Madam, - It seems incredible that a public transport agency would use a "mix and match" approach to measuring passenger capacity. But in his article of February 13th, James Manning of the Railway Procurement Agency did just that.
The RPA compares tram and bus carrying capacities, but employs two different yardsticks. Allowing for the difference between the Tallaght and Sandyford lines, the RPA states "there will be capacity for between 2,800 and 3,700 passengers" per hour on the trams. This is contrasted with buses, where the "number of passengers past a single busiest point is actually 2,500".
But for Luas trams, every vehicle is assumed to be full, in other words at its design capacity, while for buses, a count of passengers who use a given service is taken - in other words, average occupancy.
For example, the design capacity of 10 large cars queuing at traffic lights will be 50, or five per car. Taking average occupancy, the same line of cars will carry only 11 people because average car occupancy is 1.1, according to travel-to-work census data.
Dublin Bus records an average occupancy of 53 per bus for QBC and non-QBC services entering the canal zone between 7 a.m. and 10 a.m. Multiplying 55 by 45 gives approximately 2,500.
Choosing one yardstick, design capacity, and staying with it, gives 4,410 passengers per hour for QBC. This is at a vehicle design capacity of 98 per bus, the figure provided in my article of February 2nd.
For a double-decker bus, the RPA contends 88 is a more accurate figure, while the capacity claimed for a Line A tram is 235. The figure I used was 207, the source for which is an e-mail from Frank Allen, chief executive of the RPA, on October 10th last.
How do the various figures work out in terms of space per passenger? A Line A tram is 2.4 metres wide and the length of its passenger area is 26 metres, after allowing for the driver's compartments, giving it a floor area of 62 square metres. A double-decker bus has a floor area of 50 square metres.
Based on my figures, there will be two passengers per square metre on the bus and 3.3 passengers per square metre on the tram. The figures given by the RPA work out as follows: 1.8 passengers per square metre on the bus and 3.8 passengers per square metre on the tram. - Yours, etc.,
JAMES NIX, Dublin Institute of Technology, Aungier Street, Dublin 2.