Sustainability is difficult to define, more difficult to assess and even more difficult to achieve.
To assess sustainability, the effect of every part of the process needs to be fully considered - not just in direct terms, but with due regard for the consequences in the long term; and in other areas than the one directly under consideration.
Another important consideration, particulaly when looking at transport systems, is an assessment of the effectiveness of the system in achieveing its objective. A low environmental cost system which achieves nothing useful is just a waste of resources.
The total environmental cost per year of a public transport system is made up from the following factors:
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Lifetime in years |
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Years between refurbishments |
The electric tramway is almost certainly the most sustainable form of motorised transport available. The vehicles and track are made from readily available materials, with very little use of scarce resources. Most of these materials are recyclable with very little trouble.
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| The materials use in the construction of the coachwork of trams are very similar to those used in buses and are used in similar quantities. The running gear is much simpler than that of a bus and much longer-lived, fewer scarce materials are use in manufacture. | Unlike a road, the track does not require periodic resurfacing with petrochemical materials. The high energy cost of steel manufacture for the rails is offset by their very long lifetime and total recyclability when scrapped. |
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| The materials used in the bodywork of trams are fully recyclable. The running gear is so long-lived that it is often not recycled at all but is cannibalised and used to construct 'new' trams. This is even more environmentally friendly than recycling. | The steel rails are fully recyclable at the end of their long life. Other components of the track bed can be crushed and used as aggregates (which reduces the need for quarrying).The polyurethane mastic used in some resilient-mounted rail systems has a very long life but, as yet, it is not recyclable and must not be disposed-of by burning. However, it is inert and presents no actual disposal hazard. |
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| The 'fuel' of trams is electricity from the National Grid. This opens up the possibility of sustainable energy sources being used whenever they are available, without the need for adaptation of the vehicles. There are no fumes released at the point of use. All vehicles use lubricants, however the high temperatures of combustion engines are absent from trams so they do not require frequent oil changes and the used oil is not contaminated with combustion products, so it is easy to recycle | Unlike a road surface, the track suffers very little wear. A certain amount of maintenance is necessary but it consumes relatively little energy or materials. |
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| The operating life of a well-designed tram is in the region of 30 - 50 years. A mid-term refit is usually necessary and this will inevitably produce a quantity of waste and will use some resources and energy. The cost, however, is nothing like as much as the costs which would be involved in, for instance, scrapping and replacing a bus at least three times during that same period. | Heavily-used
track may occasionally need to be replaced before its usual 50-year
life has expired. However, it is much more likely that the wear
will be confined to certain sections and components which are
designed to be easily replaceable. The energy involved is minimal
and the worn components are recyclable. This is in contrast to a road where, although a certain amount of patching is permissible, usually the entire surface must be scraped-off and replaced. Environmentally expensive petrochemicals and large energy inputs are needed and the waste is difficult to reprocess economically. |
As well as being sustainable in term of materials, the tram also fulfills the other major requirement of a sustainable transport system - it is effective. Trams have a proven record for getting motorists out of their cars and onto public transport.
In Manchester, during a period when traffic has increased by 10% on most major routes, there has been a decrease of 10% on routes where the tram is available as an alternative.
The tram will only work in this way if it offers the motorist a genuine alternative - to be effective in Bath, the tramway will need to be laid out as a network, not as an inaccessible corridor.