Gravitator
Design
Gravity-assist enables much greater acceleration rates— without discomfort to passengers.
In urban transportation (relatively short distances), speed is primarily limited by the acceleration/deceleration rates. A system such as a Hyperloop, with projected top speeds of over 700mph, would not materially shorten travel times within a city, because vehicles would have to begin preparing to stop well before top speed was reached.
Acceleration rates in urban transit are limited by passenger comfort, i.e., the maximum g-forces that passengers can experience without becoming ill or experiencing discomfort that deters them from riding at all. 3 miles per hour, per second is a common maximum acceleration and braking rate. Modern subways often achieve these rates.
By accelerating on a gradient (approximately 12% or 7 degrees), much greater acceleration rates are possible without increasing longitudinal g-forces. Thus, gravity-assisted acceleration means Gravitators can travel much faster than any existing mode of transit.
How it works: Speed and Comfort
Gravity-assisted acceleration makes Gravitators much faster than conventional subways—faster than any existing mode of urban travel.
The right-of-way descends from the surface as soon as vehicles leave the station area, and it then ascends back to the surface before reaching the next station. This gravity-assisted acceleration reduces passenger longitudinal g-forces.
This means that Gravitators can have a longer right-of-way than a comparable subway (because it must descend and ascend). However, the increased length is relatively small, and the speed more than compensates for it.
Moreover, because Gravitators go deep underground beyond stations, they can avoid most underground utilities and building foundations. This frees Gravitators from following street lines, allowing them to travel in a direct line (when viewed from above).
The Second Regional Plan of New York (pp. 86-89) discusses the potential of the “gravity-vacuum” system (a related but distinct mode of transit) for urban transportation.
Gravity-Assisted Acceleration
Gravity-assisted acceleration also:
(1) makes a single, bi-directional tunnel sufficient for frequent service, cutting construction costs,
(2) brings stations to the surface where they are more convenient and much cheaper to build, and
(3) makes operation energy efficient, reducing operating costs.
Fewer Tunnels = Less Cost
Gravity-assisted acceleration allows significantly faster travel than possible with any of today’s transit modes.
In turn, the high speed allows frequent service—covering up to 2 miles—with a single tunnel, halving tunnel construction costs.
That is, a single tunnel offers the same capacity as conventional subway with a twin tunnel. This makes Gravitators more economical to construct than Hyperloop or Gravity-Vacuum Transit systems.
In addition, unlike those systems, Gravitators do not require a vacuum (such as Lawrence Edwards’ High-Speed Ground Transportation System) nor do they require a monorail guideway (such as Elfric Kearney’s High-Speed Tube system). This allows them to use conventional transit vehicles, further reducing the cost to build and operate. Gravitators use conventional propulsion systems (such as linear induction motors), though pneumatic propulsion might also be feasible.
Convenient Stations—for ⅓ the Cost
Gravity design allows stations to be at the surface, where they are cheapest to construct—⅓ the cost of underground stations—and most attractive to customers.
Customers step aboard, as easily as boarding an elevator.
The more convenient the stations, the more value to customers, and the more revenue to owners.
In addition, the gravity design allows tunnels to easily pass below existing subsurface structures, in a straight, direct route.
It’s an ideal combination for urban transit:
Stations at the surface and
Rights-of-way deep underground.