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This proposal was moved to: Transportation 2018
This proposal was reopened in Transportation 2016


MINI ELEVATED GREEN TRAINS powered by renewable energy - urban mobility for all - a comprehensive solution to public transit.





 - Fully Green Mass Transit

 - Urban mobility on a comprehensive scale 

We are proposing a design we believe to be the most efficient as a mass transit model through Mini Elevated Green Trains - in the past referred to as cTrains, Caterpillar Trains because of their appearance; however we believe that gTrains is more appropriate for their renewable energy efficiency 

The premise of our work is to find a solution to mass transit by addressing the elements that have failed to provide urban mobility in a comprehensive way that is non-polluting, comfortable, accessible, and provides coverage in all areas of human activity. A mass transit model that is fast, cheap and accessible everywhere within 0.5 km. The question we are asking is what would it take to have every major street in a city serviced by elevated trains.




The cTrain cheaper and more effective than other overhead transports because of the light weight and also the supporting structure design which make it least visually invasive on the urban landscape. The cTrain is supported by arches instead of  pillars and travels both above and bellow the  middle section of supporting arches. 

The arches are based on both sides of any  sidewalk that allows for a regular concrete light pole. By traveling always in the middle section of the supporting arch the cTrain is kept as far as possible from the built environment.

What actions do you propose?

A comprehensive solution for mass transit would need to meet the following  following essential requirements:

1.     Accessibility from within an acceptable walking distance.

2.     Frequency at a reasonable wait times.

3.     Speed at acceptable levels

4.     Comfort and privacy.

5.     Cost level acceptable to passenger and public expenditures.

6.     Emissions and noise free mass transit.

The cTrain can meet the above requirements which will be detailed further in the next sections.

Articles about the cTrain

Boston Globe, Wired, GOVTECH, etc

Linke to articles can be found here:

Overview of mass transit options

The paper will propose a design model that is believed to optimally meet the above goals which will be referred to as the six essentials features for comprehensive mass transit. Mass transit can be looked at from the perspective of three levels:

-        below ground level

-        at ground level and

-        above ground level 

Looking at mass transit in terms the three levels, underground transport is extremely expensive and takes years to build. Even in cities with high a density of stations the subway model presents shortcomings such as last-mile issues which is why taxis are in high demand in cities such as New York. Given the high, and most often prohibitive costs of building subways as a way to provide mass transit for all, it is reasonable to assume that underground transit is not likely to provide a comprehensive solution.

At ground level the barriers to a comprehensive solution are insurmountable given the limitations of available land. Moving large numbers of commuters at ground level, especially in dense areas facing traffic does not seem to be an option in meeting the six essential features needed for comprehensive mass transit.

Given that neither underground ground-level mass transit are likely to provide a comprehensive solution the only reasonable option left is above ground transit which will be referred to as elevated transport. 

Elevated Transport in the Past and Present

The main advantages of elevated transport are the fact that it is free from traffic limitations and is less expensive than underground transit. The disadvantages are the limitations of available space to be built in dense areas and the visual blight on the urban landscape, including darkening of the streets by the supporting structures for the tracks. Other disadvantages that resulted in their dismantling were the high level of noise and issues of hygiene. 


As a way to reduce visual blight the monorail presents a better alternative for elevated trains and even though it was introduced in the 1960’s it never became a widespread mode of transport. The images below show the Seattle monorail which was built in 1962 and the Mumbai monorail built in 2014. While monorails are bring significant improvements to the problems faced by elevated trains (less visual blight and noise) they are limited to areas that have sufficiently wide open space.

Personal Rapid Transit

Further progress in elevated transport has been made by using smaller vehicles on specially built guideways often referred to as Private Rapid Transit (PRT). The technology was introduced in the 70’s but never became a mode of transport to service urban environments and has been limited to areas such as airports and campuses. 

More advanced PRT models are being proposed and developed in the last few years such as at London Heathrow airport. Notably the title of an article reporting its implementation captures the history:  Fifty years on, it may be time for personal rapid transit  (RICHARD GILBERT, The Globe and Mail, Aug. 03, 2011). While this is a step forward this PRT model is limited to areas that have sufficiently open space, as are the other models, but to a lesser degree. 

One of the most advanced models to date in elevated mass transit is likely the SkyTran concept currently in testing stages of development. With its minimal height and width the SkyTran  brings progress in reducing visual blight on the urban landscape. However the hanging pods present challenges related to stability while the magnetically levitating technology is challenging and significantly more expensive than the model we are proposing. Given the need for large number of pods continuously moving over the streets the issue of visual blight continues to present a challenge. 

Proposed Elevated Mini cTrain (caterpillar train)

We propose a simpler model, a new mode of public transport, called the cTrain, to address the deficiencies of the existing public transport modes. To a large extent, it will ameliorate the problems related to last-mile access, comfort, cost and availability of public transport. In comparison with the SkyTran the cTrain model can be built on simpler technologies and at a significantly lower costs. In fact - with the exception of the software and electronics for automation - the cTrain can be built on technology as old as the advent of the electric motor.


The Catterpillar Train name comes from semblance of the cTrain to a caterpillar. 

Design principles

The cTrain concept is an automated mass transit mode of elevated light weight trains with seating room only. The cTrain is designed to minimize the visual impact on the urban landscape via the following features:

Minimal height of trains (via sitting room only)   +  Minimal width  m helps bring minimal weight and minimally visible supporting structures as well as Minimal thickness of tracks                                                     - travel both above and below the tracks

further reduces visual impact & allows the cTrain to be positioned furthest away from either side of the built environment.

At about 10 to12 seats placed in sequence (with two passengers per row), the cTrain has a low height and width for each vehicle to help minimize weight as well as visual impact on the urban landscape. The low weight of the trains also simplifies the size and cost of supporting structures as well as their visual impact. The trains are designed to move above as well as below the rails.

Compared to monorails or elevated trains the cTrain is about half the height and half the width which makes it far less visually invasive on the urban landscape.

The cTrain rails are held by arched supporting structures planted on the sidewalks designed to be no more visually invasive than an average concrete pole. Most of the weight of a cTrain is supported by the arches rather than the rails.  The thickness of the rails is a function of the distance between the supporting arches. Having at least one supporting arch at any time allows for relatively thin rails. The suggested design is for vertically oval rails at dimensions of (3x4 inches) though R&D will be needed to optimize the frequency of the arches and the thickness of the rails. Advancements in material science may allow for parts of the supporting structures to be built from transparent or semi-transparent materials to further reduce visual impact.


The cTrain is much smaller than monorails and designed to move both above and below the tracks and which are held by arches rather than crane-supporting structures. The crane-supporting structures do not fit well in the urban environment while the arches fit on nearly any street that has sidewalks that allow regular poles which hold the supporting arches. 




The suggested number of seats are 10 in tandem in an average urban environment. Each row is a private space for a single but with sufficient space for travel with a significant other. This feature is valuable especially in the West where there is a great premium on privacy. This allows for a comparable level of comfort to cars.

The concave design of the wheels allows for secure and stable rolling on the tracks. Additionally, each wheel will have at least one safety wheel running horizontally along grooves within the rails positioned to protect against derailment. The interior of the wheels has rubber covering. The rubber contact area of the wheels with the rails, combined with optimal shock absorbing systems will minimize audible noise which is expected to be less than the noise from an electric car on the street.    



The suggested design is for small electric motors on each axel – distributed at approximately one motor per passenger (in tandem); however the optimal number, size and placement of the electric motors subject to R&D, including considerations for placing the motors within the wheels versus on the axels. Electric cables may run along the rails – similar to trolley cables to power the motors. Each train will have batteries as a backup in case of power loss and also to mitigate the strain on the grid when accelerating as well as when regenerating power through braking. 

Quick and Easy Entry and Exit

In order to reduce the entry and exit time, the floor of the train is elevated above the platform of station. Given the height of the train floor above the station floor (shown by arrow) there is a reduction in the standing up and sitting down time and effort required for each passenger. The differential in height of vehicle platform versus ground level makes for easy access, similar to seating into, and getting out from, an SUV or a golf cart.  The image below is from test videos showing that for an older person it takes less than 3 seconds to exit or enter the vehicle. Given this preliminary test, with a maximum of 3 seconds required for entry and 3 seconds for exit, a stop is not expected to exceed 6 seconds, thus an average of 8 to 10 seconds stop time per station may be a reasonable assumption.


Wheelchair Access

Each cTrain will have access for a wheel chair in a dedicated area where the floor of the train is at level with the platform. Seat folds vertically to make space for wheelchair when needed.


All stations are designed with an elevator for wheelchair access. 

Easy Access to Available Seats

Given that all passengers have to be seated in a cTrain, there is a system to ensure smooth circulation for access to available seats without crowding and competing for seats. While entering a seat each passenger selects destination stop. This, combined with infrared or other technology that detects empty seats, provides passengers at upcoming stops with green light indicating where to stand for an open seat in the next cTrain. Passengers wait in a line similar to the customers in a bank waiting for the next teller light. 

Each cTrain has at least one section where two seats are facing each other to allow up to 4 people to sit together - couple with a child go to the area of designated for four seats and the green light indicating upcoming open seats. 



The capacity per train need not be high as the CTrain is designed to be built over every major street and avenue which will eliminate clustering. The image below shows a station an intersection at of two avenues with two lanes in each direction. Station is larger at intersections to accommodate passengers from both cTrain directions, otherwise a station is smaller if not at an intersection. The goal is to the cTrain service over every main street or avenue in a city so as to have sufficient coverage to have access from anywhere within a few blocks - in other words to have the equivalent of a "subway" stop at every major intersection.

Image below: design mechanism -  switch from travel above to below the tracks and vice-versa


Image below: "Vertical Depot" - based on principles in design mechanism for switching between travel on lower and upper tracks shown above.


Image below: intersection of upper tracks



Image below: intersection of lower tracks

Who will take these actions?

Given the interest we received so far the likely avenue will be for local governments to commission a test route for the cTrain.  We have had interest from a number of authorities asking to have the cTrain as part of their transit system and especially to provide coverage in underserved areas. The next phase is to develop a prototype either with business or academia, or a combination of both.

cTrain can provide an avenue for academic research to develop a prototype and make for interesting research projects in:

Civil engineering and Material Science - minimizing the visibility of the tracks and supporting structures; use of transparent materials to further reduce visual impact on the urnan landscape

Architecture - optimal design of the stations to blend with the urban environment

Mechanical - switch mechanism and process of cTrain traveling above the tracks to below the tracks

Electrical - Optimization of size, placement etc of electric motors; as well as of batteries to serve both as backups and minimizing the strain on the grid

Computer Science - developing algorithms for decisions of self driving trains for speed, number of trains to leave or return to depot, etc.

This project may be of historical relevance, in the sense that it can produce the blueprint for a mass transit model to be run entirely on renewable energy while providing coverage anywhere within a few blocks from residential places or businesses - a possible model as a global standard in the way cars and roads are manufactured an implemented worldwide.

Where will these actions be taken?

With a proof of concept in place  private companies will be commissioned by local governments to build "sample" routes and later the city and state gov. can create a charter company with a mandate to provide access in all areas at say maximum 0.5 mile distance from any building. The standard would be akin to standards requiring access to water, electricity etc. 

Any large city in the world is a good candidate for the cTrain. Though the desperation being greater in China and India for clean and efficient mass transit makes them primary candidates. Airports also make for ideal candidates as the cTrain can be built to go through terminals moving large numbers of passengers to their connections and to and from the city.

Adopting the cTrain model on a complete scale - i.e. to replace all existing modes of mass transit - provides a long list of benefits.

Replacing existing bus and train depots with the "vertical depots" represented by the blue structure in the figure below opens the land, (taken by the current depot represented by the yellow line) for commercial or residential development. Vertical Depot placement (blue structure) versus current mode of ground level depot (area marked by yellow line); example in Boston area (Brookline, Cleveland Circle Station, Massachusetts) 

Most metropolitan areas in the US have commuter rails connecting the suburbs to the downtown area. Commuter rails currently take up large amounts of valuable land. Image below shows commuter rail line in the Boston area (Cambridge, Massachussets). Green arrows show current cummuter train tracks. Blue line is a suggested replacement of the commuter rail with cTrains which could free up vast amounts of land for other uses.

How much will emissions be reduced or sequestered vs. business as usual levels?

The cTrain runs on small electric motors that can be fed from renewable energy sources. Given the light weight of each cTrain the energy required per passenger is far lower than any existing mode of mass transit. With the models we evaluated there is reason to believe that that the cTrain can be powered entirely on renewable energy.


What are other key benefits?

A comprehensive solution for mass transit - complete coverage at a lower cost than all modes to date

1.     Accessibility from within an acceptable walking distance.

2.     Frequency at a reasonable wait times.

3.     Speed at acceptable levels

4.     Comfort and privacy.

5.     Cost level acceptable to passenger.

6.     Emissions and noise free mass transit.

Further/exponential benefits:

Improved worker productivity –less stress, less time wasted in traffic less financial strain from car costs etc.

Greater, equity and employment– improved service to and from underserved areas would help both employers and workers and reduce poverty.

Improved health – lower pollution, fewer accidents, less aggravation from traffic

Improved freight transportation efficiency - fewer cars on the roads during rush hours

Lower public roads expenditures - on road repairs and and mass transit

Climate Change Mitigation

Higher revenues to local and state governments - from capitalizing one newly available land and buildings

What are the proposal’s costs?

At the present time we can only extrapolate the costs. Assuming that a supporting structure (typically an arch holding the tracks) will be needed at every 20 meters it would come to 50 arches per kilometer.

The cost of installing a light pole in one example is $3,500 (includes construction by an electrical contractor along with the City's design, inspection and processing).

We will assume from this that the cost of each supporting structure would at $10,000 x 50 per kilometer = $500k/km


Tracks resemble oval pipes and measure 4 inches vertically by 3 inches horizontally. Cost of tracks $500 per 20 meters at 50 per km = $500k/km

The cost of the stations - placed at every km estimated at $500,000 per km including the cost of elevators (the cost of a wheelchair accessible elevator in public transport is about $80k).

The electronic controls for automatic drivers including all the software and hardware estimated at $100,000/km including command and control centers for monitoring.

Each cTrain runs on electric motors and requires fewer parts and less material than an average car. Therefore we assume that it should not cost more than $50,000 per cTrain and we account for two cTrains (two directions) per kilometer.

NOTE: extrapolated numbers are based on post R&D costs and assuming construction of the cTrain over thousands of miles to benefit from economies of scale.

While the above numbers seem minuscule relative to typical costs of traditional mass transit (including monorails) there is a strong argument for the extrapolated numbers shown above. In other words concrete poles to support the arches are not any different than similar concrete poles used today. The elevators for wheelchair access at each station are not any different than similar elevators etc. 

The interesting lesson from the cTrain  is that even if the cost is many times greater than what is estimated above, the model still provides an effective solution for comprehensive mass transit.

Time line

2 years - full scale working prototype

5-15 years - a number of cities adopt the cTrain model as a comprehensive solution to mass transit and a tool against poverty and climate change. Having replaced all subways and trains cities benefit from sale/rental of land and subway stations.While running the entire system at less than a tenth of the cost needed for the old mass transit modes the coverage is extended to all areas where there is a road where people need access.

15-50 years - by the end of the period the Ctrain (or other form of elevated mass transit) is part of a global convention as a human right and as an obligation to combat global warming.

Related proposals

Other elevated mass transit models have failed to provide a comprehensive solution because of greater visual blight than the cTrain, or requiring more space to be implemented.

The most advanced model in elevated mass transit is the SkyTran:

The SkyTran requires complex maglev technologies which would be limited to capabilities available only to highly specialized companies. 

In comparison with the SkyTran the cTrain model can be built on simpler technologies and at a significantly lower costs. In fact - with the exception of the software and electronics for automation - the cTrain can be built on technology as old as the advent of the electric motor.



Last mile issues are one of the main reasons for mass transit failures researched by Dr. Ashwani Kumar.

Dr. Ashwani Kumar, PhD in Transportation from MIT will be presenting the cTrain at 14th World Conference on Transport Research - 10-15 July 2016 | Shanghai, China.

Articles and papers at: 



Capacity of the cTrain model

The capacity per train need not be high as the C-Train is designed to be built over every major street and avenue which will eliminate clustering. It appears that the optimal design is for each train to have 10-12 seats in sequence accommodating 1 passenger per seat (however each seat has enough space to accommodate parent with child or a couple traveling together).

The C-Train would have a frequency of 10 passengers every 10 seconds i.e. 3600 people per hour per direction. Providing this model on all the areas intensively (with many lines entering the city Centre) will not only obviate the need for buses, trains and subways in a city but can also wean away many commuters from cars.


Elevated mass transit holds the solution for a comprehensive cure to the ills stemming from the shortcomings of mass transit since the early days of the first streetcars and buses. The cTrain model contains a number of features that eliminate or sufficiently reduce the impediments that have to date stopped elevated transit from providing a comprehensive solution to public transport.




Evans, Gary W., and Richard E. Wener. "Crowding and personal space invasion on the train: Please don’t make me sit in the middle." Journal of Environmental Psychology 27, no. 1 (2007): 90-94.

Wener, Richard E., Gary W. Evans, Donald Phillips, and Natasha Nadler. "Running for the 7: 45: The effects of public transit improvements on commuter stress." Transportation 30, no. 2 (2003): 203-220