Compared to what? (transport chaos edition)

A while back, it looked as though the negotiations between NZ Bus and its drivers would break down and we would have bus strikes in Auckland. I considered various contingency plans: working from home for all or part of  a day, taking a train to Newmarket or Britomart and walking to the University, cycling, or catching a ride with a colleague who lives nearby. Some of these were options because we would have a week or so of warning before the strike.

If public transport in Auckland became permanently bad — if it went back to its state 20 years ago — I would have different options. I probably wouldn’t live in a house in Onehunga; I’d live in an apartment near the city centre. Moving to the city centre wouldn’t be a sensible response to a single day’s stoppage, but it would be sensible if the lack of buses was permanent.

Transport Blog has a post about the congestion benefits of the Wellington rail system, based on the week in June 2013 that it was taken out by a storm. On weekdays during this period, about 4000 people who would normally take the train into Wellington couldn’t. The roads became much more congested, and these delays can be valued (using plausible-looking assumptions) as worth over $5 million. Scaling this up to a full working year, the benefit to drivers in reduced driving time is worth rather a lot more than the public subsidy to the entire Wellington public transit system.

There’s a problem with simply scaling up the costs. If the Hutt Valley train line didn’t exist, some of those 4000 people would either live somewhere else or work somewhere else. Driving for an extra two hours each way was a rational response by them to a short-term outage, but in the long term they would reorganise their lives to not do it.

Now, there’s obviously a cost to moving from the Hutt to Wellington for these people — otherwise they’d be living in Wellington already — but the cost is less than would be estimated from the travel time during the outage. It’s hard to tell how much less without a lot more data and modelling.

On the other hand, while the storm data almost certainly overestimate the congestion-cost benefits of the train line, the magnitude of the estimated benefit is so large that the conclusion could quite easily hold even with better estimates.