Peter A. Sharp

August, 1997


The goal of this project is to apply the principles of Personal Rapid Transit (PRT) to streamlined recumbent bicycles, so as to produce the least expensive transportation systems consistent with superior service. PRT is the use of small electric vehicles on a grid system of elevated guideways, which are computer controlled to achieve nonstop, station-to-station service (no transfers) at about 30 mph for local trips, and higher speeds for intercity travel. Excellent service, high capacities, and low costs are achieved by placing all stations off-line, and by spacing the vehicles an average of only 1 second apart. Sky Bikes and Bike Trains would achieve even lower costs and higher capacities by combining personal transit and mass transit techniques.

The cost of the elevated guideway is the major cost of a PRT system, and the cost of the guideway, after providing for wind loading, is proportional to the weight of the vehicles on the guideway. So vehicles of minimum weight, such as bicycles, could be used to achieve minimum cost. Most of the weight would be that of the riders rather than the vehicles. Streamlined recumbent bicycles, using suspension and advanced materials, can weigh less than 40 pounds. Sky Bikes, equipped with a small motor/generator, controls, and additional small guide wheels, would therefor weigh between 50 and 75 pounds per rider. The weight per rider of PRT 2000 vehicles (opening in Chicago in 1998) is 500 pounds per rider, and optimized PRT vehicles, it is assumed, might weigh about 250 to 300 pounds per rider.


Many streamlined recumbent bicycles have exceeded 60 mph. Leaning back on a very comfortable mesh seat with full back support, an average person pedaling such a vehicle could easily maintain speeds of 25 to 30 mph, which is a typical speed in cities for PRT vehicles. Aerodynamic drag, which absorbs most of a cyclist's energy, could be further reduced by arranging bicycles in a train configuration. Such trains would permit average riders to maintain speeds of 50 mph, and higher speeds if auxiliary power were used. If these speeds were used on an elevated guideway, with all stations off line, the average speeds would be higher than for automobiles using city streets and freeways. Door-to-door service could be provided using dual mode bicycles, called "tetracycles", capable of traveling both on the guideway and on roads.


A small gas motor (or battery) assist would permit such bicycles to climb steep roads. John Tetz has demonstrated, by riding for thousands of miles in city, country, and mountains, that the average gas mileage for assist motors is between 1,000 and 1,3000 mpg. This high mileage would make the use of fuel crops affordable, thus eliminating net CO2 emissions. On the guideway, electricity would be required primarily for control rather than power, so the necessary energy could be easily supplied by renewable energy sources. Dual mode tetracycles would have castered outrigger wheels on hinged arms that could be lowered by pulling back on the handlebars. Tetracycles would lean but not fall (the outrigger wheels would extend farther to the side when leaning). Tetracycles would have the advantages of both bicycles and tricycles, but without their disadvantages.


To further reduce the energy requirements of the guideway system, regenerative braking would be used. This would enable slowing or descending bicycles to provide additional energy for accelerating and ascending bicycles, thus "leveling" the guideway grid system. Stationary flywheels could be used to act as electrical power buffers if necessary. Additional energy would be generated by permitting aggressive or impatient riders to "speed" on passing lanes that ended prior to intersections (located every 1/2 mile). Their braking energy, from small motor/generators, would be distributed to propel empty vehicles and vehicles with riders who were unable to pedal. The motor/generators would insure the proper computer controlled speeds at all times. The passing lanes would add very little weight to the guideway, since the guideway would only need to be widened, but no additional vehicle weight would be carried. The passing lanes would also permit stalled vehicles to be serviced and bypassed, thereby improving the overall reliability of the system.


Most Sky Bikes would be one of 3 types: single person (plus space for one child), tandems (plus space between back to back riders for one adult passenger, or two children), and cargo bikes (with space for a wheelchair or conventional bicycles). The top of the vehicles would be hinged at the front, with the side doors attached to the top.


Bike Trains could be formed and constructed in various ways depending upon their application. Train forming could be done while moving at full speed by inserting the horizontal nose of one Sky Bike into the matching flexible tail section of another Sky bike. This could also be done at stations. Bike Trains could be constructed as permanent units using recumbent monocycles behind a front wheel drive bicycle. A versatile design would use bicycles with inexpensive tubular bodies, with flat fronts and backs, that would enable trains, while passing through stations, to automatically disassemble and reassemble with new bicycles.


Sky Bikes and Bike Trains could be used in 3 basic ways. The first way would be to use Sky Bikes (30 mph) for local travel, and to temporarily combine them into Bike Trains (50 mph) for longer commute distances requiring higher speeds. This option would permit the use of dual mode tetracycles all across the system. The second option would be to use separate guideways for Sky Bikes and for permanent Bike Trains (monocycle trains), and to require riders to transfer (with little or no delay) from one to the other. And the third option would be to use only Bike Trains (Stopless Bike Trains).


The trains would never fully stop. When approaching stations, a train would pull on to the station's through-guideway and slow down (to about 10 mph) while the separate tubular bodied bicycles (with flat front and rear ends) would spread apart. Bicycles destined for the station would pull into loading berths while the other bicycles continued forward to be joined by accelerating bicycles leaving the station, which would merge, and then all of the bicycles would condense to form a train before accelerating onto the main guideway. The aerodynamic nose and tail sections would be riderless bicycles. So as to minimize trip times, express trains would service every fifteenth station, intermediate trains would service every fifth station, and local trains would service every station. Through trains would pass other trains while they were reassembling at off-line stations. The length, frequency, and speed of the trains would be varied to match demand. Train bicycles that were not needed would be stacked in station garages so as to minimize the number of empty vehicles.


Stations would be located about every 1/2 mile near guideway intersections, placing them within about 1/4 mile from almost everyone. For Sky Bikes, stations could be located outside the modified windows of converted office spaces on the second floor, or inside buildings (by entering through modified windows), and on flat roofs in regions with mild climates. On-street stations requiring many boarding berths would use 4 stacked guideways, with access for wheelchairs and/or dual mode vehicles at street level. The width of a station guideway and its loading berths would be about 7 feet, which would easily fit within the space used for parking automobiles at the curb.


To maximize coverage, while minimizing cost, alternating one-way guideways would be spaced about every 1/2 mile on major streets. Guideway intersections would be of 3 main types: over/under, hour glass, and dominant/subordinate. Over/under intersections would permit high speeds and wide radius turns, but using different elevations costs more. The other two intersections would keep both guideways at the same level. Hour glass intersections would have a common section of guideway oriented diagonally above large street intersections. Vehicles on the crossing guideways would merge into the common section before diverging in the preferred direction (straight or turn). Dominant/subordinate intersections would permit the dominant guideway to pass straight through. The subordinate guideway would turn and merge with the dominant guideway, and then one block later it would diverge and turn toward its original direction. So the subordinate guideway would be traveling in its original direction once again, but it would be displaced one block to the side. At the next intersection, it would be displaced one block back again to its original line. If crossing guideways share a common section of guideway, bottlenecks can occur. But PRT studies indicate that careful attention to speeds and spacing can avoid this problem.


The guideway would have a "U" shaped cross section (3 feet by 3 feet) with a flat bottom. The sides of the "U" would be triangulated trusses. They would be carefully designed to make them visually appealing. At the two tops of the "U" would be balancing rails. At the middle bottom of the guideway would be two closely parallel guide rails. The bicycle wheels would ride between the guide rails. Fixed guide wheels would keep the bicycle wheels from touching the guide rails. A switching wheel would be located on the outward side of each guide rail. For normal running, both switching wheels would contact their guide rails. For switching, one of the switching wheels would be retracted upward by a solenoid. That would permit the bicycle to follow the other guide rail. To balance the bicycle, fixed balancing wheels would contact the inward side of both balancing rails. These would be located at about shoulder height for the seated rider. Retractable balancing wheels would contact the outward side of the balancing rails. For switching, one of the retractable balancing wheels would be tilted upward, above its balancing rail, by a solenoid. These balancing wheels would be located in streamlined enclosures that would look like small, stubby wings.


The bicycle could be guided and balanced by either side of the guideway. Prior to turns, the bicycle would switch to one side of the guideway. Then the two sides of the guideway would move apart until there was room enough to form two separate guideways. One of the guideways would turn. The bicycle would follow the guideway it was on. For boarding at stations, one side of the guideway would be briefly discontinued so as to allow access to the vehicle.

In cold climates, the bicycle wheels would be supplemented or replaced by two small rail wheels each, which would ride on top of the guide rails, and the guide rails would be spaced more widely apart. This would permit the rail wheels to be partially covered so as to protect them from snow, while leaving an open gap between the guide rails for drainage. The guide wheels would be the same, or, the inside guide wheels could be replaced by inside flanges on the rail wheels. The balancing rails would be partially covered as well. In all climates, the guide rails might eventually be used in combination with linear electric motors to minimize weight and to maximize power.


The guideway would be elevated 15 to 20 feet above the middle of streets, except at intersections where the guideway would move to one side of the street. Support posts would be used at intersections. Between intersections, the guideway would be supported by graceful pointed arches and thin bracing cables. The feet of the arches would be located on opposite curbs. The guideway would run below the point of the arch. Bracing cables would extend out from the upward sides of the arch so as to provide both vertical and horizontal bracing for the guideway. This should permit an exceptionally light yet unusually strong guideway.


Because the cable-braced guideway would be able to withstand high lateral forces, and high twisting forces, small symmetrical wing sails could be added near the rear of the bicycles, above the balancing wheels. These wing sails would be useful along windy intercity routes, such as coastlines or ridge lines. Normally, the enclosed bicycles would be about 4 feet high, and perhaps 10 to 12 feet high with wing sails. In some areas of the country, the wing sails might be able to produce surplus energy.


Dual mode PRT systems require careful inspection of private vehicles before allowing them on the guideway system because private maintenance is not reliable. But inspections can be expensive and cause delays. It should be possible to solve the inspection problem for dual mode bicycles. At street level, they would be funneled onto a "runway" guideway where a diagnosis of function (switching, etc.) and structural integrity would be performed. Because the vehicle bodies would be standardized, laser scanners could be used to check, using reflective grid lines painted on the vehicles, for any cracks or deformations. Vehicles exhibiting functional or structural flaws would be guided off the end of the runway and back onto the street. Accepted vehicles would be switched to the "takeoff" ramp which would climb to the guideway. Periodic vehicle maintenance inspections would also be required.


An emergency button would stop the vehicle and release the top latch. Emergency escape would be by tipping the top of the vehicle all the way forward and climbing out the front end, walking down the guideway, and descending spiral stairs located on support posts. In cold climates, walkways on the guideway would be made to fold up when not in use so as to not collect snow and add weight to the guideway. Vehicles stalled during extremely cold weather would have sufficient insulation to keep riders warm using only their own body heat. Small light bulbs, powered by pedaling, would provide additional heat, light, and signaling during emergencies. Windows would not open. Ventilation would be through low drag openings.


Vehicles not in use on the guideway would be stored in garages where they would be stacked to minimize space. Vehicles would be arranged by type; first in, first out.


There are still many unknowns, but a conservative estimate would be that Sky Bikes and Bike Trains would cost about half as much as other optimized PRT for the same capacity. Compared to optimized PRT, Sky Bikes would have about half the weight, and Bike Trains would have about twice the capacity (for the same weight as PRT vehicles). So in each case, the cost should be about half. Some calculations show a considerably greater advantage, but a detailed examination is required to determine their reliability. PRT is expected to cost 1/4 as much as light rail, and to make a profit rather than require subsidies. Consequently, Sky Bikes and Bike Trains would cost 1/8 as much as light rail, and their profit potential would be quite high. They could become a major source of revenues for cities. The first guideways should be constructed, preferably, to provide short tours for tourists, so as to gain experience with the operation of the guideways. The fares would then be used to gradually extend the guideways across the rest of the city.


Given that PRT requires only 1/6 to 1/10 the number of vehicles to provide the same service as automobiles, and given that Sky Bikes would require only a minimum of space when on roads and in storage, a large percentage of each city devoted to automobile use (some estimates go as high as 40% in some cities) would become available for other purposes.

This newly available space would provide land for housing and industry. It could be sufficient to eliminate further urban sprawl, which is causing the loss of crop lands, grazing lands, marsh lands, and bays. It would also free land for urban farming, parks, and restored wetlands. Growth boundaries, green belts, and sustainable ecocities would become affordable options. Only a few automobiles (probably Hypercars - 150 to 300 mpg using hybrid power) would be required for trips beyond the guideway. As guideways expanded, the population of automobiles would contract. The transition would be gradual, thus permitting most of the approximately 1/6 of the U.S. population employed in automobile related jobs, to find other occupations. Enormous capital would become available for other industries. The reduction of current CO2 emissions would be 20% or more, and a far greater savings would be achieved by diverting cycling countries like China and India from becoming dependent on automobiles. Within the next hundred years, the majority of the world's 8 to 12 billion people, most of them poor, will be living in megacities. If we are going to win the race to save the planet, we will need to do it on Sky Bikes and Bike Trains.


The concept of bicycles in trains, to achieve higher speeds, was recently proposed by Bob Malcomb PE in HPV News. Excellent articles about PRT by Dr. J. Edward Anderson served as the information base for this project. Dr. Jerry B. Schneider stimulated this project by providing the web site "Innovative Transportation Technologies" at the University of Washington, in Seattle. Dr. David Gordon Wilson, author of Bicycling Science, and editor of Human Power (the technical journal of the IHPVA), has for many years encouraged human powered vehicle innovations.


Sky Bikes and Bike Trains is a new, not for profit, public service project. Drawings are not yet available. If you have suggestions, criticisms, or wishes, or would like to help in some way, please let me know. The success of this project now depends upon one person: you.

For more details, contact: Peter A. Sharp , 2786 Bellaire Place, Oakland, CA 94601, USA [e-mail:] This summary was written by Peter A. Sharp from a longer, more detailed paper.


Last modified: August 21, 1997