by John Rankin
Wellington’s public transport through the CBD needs four lanes — two for buses and two for rapid transit, of which the most cost-effective option is probably light rail.
For light rail to be most effective, it needs a dedicated right of way with priority over other traffic at intersections. Any sections with shared rights of way will potentially lower the quality of service (making it less reliable) and need to be avoided where possible. In Wellington this will be hard in places, but we should still try.
The international data shows that light rail is more cost effective than buses when the ridership exceeds about 3000 people per hour. The Golden Mile currently carries 6000 people per hour during the peaks. Not all bus trips would be suitable for replacement by light rail, but 4000 on light rail and 2000 on buses should be readily achievable, comfortably above the 3000 people per hour threshold.
The WCC predicts the population of Wellington city will grow by at least 50,000 people over the next 25 years. Even if we assume no mode shift from cars to light rail on the corridor from the station to the airport, that’s still 5000 light rail trips per hour (25% growth). This is why there are many cities in France and other countries, the same size as Wellington or smaller, with successful light rail systems. And while Wellington has good public transport ridership in comparison with other Australasian cities, the evidence from comparable Canadian cities is that we could aim to double the ridership per capita, as people choose to mode-shift from cars to light rail.
There is a rule of thumb that when you have more than about 75 buses per hour on a corridor, light rail is a cost-effective alternative. Wellington currently peaks at about 140 buses per hour on the Golden Mile. Auckland is justifying light rail on Dominion Road in part on the basis that there are 130 buses per hour.
We do need to make sure that light rail is affordable. To do this we can ask two questions: How does the cost of light rail from the airport to the railway station compare to the cost of extending the motorway from the Terrace Tunnel to the airport? And which will deliver a congestion-free journey – light rail or a motorway?
The best advice I have ever read for cities contemplating their first light rail line is from Jane Jacobs:
“Fixed transit routes [are] expensive failures when they [are] not preceded by evidence of sufficient demand…. Choose to locate rail routes by observing which bus routes are most heavily used…. [Otherwise], they don’t have enough passengers.”
The high capital cost of light rail, relative to buses, means light rail is best value on a high-demand corridor, operating at a high frequency, all day every day, on a dedicated right of way — if a city compromises any of these (for example, targeting peak hour travel only), the benefit-cost ratio reduces
On high volume corridors, the operating cost of light rail per passenger is significantly lower than that for buses, because one driver is carrying about 6 times as many people (and it’s possible that by the time Wellington builds light rail, autonomous in-street light rail will be commonplace, further reducing operating costs).
Opportunity is the mother of invention and LGWM is a once-in-a-generation opportunity, so let’s take it.
[Parts of this article were first published by Wellington.Scoop as a comment on Sunday.)