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The capacity of a single tram vehicle is limited by its size, which must be kept within reasonable bounds and legal limits. To take advantage of the extra revenue to be made during busy periods, but without the need for extra vehicles and crews, the standing capacity of a tram is often double that of its seating capacity and that contributes greatly to its revenue-earning ability. In addition, it is usual to increase the carrying capacity of a single unit by one of several other methods.

1) A trailer (or several) can be attached to the rear of the powered vehicle.
This is cheap and can easily be detached when it is not needed, economising in power and wear-and-tear. It slows down the service and imposes extra load on the towing vehicle and it will usually necessitate the employment of a second conductor. In the distant past, the safety record of trams with trailers cast doubt on their use.
If low floor access is necessary to all sections, considerable trackside works will be required at all stops so as to align with the multiplicity of doors.

2) A powered trailer, in effect another tram, linked to the controls of the parent vehicle.
This does not slow the service but suffers from all the other defects of 1) above. It may not be as easy to uncouple as an unpowered trailer but may be used as a vehicle in its own right when required.

3) Make a multiple vehicle as a long articulated unit with through access.
This allows the use of a single conductor if the passenger load is not too great, but does not allow any reduction in vehicle size during off-peak periods. Similar access problems to 1) above, as people with impaired mobility might have to traverse the length of the vehicle to leave by the only door with level access unless long trackside platforms are provided.

Picture of long tram-stop platform at Sheffield [65kb]

Many currently-available articulated trams do not have all wheels driven, especially some low-floored types where there is insufficient room for the motors. These could not be used in Bath because they would have insufficient traction to cope with the hills.

4) Use a double-decked vehicle.
This may be ruled out on certain routes by external factors such as low bridges.
The Oldfield Park route might only be accessible to single-decked vehicles as it passes under a railway bridge with 4 metres headroom, so a mixed fleet of double and single-deckers will probably be the best option for Bath.

A double-decked design with a large, low floor central foyer (Foyer of modern single-decked articulated tram)could include provision for wheelchairs, bicycles and luggage and a sufficient number of seats which should be given-up to mobility-impaired passenger upon request. Able-bodied passengers would have no difficulty using the top deck and many people prefer to ride on top. There is greater tourist potential in such a vehicle, although there are objections to private property being overlooked in this manner.
The single central doorway could be wide enough to allow sufficiently rapid loading and unloading to cope with the service needs of Bath; this would only require a short length of raised footpath at each stop.

Pictures of ramped footpath and modern tram doorway (Caution 300k file)
More on tram stops ?

The depot area required by double-decked vehicles is about half that required by single-decked ones and the road space occupied by each vehicle would be similarly reduced, allowing greater freedom in the choice of stopping places and enabling more stops to be provided if required.
The Continental practice of placing all the electrical control gear on the roof would compromise stability, so reversion should be made to the British practice of placing it under the floor or under the staircases. The wheel loading is greater for a double-decked vehicle although with good quality modern trackwork, this should make little difference.
The possibility of vandals resorting to the top deck in order to practice destructive or anti-social habits unobserved, could be discouraged by the standard security measures which might nowadays prove necessary anywhere.

Alarm panels on modern trams

More about the trams proposed for Bath ?

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