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Transport - general

Aug 16, 2017

Can public transport define the 20-minute city?

We make a vanishingly small percentage of short trips by public transport and it's mostly because we prefer the alternatives for this sort of travel. Transit's strengths lie elsewhere

Distribution (%) of trip times for cars and for public transport, Melbourne (source data: VISTA)

It’s evident from the exhibit that the duration of weekday trips in Melbourne by car tend on average to be short while those by public transport tend to be long. For example:

  • 60% of car trips take less than 20 minutes, compared to 3% by public transport
  • 55% of trips by public transport take more than 50 minutes, compared to 12% of car trips.

The average weekday car trip in Melbourne is 20 minutes; the average weekday trip by public transport is 58 minutes. This difference is large even in the inner suburbs, where cars average 19 minutes and public transport averages 48 minutes.

The numbers are from the Victorian Integrated Survey of Travel and Activity (VISTA), a continuous survey that samples around 14,000 residents of Victoria. It’s important to note that the exhibit shows the proportion of trips by time category for each mode. It’s in percentages, so bear in mind the total number of car trips is more than eight times greater than the total number of public transport trips.

For example, while only 5% of car trips take 40-49 minutes compared to 17% of public transport trips, the number of car trips in this category is 484,650 versus 179,258 public transport trips. In terms of absolute numbers, Melburnians favour cars over public transport for all trip durations up to an hour.

That said, the difference shown in the exhibit has obvious and enormous relevance for the practicality of the “20-minute city”, which seeks to set a maximum trip duration by active modes, including public transport. The 20/30-minute city is embraced enthusiastically by politicians at federal and state level but it’s much more about clever politicking than good policy-making (see Is the “20-minute city” mostly spin? and Are the politicians trying to con us on this one?).

Of course, the current pattern of travel is in part a product of the existing transport system. Some argue that public transport isn’t used for short trips for the simple reason the available options aren’t good enough. I think there’s something in that argument, but it can’t be taken very far.

Consider that Melbourne has a relatively dense network of trams, trains and buses in the inner suburbs. Yet only 3% of public transport trips take less than 20 minutes and 2.5% are less than 2 kilometres. In a city with a claimed half a million tram boardings per day on average, a mere 35,000 trips of less than 20 minutes duration per day by all public transport modes isn’t primarily down to poor public transport.

While it’s mostly driving that’s the preferred mode for short trips (there are 5,328,014 car trips taking less than 20 minutes compared to 35,000 by public transport), walking out-competes public transport too. There are over forty times as many walking trips that take up to 20 minutes – and over sixty times as many that cover up to 2 km – as public transport trips. There are also three times as many bicycle trips under 20 minutes – and three times as many under 2 km – as public transport trips.

The key reason public transport is barely used for short duration trips is the time involved in walking to a stop and waiting for a service – even a frequent one – makes up a large percentage of what is a brief trip (the average duration for all trips up to 20 minutes is around 12 minutes). That makes it uncompetitive with the alternatives, especially driving, which requires no wait time, no timetable, usually no walk time at origin or destination, goes direct, travels at higher average speed, and is entirely private. I expect many short trips are also made when congestion is low and hence driving is especially attractive e.g. near home and/or outside peak hours.

Some of those who walk and cycle might choose to take public transport instead if what was on offer were better, but it’s fair to ask if that would be a better outcome and if the cost would be justifiable.

The lessons for policy makers are, firstly, that the greatest potential for public transport is in medium to longer time/distance trips and, secondly, that public transport won’t win a larger share of shorter trips unless car use is actively suppressed in some way. Restricting parking at rail stations is one way to promote use of feeder buses.

At a practical level, there’s a clear implication for the politician’s favourite i.e. the 20-minute city designed around active transport. The travel limit can’t sensibly be set by public transport or, as I’ve argued before, by bicycle; it must be set by the distance the great majority of residents are able to walk.

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One thought on “Can public transport define the 20-minute city?

  1. Tony Morton

    I’d draw this same conclusion and express it slightly differently.

    Public transport primarily functions as an *extension* of walking, while car travel functions as a *substitute* for it. By and large, in less car-dependent cities or parts of cities, the pattern is for people to do short trips on foot or by bike and use public transport for travel that’s beyond walking/cycling distance. So it’s reasonable to expect that public transport use will be biased toward longer trips.

    Conversely, when car use is the default option it’s used for all trips regardless of distance – even where it’s easier to walk – because the vehicle has to come with you. And because short trips are the majority pretty much everywhere, this adds up to a lot of short-distance car travel, much of which substitutes for walking or cycling rather than public transport. (And of course it often goes hand in hand with local environments that make walking or cycling unattractive, and/or have poor public transport options.)

    One PTUA objective is planning policy that supports walking and cycling alongside greater public transport use. Accordingly we’re not really agitating for greater public transport use for those very short trips that could be covered in a 10 minute walk; what we favour are planning interventions that reward walking, to remove the very first barrier to accessing public transport and promote the easiest, simplest alternative to getting in the car for those short trips.

    Of course, urban planning that brings more facilities within walking distance is a big part of reducing car dependence and reducing transport’s energy footprint. But in a city like Melbourne I don’t think we’ll see fully walkable neighbourhoods right across the metro area any time soon. The next best thing is what official planning policy has supposedly been aimed at from 1970 onward: ample suburban district centres that are co-located with public transport hubs and favoured for more intense commercial and residential development. A primary aim of local public transport is then to provide convenient access to these district centres for the many residents who live beyond walking distance.

    And in the end, whether the total journey time from home to district centre is less than or greater than 20 minutes, after walking is factored in, is ultimately less important than whether people are able to get their day-to-day activities done in sufficient time this way. Given person A may spend as much time finding a car park at the local mall as person B spends waiting for a bus, there are a lot of factors to consider.