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|Federal Highway Administration > Publications > Public Roads > Vol. 58 · No. 2 > Tube Freight Transportation|
by Lawrence Vance and Milton K. Mills
Under a research program on advanced freight movement, the Federal Highway Administration (FHWA) with the support of the John A. Volpe National Transportation Systems Center is examining the technical and economic feasibility of tube transportation systems to address future freight transportation requirements.
Tube freight transportation is a class of unmanned transportation systems in which close-fitting capsules or trains of capsules carry freight through tubes between terminals. All historic systems were pneumatically powered and often referred to as pneumatic capsule pipelines. One modern proposed system called SUBTRANS uses capsules that are electrically powered with linear induction motors and run on steel rails in a tube about two meters (6½ feet) in diameter. The system can be thought of as a small unmanned train in a tube carrying containerized cargo.
An underground tube transportation system can carry high-volume freight into highly congested areas with minimum effect on surface transportation systems. If this system were implemented in congested areas, passenger vehicles could be separated from freight vehicles with improvements in efficiency and safety for both modes. The improvement in efficiency would result in lower freight rates and a lower environmental impact on air quality and noise. Also, the Texas Transportation Institute at Texas A&M estimates that productivity lost to traffic congestion costs more than $40 billion per year.
The separation of trucks and automobiles was recommended by the Hoover Commission on Highway Safety in the late 1920s. The concept has been reevaluated periodically. It is now timely to initiate a reevaluation. Such an analysis should be based on current and future highway needs in the framework of the emerging economic and market environment anticipated in the early 21st century.
However, it must be stressed that tube freight transportation is a promising concept for a future system. A great deal of additional research and development and the commitment of substantial resources are necessary to produce even a prototypical operational system. The initial operational systems are most likely in major metropolitan areas where current and projected traffic congestion inhibits increased movement of freight by trucks; a nationwide tube freight transportation network will not be feasible for many years, if at all. While tube freight systems have considerable potential to move goods efficiently and offer significant advantages, such systems are not likely to have any near-term impact on the trucking or railroad industries.
This article will discuss the history and advantages of tube freight systems, current tube freight system proposals, and issues relative to implementing such a freight system.
Tube Transportation History
Tube transportation has a history that extends back at least 200 years. During this period, systems for both passengers and freight have been built and operated. Some are in operation today. In addition, there have been many more proposals that were never built. All of the historical tube transportation systems were pneumatically powered.
George Medhurst, a London businessman, is considered the earliest proponent of pneumatic-powered railways although there were a few earlier, brief suggestions from others. He first published a freight proposal in 1810, a passenger proposal in 1812, and a more comprehensive set of proposals in 1827.
Despite four demonstration systems, including a 95-m (312-ft), underground system built in New York City in 1869-70, no large-size tube transportation system has been introduced into common carrier service. The primary result of this activity was to lend support to the development of underground electric railway systems for urban passenger transportation. However, small diameter pneumatic pipelines have been providing reliable freight transportation around the world for more than 150 years.
Common applications of pneumatic pipelines before World War II were the high-priority movement of documents and parts in industrial environments and movement of letters and telegrams under city streets to bypass congestion. These systems were built with tubes ranging from 5 to 20 centimeters (2 to 8 inches) in diameter. Such systems are still being built today to expedite small shipments.
After World War II, larger pneumatic systems were developed and built in Japan and Russia to move bulk materials such as limestone and garbage. These systems had considerably greater throughput as a result of both their increased diameters of 0.9 to 1.2 m (3 to 4 ft) and their mode of operation, which allowed more capsules to move through the tube at one time. By the early 1970s, several groups began to give consideration to the use of these pipeline designs for common carrier, general merchandise freight applications using tubes 1.2 to 1.8 m (4 to 6 ft) in diameter.
Future Freight Growth
By 2015, surface transportation is expected to grow well beyond current traffic levels with significant constraints on construction of new highways due to economic and environmental considerations. Figure 1 shows truck traffic growth from 1960 through 1990 with projected traffic through 2020. (1) By the year 2020, intercity trucking is projected to increase by more than 50 percent over 1990 levels. Since new transportation routes are expected to be difficult to obtain, major emphasis is presently being placed on intelligent vehicle-highway systems (IVHS) that will more efficiently use the present highway system. Use of subsurface tube freight transportation in highly congested areas would allow IVHS type systems to operate more efficiently by removing some truck traffic carrying freight.
Potential Advantages of Tube Freight Transportation Systems
Tube transportation systems have a number of attractive features that make them worthy of evaluation as alternatives for future freight transportation systems. Because such systems are unmanned and fully automatic, they are safer than truck or railroad systems. When traveling down grades, the capsules may be able to regenerate energy for improved energy efficiency. Because they are enclosed, they are unaffected by weather and are not subject to most common rail and highway accidents. Hazardous cargo can be more safely transported than on surface systems. The tubes could also be used as conduits for communication cables for the future information highway. Benefits from reducing the number of trucks carrying freight in congested areas by tube freight transportation systems are:
The tubes can be placed above, on, or below ground. Underground locations are useful in environmentally sensitive areas and are important where surface congestion makes surface right-of-way difficult or expensive to obtain. Much right-of-way potentially exists below our present highway system. However, there are potential environmental impacts of construction, especially if cut and cover construction is used.
Current Tube Freight Transportation Proposals
The SUBTRANS concept is to provide long-haul freight transportation in capsules running in a tube about two m (6½ft) in diameter (see figures 2 and 3). (2) The capsules would be propelled by linear induction motors. Non-pneumatic propulsion of the system is the subject of a U.S. patent granted to William Vandersteel of North Bergen, N.J., in 1984 (patent number 4458602). The system would be totally automated and is intended to operate at a constant speed of about 100 kilometers per hour (60 miles/h). Capsules are expected to be switched from the main routes to terminals or other routes at speed using electromagnetic switching techniques. The capsules are unconnected; pneumatic pressure provides buffering between capsules because of the small clearance between the capsule and the tube. The SUBTRANS capsules are designed to accept pallets to facilitate rapid loading and offloading. Automated warehousing is an option in this concept with the capsules being used for temporary warehouse storage. The developer claims a maximum throughput of 1875 capsules per hour, which is roughly 16,500 metric tons/h (18,200 short tons/h)(1) at average cargo densities. At this time, SUBTRANS is an undeveloped concept.
Professor Masaki Koshi of the University of Tokyo has proposed an underground freight transportation system for the city of Tokyo. (3) This system uses standard subway clearances between the capsules and the tube; therefore, the capsules do not develop pneumatic pressure between themselves. The purpose of this automated freight system is to significantly reduce truck traffic. This system, which proposes to use linear induction traction, is currently being evaluated and developed by the Ministry of Construction. Non-standard containers are designed to be moved through 5.5-m- (18-ft-) diameter tubes. Automated loading and unloading of the containers at terminals is part of this concept. A 300-km- (186-mi-) network is projected with automated terminals that move the containers to the first basement of major shippers/receivers or to street level for local distribution to small consignees. An experimental line a few kilometers long is expected to be initiated soon.
Previous Tube Freight Transportation Proposals
A proposal similar to SUBTRANS was made by the British Hydro-mechanics Research Association (BHRA) in the early 1970s for a British national tube transportation system for general commodity freight. The British system proposed 11-metric ton (12.1-short ton) capsules operating in a 1.5-m- (5-ft-) diameter tube. (4) Speeds of 30 to 50 km/h (20 to 30 mi/h) were anticipated at a rate of 100 to 150 capsules per hour. Pneumatic pressures for propulsion are generated by jet pumps developed and patented by BHRA. Although the British are no longer actively promoting this technology, we assume they, as well as others who are still active in the field, remain interested in general cargo applications.
Current Tube Freight and Passenger Transportation Proposals
The Swiss high-speed, magnetic levitation (maglev) proposal would use a 4.5-m- (15-ft-) diameter tube. (5,6) The tube would be buried 40 m (130 ft) deep in most areas, deeper under mountains. Speeds in the range of 250 to 300 km/h (124 to 186 mi/h) are projected. Linear induction motors are to be used. The purpose of the tube transportation approach is to reduce tunneling costs by reducing the tunnel diameter. Air resistance is reduced through evacuation of the tunnel. The alternative would be to use a very large cross-section bore to minimize aerodynamic drag and undesirable pressure changes at tunnel entrances and exits. This proposed system is currently under serious evaluation by the Swiss government. The primary motivation for this system is to obtain the benefits of a high-speed passenger system in a region where there are major environmental constraints and new right-of-way is unavailable.
The National Aeronautics and Space Administration "New Millennium Transportation System" proposes two national maglev systems. (7) The first, a surface system, is not a tube system. The second, a "hypervelocity" system, would be an underground system operating in evacuated tunnels at speeds up to 6,400 km/h (4,000 mi/h).
Operational Pneumatic Tube Transportation Systems for Bulk Materials
Nippon Steel Corporation and Daifuku Machinery Works Ltd., using an early license from TRANSCO of Houston, Texas, have built a 0.6-m- (2-ft-) diameter, 1.5-km (0.9-mi), double line to move burnt lime in Nippon Steel's Muroran Number 2 steel plant. (8) This elevated line (figure 3) was built in the mid-1980s and uses capsule trains (two cars per train) to move 22,000 metric tons (24,266 short tons) per month. This system is called AIRAPID.
Sumitomo Cement Co. built a similar system in 1983 to move limestone 3.2 km (2 mi) between a mine and their cement plant. (9) The 1-m- (3.2-ft-) diameter pipe carries three car capsule trains delivering 2.2 million metric tons (2.43 million short tons) per year. This system was originally based on a Russian license but was considerably redesigned by the company.
A number of tube systems, called TRANSPROGRESS systems, for moving crushed rock are being used in the former Soviet Union. (10) An 11-km (6.8-mi) line for garbage was built in 1983 from St. Petersburg to an outlying processing facility using TRANSPROGRESS technology. This technology has also been applied to intraplant systems.
Technical Feasibility and System Considerations
Tube transportation systems for common carriage exist primarily as concepts at this time. Encapsulated freight may be conveyed through air tubes propelled by differential (pneumatic) pressure acting on the opposite faces of capsules closely fitted in the tubes. Other systems of propulsion could include conventional electric motors, linear induction motors, or mechanical/cable drives.
Pneumatically powered systems are clearly feasible because they have been built and operated in the past, although not in general merchandise service. Linear induction motor powered systems are also technically feasible although such systems have not been demonstrated or, in fact, designed in detail yet. These systems are not off-the-shelf; they will require specific designs for specific applications. The design features for a number of necessary elements are presently undefined.
All capsule systems will require power distribution systems and facilities for inspection and monitoring, maintenance, and control and communication. The simplicity in the design and operation of the capsule will bear directly on the costs associated with these requirements.
Simplicity of the design and operation, coupled with a simple capsule configuration promising relatively easy and inexpensive fabrication and operation, is the advantage claimed for linear induction propulsion.
It is in the area of automatic control that tube transportation would seen to have advantages over competing modes of freight shipment. With a dedicated, weather-proof, intrusion-proof capsule and guideway system, automatic controls available today could provide almost complete automation from point-of-freight origin to destination. Given the state of the art and development of existing control systems for passenger transportation, where safety and operational standards are much higher than they would be for freight, it can be assumed that automatic controls would be somewhat readily available and adaptable. This would apply regardless of the electric and/or pneumatic elements of the propulsion system.
It is assumed that substantial portions of any tube transportation system will be constructed underground, especially in urban areas. Because tunneling costs are so high, many tube system proponents scale their concepts down in size. But even with scaled down tubes of about 1.8 m (6 ft) inside diameter, these systems have more potential throughput capacity than railroads. And it is in the major urban areas that underground tube systems are most promising and most needed to reduce traffic congestion and air pollution caused by trucks.
There are numerous design and construction issues to be resolved -- for example, size of the tube, configuration of the system (separate tubes for each direction or a looped line, direct system access for customers, intermodal transfer capabilities, short-term storage capacity), capability to move refrigerated freight, appropriate venting of tunnels, and switching. Switching, the transfer of capsules at speed from one line to another, remains somewhat problematic in tube transportation systems. Current monorail and maglev switch mechanisms are large and cumbersome and cannot handle speeds up to 100 km/h (60 mi/h) during switching.
Economics of Tube Freight Transportation Systems
Tube transportation systems are inherently high capital cost, low operating cost systems, but the economic feasibility of tube transportation systems carrying general merchandise is unknown as no such system has been built and operated in commercial service.
A study of the economics of tube transportation that was sponsored by the U.S. Department of Transportation in the late 1970s indicates tube transportation may be competitive with long-haul truck and railroad operations. (11,12) This study by the University of Pennsylvania was performed without detailed tube designs and associated cost data. Such data for currently proposed concepts is also lacking as previously noted.
As a result, engineering development studies and concept demonstrations are needed to provide refined estimates of the system economics. Cost estimates need to be made for specific routes because a major part of the capital requirement is tunneling costs, which are highly variable and site specific. Port or urban core access corridor lines, where high land values and surface congestion would enhance the value of tube transportation, would appear likely study candidates. Package delivery firms, less-than-truckload trucking firms, and the U.S. Postal Service are potential users of such a system.
A national tube transportation network would clearly be in competition with both motor carriers and railroads; however, development of a nationwide system is unlikely.
Fully automated tube freight transportation systems have the potential to provide reliable, predictable, rapid, safe, and secure service. Because each capsule can be dispatched when loading is completed, there is no delay while sufficient cars are loaded and assembled into a train as in standard railroad practice. Since the system is very predictable in operation, complete and real-time information on the location of each capsule can be maintained very inexpensively. These attributes result in a high level of service and should be particularly attractive to just-in-time manufacturers.
A major benefit of tube transportation is safety. Tube freight systems, since they are automated, without onboard personnel, and operate in isolation, are likely to be far safer than trucks in congested areas with mixed traffic. Currently, several national organizations are lobbying for a reduction in heavy truck traffic. Tube transportation is also safer than railroads since its design will eliminate highway crossings and unauthorized intruder accidents. Highway accidents involving heavy vehicles result in about 4,000 fatalities per year in the United States, and railroad accidents cause about 1,000 fatalities each year.
In addition, pneumatic pipeline freight systems, the antecedents of current tube transportation proposals, have had high operational reliability virtually free of accidents and with an extremely low rate of cargo damage. Tube transportation systems offer clear environmental and energy-saving benefits, particularly in comparison with trucks. All current tube transportation proposals envision the use of electrical power, and they are likely to be very clean and energy-efficient. Air pollution from trucks will be reduced in proportion to the number of trucks removed from the road. Underground systems reduce intrusion in environmentally sensitive areas, and they are especially beneficial where surface land values are high, where surface conditions are already congested, or surface routes are unavailable. These are not new issues, but they are becoming more important with nationwide urban growth. (13) Tube transportation has no significant energy advantage over railroads, but if trucks were removed from the congested areas, highway fuel use would be reduced.
Historically, there is a precedent for underground freight operations. The most notable underground freight system was the 80-km (50-mi) electric railway system built under the city of Chicago for the collection and distribution of general cargo and coal. The Chicago system operated from 1904 to 1958, interfacing with the main-line railroads. The Tokyo tube transportation proposal previously mentioned would perform the same function as the Chicago system, except that the system in Tokyo would be automated and would interface primarily with trucks.
Any tube freight system operating as a common carrier will be required to transfer freight to other carriers for final delivery, except to large consignees with private, direct access (like railroad sidings). In most cases, trucks are the most likely off-line carrier. Currently, intermodal transfers between trucks, railroads, and ships are facilitated by the use of standard intermodal containers. (14) In addition, truck trailers act as containers when they are hauled on railroad flat cars. Intermodal shipments are increasing. To be successful, any tube freight system must have some means of efficient intermodal transfer, such as standard containers. However, to handle the current standard intermodal containers, tube diameters of about 3 to 3.66 m (10 to 12 ft) are necessary, and such tubes would require about four times the capital cost of the 1.8-m- (6-ft-) diameter tubes advocated by most promoters and, thus, would be much less economically attractive.
Approaches to Introduce Tube Freight
It is evident that a comprehensive tube freight system cannot be financially and physically implemented overnight even if this were a national objective. Several transitional approaches can be envisioned.
The first option is to build the most needed and financially viable segments in congested areas. This approach has the obvious disadvantage of requiring standardization after initial segments are built and operating.
A second approach is to develop a national plan with appropriate standards established in advance. This was the general approach taken to implement the interstate highway system. This approach would appear more appropriate for the introduction of tube freight transportation in congested areas. However, it has the disadvantage of requiring an extensive period of planning, consensus-building, and enactment.
A third approach is to assume tube freight transportation would only provide niche, general commodity services and allow totally private planning and development with limited enabling legislation and, perhaps, access to federal rights-of-way.
Future Tube Freight Transportation Plans
A panel of transportation experts -- representing truck and rail companies, freight users, state and local governments, construction companies, and others -- will review the current status of tube freight transportation and develop a recommended federal position concerning future research and development of such systems. Two research tasks will provide estimates of future tunneling costs, tunnel liners, capsules, linear induction motors, and associated systems. In addition, estimates of future freight capacity requirements, particularly in congested areas, will be determined.
Likely increases in freight traffic beyond the year 2000, combined with increasing restrictions on the expansion of surface facilities, has led FHWA to examine some alternatives for use in congested areas. Tube transportation is one alternative that is gaining worldwide attention. Use of existing highway rights-of-way is an attractive feature of tube transportation. There are a number of other desirable features and advantages relating to productivity, safety, environmental issues, and energy savings. Because of the potential of such systems, FHWA is currently studying estimated costs of tube transportation systems, particularly liner induction motor-powered approaches, as a first step in the process of examining their economic viability. A necessary part of cost estimation is development of conceptual designs, which could lead to functional specifications.
(1) National Transportation Statistics, Annual Report, Historical Compendium 1960-1992 (with linear projection to 2020), Bureau of Transportation Statistics, U.S. Department of Transportation, September 1993.
(2) William Vandersteel. The Future of Our Transportation Infrastructure, Ampower Corporation, North Bergen, N.J., 1993.
(3) Masaki Koshi. "An Automated Underground Tube Network for Urban Goods Transport," Journal of International Association of Traffic and Safety Sciences, Vol. 16, No. 2, 1992.
(4) R. Livesey. "Blown Freight Is a Lovely Change From Road and Rail," The Engineer, London, England, Oct. 28, 1971.
(5) "Im Nächsten Jahrtausend in 57 Minuten von Genf nach Zürich," Der Bund, Sonderbeilage, Bern, Switzerland, Sep. 8, 1992.
(6) "Vacuum Technology Weighed for Swiss Maglev Proposal," MAGLEV News, Vol. 1, No. 15, May 17, 1993.
(7) "New Millennium Seeks Support From NMI Officials," MAGLEV News, Mar. 22, 1993.
(8) "AIRAPID Capsule-Tube Transport System," promotional brochure of Nippon Steel Corp., Daifuku Machinery Works Ltd., Chiyoda-Ku, Tokyo, Japan, undated.
(9) "The Capsule Liner," promotional brochure of Plant Engineer Division of Sumitomo Metal Ind. Ltd., Chiyoda-Ku, Tokyo, Japan.
(10) "TRANSPROGRESS Systems for Pipeline Pneumatic Container Freight Transportation," promotional brochure of Licinsintorg, Moscow, Russia, 1986.
(11) I. Zandi, W.B. Allen, E.K. Morlok, K. Gimm, T. Plaut, and J. Warner. Transport of Solid Commodities via Freight Pipeline, Department of Civil and Urban Engineering, University of Pennsylvania, Philadelphia, Pa., published in five volumes for the Department of Transportation, Publication No. DOT-TST-76T-35 through DOT-TST-76T-39, July 1976.
(12) I. Zandi, J. Warner, B. Allen, J. Kerrigan, C. Younkin, and K. Thomas. Transport of Solid Commodities via Freight Pipeline, Department of Civil and Urban Engineering, University of Pennsylvania, Philadelphia, Pa., published in two volumes, December 1978.
(13) The Need for a National System of Transportation and Utility Corridors, U.S. Department of the Interior, Washington, D.C., July 1, 1975.
(14) Eric Rath. Container Systems, John Wiley & Sons Inc., 1973.
Lawrence Vance has worked in the field of new systems studies since he did a study of new and novel transportation systems for the Bay Area Transportation Study Commission in 1968-69. At the John A. Volpe National Transportation Systems Center since 1971, he has performed a number of new systems studies interspersed with other assignments. He recently spent five years aiding the U.S. Air Force to automate their transportation information systems. He received his doctorate in engineering from the Institute of Transportation and Traffic Engineering (now the Institute of Transportation Studies) of the University of California at Berkeley in 1970. He also has degrees in mechanical engineering.
Milton K. (Pete) Mills is an electronic engineer in the FHWA's Office of Advanced Research. From 1963 to 1966, he tested and evaluated aircraft antenna systems at the U.S. Naval Air Test Center, Patuxent River, Md. From 1966 to 1968, he designed and patented a number of spacecraft antenna systems at NASA's Goddard Space Flight Center in Greenbelt, Md. At the FHWA's Turner-Fairbank Highway Research Center in McLean, Va., since 1968, he has managed the development and evaluation of vehicle sensor systems. He received his bachelor's degree in electrical engineering from North Carolina State University and his master's degree in electrical engineering from Catholic University in 1975.
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