by Galen J. Suppes
Department of Chemical & Petroleum Engineering
The University of Kansas
4006 Learned, Lawrence, KS 66045-2223
(913) 864-3864, FAX (913) 864-4967
email: gsuppes@cpe.engr.ukans.edu
A critical review of maglev trains and convention wheeled trains was presented in an attempt to identify performance advantages of maglev. Traditionally claimed advantages of maglev were not found to hold up to wheeled train systems incorporating similar non-contacting propulsion; however, performance advantages were identified for velocities greater than 500 mph (805 km/hr). At these high velocities, travel at atmospheric pressure is not practical, and so, an analysis was made for applications in tubes of reduced pressures.
The feasibility of a personal rapid transit (PRT) system designed with maglev suspension and for travel in tubes of reduced pressure was evaluated. The PRT maglev would have superior service capabilities yet no obvious technological barriers. An economic comparison to maglev train systems suggested that the PRT maglev costs about 40% less while providing appeal to a broader audience. Proposed performance advantages of the PRT maglev include reduced energy consumption, reliance on electrical power, and significantly reduced transit times as compared to air or train systems. A practical approach to implementation is presented and consists of initially using lower velocities, higher tube pressures, and PRT vehicles connected as train units. Proposed evolution of the system includes attaining higher velocities and incorporating superconductive elements in the rail embodiments.
Key Words: Maglev, PRT, Train, High Speed, Vacuum
As noted by Sinha (1), it was only in the 1960's that fast electromechanical control gears and the advent of solid state electronics made maglev vehicles feasible. In 1958 Polgreen (2) filed for one of the first maglev patents on a maglev transit system based on repulsion between permanent magnets on the vehicle and along the guideway. Shortly thereafter, Silverman (3) filed for a patent based on attractive levitation using overhead rails and preferably electromagnets on the vehicle. These patents largely specify the genesis era of maglev transit during the late 1950's and early 1960's.
While systems could be conceived during the early 1960's, it was only in the later 1960's when technical issues such as stable suspension, low speed switching, and manageable rail tolerances made maglev transit a practical reality. Powell (4) led the way in truly feasible systems with the unprecedented introduction of (1) inductive suspension allowing vehicle-rail gaps in excess of three inches, (2) electrodynamic lateral stability, (3) incorporation of superconducting magnets, and (4) non-contact propulsion via jet engines. During this second, pragmatic era other significant advances were also made on switching (low speed) without moving parts (5, 6), linear induction motors which would allow the engine noise and fuel weight to be removed from the train (7, 8) and control methods for stable suspension (9, 10).
These and other advances led to several maglev demonstration projects (11) in the early 1980's. Throughout the 1980's attractive EMS suspension systems were advanced in Germany, and repulsive suspension (EDS) systems were advanced in Japan. During this same time period no significant projects were sponsored by the U. S. government. EDS system technology developed during this era is currently being offered for sale by the HSST Corporation of Japan .
The latest era of maglev transit in the United States is perhaps best described as the romantic era due to our governments romance with an idea of advanced transit over a cushion of air and without wheels. The funding made available in the early 1990's was politically motivated by a desire to regain superiority in this intriguing technology. The most significant production from this romantic era are the maglev system cost estimates reported in the Compendium of Executive Summaries from the Maglev System Concept Definition. Final Reports (12). While several U. S. markets consider implementing maglev train systems, no routes greater than a few miles appear to be in the near future.
Cited advantages of maglev trains over wheeled trains (1, 12) include:
1) Wheels produce medium to high environmental noise levels.
2) Wheeled systems rely on propulsion through wheel-rail friction, and the high aerodynamic drag forces lead to upper speed limits due to limited wheel-rail adhesion.
3) Maglev vehicles can accelerate and decelerate rapidly and bank steeply on curves.
4) Suspension through point contact (up to 70,000 psi or 482 MPa) leads to increased structural requirements and increased wear/maintenance.
5) Maglev trains have a certain romantic appeal.
Alternatively, advocates of wheel based trains justify high speed wheel based systems due to an already extensive rail network.
Already existing rail networks give merit to continuing with wheel based systems. However, as discussed subsequently, several cited advantages of maglev have a weak foundation.
While wheels are generally noisier than magnets, at high travel velocities aerodynamic noise greatly exceeds that from wheels (personal conversation with J. Harding, former director of U.S. Maglev Initiative, July, 1993). In perspective, minimal noise reductions are achieved by high speed maglev.
In a similar comparison of propulsion systems, linear synchronous motors (LSM) are capable of overcoming greater aerodynamic drag than wheels and have greater acceleration and deceleration capabilities than wheels. This non-contacting propulsion can be used with wheeled suspension and maglev systems alike. Combinations of LSM propulsion with wheeled suspension would provide needed propulsion without the expense of an entirely new rail system. The Detroit Metro already uses non-contacting linear induction motors (LIM) for propulsion (13, 14). Among its many advantages over conventional wheel propulsion are lighter weight vehicles, reduced height of train cars (15), and improved traction at all weather conditions, velocities, and grades. Figure 1 shows how the LSM propulsion system of the Magneplane concept (12) can be readily incorporated into the vehicles and tracks of a conventional train system. Cited advantages 2) and 3) are specific to LSM propulsion, not maglev suspension, and can be attained by wheeled and maglev systems alike.
An analysis of maintenance costs is simplified when making the assumption that maintenance costs are directly proportional to the weight of the vehicle. Such an assumption would be exact for a hypothetical system designed to have the exact same weight on all wheels, and where reductions in weight would result in eliminating some wheels.
For wheeled propulsion additional weight is advantageous to provide needed traction; however, lighter weight vehicles would be preferred with LSM propulsion. A 70% reduction is vehicle weight would be feasible (1) and would result in 70% reductions in maintenance costs. Furthermore, the application of high performance polymers and shock absorbers incorporating magnetic forces could further reduce maintenance costs.
Public perception be as it may, maglev trains will tend to have a romantic appeal. The romantic appeal and several successful demonstrations of maglev train systems make maglev trains a real alternative. However, for typical applications the slightly higher cost of maglev train systems and advantages of using exiting routes for wheeled alternatives have given the edge to wheeled systems.
In summary, maglev trains have limited advantages and significant disadvantages when compared to high speed wheeled trains using the latest non-contacting propulsion technology. To that end, the most advantageous applications of maglev appear not to be with conventional train systems. Alternatively, transit in low pressure environments and transit by personal rapid transit vehicles (PRT's) are two applications where maglev appears to have performance advantages.
While in 1992 PRT concepts were considered dead, the funding of the PRT2000 (16) demonstration may revive the expectations of PRT systems (17). In particular, PRT systems would have advantages of 1) reducing traffic congestion through automation, 2) reducing travel time by providing service non-stop from origin to destination, 3) reducing travel time by having access to a continuous supply of vehicles rather than periodic, and 4) relying upon electrical energy.
Disadvantages (personal conversation with J. Perkowski, Bechtel, San Francisco, May, 1994) identified during the 1970's included 1) performance limitations of available control technology, 2) perceived high cost of the extra number of vehicles, 3) distasteful appearance inside cities, and 4) potentially poor ride quality due to routing problems. Of these disadvantages, advances in electronics since the 1970's should alleviate questions on control technology and mass production of smaller vehicles actually costs little more than the production of fewer large vehicles. In particular, modern RIM polymer technology has gone a long way in reducing costs for vehicles produced in lower quantities. Remaining disadvantages on appearance and routing are design specific.
Routing is made easier and more accommodating due to the small cross-sectional areas of the PRT tubes as illustrated by a comparison of the PRT structure to the Bechtel concept (12) structure. The over-under arrangement of Figure 2 could be made even more accommodating by separating the bi-directional tubes when necessary for routing. Single vehicle tubes of six feet diameters could actually go through buildings. The low pressure environment and maglev suspension reduce noise levels and make such routing practical. Tube walls could be designed similar to enclosed walkways presently used to connect buildings over busy streets in cities. Routing at grade and under highways would also help alleviate distasteful appearances. In addition, reduced pressures would allow smaller tubes to be used and these tubes would have greater routing flexibility. The use of maglev suspension would also further reduce vehicle maintenance costs. All-in-all, the combination of PRT with maglev is a good match.
A common concern with maglev for intra-city transit is the high magnetic drag at low velocities for EDS suspension. These problems could also be addressed by using control technologies that provide non-stop service to minimize low velocity travel and by incorporating magnets in rails at station locations. Non-stop service would also allow higher velocities to be effectively used and would improve system performance. Cruising velocities in excess of 100 mph (161 km/hr) would be practical within many cities due to 1) greater acceleration, 2) non-stop service, and 3) transit corridors of reduced pressure.
Finally, a PRT Maglev operating in tubes of reduced pressure would be practical for intracity and intercity service with the same system. PRT systems may not have previously be considered for routine inter-city service; however, reduced aerodynamic losses in low pressure tubes and dynamic formation of trains would alleviate disadvantages for this application. Intercity transit is perhaps the best application of PRT since it is during intercity transit that passengers spend hours awaiting the departure of jets or making connections. Proposed intercity service of SWISSMETRO (18, 19) would have transit times of 12 minutes between cities, innately eliminating advantages of larger train-size vehicles.
Figure 2 compares the guideway of a PRT maglev to that of SWISSMETRO and the Bechtel concept. For the PRT maglev, vehicular suspension structures are located in front of and behind the passenger cabin. A cost comparison is given in Table 1 (20).
Goddard (21, 22) first proposed transit (non-maglev) in evacuated tubes; however, it was not until the 1973 RAND study (23) detailed the synergism of maglev and low air resistance that high speed transit in evacuated tunnels became feasible. Development of these concepts continue with NASA's New Millenniums Concept (John Rather, NASA Headquarters) and with SwissMetro (18, 19, 24). Modifications to the base concept include using of gravity to store energy (25, 26) and extending the concept to personal rapid transit (PRT) (27, 20). The extension to PRT service can actually have a greater impact on transit time than higher velocities.
The 1973 RAND study led the course for maglev transit in evacuated tubes and identified all-encompassing technologies which were available in 1973. In fact, the greatest hurdle to implementation was identified as tunneling technology, or rather, tunneling costs.
Suppes (20, 27) directly addressed these tunneling costs by identifying methods for reducing tunnel diameters, reducing the number of necessary tunnels, and allowing above-ground tubes. Both reduced tunneling costs and at-grade routing were made possible by using smaller vehicles which could travel is smaller tubes. Figures 2 and 3 illustrate the vehicle and tube sizes for the PRT maglev. As detailed in Table 1 , these PRT tubes would actually cost less than high speed train routes.
SWISSMETRO uses two tunnels connecting the stations (see Figure 2 ), and the tunneling costs represent about 75% of the capital costs. The PRT maglev could offer bidirectional service in one tunnel (see Figure 2 ). Eliminating one tunnel would reduce the SWISSMETRO cost by about 37.5%.
Initially proposed tunnel pressures for SWISSMETRO and the PRT maglev are similar to those surrounding supersonic aircraft at cruising altitudes, and similar to aircraft, the passenger compartments would be pressurized to maintain passenger comfort. By using pressures ranging from about 0.01 to 0.1 atm, SWISSMETRO would use smaller diameter tunnels to reduce capital costs while simultaneously reducing the energy consumed by the trains. Key advantages of SWISSMETRO to the Swiss public are reduced energy consumption and reduced environmental impacts due to smaller tunnels.
Upon first consideration, the concept of travel in low pressure environments can be rather distressful; however, low pressure travel environments are routinely used by passenger aircraft. While on earth's surface our body is accustomed to pressure of 1 atm (101 kPa), at typical passenger jet cruising altitude of 30,000-40,000 ft (9000-12000 m), the pressure ranges from 0.30-0.20 atm (30-20 kPa). In aircraft, scoops and compressors gather air to maintain pressure in the passenger cabin. Similar methods would be used for SWISSMETRO and the PRT maglev. It would be prudent to design initial PRT Maglevs to operate at the lower pressures (0.2 atm) presently used by commercial aircraft so as to minimize initial development needs. Optimal pressures for low pressure applications would depend on travel velocity and would vary from approximately 0.2 atm (20 kPa) to approximately 0.001 atm (0.1 kPa).
The upper curve of Figure 4 estimates (does not account for trans-sonic and super-sonic variations in drag) a constant aerodynamic drag and shows how pressure can be reduced to compensate for otherwise increased drag at higher velocities. Optimal pressures depend upon many factors including the dynamic use of train units, the use of aerodynamic designs, tube diameters, and technology on propulsion systems. The walls of the tube would increase drag, and for purposes of this paper the walls are assumed to double the aerodynamic drag. To streamline the PRT Maglev trains, the lower vehicle design of Figure 3 would be preferred.
Equation 1 accounts for formation of train units. Wall effects were incorporated into equation 1 by multiplying Ra by a factor of 2 and air density is taken into account by multiplying by a further factor equal to the tunnel pressure in atmospheres pressure.
To minimize systematic errors, calculations using equation 1 were made relative to the Bechtel concept. The perimeter of a train is assumed to be approximately 2.7 times greater than that of the PRT Maglev, and the length of the PRT Maglev train is a factor of two greater due to only having three passengers seated across rather than six (only five are pictured; however, the Bechtel concept proposes six seats across) as with the Bechtel concept. Another 50% increase in length is added to accommodate improved comfort and PRT vehicle constraints. In total, a PRT Maglev train would have an average length approximately three times greater than a train accommodating the same number of passengers.
Based on this analysis summarized in Table 2 , at 300 mph (482 km/hr) and 0.2 atm (20 kPa) of pressure, the PRT Maglev would have 63% less aerodynamic drag than a 300 mph (482 km/hr) train operated at atmospheric pressure. Using similar calculations at 500 mph (805) and 0.05 atm (5 kPa), the PRT Maglev would consume 75% less energy than to train to overcome aerodynamic drag. To reduce greenhouse gas emissions, combinations of low pressure and velocity could be used to reduce energy consumption to 50%, 20%, 10% . . . of the energy consumed by the best available alternatives.
For electrodynamic suspension, magnetic drag losses are proportional to the weight of the vehicle and are inversely proportional to travel velocity. The generally accepted form of the drag equation is given by equations 2 and 3 for high velocities. Here Fy is the vehicle weight, n is the total number of coils in magnets, I is the current in each coil, h is the height of levitation, t is the thickness of the conductive track, and s is the conductivity of the track.
For the Bechtel 64 Mg maglev train traveling at a velocity of 300 mph (483 km/hr), the magnetic drag energy consumption is estimated at 0.64 MW while the aerodynamic drag energy consumption is estimated at 5.4 MW. Aerodynamic drag dominates the energy consumption for both the Bechtel concept and the present PRT Maglev concept operating at 0.2 atm (20 kPa). At 500 mph (805 km/hr) and approximately 0.03 atm (3 kPa), magnetic and aerodynamic drag would be approximately equal, and at less than 500 mph (805 km/hr) and 0.01 atm (1 kPa) the presence of magnetic drag significantly diminishes advantages of lower tube pressures.
Analysis such as this can be used to define feasible pressure versus velocity profiles such as that shaded in Figure 4. Figure 4 is specific to the PRT Maglev. Larger vehicles, lower magnetic drags, and different vehicle-tube clearances would change the window of opportunity.
Energy consumption for tube evacuation would originate from the three needs of 1) periodic "total" tube evacuation, 2) evacuation associated with vehicle/passenger entry and departure, and 3) air leaks of the tube system. Of these, further information is needed to evaluate the impact of air leaks. In practice the cost of leaks would justify use and development of advanced leak detection methods and coatings which would bring leaks under control.
The cost of total tube evacuation would be incurred periodically when the tube is exposed to atmospheric pressure for maintenance or for emergency procedures (e.g., emergency evacuation by flooding the tubes with air and having passengers walk to a tube exit). Standard adiabatic compression calculations were used to estimate the compression energy. Compression was modeled as a dynamic process with tube pressure decreasing as evacuation progressed.
For four tube evacuations per year, a compression efficiency of 80%, and a tube length of 800 km; 3.6, 5.6, 8.4, and 9.2 million MJ are required to remove 16 Gg of air and produce a pressure of 0.2, 0.1, 0.01, and 0.001 atm respectively. As listed in Table 3, this translates to 360-920 J per passenger mile or < $0.00002 per passenger mile. A similar calculation for the evacuation of the volume of a vehicle exterior for entry of a vehicle into the tube equates to < $0.0001 per passenger mile.
While periodic tube evacuations and vehicle entries have evacuation costs which level out at lower pressures, compression costs associated with continuous removal of air (from leaks) increase rapidly with lower internal pressures. At pressures less than 0.02 atm (2 kPa), these compression costs could become significant. Insufficient data is available to make estimates on these costs.
In addition to comparing evacuation costs of the PRT Maglev to train system costs, these evacuation costs should also be compared to corresponding costs for air travel. For air travel, energy is expended to overcome earths gravity to achieve higher altitudes where lower pressures are available. At a mass of 500 kg per seat and a cruising altitude of 12,200 m (40,000 ft), 59.8 MJ of energy are consumed in overcoming gravitational forces. This compares to approximately 2.5 MJ of evacuation energy per passenger. Considering other factors such as energy for aircraft takeoff and the initial and final travel at atmospheric pressure by the aircraft, over forty times more energy is consumed to transport a passenger to low pressures by an aircraft than would be needed to maintain/enter low pressures in PRT Maglev tubes on earths surface for travel.
The cost estimates of Table 1 include both capital and energy consumption costs. A basis of 10 million roundtrips per year (3,500 passengers per hour per direction for eight hours per day for 365 days in a year) was used to allow capital and energy consumption costs to be compared.
Energy consumption is based on Bechtel's (12) oneway trip energy consumption of 19,000 kWh for a 497 mile (800 km) trip. (The 19,000 kWh is from Table A-3 of reference 12 and is based on the total trip and not just cruising velocities.) At 60% occupancy, 120 seats per vehicle, and $0.08 per kWh; the electrical energy costs $42.2 per passenger roundtrip or $0.85 million per year per mile of bidirectional track. As detailed in Table 2 , the 0.2 atm 300 mph PRT maglev has about 37% of the aerodynamic drag of Bechtel's concept or about $0.38 million per year per mile of bidirectional track with similar magnetic drags. These costs as well as vacuum and magnetic drag costs are also summarized by Table 3.
Capital costs are based on a direct comparison to Bechtel's reduced first cost estimate (12) which uses a higher cost for electrical power ($0.08 per kWh versus $0.055) with the advantage that local electrical companies would construct and manage guideway electrification facilities. Cost reductions in the PRT maglev capital reside in 1) reduced structure costs, 2) reduced propulsion costs, 3) reduced costs for stations and parking, and 4) reduced vehicle costs.
A 40% reduction in structure costs is based on a less expensive combined structure illustrated by Figure 2 . A further 25% reduction (12) is based on at-grade construction which is feasible due to a smaller cross section of the PRT maglev route.
Reduce propulsion system costs are claimed due to a 55% reduction in the combined aerodynamic and magnet drag of the PRT maglev as well as the use of a train unit which is three times longer for the PRT maglev. In total, the cruising propulsion requirements of the PRT maglev are only 15% of those of Bechtel's concept on a thrust per length of guideway basis.
Reduced station costs are associated with the smaller size of stations and incorporation with local metro service. Reduced vehicle costs are based on RIM production methods and shorter transit times leading to a need for fewer seats.
As a final comparison of costs and energy consumption, Table 3 compares the present calculations to those calculated in the analysis of a Canadian maglev system (1) as well as the Bechtel concept. The largest contribution to transit costs with maglev trains is the interest on capital and the second largest expense is that for electrical power. Costs to produce a tube pressure of 0.2 atm are negligible. A cost estimate including interest and energy costs amounts to a mere $0.059 per mile of travel.
The advantages of train systems in comparison to air travel can be readily seen. The savings in energy between the 300 mph, 0.2 atm PRT Maglev (483 km/hr, 20 kPa) and a B757 translate to about 264 Wh/seat-km or about $0.013 per mile of track at an energy cost of $0.03/kWh.
An initial PRT Maglev system operating at 300 mph and 0.2 atm (483 km/hr and 20 kPa) would be faster and more convenient than any other land based transportation system; however, air travel would have advantages at greater distances. To calculate the point at which air travel would have reduced transit times as compared to the PRT Maglev, certain assumptions must be made on the transit to airports, wait before departure, layovers, and wait after arrival. Table 4 lists the assumptions used for a comparative analysis. The source of the data includes published sources (29), airlines (recommendations on when to arrive at airport before departure), and personal experience.
The basic difference between the two air transit scenarios is that Air 1 is a direct flight and Air 2 includes a layover. The basic difference between the PRT Maglev scenarios is that PRT A operates at a maximum velocity of 300 mph (483 km/hr) and PRT B operates at a maximum velocity of 500 mph (805 km/hr). Both PRT Maglev systems assume access from several locations within both cities and therefore have the average 10 minute transit time to the station.
As illustrated by the data of Table 4, a PRT Maglev with a maximum velocity of 300 mph (483 km/hr) would have shorter transit times than air travel at distances less than 907 miles (1460 km). With a maximum travel velocity of 450 mph (724 km/hr), the PRT Maglev would have shorter travel times for all travel within the continental United States. Based on these results, initial PRT Maglev systems having a maximum travel velocity of 300 mph would be the best available alternative for destinations up to 907 miles distant. A later increase in velocity to 500 mph lead to service better than any alternative in the continental United States.
The PRT Maglev system could become a transportation network similar to our present highway system based on our interstate highway network. Local metro PRT Maglev tubes would be connected to interstate tubes, and each section would have a speed limit (speed set-point) for normal operation. Propulsion power would be supplied by linear motors along the tracks. Auxiliary propulsion from the vehicle would allow deviation from the speed set-point to allow the dynamic formation of trains to accommodate entering and exiting traffic. As high temperature superconductivity becomes reality, electric powered cars could be manufactured with magnetic suspension systems located within the four quarter-panels and, similar to HOV lanes, wheeled vehicles could literally drive onto and into a maglev transit corridor where automated maglev suspension would take over for much of the trip.
Local metro service could provide much needed pollution-free service to our cities. For cities, typical maximum upper speed set-points would initially be approximately 100 mph (161 km/hr). Depending upon the distance of travel, service could be in low pressure tubes or open to the atmosphere. The interstate network would be connected to local metro lines, and for the interstate network initial upper speed set-points would be approximately 300 mph (483 km/hr) with later speed set-points up to 3,000 mph (4,830 km/hr).
The combined network of local, intercity, and even transcontinental routes would provide PRT service from a location close to travel origination to a location close to the final destination, and travel in low pressure environments makes very fast travel possible and minimizes environmental impact. Service would readily evolve to operation similar to an elevators where no advanced reservation is necessary and where railway stations are replaced with elevator entrances at multiple locations within cities. The high energy efficiency, low maintenance (due to very few moving parts and isolation from environment), and comparatively low capital costs would allow PRT Maglevs to cost less other modes of transportation. Lastly, reliance on electrical power allows ecological impact and cost to improve with new technology on electrical power generation.
The PRT Maglev concept is new, and as such, many opportunities exist to improve.
One important area already emphasized is associated with operation at reduced pressures. It would be advantageous to operate initial systems at 0.2 atm (20 kPa) since this is an established standard for commercial aircraft, equipment is available, and the public has already accepted transit with vehicle exteriors at these pressures. Advancing to travel at increasingly low pressures leads to increased velocities, reduced energy consumption, and reduced travel times.
Improved tunneling, structures, and routing methods could reduce costs by reducing the guideway structural costs. Much could be gained from a concentrated research and development effort in this area.
Additional advantages could be realized by reducing the vehicle weight. Weight reductions should be able to match the specific weights for an automobile (300 kg per seat). Reduced vehicle weight leads to reduced forces on guideways and reduced magnetic drag.
An additional area for advancement would be the incorporation of superconducting rails for repulsive levitation. The NMI study (12) lists magnetic drag as ranging from 6 to 40 kW/ton for conventional conductors. Superconducting rails would reduce these values many fold and allow lower pressures to be used to reduce energy consumption costs to approximately one dollar for a 1600 km roundtrip. Such advances would make parcel service (30) of all sized packages feasible with maglev. Automated transit during off-hours could ship such freight with minimal increased capital and significantly increased profits. Without superconducting rails, freight could be shipped at costs of approximately $0.000023 per kg per mile during off-peak (11:00 PM to 6:00 AM) hours at lower velocities of approximately 200 mph.
Compared to 300 mph (483 km/hr) maglev trains, a 300 mph, 0.2 atm (20 kPa) PRT Maglev would require approximately 56% of the infrastructure cost at $10 million per mile as compared to $17.9 million per mile of bi-directional guideway. The energy requirements of the 300 mph Maglev would be approximately 45% of that corresponding to a train system. Such a 300 mph, 0.2 atm PRT Maglev would operate at low pressures typically encountered by commercial aircraft and no new developments or breakthroughs would be needed for maintaining cabin pressure.
A similar PRT Maglev system at 500 mph (805 km/hr) would offer a 25% reduction in travel time due to higher velocities and even further time reductions due to PRT service. However, a 500 mph, 0.2 atm PRT Maglev would consume a similar amount of energy as the 300 mph Bechtel concept and would have similar system costs. On option for alleviating the higher costs at 500 mph is to reduce internal tube pressures to between 0.03 atm and 0.1 atm (3-10 kPa). Both increasing velocities to 500 mph and decreasing pressures to 0.05 atm could be performed as evolutions to an initial system operated at 300 mph and 0.2 atm.
The proposed PRT maglev is similar to SWISSMETRO which is currently being developed in Europe; however, the PRT maglev would require 37.5% less capital in the form of tunneling costs. In addition, many US routes would have preferred routing at-grade rather than in underground tunnels. At-grade routing would reduce costs but may limit travel velocities. For the present purposes, acceleration and comfort considerations were defaulted to be those used by the NMI studies (12).
Based on the results of this preliminary study, a PRT maglev designed with a cruising velocity of 300 mph in tubes at 0.2 atm would be faster than present alternatives up to distances of 907 miles (1460 km). In addition, the energy to maintain tube vacuum is greater than forty times less than the energy needed to attain altitudes of similar low pressure. This PRT maglev would be able to evolve such that lower tube pressures and increased velocities would allow the PRT Maglev to have reduced travel times for all travel routes viable with surface routing. A mature system would include velocities up to 3,000 mph (4,830 km/hr) and connections between Asia and America.
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Galen J. Suppes is Assistant Professor, Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045. He can be reached by phone at: 913.842.4785 (residence). His smail address is: 532 Canyon Drive, Lawrence, KS 66049-2440. A print version of this article may be found in the Transportation Research Record, No. 1496, 1995, pp103-111.
Last modified: August 18, 2002