- The future of transportation

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Possibly the most controversial aspect of the design is that of being "at grade", meaning it runs at ground level.  The concern is not that vehicles would collide with automobiles (they don't coexist), but rather with pedestrians, bicycles, and such.  This is no doubt a challenging engineering hurdle, but recent developments in robotics made possible by the DARPA Grand Challenges suggest that machine will inevitably be safer than humans.


     Unlike the DARPA vehicles, PRTProject vehicles are confined to rails.  So the challenge is not "what direction" but rather "is it safe to proceed".  Furthermore the sensory input into the system is not limited to what's mounted on the vehicle, but instead includes the combined sensory input of every vehicle in the system, input from a command center, and sensing equipment embedded into the infrastructure.

While the DARPA Challenges have a military objective, I believe the greatest benefit will ultimately be to the field of transportation.  PRT scales extremely well.

Here's a video showing a DARPA vehicle in action:


The vehicles are controlled at two distinct levels: an onboard vehicle control system (VCS) handles local functions (opening doors, user safety, etc) and a central control system (CCS) monitors and routes the fleet according to the needs of the system.

VCS (Vehicle Control System)

The VCS is in constant communication with the central control system.  The VCS utilizes onboard video cameras and motion sensors to monitor activity both outside and inside the vehicle.  Outside sensors allow the vehicle to track and avoid obstacles such as children, animals, or other vehicles.  Inside systems allow the vehicle to detect when passengers are safely seated, and so forth.  The VCS interacts with passengers via voice recognition to interpret commands ("stop here", "take me to school", etc).  Each passenger has a profile in the system such that "school" has a specific meaning depending on the user.  A touch screen is also provided as an additional way of communicating with the passenger, displaying route maps, event times, etc.

CCS (Central Control System)

The vehicle communicates with the central control system (CCS) to receive routing instructions and communicate various events across the system (a dog on the tracks, etc).  As a safety precaution, either system (VCS or CCS) can bring the vehicle to a full stop.  Likewise both systems must approve of all vehicle movement.  The result is that, even if the CCS sends faulty instructions, the vehicle will still have sufficient onboard intelligence to detect and prevent collisions.  Alternatively, if a vehicle is malfunctioning, the CCS will detect the behavior through GPS tracking and initiate a shutdown of the vehicle, if necessary by triggered by stop points on the tracks (described later).  This redundancy of control insures the safety of the total system.

While control is shared between the VCS and CCS, the passenger always has the final word due to safety reasons.  The passenger can always stop the vehicle in the event of an emergency (fire, etc).



PRT vehicles are powered by a 3rd electrified rail, running a non-lethal 48V.  A battery in included in the design, but only for bridging unpowered sections of track and conditioning the power input.

The vehicles do not have a designated front or back, but instead travel equally well in either direction.

While conventional trains and lightrail systems rely solely on gravity to keep vehicles on the track, the PRT vehicle is considerably lighter and requires an additional set of guide wheels for safety purposes, similar to that employed with roller coasters.  The guide wheels are mounted such that they connect with the inner side of the rails.  Those illustrated here are probably more extensive than what would actually be needed for PRT vehicles.



Vehicle Specialization

PRT vehicles are a shared public resource, available on demand, rather than individually owned.  While the majority of the vehicles will be dedicated to basic passenger service, the system also provides for specialized vehicles...

If an individual were to make a large purchase at the local hardware store, a specialized freight vehicle would be summoned.  This fulfills the need of individuals who currently own pickup trucks for occasional weekend home improvement projects in a much more economical way.

Specialized freight PRT vehicles will also replace the need for traditional truck and train transport.  On the occasion where excessively large objects need to be moved (crane, etc), side access roads can be utilized.  Remember, PRT tracks require only a fraction of the existing road surface, leaving the remainder for foot & bicycle traffic, and service access as just mentioned.


Vehicles can be leased to businesses for a variety of customizations, although modification of underlying chassis or mechanics would not be allowed.  Vehicles in this category would not receive preferential routing.


Vehicles will also be customized for government functions such as emergency services - police, fire, and ambulances.  Vehicles of this sort would receive priority routing and include manual control overrides for dealing with emergency situations.

As with conventional rail systems, the PRT system itself will also require specialized vehicles to handle track repair and inspections, clear debris from the rails, and so forth.


There may also be specialization within passenger vehicles, possibly a one-person unit since most travel consists of a single passenger.

Bicycle-Weight Technology

Without the danger of vehicle to vehicle, or vehicle to stationary object collisions, there is no need for mass designed solely for protection. An automobile at standard occupancy weighs a ton per passenger. An Amtrak car - 1200 pounds. A bicycle - 20 pounds.

Track Design

Traditional rail systems run parallel to the existing roadways, requiring vast infrastructure investments due to raised platforms, tunnels, and land acquisitions.  Lightrail systems can cost as much as $70 million per mile and take years to construct even short distances.    


The PRT rails are instead mounted atop the existing road surfaces, greatly reducing the construction costs and implementation times.

The tracks are supported at periodically spaced columns embedded into the ground.  The intersection of the columns and the track would be designed to allow adjustments to compensate for ground settling, keeping the tracks extremely level.  Tracks segments could also be detached from the columns during street maintenance (underground utility work, etc).  The paved surface below the rails would last much longer since it would no longer be experiencing direct traffic, a significant cost savings.

Device For On–Board Rail Vehicle Switching
Passive track infrastructure with self steering wheelbase guided by interlocked movable steering arms.
Courtesy of Mark E Townend, 09/04/2013

PRT uses "in-vehicle" switching.  This means the vehicles control the switching operation, providing the mechanical energy necessary to throw the switch, thus simplifying the switches themselves.  It will be important to keep the cost of the switches low given the large quantity required.  In trains, faulty or incorrectly set switches are often the cause of accidents.  To address this concern, the central routing system will assume that the vehicle is still on the main line until (1) the vehicle reports the exit as successful and (2) a sensor in the sidetrack verifies the vehicle location.

The design criteria for passenger loading / unloading requires that no single vehicle blocks another.  So if a neighbor is busy loading luggage into a vehicle, you would not be late for work.  So the only delay would be it time it takes the vehicle to arrive.  If the central routing system detects a pattern, say you leave for work every weekday morning at 7:00am, it will proactively start sending a vehicle to your location in anticipation of your need.

residential track layout

At locations involving high volume loading / unloading, such as the local mall, people would line up for the next available vehicle (a "taxi line").  Such a location would maintain multiple sidings, depending on volume.



customers queuing up for vehicles

At key points on the track, stop points will be implemented, controlled by the central routing system.  If a stop point is activated, any passing vehicle is disabled (stopped) when it makes contact.  This is a safety precaution in the event of a runaway vehicle.

This much rail covering our streets will certainly be a challenge, especially to pedestrians and bicycles.  At numerous key points we will need appropriate ramping to make crossing safer, especially at locations where the rails and path cross at diagonals.  Here's one technology that handles the task...


Biking on railroad tracks with rubber-filled flangeway from Steven Vance on Vimeo.



While the current PRT design calls for steel wheels on conventional steel rails, there's also the possibly of utilizing maglev or hover technologies.  MAGLEV has it's advantages, but given the low speed and large amount of track involved with the PRT, MAGLEV technology may not be a good fit for PRT.  Here are a few good links on the subject...

MAGLEV described:

This article argues against the MAGLEV approach:



Click here for information on the transition...









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