Make Good Bus Routes Great

How do we make public transport in Christchurch better? We have several good bus routes in Christchurch that have OK frequencies, some level of bus priority and not terrible infrastructure. I think we need to focus on these routes to get them from just good, to really great. But I’ve been hearing more and more conversations lately that contradict this and so I thought I’d jot down why this is what we should be doing.

In a city like Christchurch, where it’s relatively easy to drive, most trips take longer if you choose to make them on a bus compared to if you drive. And most people in Christchurch have the option of driving, we have one of the highest rates of car ownership in the world. If the same trip takes 51 minutes on a bus or 11 minutes in a car, the vast majority of people will choose the car. For example, this trip from Hornby to Ilam.

However there are some trips where taking the bus is comparable or even faster than driving. This occurs in places that have bus lanes, high frequencies, and traffic congestion. For example Halswell to the city in rush hour.

The graph below shows an equation transport planners use when trying to predict people’s choice of travel mode. It has been derived from observations of real-life behaviour in Christchurch. The horizontal axis shows the relative attractiveness of taking a trip on public transport compared to driving. For most trips the relative attractiveness is negative, meaning that driving is more attractive than catching the bus. “Attractiveness” is a number that’s calculated from a range of factors, but the most important one is the door-to-door travel time. For the rest of this blog just think “travel time” whenever I say “attractiveness”. The vertical axis shows the proportion of people who will choose to make that trip on public transport.

The graph shows that if, for a specific trip, catching the bus is much less attractive than driving, then hardly anyone will catch the bus. An example of this would be the Hornby to Ilam trip above.

For a trip where catching the bus is more attractive relative to driving, then more people tend to catch it.

At the point where driving and bussing are a similar level of attractiveness (zero on the horizontal axis), then we observe about 15% of people will catch the bus. An example of this would be the Halswell to city trip above.

As the bus gets more attractive than driving then this ramps up to 30% and higher.

Note that the slope of the line gets steeper as you go further right. If you improve the bus from being massively less attractive than driving to being just moderately less attractive, you’re still going to find that not many people catch it (left-hand red arrow below).

Whereas if you can find a trip where buses are only slightly less attractive than driving, and improve the buses so that they flip over to being more attractive than driving, you’ll find that you get a big increase in the proportion of people choosing to catch it (right-hand red arrow).

The implication for Christchurch is that we should look at the parts of the city where bus provision is already relatively good, like Halswell, Riccarton, Papanui, and Linwood, and try to amp up the public service offering there so that it flips to being more attractive to bus than drive. If we can do that then we’ll see a big uplift in usage.

And we shouldn’t spend too much of our energy on the places with poor or no provision, like Redwood, Bromley and Sockburn. Investing a whole lot of money in those areas to get public transport from being terrible to merely mediocre – that will not attract people in any meaningful volumes.

Investing more into the areas where public transport is already good, and investing less in the areas where it is worst, might seem counterintuitive and somewhat unfair. It really depends on what outcomes you are looking for. Jarret Walker has written extensively on the trade-off between coverage and patronage.

Personally I feel Christchurch’s bigger failure is on the patronage side and that is where we more urgently need to up our game. To do that we need to collectively accept this principle, forget about creating more mediocre services, and focus our efforts on making our good bus routes great. The only reason to not do this is if coverage (and equity) concerns are more important to you than patronage. That’s a legitimate position to hold, but if that’s your position you need to be honest about it and accept that means investing money in something that won’t increase patronage meaningfully.

Too-Long-Didn’t-Read: If increasing public transport use is our goal (and I think it should be), then we should be focussing our energy into making our good bus routes great, not our terrible bus routes mediocre.

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