from each station separated by a circular arc section having radius equal to the distance between the point of maximum tube depth and the earth'"'"'s center.

40. A method of operating a rapid transit system as defined in claim 36 wherein said tube follows a catenary path in a vertical plane for a substantial portion of the distance between two adjacent stations.

41. A method of operating a rapid transit system as defined in claim 36 further comprising the steps of:

starting the vehicle at a station by on-board propulsion means using energy stored on-board the vehicle;

braking the vehicle at another station by on-board regenerative dynamic braking means; and

storing the energy from the regenerative braking on-board the vehicle.

42. A method of operating a rapid transit system as defined in claim 41 wherein said on-board energy storage means comprises a flywheel inertial energy storage means and a motor/alternator means for storing and extracting energy from the flywheel means comprising the steps of:

spinning up the flywheel means during braking and slowing down the flywheel during starting.

43. A method of operating a rapid transit system as defined in claim 41 further comprising the steps of:

increasing the vehicle'"'"'s speed while in transit between stations by on-board regenerative propulsion means using energy stored in an on-board energy storage system;

braking the vehicle while approaching a station by regenerative dynamic braking that returns energy to the on-board energy storage system.

44. A method of operating a rapid transit system as defined in claim 43 further comprising converting excess vehicle kinetic energy to flywheel inertial energy by regenerative braking at a relatively lower elevation station;

and converting flywheel inertial energy into additional vehicle kinetic energy by auxiliary propulsion means so that it can climb to a higher station elevation having higher gravitational potential energy.

45. A method of operating a rapid transit system as defined in claim 43 wherein said on-board regenerative propulsion means comprises the steps of:

establishing a reaction rail inside the vacuum tube;

propelling the vehicle by a regenerative linear motor reacting against the reaction rail by drawing energy from an on-board energy storage system; and

braking the vehicle by regenerative dynamic braking by said linear motor and storing the recovered energy in the on-board energy storage system.

46. A method of operating a rapid transit system as defined in claim 45 further comprising the step of applying magnetic repulsive forces laterally relative to the vehicle'"'"'s length for lateral stabilization of the vehicle.

47. A method of operating a rapid transit system as defined in claim 41 further comprising regeneratively decelerating the vehicle as it approaches each station so that it comes to a stop at a predetermined location.

48. A method of operating a rapid transit system as defined in claim 36 further comprising the additional steps of:

suspending the vehicle by a wheel and rail suspension system in the immediate vicinity of a station while moving at low speeds; and

levitating the vehicle by magnetic forces while moving at high speeds between stations.

49. A method of operating a rapid transit system as defined in claim 48 wherein said magnetic levitating comprises the steps of:

mutually repelling a plurality of permanent magnetic rails on-board the vehicle by magnetic repulsion forces against a plurality of magnetic rails in the tube.

50. A method of operating a rapid transit system as defined in claim 36 further comprising the additional steps of:

forming an air-lock between a car door and a tube door adjacent each car door;

pressurizing the air-lock to atmospheric pressure;

opening the car door and tube door after the air-lock has been pressurized for passenger transfer;

closing the car door and tube door and evacuating the air-lock after passenger transfer;

at least partially evacuating the air-lock by dumping residual air into a high volume, high vacuum storage tank; and

opening the air-lock prior to vehicle departure.

51. A pressurized rapid transit vehicle adapted for travel in a vacuum tube guideway composed of a train of detachably coupled, independently pressurized cars;

means for allowing said train to negotiate curves in both horizontal and vertical planes;

means for pressurizing each car independently of all other cars in said train, said pressurizing means comprising;

a car coupling system that comprises an air-tight coupling seal around the end periphery of each car;

air-tight bulkheads located near each end of each car such that the chamber formed by the bulkheads at the ends of a pair of coupled cars and the car hulls on each side of the air-tight coupling seal forms an airlock between each pair of coupled cars; and

means for pressurizing or evacuating said airlock independently of each adjacent car without disturbing the pressure environment in the interior of each adjacent car in the pair;

said airlock adapted for transferring passengers from one car to an adjacent car and sealing off each car from the remaining cars of said train without having to stop the train or without having to repressurize the vacuum tube guideway and comprising an airtight chamber between adjacent cars including a flexible articulated wall portion and an airtight pressure door at the end of each car communicating between the interior of such a car and the airtight chamber;

said airlocks partitioning said train into several independently pressurized car cabins.

52. A pressurized rapid transit vehicle as defined in claim 51 wherein a means for evacuating an entire train stranded between stations is provided by transferring its passengers into the train immediately ahead or behind the stranded train without having to repressurize the vacuum tube or without having to perform the evacuation by a special rescue vehicle.

53. A pressurized rapid transit vehicle as set forth in claim 51 wherein the pressure hull near each end of each car is composed of a slightly flexible material so that said air-tight coupling between adjacent cars forms an air-tight articulated section that allows said train of coupled cars to negotiate curves in both horizontal and vertical planes.

54. A rapid transit system comprising a tube and a plurality of vehicles adapted for travel through the tube, wherein said tube is partitioned along its horizontal mid-plane throughout its length forming two corridors, each said corridor adapted to guide a vehicle so as to allow two-way traffic in opposite directions through a single tube;

an escape system on each vehicle moving on upper and lower level corridors of said tube, said escape system being means by which passengers stranded between stations in a disabled vehicle can be safely rescued from it without requiring the passengers to enter a corridor guideway or without having to tow the vehicle to the next station, said means comprising;

a plurality of escape hatches mounted on the floor of each upper level vehicle and on the ceiling of each lower level vehicle and spaced apart so that when a lower level vehicle is directly below an upper level vehicle, the escape hatches on each side of the tube partition in each vehicle are opposite each other;

a retractable, flexible tube mounted around each escape hatch for manual extension to engage and completely surround an opposite escape hatch;

means for opening each escape hatch after engagement so that passengers can be evacuated without entering any guideway corridor, whereby every upper level vehicle can be used to rescue passengers stranded in a disabled lower level vehicle and every lower level vehicle can be used to rescue passengers stranded in a disabled upper level vehicle anywhere in the tube.