Wikipedia
MonoMetro is a transportation planning company formed in 1997 to promote a new design of suspended narrow-gauge monorails, with Y-shaped pillars. Its main activity has been to promote this as an answer to London's congestion problems, but interest has also been shown in the system by other cities. MonoMetro claims its system would be cheaper to introduce than a tram as it would not be necessary to divert or strengthen sewers along its route and that it is also superior to monorail systems.
The system infrastructure costs calculated on mean fabricated tonnage of steel and construction quantities reference a twin track system with a parallel platform station located every 750 metres. Costs including planning, required Acts of Parliament, professional and tendering costs, electrical supply costs and street diversion costs for central London implementation were estimated at £15 million per kilometre (2005 estimate). Costs outside London must be based on approx 1000 tonnes of fabricated steel per km plus the local cost of planning etc. By comparison to tramway implementation MonoMetro costs around 60% of the cost of building a tramway. The difference however is that MonoMetro is a mass transit system offering 20,000 passengers an hour capacity, trams offer 3000 - 7000 passengers an hour capacity.