Radio New Zealand reports that an international consultant is urging Wellington to consider introducing trackless trams, as a way of easing the capital’s congestion. How well do the consultant’s claims stack up?
1. They can carry 300 people. Really? Canberra’s light rail vehicles are a metre longer and the same width, with a stated capacity of 250 people at 4 standing passengers / m2. Has the consultant actually seen a trackless tram with 300 people on it? At 250 passengers per vehicle, an on-street trackless tram system has a maximum carrying capacity of 5000 passengers / hour. An on-street light rail system has a maximum carrying capacity of about twice this: 10,000 passengers / hour.
2. They cost as little as a tenth of the price of light rail. Presumably in large part because “you just paint the lines on the road.” There are 3 main reasons light rail systems have a prepared road bed and rails:
- the road bed is zero maintenance for at least 25 years, so there is no disruption to service for road repairs
- underground utilities can be relocated, so there is no disruption to service because of utility line faults
- a high quality road bed with rails on sleepers delivers a high quality ride without damaging the road bed
Trackless trams on Wellington’s low quality roads would deliver a low quality ride, while requiring regular road repairs. Supposedly that’s not a problem, because …
3. The vehicle can deviate around obstacles on the track. In real-world transit operations, this is a bug, not a feature. If we look at cities overseas with on-street light rail, obstacles on the track very rarely disrupt service. So the trackless tram solves a non-existent problem. But having a vehicle that can leave the tracks tells every other vehicle on the road that it’s OK to park in the tram lane, because the tram can drive around you. If in doubt, see any bus lane in Wellington. Perhaps the real reason is trackless trams have to be able to navigate around road works, to repair damage the vehicles have caused or to get at underground utilities. When the trackless tram leaves its dedicated lane and mixes with other traffic, the service becomes less reliable.
4. They can be configured to run without a driver. This is a game-changer and a great feature. It breaks the tyranny of frequency, because you can afford to run a very high frequency service at very low marginal cost. However, I suspect the current state of the art is that you can have autonomous operation or the ability to navigate around any obstacle on the track, but not both.
5. Trackless trams would be perfect for Wellington. Would they? The practical limit for on-street operation is about 20 trackless trams per hour, giving a capacity of about 5000 passengers per hour in each direction. Using GW’s ridership figures and growth projections, if a trackless tram line opens on the railway station to airport corridor in 2025, it will be at capacity by 2030. What is the upgrade plan? Would we have to replace it with higher-capacity light rail and if so, how would we carry out the upgrade? To increase the frequency to 30 or more trackless trams per hour would require grade separation along large parts of the line, which would cost at least as much as building light rail in the first place.
Wellington would be wise to let somewhere else be the pioneer for trackless trams. I fear the reality is that you can have light rail quality of service or you can spend a tenth the cost of light rail, but not both. For reliable, frequent, high capacity rapid transit, light rail still looks like the best option for Wellington’s station to airport corridor.