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Trams without rails

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The world’s cities are getting bigger. Between 2016 and 2030, the planet’s urban population is forecast to grow from 54 to 60 per cent of the world’s total. Over these years, the number of cities with one million inhabitants is expected to increase from 512 to 662.

As a result, there is an increasing demand for urban metro systems, particularly in the Middle East, India and China where, in 2015, and at an estimated total cost of £15 billion, around forty metro systems opened or were under construction.

Although this would seem to be good news for the rail supply industry, developments in autonomous vehicle technology indicate that urban transit systems without rails may be more cost effective.

Zhuzhou’s ART

In October, Zhuzhou in central China’s Hunan province saw the first test run of an Autonomous Rapid Transit (ART) system developed by the CRRC Zhuzhou Locomotive Company. The ART has been described as a cross between a bus, tram and train.

It is an autonomous vehicle that runs on rubber tyres on the road network with a dual redundant multi-axle steering system. Its route is marked by double-dashed white lines that are followed by sensors which also detect any obstructions. However, at its early prototype stage, the ART has a driver who is given warnings if it deviates from its route.

The ART is a modular unit of three, four or five cars. The three-car unit is 32 metres long, has a maximum speed of 70km/h and can carry up to 300 passengers. It is powered by lithium-titanate batteries that can run for 25 kilometres on a 10-minute charge and 40 kilometres on a full charge.

It has successfully undertaken 24 hours of non-stop tests and is to start passenger service next year on a three-kilometre route with four stations. A further nine-kilometre route is planned. CRRC claims that the system costs a fifth of a traditional tram system and so will save 120 million yuan (£14 million) per route-kilometre.

The ART has been nominated for an award in the “Beazley designs of the year”, which is the subject of an exhibition at London’s Design Museum.

Cambridge’s AVRT

In Cambridge, a university study has developed the concept of an affordable very rapid transit (AVRT) system for the city.

Current metro systems cost around £20 million per kilometre, or around a billion pounds for a 50-kilometre network. Only large cities can generate the 5-10,000 passengers per hour needed to justify such schemes. Moreover, such projects are highly disruptive and may be unacceptable in a city such as Cambridge, with its multitude of ancient buildings.

The study considers that a 55-km Cambridge mass transit network would generate around 2,500 passengers per hour and so, to be viable, would need to be provided at half the cost of a conventional metro. To do so, the AVRT proposal reduces infrastructure costs by eliminating overhead power supplies and rails, decreasing vehicle cross-section to minimise tunnelling costs and replacing conventional signalling with a simplified concept of operations.

The proposed AVRT vehicle would operate in both directions at 120km/h, weigh 16 tonnes and have eight 150kW electric motors powered by a 200kWh hour battery. With 2+1 seating, it would seat 40 passengers and be 16 metres long, 2.2 metres wide and 2.5 metres high. In a 3.7-metre diameter tunnel, this is 43 per cent of the cross section, which enables the vehicle to achieve the required running speed.

The operational concept is for each leg of the system to have a shuttle service on its single trackway. To provide a service frequency of three to four minutes, each leg would require four vehicles, one running on the trackway, one waiting to depart with the other two charging their batteries whilst loading or unloading.

This arrangement gives each vehicle 12 minutes to charge its batteries whilst stopped at the interchange. An electric token system would ensure that only one vehicle was on the trackway at any one time.

Each leg of the system would be a simple tarmac-surfaced trackway without any intermediate stations. The outer extra-urban legs would be around ten kilometres long and, as far as possible, be at surface level. Urban legs of around five kilometres would run in 3.7-metre diameter tunnels. Interchanges would be up to four-way, with a footprint designed for optimum footfall to ensure passengers could move easily between each leg’s docking area. Except for the city centre station, interchanges would be built on the surface.

One disadvantage of this concept is that it does not provide through journeys. However, the experience of systems such as London Transport is that passengers are willing to change if there is a frequent service and easy interchange.

For such a system to be viable, it must attract a substantial percentage of the estimated 40,000 drivers, who commute into Cambridge by car, to the park and ride stations at the end of its outer-urban legs for the last ten kilometres or so of their journey. To do so, the system has to offer a substantial reduction in journey time over this distance and a service frequency that does not require drivers to worry about a timetable.

The AVRT concept both satisfies this requirement and, with its use of autonomous vehicles, is likely to cover its running costs without public subsidy.

Will it catch on?

Whether the ART or AVRT concepts will be widely adopted remains to be seen. However, it is certainly true that they offer urban mobility at substantially less cost than conventional metros.

The United Nations predicts that, between now and 2030, the number of medium size cities (500,000 to one million) will increase from 551 to 731. It is these cities that need the affordable public transport systems offered by new and future technologies.

Read more: Crossrail 1.5?