It's a "no-brainer", right? Muenster Germany 1991

Something I hear way too often in discussions about cities is the phrase: “it’s a no-brainer”. It’s jarring because I’ve seldom come across an issue where the explanation is so obvious it can be taken 100% on faith.

Most times the phrase refers to a statement that simply accords with the speaker’s existing biases. The reptile part of our brains is eager to make sense of new information by filing it against existing summary narratives, often stored away long ago.

So when a politician claims, for example, that she’ll eliminate traffic congestion by building a new freeway, most of the population believe her. Doubling road capacity must get rid of congestion; it’s a “no-brainer”!

The propensity to slip concepts uncritically into an existing mental framework isn’t restricted to the roads lobby. Consider the first exhibit; it’s a famous photograph staged in Muenster Germany in 1991 comparing “the space required to transport 60 people” by car, bus and bicycle.

Here’s another more recent (animated) one, as well as a version done in Canberra. There are now many versions done in various cities around the world, usually to the same formula as the original.

The comparison seems to make sense. Any time a large number of people are travelling to the same destination there is enormous scope for economies.

On a per-traveller basis, public (i.e. shared) transport like a bus or train requires smaller infrastructure, uses less energy, and emits less pollution and emissions than cars require to transport the same number of travellers to a common destination.

It seems obvious that cars are the bad guy here. But these sorts of exhibits don’t provide a sensible or useful comparison. The key shortcoming is the creators assume the bus is full while the cars have no occupants other than the driver, or they have an average occupancy of around 1.1 i.e. the driver plus 0.1 passengers. (1)

But the only circumstances where these assumptions usually apply in Australian cities is when two conditions are met. First, where the journeys are made in peak hour between home and work; and second, where the jobs of those commuters are located in or close to the CBD.

Travellers already understand that cars aren’t a good choice when these particular conditions apply. For example, only around 18% of workers in Sydney’s CBD drive to work. The corresponding figure for Melbourne is around 26%. In contrast, public transport’s share of all trips in these cities is only 10%-12%.

But these conditions aren’t typical of most travel in Australia’s cities. Only around a fifth of all trips in cities like Sydney and Melbourne are journeys to work.

Moreover, only a relatively small proportion of work trips are to the CBD. In Melbourne, for example, only about 15% of all jobs in the metropolitan area are located in the CBD (defined to include Docklands, Southbank and Carlton).

A more useful and realistic comparison is between buses and cars at the average occupancy for both. That covers all trip purposes and all locations, not just the CBD (which of course is the hub of the radial public transport systems in Australian cities).

Public transport tends to be loaded to capacity in peak hour, but at all other times those large, heavy vehicles carry many fewer passengers. Even in peak hour, they’re not fully loaded for the length of each trip. They have to do return journeys against the peak as well.

A metropolitan public transport system can’t be limited to busy periods or to one or two very large and dense destinations; it has an equity function and has to operate across the whole metro area, during the middle of the day, at night, and on weekends.

The advantage of trains, trams and buses is high load factors i.e. lots of passengers to spread negative externalities like GHG emissions across.

But according to a study prepared for the 2008 Victorian Climate Change Summit, the average occupancy of buses in Victoria isn’t 60; it’s just 3.7 passengers. That compares to an average occupancy of cars of 1.6.

The average occupancy of trams is around 21 passengers and for trains around 119. That’s a lot better than buses (which tend to be used on marginal and feeder routes) but still well below their maximum capacity. (2)

In 2008, Victoria’s former Commissioner for Sustainability said modes that rely on coal-fired electricity, such as Victoria’s trams and trains,

have GHG full fuel cycle intensity levels on an average per person-kilometre basis that are comparable to motor vehicles.

The GHG intensity of cars in Victoria is only 13% higher per passenger kilometre than either trains or trams. Emissions from buses are 27% higher than those from cars.

The explanation for the relatively modest difference between cars and public transport is partly about factors like how the electricity is generated (e.g. Victoria uses brown coal), but it’s mainly the result of low load factors.

When public transport operates as “mass transit” it performs exceptionally well relative to cars on key measures such as energy use, emissions and infrastructure requirements. Dense concentrations of jobs like the CBD wouldn’t be possible without it.

The exhibit is relevant to smaller cities like Adelaide and Perth where public transport carries a large proportion of CBD commuters but cars still carry the majority (65% in Adelaide and 62% in Perth).

But public transport doesn’t offer anything like the advantage for the vast majority of trips that’s implied by these sorts of exhibits, at least in the case of Australian cities where car use continues to be relatively unchecked by policy makers.

This critique doesn’t mean increasing mode share isn’t a worthwhile goal. It does suggest though that the sorts of policies required to address most trips are likely to be different to those that make sense for the relatively small “market” of CBD commutes.

Advocates who believe the ends justify the means will doubtless continue to publicise these sorts of comparisons, but those who’re interested in healthy and honest public debate should recognise them for what they are i.e. they’re more like propaganda than a no-brainer.


  1. In fact the Muenster photo demonstrates that “tea-partying” isn’t a recent invention. The image of the cars is shamelessly zoomed to fill the frame, whereas the small space requirement of the bus and bicycles is emphasised by the use of a considerably longer perspective.
  2. Here’s one done for Sydney using graphics; it’s (misleadingly) generous to cars, giving them a range of occupancies between one and four persons, but nevertheless assumes the train is always full with 1,000 passengers.