by Kerry Wood
Not a wish but a prediction: Wellington’s public transport spine will be light rail. The Regional Council’s Transport Committee has approved Bus Rapid Transit, mayoral hopefuls have stomped all over light rail, so what is there to say? In a word: capacity.
Bus Rapid Transit, BRT, comes in three sizes: huge, large and small. Route capacities are up to around 100 000, 30 000 and 3000 passengers an hour, each way. The Regional Council wants small-BRT and bendy-buses. That will give about half the passenger capacity of the existing central-city buses, about 3000 passengers an hour. It already looks risky.
Brisbane has large-BRT, carrying over 20 000 passengers an hour, twice as many as expected when it opened. The stops are twice the width of Manners Mall (because the buses need overtaking lanes), and it crosses almost all existing roads on bridges or in tunnels. It is too big for Wellington.
Small-BRT is used in Europe more than Asia or the Americas because European cities rarely have the space for large-BRT. And central Wellington is like a European city. Small-BRT goes through city junctions like an ordinary bus route. It needs traffic-signal priority for quality timekeeping, but a high priority uses up green-time at junctions. Traffic signal priority for too many small-BRT buses causes congestion for other vehicles.
Small-BRT doesn’t work if there are too many buses. A table of selected European systems shows peak-hour services of only 8–18 buses an hour, or say 1500 passengers an hour. The city of Nantes, in France, started with 15 buses an hour, increased that to 17 because of crowding but is unlikely to go higher: more capacity will come from longer buses.
The Regional Council proposes 32 buses an hour on Lambton Quay, plus another 21 local buses an hour on the same lane. Those local buses will have to go. They could run on the secondary spine on Featherston Street and the Waterfront.
Sixteen small-BRT bendy-buses an hour are to run down Adelaide Road in the morning peak, and join another 16 buses an hour from the Mount Victoria Tunnel. But the buses in the tunnel are already overloaded when the service opens: 101% of capacity. (All this is from Tables 6, 7 and 31 of the Evaluation Report, and Table 7.4 of the Modelling Report. Both are available on the Regional Council website).
Inconsistencies between the tables make for uncertain passenger numbers. Totals in 2031 might be 2500, 2600 or 3600 an hour. Overloading might be worse than it looks.
The Regional Council is not expecting any new passengers — or so the model says. However, experience shows that quality public transport is alway well-used. Trams in the UK have averaged about 5% annual patronage growth, the Brisbane Busway 8% city-wide, Auckland’s Britomart Interchange 16%. Wellington ought to plan for 5%?
A five percent growth rate would need 50 buses an hour on Lambton Quay by 2031. It would push small-BRT to the limit or beyond, within ten years.
Obviously, there is room for more buses. If the Golden Mile can handle 120 buses an hour in the 2010s it can do it in the 2030s. But look out for unreliable services, ‘cascading delays’ and long ‘platoons’ of buses waiting traffic signals. This is the problem that small-BRT was to solve.
If small-BRT runs out of capacity the options are bleak, with capacity falling dramatically:
– Turn off traffic-signal priority.
– Find bigger buses, if possible.
– Take out bus seats: two seats occupy standing space for four.
– Find another route (not the secondary spine: that’s already needed for local buses).
The capacity of light rail might suddenly look interesting. It is about three or four times higher than small-BRT.
Light rail isn’t as costly as it looks. Take out two unnecessary tunnels, three unnecessary route-kilometres of track and the four trams that were going to run on them, and you get a much more sensible-looking figure.
The problem with light rail is that the first line in a new city takes about ten years–not something to find out after small-BRT has failed.
Kerry Wood is a retired engineer with a long-standing interest in transport matters.